Heinemann Science Scheme Book 1

Transcription

Teachers' resource Pack
Heinemann Science Scheme
Book 1
Unit E
Sample pages
Please note: There is additional material to be added to this unit, for example,
teachers' notes and answers; charts showing Science 1 opportunities etc. There may
still be some uncorrected errors in these pages.
1
q I Bradley, C Tear, M Winterbottom, S Young, 2001, The Heinemann Science Scheme
2
E1
What are acids
and alkalis?
Learning objectives
(from QCA Scheme of Work)
Pupils should learn:
l
l
l
l
E2
How can we
identify acids
and alkalis?
l
l
l
E3
How strong are
acids and
alkalis?
l
l
l
E4
Acids and
alkalis in
everyday
situations
l
l
l
Teaching
activities
that many household materials
and acids are not hazardous
to recognise and interpret
common hazard signs
how to deal with acids or alkalis . . .
that adding water to an acid or
alkali dilutes it and makes it less
hazardous
Learning outcomes
Pupils:
l
l
l
l
that acids and alkalis can change
the colours of some dyes
the names of some common
laboratory acids and alkalis
to classify solutions as acidic,
alkaline or neutral
l
l
E3 Core
Measuring the pH
of different
solutions
that acids and alkalis are used in
a range of everyday situations
that when an acid is added to an
alkali, it lowers the pH
that a neutral solution can be
obtained by adding an acid to
an alkali
E4 Core
Acids and alkalis
cancel out
E4a Extension
How does pH
change as alkali is
added to acid?
E4b Extension
Does the temperature
change when an acid is
added to an alkali?
l
l
l
l
l
l
Specials
(learning support)
identify some acids and
everyday uses of acids
identify hazard symbols
describe how to work safely
with acids and alkalis
explain that if water is added to
an acid or alkali, it dilutes the
solution
E1
Hazards
E1
What are acids
and alkalis?
(Cloze and
matching
activities)
recognise that solutions of dyes
that show one colour in acids
and another colour in alkalis are
called indicators
recall the names of some acids
and alkalis
E2
Indicators
E2
How can we
identify acids
and alkalis?
(Cloze and
colouring
activities)
identify the pH of a given
solution from a colour chart
classify the solution as strongly
or weakly acidic or alkaline, or
neutral
relate the classification to the
use and associated hazards
E3
Weak or strong
E3
How strong are
acids and
alkalis?
(Cloze and
labelling
activities)
identify uses of acids and alkalis
describe that when an acid is
added to an alkali, the pH falls
explain how to produce a
neutral solution
E4
Using pH
E4
Acids and
alkalis in
everyday
situations
(Cloze passage)
Extension
resources
Scheme of Work
that universal indicator gives a
range of colours in acidic and
alkaline solutions
that pH numbers indicate how
acidic or alkaline a solution is
that neutral solutions are pH 7,
acidic solutions below 7 and
alkaline solutions above 7
Homework
resources
Unit E Acids and alkalis
Book
spread
E5
What happens
when acids
react with
alkalis?
Learning objectives
Pupils should learn:
l
l
l
l
how to frame a question that
can be investigated
to choose appropriate
techniques and equipment
to compare investigative
techniques and evidence
to summarise and evaluate
Teaching
activities
E5 Core
How good is an
antacid?
E5 Extension
Are acids and
alkalis used up
during
neutralisation?
Learning outcomes
Pupils:
l
l
l
suggest how to investigate a
question about antacids
summarise what they have
found out
use the evidence collected to
evaluate an indigestion remedy
Homework
resources
E5
Testing
remedies
Specials
Extension
resources
E5
What happens
when acids
react with
alkalis?
(Cloze passage)
E5
Are acids and
alkalis used up
during
neutralisation?
(Paper
alternative to
Activity E5
extension)
(learning support)
Book
spread
3
Scheme of Work
Teacher and technician notes
Measuring the pH of different
solutions
Resources available
Core sheet
solutions
CD-ROM
Results table blank: customise
with names of solutions you
want to use
Printable UI comparison
charts for pH 1±14 and also
pH 1±11
E3
Core
clean and dry the tiles when all twelve dimples
have been used.
If there is a wide spread of attitude or ability,
vary the number of solutions to be tested or
suggest that quicker workers check results or
start questions.
Watch out for people swapping droppers
between beakers!
Materials required
Per group
Links with:
Book 1
SoW
Sc 1
E3
7E page 2
2 f, g, h, k
Safety
Eye protection is needed. The main hazard here
is that a pupil could deliberately or accidentally
squirt one of the solutions from a dropper. If
this is likely to be an issue then replace the
dropper with a glass tube (dip the tube in the
solution, finger over the end, transfer to tile and
remove finger). Do NOT use finely drawn out
glass tubes fitted with large teats.
Activity procedure
1 Demonstrate test procedure. Emphasise one
OR two drops ± more than this causes
dilution effects and likely overflow into other
dimples causing contamination.
2 Set up the room while class prepare results
tables.
3 Small groups (individuals if you have enough
tiles) go to each station to test the solution
there, record their results then move on.
Order of stations is unimportant.
4 Recap results with group.
l
One dimple tile
l
Access to UI solution (preferably tiny bottle
& dropper) or paper strips cut into squares
l
UI comparison chart
Access to
Dropper and labelled beaker of 50 ml each
solution. Suggested solutions (all max 0.4 M
with pH given in brackets): hydrochloric acid
(1), sulphuric acid (1), nitric acid (1), lemon
juice (citric acid) (2), white vinegar (acetic acid)
(3), boric acid (5), distilled water (7*), sodium
bicarbonate solution (8), calcium hydroxide
solution (limewater) (10), ammonia solution
(11), sodium hydroxide solution (14). Also milk
(6), apple juice (3), white wine (4), rhubarb (3),
lemonade (4) (most foods are acidic). In the
absence of solutions to a desired pH value, refer
to The CLEAPSS Laboratory Handbook or similar
publication, and make up buffer solutions.
