t3-sc-279-ks3-acids-and-alkalis-whats-your-idea-powerpoint.ppt

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1. What’s Your Idea?
Chemistry - Acids and Alkalis
Photo courtesy of (Amy Loves Yah @flickr.com) - granted under creative commons licence - attribution

2. W
h
at’s yo
u
r id
ea?
?
A pH indicator shows how much
acid something contains.
There are different types of
indicators; not all of them
show all of the pH scale.
Acids always turn red and
alkalis turn blue or purple.
A pH indicator shows you how
dangerous a chemical is by
changing colour.
The students are discussing what pH indicators show.

3. Possible Points of Discussion
A pH indicator shows you how dangerous a chemical is by changing
colour.
The pH indicator changes colour to show the pH (acidity or alkalinity)
of the substance rather than how dangerous it is. Although some
acids can be dangerous, many are in everyday use e.g. vinegar and
citric acid. Alkali burns often cause more harm than acid burns.
Acids always turn red and alkalis turn blue or purple.
This is the case with universal indicator. Other indicators may only
show the presence of a certain range of pH and might not show the
same full colour spectrum. For example, phenolphthalein is colourless
between
pH 0 and 7.

4. Possible Points of Discussion
There are different types of indicators; not all of them show all of the
pH scale.
The pH scale is a measure of how acid or alkali a substance is.
Universal indicator solution shows the pH from 0 to 13 and is the most
commonly used and referred to indicator. Other indicators may only
show the pH of a substance within a certain range of the scale – for
example, methyl red indicates pH between 4.5 and 6 (approximately).
A pH indicator shows how much acid something contains.
A pH indicator is used to show visually how acidic or alkali a substance
is. It will change colour depending on the pH of the substance being
tested.

5. The reaction makes the pH
indicator turn green.
It doesn’t turn into plain
water, it turns into salt water.
The two chemicals mix
together and turn into water.
Neutralisation is a chemical
reaction when you mix an acid
and alkali.
The students are discussing their ideas about neutralisation.

W
h
at’s yo
u
r id
ea?
?

6. Possible Points of Discussion
Neutralisation is a chemical reaction when you mix an acid and alkali.
A neutralisation reaction occurs when acid and alkali are combined in
proportions that result in a product with no acidity or alkalinity – they
cancel one another out and produce a product that has a neutral pH.

7. Possible Points of Discussion
The two chemicals mix together
and turn into water.
Nearly – they will make water and
a salt.
It doesn’t turn into plain water, it
turns into salt water.
The acid and alkali will react to
make new products – always
water and a salt.
The reaction makes the pH
indicator turn green.
Yes - this indicates a neutral pH in
the resulting solution.

8. Antacids work by reacting with
the acid in the body.
They are ‘anti’ acid, so they
must be alkaline, right?
The medicine soaks up all the
stomach acid.
The medicine works because it
coats all the acid and stops it
burning your throat.
The students are discussing how antacid medication works.

W
h
at’s yo
u
r id
ea?
?

9. Possible Points of Discussion
The medicine works because it coats
all the acid and stops it burning
your throat.
Not quite. The medicine works by
reacting with the acid to neutralise
its pH and, therefore, reduce the
acidity.
The medicine soaks up all the
stomach acid.
The medicine is administered orally
and used to counter the symptoms
of acid reflux or heartburn. It
neutralises the acid in the digestive
system rather than soaking it up,
however.

10. Possible Points of Discussion
They are ‘anti’ acid, so they must be
alkaline, right?
Most antacids contain an alkali
ingredient, yes. This is usually calcium
carbonate, magnesium hydroxide,
aluminium hydroxide and/or 
sodium bicarbonate.
Antacids work by reacting with the
acid in the body.
Yes - the antacid works by reacting
with the acid in a neutralisation
reaction.

11. Photo courtesy of (Amy Loves Yah @flickr.com) - granted under creative commons licence - attribution