What’s Your Idea?
Chemistry - Acids and Alkalis
The students are discussing what pH indicators show.
A pH indicator shows you how
dangerous a chemical is by
changing colour.
Acids always turn red and alkalis
turn blue or purple.
There are different types of
indicators; not all of them
show all of the pH scale.
A pH indicator shows how much
acid something contains.
?
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.
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.
The students are discussing their ideas about neutralisation.
Neutralisation is a chemical
reaction when you mix an acid
and alkali.
The two chemicals mix together
and turn into water.
It doesn’t turn into plain water,
it turns into salt water.
The reaction makes the pH
indicator turn green.
?
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.
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.
The students are discussing how antacid medication works.
The medicine works because it
coats all the acid and stops it
burning your throat.
The medicine soaks up all the
stomach acid.
They are ‘anti’ acid, so they must
be alkaline, right?
Antacids work by reacting with the
acid in the body.
?
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.
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.