*check pH is 7 before the lesson
Sample results
See numbers in brackets for a guide to pH
numbers only. Test your own samples before use.
Answers
5 Group complete appropriate questions.
1 From practical.
Running the activity
2 Extremes of pH tend to give rise to hazard
warnings.
Suggested organisation: put beakers with one
dropper already in the solution around the
room, and send small groups (preferably 2's)
around with their dimple tiles to each station.
If you have 12-dimple tiles, either limit the
number of solutions to twelve or explain how to
3 The colour of the indicator changes slowly
over a few minutes.
4 (i) dilution of the colour gives false reading,
(ii) if the dimple is overfilled the liquid will
flow into other dimples contaminating them
and changing other readings.
4
Acids and alkalis cancel out
E4
Core
out with a pH probe and/or with a temperature
probe (see Activity E4 a/b).
Resources available
Core sheet
Extension
sheet
How does the pH/
temperature change as acid is
added to an alkali
Materials required
l
Universal Indicator comparison chart
Sample datalogger/
spreadsheet files of extension
material results
l
Universal Indicator solution
l
2 100 cm3 beakers
l
2 25 cm3 measuring cylinders
l
2 droppers
l
stirring rod
l
Reactants (100 cm3 of each)
0.4 mol/dm3 hydrochloric acid (aq)
0.4 mol/dm3 sodium hydroxide (aq)
CD-ROM
Links with
Book 1
SoW
Sc 1
E4
7E page 3
2 f, g, h, k, p
Safety
Eye protection is needed. The concentrations
used here are not rated higher than ìrritant'.
Be aware of droppers being used to squirt liquid.
Per group
Notes on materials preparation
Refer to The CLEAPSS Laboratory Handbook,
HazCards, or similar publications for
information on making up solutions.
Sample results
Activity procedure
1 Students measure out an excess of acid and
20 ml of alkali. Watch for contamination ±
there is a separate measuring cylinder and
dropper for each solution.
2 Put the indicator in the alkali (so it goes blue
± easy to check as you go round) and add
acid with a dropper in quantities of 0.5 cm3
to 1 cm3 until the mixture is neutral or
beyond. At this point students should
measure the remaining acid and subtract
from the original volume to find out how
much has been used.
If the HCl and NaOH are the same
concentration, the same amount (20 cm3 ) of
each should be required to give a neutral
solution. If you change the acid to sulphuric,
half the volume of the alkali would be needed.
Answers
1 Less (less alkali to neutralise).
2 Not very. Inaccuracies may be present in
measuring, end point, remeasuring or
calculation, not to mention contamination!
3 Open, but there is no reason to expect that a
different substance would behave in the same
way or to the same degree.
Demonstrate the procedure first. Have some
strips of UI paper in your pocket for testing the
contents of containers as you go round ±
students love to add sodium hydroxide to itself
in the hope that it will be neutralised . . .
There is plenty of room to extend this activity,
by repeating to improve technique at the end
point (improves accuracy) and to check results
(reliability of results). If you wish to do this with
smaller or larger quantities, change the
worksheet to suit. The activity could be carried
5
The changes in temperature
and/or pH during neutralisation
Resources available
Extension
sheets
CD-ROM
E4a/b
Extension
Materials required
How does pH or temperature
change as acid is added to an
alkali
Sample datalogger/
spreadsheet files of extension
material results
Links with
Book 1
SoW
Sc 1
E4
7E page 3
2 f, g, h, i, k, m
Safety
Be aware of droppers being used to squirt liquid.
Activity procedure
Students measure out 75 cm3 (an excess) of acid
and 50 cm3 of alkali. Watch for contamination ±
use a separate measuring cylinder and dropper
for each solution. Put the acid into a dropping
funnel then arrange the apparatus. Check the
logger is operating.
Per group
l
250cm3 beaker
l
100cm3 beaker
l
1 100 cm3 measuring cylinder
l
l
2 droppers
l
dropping funnel
l
magnetic stirrer
l
datalogger
l
pH or temperature (or both) sensor(s) for
logger
l
Reactants (100 cm3 of each):
0.4 mol/dm3 hydrochloric acid
0.4 mol/dm3 sodium hydroxide soln
Sample results
The pH does not change steadily as students
might expect, but within a very narrow band.
The temperature effects can vary depending on
the environment and how much (if any)
insulation the beaker has, but will tend to lag
behind the pH (if both are logged) due to the
time taken for the heat to spread through the
mixture.
Answers
This activity can be used as small-group
extension work or could be done as a
demonstration to give wider access.
The activity could be carried out with a pH
probe and logger to get a graphical output of pH
change against time or with a temperature probe
to measure the energy change during
neutralisation (HCl NaOH is exothermic).
You might try temperature and pH at the same
time if you are sure that the students can sort
out the multiple lines on the graph. By default
you will log against time, but if you can log
against mass (with an electronic balance) then
that would provide a measure of the amount of
acid added. Clearly this is a procedure that needs
trialling.
These are derived from the students' graphs. A
suitable answer to question 1 might be of the
form ``the pH of the sodium hydroxide solution
was 14 and that remained the same for x seconds
and then rapidly changed during the next
y seconds until it stopped changing at pH1
showing that there was an excess of hydrochloric
acid.''
6
How good is an antacid?
Resources available
E5
Core
Materials required
Per group
Core sheet
Extension
sheet
Are acids and alkalis used up
during neutralisation?
Links with:
Book 1
SoW
Sc 1
E5
7E page 3
2 f, g, h, k, o, p
Safety
Activity procedure
1 Demonstrate how to make a paper dish for
the antacid, and revisit tareing the balance if
necessary.
2 Students measure 40 cm3 of dilute
hydrochloric acid and add a few drops of
indicator.
3 Students add one spatulaful of antacid at a
time and check to see if the acid has been
neutralised. When it has, they reweigh the
antacid and subtract this from the original
mass of antacid to find the amount used. The
procedure is repeated for each antacid.
Remind students that when the right amounts of
acid and alkali are mixed together they make a
neutral solution. A good way to find out if
anything has been ùsed up' is to weigh before
and after a change. It is preferable to have more
than one balance if possible, to avoid students
having to wait. UI paper can be used instead of
the UI solution by dropping one strip into the
acid ± the colour leaches into the liquid. If all
the antacids are carbonate (or bicarbonate)
based the experiment can be done just by
looking for fizzing, although this will then miss a
valuable opportunity for reinforcement of
neutralisation.
l
100 cm3 beaker
l
50 cm3 measuring cylinder
l
dropper (for measuring acid)
l
spatula
l
stirring rod.
l
UI solution
Access to
l
top-pan balance
l
0.4 mol/dm3 hydrochloric acid
l
various antacids (made by mixing different
proportions of sodium hydrogen carbonate
and salt, labelled with letters.)
Notes on materials preparation
Refer to The CLEAPSS Laboratory Handbook,
HazCards, or similar publications for
information on making up solutions.
Sample results
If you use 0.4 M hydrochloric acid, 40 cm3 of the
acid should react with 3.36 g of sodium
hydrogen carbonate or 6.72 g of 50:50 mix, so
you can work out the expected answers for each
of your own mixes.
Answers
1 See above.
2 Which needed the smallest amount of antacid
to use up the acid.
3 Because that is what you want the antacid to
do to cure the indigestion.
4 Add the masses found during this experiment
all at once, and see which stops fizzing first ±
which reacts the fastest.
You could add an exercise on which is the
cheapest, by allocating each antacid a cost and
asking students to work out the cost of the
`dose'.
The results can be pre-ordained by the mix used
for each `àntacid''. If the beaker is stood on
white paper or a tile, the indicator colour is
easier to see.
7
Activity
solutions
E3
Core
Aim
To measure and record the pH of solutions
Take care when using
acids and alkalis!
Equipment:
l
l
Universal Indicator (UI) paper
comparison chart
l
l
dimple tile
different solutions
What to do
1 Cut each strip of UI paper up
into squares ± you should get five
or six from each strip.
2 Make sure your results table is
UI Solution
ready to record your results.
3 Put one square of UI paper into
dropper of test solution
each dimple of the tile.
4 Put one (or at most two) drops of
UI solution
the first solution you want to test
on to one piece of the UI paper
squares of UI paper
with the dropper.
HAZARD: some of the solutions you will test are hazardous. Treat them all with care.
5 Immediately compare the colour that the UI paper turns with the UI comparison
chart.
6 Write down the colour of the UI paper in your results table.
7 Write down the pH number that corresponds to the colour of the UI paper in your
results table.
8 Repeat this test with the other test solutions.
Results
Name of solution
Colour of UI paper
pH of solution
Hydrochloric acid
red
pH 1
Questions
1 For each substance, classify it as a
strong acid, weak acid, neutral, weak
alkali or strong alkali.
2 How does the pH relate to the hazard
warning symbols found on the
substances?
3 Why is it important to compare the
colour of the paper to the comparison
chart straight away?
4 Give two reasons why you shouldn't
add too many drops of the test
solution to the UI paper.
8
Activity
E4
Core
Aim
To find out how much hydrochloric acid is needed to use
up 20 cm3 of sodium hydroxide solution.
Equipment
l Universal Indicator (UI) comparison chart
3
l 2 100 cm beakers
l 2 droppers
l hydrochloric acid
l
l
l
l
acids and alkalis!
UI solution
2 25 cm3 measuring cylinders
stirring rod
sodium hydroxide solution
What to do
3
3
1 Measure 40 cm of hydrochloric acid. Put it in a 100 cm beaker.
2
Measure 20 cm3 of sodium hydroxide solution. Put it in a 100 cm3 beaker.
3
Add five drops of UI solution to the
sodium hydroxide solution in the
beaker. The indicator should turn
dark blue or purple.
4
5
Use a dropper to add the hydrochloric
acid to the sodium hydroxide
solution, a little at a time and stir
gently to make sure they are mixed.
stirring rod
dropper of
hydrochloric
acid
dilute
hydrochloric acid
Check the colour of the indicator. If the blue
colour has changed to light green the solution is
neutral and you should stop. If the indicator has
turned yellow or orange you have added a little too
much acid, but you should still stop.
6
Measure the amount of hydrochloric acid you
have got left by carefully pouring it into the
correct measuring cylinder.
7
Repeat the experiment to check your result.
;;;
;;;
;;;
sodium
hydroxide
solution with
UI solution
left-over
hydrochloric acid
measuring
cylinder for
hydrochloric acid
Results
Write down the amount of hydrochloric acid that you needed to use up all the
sodium hydroxide solution.
Questions
1 If the sodium hydroxide was diluted with water, do you think it would need more
or less acid to use it up? Explain why you think this.
2 How accurate do you think your answer is? Explain why you think this.
3 Do you think that you would need the same amount of a different acid to use up
20 cm3 of sodium hydroxide solution? Explain why you think this.
9
Activity
How does the pH change as an
acid is added to an alkali?
E4a
Extension
Aim
acids and alkalis!
Equipment
l
l
l
l
250 and 100 cm3 beakers
100 and 50 cm3 measuring cylinders
2 droppers
magnetic stirrer
l
l
l
l
datalogger
pH sensor for logger
hydrochloric acid
;;
;
;
;
What to do
3
1 Measure 75 cm of hydrochloric
75 cm3 dilute
acid. Put it in to a dropping
hydrochloric acid
in dropping funnel
funnel.
3
2 Measure 50 cm of sodium
hydroxide solution. Put it in a
250 cm3 tall-form beaker.
50 cm3
sodium
hydroxide
3 Stand the beaker on a magnetic
solution
stirring plate and put the stirrer
in the beaker. Start the stirrer.
4 Clamp the pH probe so that it is in the liquid.
5 Arrange the dropping funnel so that it can drip into
the liquid.
6 Start the datalogger.
7 Open the funnel tap slightly so that the hydrochloric
acid drips in to the sodium hydroxide solution,
approximately one drop every second. Count the drops
in 30 seconds.
8 Continue adding the acid until the pH stops changing
(about pH 1 or 2).
9 Stop adding the acid, turn off the stirrer and logger.
;
DATALOGGER
pH sensor
magnetic stirrer
Results
Print the graph of the data collected by the logger.
Questions
1 On your graph, mark the point where
the mixture was exactly neutral.
2 How long did it take for the mixture
to go from pH 14 to pH 1?
3 How many drops of hydrochloric acid
dripped into the sodium hydroxide
solution in thirty seconds?
solution to change it from pH 14 to
pH 1?
5 Write a paragraph to describe how the
pH of the mixture changes as the acid
runs into the alkali.
10
Activity
How does the temperature change
as an acid is added to an alkali?
E4b
Extension
Aim
acids and alkalis!
Equipment
l
l
l
l
250 and 100 cm3 beaker
50 and 100 cm3 measuring cylinder
2 droppers
magnetic stirrer
l
l
l
l
datalogger
temperature sensor for logger
hydrochloric acid
;;
;
;;
What to do
3
1 Measure 75 cm of hydrochloric
75 cm3 dilute
acid. Put it in to a dropping funnel.
hydrochloric acid
3
in dropping funnel
2 Measure 50 cm of sodium
hydroxide solution. Put it in a
250 cm3 tall-form beaker.
3 Stand the beaker on a magnetic
50 cm3
stirring plate and put the stirrer in
sodium hydroxide
solution
the beaker. Start the stirrer.
4 Clamp the temperature sensor so
that it is in the liquid.
5 Arrange the dropping funnel so that it can drip into
the liquid.
6 Start the datalogger.
7 Open the funnel tap slightly so that the hydrochloric
acid drips in to the sodium hydroxide solution,
approximately one drop every second. Count the drops
in 30 seconds
8 Continue adding the acid until the temperature stops
changing.
9 Stop adding the acid, turn off the stirrer and logger.
;
temperature
sensor
magnetic stirrer
Results
Print the graph of the data collected by the logger.
Questions
1 On your graph, mark the point where
the temperature started to change and
the point where the temperature
stopped changing.
solution in thirty seconds?
3 Write a paragraph to describe how the
temperature of the mixture changes as
the acid runs into the alkali.
11
Activity
E5
Core
Aim
To compare different stomach remedies.
The main question to answer when deciding which is the
`best' antacid is `how much acid does the antacid
remove?' This experiment allows you to answer that
question.
acids and alkalis!
Equipment
l
l
l
l
100 cm3 beaker
hydrochloric acid
samples of antacids
spatula
l
l
l
l
50 cm3 measuring cylinder
Universal Indicator solution
balance
stirring rod
What to do
3
1 Measure 40 cm of
spatula full of antacid
hydrochloric acid.
2 Put the acid in a
100 cm3 beaker with a
few drops of Universal
Indicator solution.
3 Measure out 10 g of one
of the antacids on a piece
of paper.
sample of antacid
4 Add one spatulaful of antacid to the acid and stir.
5 If the mixture fizzes and the indicator stays red, orange
or yellow, repeat step 4. If it goes green, and stays
green, go on to step 6 .
6 Measure the amount of antacid you have left, and
work out how much you have used. Don't forget to
allow for the weight of the paper!
7 Repeat the experiment using different antacids.
stirring rod
40 cm3 of hydrochloric
acid with a few drops of
UI solution
Results
Write down the amount of each antacid that was needed
to use up 40 cm3 of the acid.
Questions
1 Which antacid was best at using up
the acid?
2 How did you decide which the best
antacid was?
3 Why is the amount of acid the antacid
removes important?
4 How could you find out which
antacid works the most quickly?
12
Activity
E5
Extension
Aim
To find out if acids and alkalis are used up during
neutralisation.
acids and alkalis!
Equipment
l
l
l
2 250 cm3 beakers
2 droppers
l
l
l
hydrochloric acid
top-pan balance
What to do
3
1 Measure 100 cm of hydrochloric acid. Put it in to the
250 cm3 beaker.
2
Put the beaker carefully on the balance and write down
the mass.
3
Measure 100 cm3 of sodium hydroxide solution. Put it
in to the other 250 cm3 beaker.
4
Put the beaker carefully on the balance and write down
the mass.
5
Check your readings by putting both beakers on the
balance together and make sure that the total mass of
the two beakers and their contents is the same as the
sum of the individual masses.
6
Take the beakers off the balance and carefully mix the
acid and the alkali together.
7
Put both beakers carefully back on the balance (make
sure no acid or alkali touches the balance) and record
the total mass again.
Results
Present your measurements in a clear format. You could
use a table if you like.
Questions
1 What is the difference between the
total mass of the beakers and the
chemicals before and after the acid
and alkali were mixed?
2 Do you think the acid was used up?
beaker containing
100 cm3 of
hydrochloric acid
top pan balance
beaker containing
100 cm3 of sodium
hydroxide solution
top pan balance
;;
;;
beaker containing
mixture
empty beaker
top pan balance
3 Do you think the alkali was used up?
4 What do you think we mean when we
say that the acid and alkali are `ùsed
up'' during neutralisation?
13
Homework
Hazards
E1
Design your own hazard warning symbol
to show that a substance is explosive.
Remember that your symbol can only be
black on orange.
Look around your house for containers
with chemicals in. Some of these
containers will have hazard warnings and
some won't. List all the chemicals you
find in the table below, and when they
have a hazard warning sign, tick the
correct column to show the hazard.
Name
of
chemical
No
hazard
warning
Harmful
Irritant
Corrosive
Use the information you found to answer
these questions
1 Which was the most common hazard
warning symbol in your house?
2 In which room were the largest
number of hazardous chemicals kept?
3 Write a few sentences about how and
where the chemicals were stored. For
example, were they kept out of reach
of young children?
4 Write a safety report for the chemicals
in your house, mentioning good
things (when chemicals are stored
properly) and bad things (when they
aren't).
"
.........................................................................................
Homework
Indicators
1 Copy out the statements below so that
they are in the correct order to extract
an indicator from some red cabbage
leaves.
l Cut up the cabbage leaves.
l Filter the mixture.
l Put the cabbage leaves in a mortar
with some sand and a little water.
l Pick the cabbage leaves.
l Grind the leaves with a pestle to
release the dye from the leaf cells.
E2
3 Raw beetroot can be used to make an
indicator. Why shouldn't pickled
beetroot be used?
4 Litmus solution turns pink in acids
and blue in alkalis. Copy and complete
the box showing the colour that the
litmus would turn in that solution.
The first two have been done for you.
2 Collect advertisements for products
which are either acids or alkalis, or are
made from them. Make a display of
your advertisements to show the range
of products that can be made from
acids and alkalis.
14
Solution
hydrochloric acid
pink
sodium hydroxide
blue
citric acid
potassium hydroxide
phosphoric acid
water
Homework
Weak or strong?
E3
1 Copy the pH number and match each number to the
meaning
pH 1
pH 5
pH 7
pH 9
pH 13
weak alkali
neutral
strong alkali
weak acid
strong acid
2 Copy and complete the table using the pH numbers
and colours from the list below. Use each number or
colour once only.
Solution
Type
hydrochloric acid
strong acid
boric acid
weak acid
sodium hydroxide
strong alkali
sodium bicarbonate
weak alkali
distilled water
neutral
pH number
Colour of UI paper
pH numbers: 1, 5, 7, 9, 14
Colours:
purple, red, yellow, light green, dark green
15
Homework
Using pH
1 Which of these statements are true
and which are false?
a All acids have pH numbers less
than 3.
b All alkalis turn pH paper blue.
c Neutral solutions have a pH of 7.
d pH 5 means neutral
e Stronger acids have low pH
numbers.
f High pH numbers mean strong
alkalis.
2 Bee stings and wasp stings are very
different to each other. Wasp stings can
be treated with vinegar and bee stings
with bicarbonate of soda solution.
Explain why each treatment works.
E4
3 You find an unlabelled bottle on the
bench. When you test the liquid in the
bottle with Universal Indicator, you
find that the liquid has a pH number
of 4. Which of the following
statements are true?
a
b
c
d
e
The liquid is salt solution
The liquid is an acid
The liquid is an alkali
The liquid is a weak acid
The liquid is sodium hydroxide
solution
f The liquid is hazardous
"
.........................................................................................
Homework
Testing remedies
Razak wants to know which indigestion remedy works the
most quickly. He has three remedies he wants to test,
remedy A is a powder, remedy B is a tablet that has to be
dissolved in water before drinking it and remedy C is a
liquid that is taken from a teaspoon.
Write a plan for one or more tests that will answer
Razak's question. You can make use of any laboratory
equipment or chemicals you normally use.
16
E5
Specials
What are acids and alkalis?
E1
1 Use the words below to fill the gaps in these sentences.
You may need to use a word more than once.
chemicals
acids
stomach
alkalis
burn
corrode
Acids and alkalis are two important groups of
soap
.
often have a sharp or sour taste.
Strong
can wear away or
metals
but many are weak and harmless.
Many strong
are described as caustic, which means they
can
living tissue.
We can find acids and alkalis all over the place, in foods,
shampoo and even in your
,
.
2 Below are chemical hazard symbols and descriptions of
what they mean. Match the symbols to the correct
description.
Attacks and destroys living tissue,
including eyes and skin
h
Can make you ill if swallowed, breathed
in or absorbed through the skin
May cause reddening or blistering of
the skin
i
17
Specials
How can we identify acids and
alkalis?
E2
colourless
litmus
Universal Indicator
hydrochloric
hydroxide
colour
indicator
petals
leaves
a Many acids and alkalis are
liquids, so you can't tell
them apart just by looking. We can use an
to tell
whether a substance is an acid or an alkali.
in acids and alkalis. They can be
b Indicators change
made from plant material such as
and
. Two indicators that are often used in schools
are
and
c
acid is an acid, and sodium
is an alkali.
2 The drawings show litmus paper in a beaker of acid
and a beaker of alkali. Show what colour it would turn
in each one by colouring it in or writing the colour.
litmus paper
ACID
ALKALI
18
Specials
How strong are acids and alkalis?
E3
strong
Universal Indicator
Sulphuric acid is a
weak
higher
pH scale
acid, but cows' milk is
a
acid.
acids and alkalis tend to
react more quickly than weak acids and alkalis. We use
to
tell us how strong acids and alkalis are.
The
shows the range of strengths of acids and alkalis.
Alkalis have
pH numbers than acids.
2 On the pH scale, pH 7 means neutral and pH 1 means
a strong acid. On the pH line below label the three
arrows to show where a weak acid, a weak alkali and a
strong alkali would appear.
0
1
strong
acid
2
3
4
5
6
7
8
9
10
11
12
13
14
neutral
19
Specials
Acids and alkalis in everyday
situations
E4
vinegar
fertilisers
acidic
lime
skin
plastics
neutralise
Acids and alkalis are used to make chemicals such as
soaps,
,
, paints and drugs. Some foods can be pickled by
soaking them in
which is an acid. pH 5.5 is the best value
for your
.
Ant bites and bee stings are
, so they can be treated with a
weak alkali. Acidic soil is made better for growing crops by spreading
onit.Acidsandalkaliscancanceleachotherout.Wesaythatacids
can
alkalis.
"
.........................................................................................
Specials
What happens when acids react
with alkalis?
E5
1 Use the words below to fill the gaps in these sentences. You may need to use a
word more than once.
neutral
antacids
acid
A common cause of stomach ache is
green
indigestion.
Indigestion remedies contain
which use up the excess acid.
To find out which antacid uses up the most acid, we would have to add
the
to a mixture of antacid and Universal Indicator, to
see how much acid was used up before the UI turned
show it was
.
20
to
Extension
Aim
To find out if acids and alkalis are used up during
neutralisation.
When the right amounts of an acid and an alkali are
mixed together, they make a neutral solution. We say that
the acid and alkali have cancelled each other out. Could
this mean that the acid has `ùsed up'' the alkali? Or has
the alkali `ùsed up'' the acid?
A good way to find out if something has been used up is
to weigh it before and after a change: if the mass goes
down, something may have been used up.
Xavier and Jeannette carried out the experiment below to
find out if anything had been used up during
neutralisation.
3
l They measured 100 cm of hydrochloric acid and put it
in to the 250 cm3 beaker.
l They put the beaker carefully on the balance and wrote
down the mass.
3
l They measured 100 cm of sodium hydroxide solution
and put it in to the other 250 cm3 beaker.
l They also wrote down the mass of this beaker.
l They carefully mixed the acid and the alkali together.
l They put both beakers carefully back on the balance
and recorded the total mass again.
Results
E5
beaker containing
100 cm3 of
hydrochloric acid
top pan balance
beaker containing
100 cm3 of sodium
hydroxide solution
top pan balance
;;
;;
beaker containing
mixture
empty beaker
top pan balance
Mass of hydrochloric acid + beaker = 179 g
oxide
Mass of sodium hydr
+ beaker = 185 g
ts = 364 g
Both beakers + conten
Mass of mixture
+ 2 beakers = 364 g
Questions
1 What is the difference between the total mass of the
beakers and the chemicals before and after the acid and
alkali were mixed?
2 Do you think the acid was used up?
3 Do you think the alkali was used up?
4 What do you think we mean when we say that the acid
and alkali are `ùsed up'' during neutralisation?
21
Test yourself
Acids and alkalis
Unit E
1 Match each hazard warning symbol to its meaning.
Can make you ill if swallowed, breathed
in or absorbed through the skin
i
May cause reddening or blistering of the
skin
h
Attacks and destroys living tissue
including eyes and skin
2 Litmus solution turns pink in acids
and blue in alkalis. Complete the
table below by writing in the colour
that the litmus would turn in that
solution. The first one has been
done for you.
Solution
Colour of litmus
hydrochloric acid
pink
sodium hydroxide
citric acid
potassium hydroxide
phosphoric acid
water
3 Put the following words in the correct places in the table:
neutral
pH1
strong alkali
light green
weak acid
Substance
Strength & type
hydrochloric acid
strong acid
pH
pH 5
sodium hydroxide
pH 14
distilled water
purple
Colour of UI
red
boric acid
sodium bicarbonate
pH 9
weak alkali
yellow
dark green
pH 7
4 Which of these statements are true and which are false?
l
l
l
l
l
l
Acids have pH numbers less than 7
Some alkalis have pH numbers greater than 9
A neutral solution has a pH anywhere between 5 and 9
pH 7 means neutral
The lower the number, the stronger the acid
The lower the number, the stronger the alkali
22
True/False
True/False
True/False
True/False
True/False
True/False
Test yourself
Acids and alkalis continued
Unit E
5 You find an unlabelled bottle on the bench. When you
test the liquid in the bottle with universal indicator,
you find that the liquid has a pH number of 5. Which
of the following statements are true?
l
l
l
l
The liquid is an alkali
The liquid is a weak acid
The liquid is sodium hydroxide solution
The liquid is hazardous
6 Choose the right words to complete the sentences by
crossing out the wrong words:
Acids turn Universal Indicator red/green/blue, and
have a sharp/sweet/blunt taste.
Some alkalis are described as acidic/caustic/alkaline
because they can burn living tissue.
Alkalis turn Universal Indicator red/green/dark green if
they are weak/strong/neutral.
When acids and alkalis are mixed together, they
add up/cancel out/disappear.
The word scientists use to describe this is
evaporation/condensation/neutralisation.
7 Complete the crossword. If you get stuck,
the answers are all written below,
but try not to use them!
1
Across
1 To cancel out an acid and alkali
4 Substance with a sharp taste
6 These fruit are acidic
8 A laboratory acid
Down
1 Not an acid or an alkali ± pH 7!
2 These can be caustic!
3 Shows what is an acid and what is an alkali
5 Another name for calcium oxide
7 Solid form of a common, neutral substance!
8 Is hydrochloric acid an alkali?
2
3
4
5
6
7
8
8 Which group of pH numbers would ALL indicate the presence of acids?
A
1
3
5
B
1
5
7
C
7
9
11
D
9
11
13
Answers: Acid, alkalis, ice, indicator, lemons, lime, neutral, neutralise, nitric, no
23
End of unit test
Acids and alkalis
Unit E
Tier 3±6
1 a Which of these substances could have this sign?
(1 mark)
A weak acid
A strong acid
A weak alkali
A strong alkali
i
b Put these substances in order, most hazardous
first. (2 marks)
;;
;;
;;
A
B
C
h
i
c Explain why should you add water to an acid if the
acid spills on your skin. (1 mark)
2 Shaheen has three colourless liquids labelled A, B and C.
a When she puts Universal Indicator into solution A
it turns red. When she puts it into solution B it
turns purple. Copy out the correct statement.
(1 mark)
l A and B are both strong acids
l A is a strong acid, B is a strong alkali
l A is a weak acid, B is a weak alkali
l A and B are both weak alkalis
b Shaheen now puts Universal Indicator into solution
C and it turns green. What does this tell her about
the liquid? (1 mark)
c Suggest what substance C might be. (1 mark)
d Below is a pH scale with some values marked in.
Copy the scale and mark Shaheen's 3 substances
where you think they would be on the scale.
(3 marks)
pH 0
1
4
7
Letter of
substance
24
9
13
End of unit test
Unit E
Tier 3±6
3 If you have a stomach ache this is often caused by àcid
indigestion'.
a What causes acid indigestion? (1 mark)
b You can buy indigestion remedies to cure this.
What do many of them contain? (1 mark)
c Explain how an indigestion remedy can cure acid
indigestion. (1 mark)
d Nettle stings are caused by formic acid. Many people
say that rubbing a dock leaf on a nettle sting will
cure it. What test would you carry out on the dock
leaf to see if this could be true? (1 mark)
4 The graph shows how the pH
of sodium hydroxide solution
changes as hydrochloric acid is
added slowly to it.
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
pH of mixture
a How much hydrochloric
acid has been added when
the solution becomes
neutral? (1 mark)
b Explain why the pH of
the mixture above
changes as it does.
(1 mark)
10
0
20
30
40
50
60
cm3 of hydrochloric acid added
70
80
5 Two students carried out an experiment to investigate
temperature changes during neutralisation. They added
acid slowly to an alkali and recorded the temperature
after each 5 cm3 of acid added. Here are their results:
amount of acid added (cm3 )
5
10
15
20
25
30
temperature (8C)
15
15
18
22
30
24
a Draw a line graph of the students' results.
(2 marks)
b Describe what happens to the temperature during
the experiment. (1 mark)
c Mark on your graph the point where you think the
neutralisation had finished. (1 mark)
25
End of unit test
Acids and alkalis
Unit E
Tier 2±5
1 Find one acid and one alkali in the following passage:
Peter got up one morning and had a wash with soap
and water. For breakfast he had orange juice and
cereal with extra iron in it ± but no milk! On his
way to school he ate a chocolate bar.
a Which is the acid? (1 mark)
b Which is the alkali? (1 mark)
2 a Look at the list below and pick out one acid and
one alkali which you might find in the school
lab. (2 marks)
Hydrochloric acid, sodium hydroxide solution,
copper sulphate solution
b Name one other acid (1 mark)
3
a Copy the sentence below that describes what this
symbol means? (1 mark)
l Can make you ill if swallowed, breathed in or
absorbed through the skin
l May cause reddening or blistering of the skin
l Attacks and destroys living tissue including eyes
and skin
b Name one of these substances which could have this
sign. (1 mark)
l A weak acid
l A strong acid
l A weak alkali
l A strong alkali
c Put these substances in order,
most hazardous first.
(2 marks)
;;
;;
;;
A
B
C
d Explain why you should add
water to an acid if you spill
acid on your skin.
(1 mark)
26
h
i
End of unit test
Unit E
Tier 2±5
4 Shaheen has three colourless liquids labelled A, B and C.
a When she puts Universal Indicator into solution A
it turns red. When she puts it into solution B it
turns purple. Copy out the correct statement.
(1 mark)
l A and B are both strong acids
l A is a strong acid, B is a strong alkali
l A is a weak acid, B is a weak alkali
l A and B are both weak alkalis
b Shaheen now puts Universal Indicator into solution
C and it turns light green. What does this tell her
about the liquid? (1 mark)
c Suggest what substance C might be. (1 mark)
d Below is a pH scale with some values marked in.
Copy the scale and mark Shaheen's 3 substances
where you think they would be on the scale.
(3 marks)
pH 0
1
4
7
9
13
Letter of
substance
5 If you have a stomach ache this is often caused by àcid
indigestion'.
a What causes acid indigestion? (1 mark)
b You can buy indigestion remedies to cure this. What
do many of them contain? (1 mark)
c Explain how an indigestion remedy can cure acid
indigestion. (1 mark)
d Nettle stings are caused by formic acid. Many people
say that rubbing a dock leaf on a nettle sting will
cure it. What test would you carry out on the dock
leaf to see if this could be true? (1 mark)
27
Mark scheme
Acids and alkalis
Unit E
Tier 2±5
Question
Part
Answer
Mark
Level
1
a
Orange juice
1
2
b
soap
1
2
a
Acid hydrochloric acid,
alkali sodium hydroxide solution
1
1
3
b
Any other acid
1
3
a
Attacks and destroys living tissue
1
3
b
A strong acid or a strong alkali
1
4
c
A then C then B: 1 mark for A, then 1 mark for C
2
3
d
It stops the acid doing so much damage by washing
some away/by diluting it (credit either). Credit `ìt
makes the acid weaker''
1
5
a
A is a strong acid, B is a strong alkali
1
4
b
Neutral
1
4
c
Any neutral liquid eg water, salt solution
1
4
d
A linked to pH 1
B linked to pH 13
C linked to pH 7
1
1
1
4
4
4
a
Too much stomach acid
1
4
b
Antacid, allow `àlkali'' or ``carbonate''
1
4
c
Neutralises/cancels out/uses up excess acid
1
5
d
Something to the effect of: extract the juice from a
dock leaf and test it to see if it is an alkali or if it
neutralises an acid. Accept ``pH test''
1
4
2
3
4
5
Scores in the range of:
Level
3±5
2
6±10
3
11±14
4
15±20
5
28
Mark scheme
Acids and alkalis
Unit E
Tier 3±6
Question
Part
Answer
Mark
Level
1
a
A weak acid or a weak alkali
1
4
b
C then B then A: 1 mark for C, then 1 mark for B
2
3
c
It stops the acid doing so much damage by washing
some away/by diluting it (credit either). Credit `ìt
makes the acid weaker''
1
5
a
A is a strong acid, B is a strong alkali
1
4
b
Neutral
1
4
c
Any neutral liquid eg water, salt solution
1
4
d
A linked to pH 1
B linked to pH 13
C linked to pH 7
1
1
1
4
4
4
a
Too much stomach acid
1
4
b
Antacid, allow `àlkali'' or ``carbonate''
1
4
c
Neutralises/cancels out/uses up excess acid
1
5
d
Something to the effect of: extract the juice from a
dock leaf and test it to see if it is an alkali or if it
neutralises an acid. Accept ``pH test''
1
4
a
42 cm3 accept answers in range 40±45, with units
1
5
b
pH stays at 14 while there is excess alkali, then falls
quickly to 7 as the alkali is neutralised and then to 1 as
the excess of acid is established.
1
5
a
Appropriate scales (0±30 cm3 on x axis, 0±308C on
y axis)
1
6
Points and line correct (make an acetate overlay)
1
6
2
3
4
5
30
25
20
°C 15
10
5
0
0
5
10
15
20
cm3 acid
25
30
29
Mark scheme
Acids and alkalis
Unit E
Tier 3±6
b
Temperature increases as you add more acid until
about 25 cm3 of acid has been added, then the
temperature falls as you add more acid.
1
5
c
Credit mark at highest temperature (although
neutralisation will have occurred before the highest
temperature is reached).
1
5
Scores in the range of:
Level
4±7
3
8±11
4
12±14
5
15±20
6
30
Student record sheet
Acids and alkalis
I can
do this
very
well
I can
do this
quite
well
I need
to do
more
work
on this
I can identify some acids and describe how they are used
in everyday life
I can identify some alkalis and describe how they are
used in everyday life
I know the hazard symbols for harmful, irritant and
corrosive substances
I can describe how to work safely with acids and alkalis
I know what happens when water is added to an acid or
alkali
I know what an indicator is
I can describe the effect of acids and alkalis on indicators
I know the names of some acids and alkalis we can find
in the school lab
I can use a colour chart to find the pH of a substance
I can use the pH value of a substance to identify it as
acid, alkali or neutral
I can use the pH value to describe how weak or strong
an acid or alkali is
I can describe what happens to the pH when an acid is
added to an alkali
I can describe what happens to the pH when an alkali is
added to an acid
I know what neutralisation means
I can explain how to get a neutral solution
What I enjoyed most in this unit was
The most useful thing I have learned in this unit was
I need to do more work on
31
Key words
Key word list
acid
alkali
antacid
caustic
corrode
harmful
hazardous
indicator
lichen
lime
neutral
neutralise
neutralisation
pH paper
ph scale
pH values
symbol
universal indicator
"
.........................................................................................
Glossary
Glossary
acids
substances that react with
alkalis and sometimes have a
sour taste
alkalis
substances that react with
acids
antacid
substance that uses up or
cancels out an acid
caustic
substance that can burn living
tissue
corrode
to eat away a substance
harmful
can make you ill if swallowed,
breathed in or absorbed
through the skin
hazardous
has some risk connected with
it
indicator
a chemical that changes colour
in acids and alkalis
lichen
kind of plant
lime
everyday name for calcium
oxide
neutral
neither acid nor alkali
neutralised
made neutral
neutralisation
using up or cancelling out an
acid or alkali to make it
neutral
pH paper
universal indicator on filter
paper to make it easy to use
ph scale
range of strength of acids and
alkalis, from 1 to 14
pH values
numbers that mean how acid
or alkaline something is
symbol
sign that means something
universal
indicator
mixture of dyes that show the
strength of an acid or alkali
32
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Heinemann Science Scheme Book 1

Transcription

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