Answer these questions in the
back of your book.
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What is a chemical reaction?
What is a physical reaction?
What is an acid?
What is an alkali?
What is a base?
What does neutral mean?
What does neutralisation mean?
Objectives
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To be able to test chemicals and decide if
they are acid/alkali/basic/neutral.
To be able to record chemical reactions in
word and symbol equations.
Facts about acids
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Weak acids, like lemon juice and vinegar,
taste sour.
Strong acids are corrosive and can “eat
away” at metal, stone and flesh!
Acids turns blue litmus paper red.
Acids have a pH of less than 7.
Acids can be neutralized with alkalis.
Facts about alkalis
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Alkalis feel soapy and are used in household
cleaning materials.
Strong alkalis are caustic.
Alkalis turn red litmus paper blue.
Alkalis have a pH of more than 7.
Alkalis can be neutralized with acids.
pH scale
http://www.phschool.com/atschool/science_activity_library/images/acids_and_bases_phscale.jpg
Testing the pH of chemicals
Practical
There are a wide variety of
indictors
Universal Indicator
Litmus
Phenolphthalein
Methyl orange
Neutralisation
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Compounds of alkali metals called salts can
be made by reacting solutions of their
hydroxides, which are alkaline, with acids.
The general equation is:
Names of salts
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When we replace the hydrogen in an acid by a
metal, we get a salt.
Acid
Name in salt
Example
Hydrochloric
Sulphuric
Nitric
Symbol equations
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No atoms are created or destroyed in a
chemical reaction.
There should be the same number of atoms of
each type of element each side of the
equation.
Nitric acid + potassium hydroxide
potassium nitrate + water
State symbols
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(s)
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(l)
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(g)
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(aq)
You try
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Measure 20cm3 of hydrochloric acid into a
beaker.
Add a few drops of UI soln.
Using a pipette, add sodium hydroxide to the
acid.
Observe please note that an indicator can be
used to show when acidic and alkaline solutions
have completely reacted to
produce a neutral salt solution.
Write a word and balanced
symbol equation for the reaction
(can you add state symbols?).
Plenary – true or false?
1.
2.
3.
4.
5.
Bases and alkalis are the same.
Acids have a pH of less than 7.
Neutralisation reactions always produce
water.
Symbol equations must always be
balanced.
(aq) means liquid.
Homework –
complete the following:
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Hydrochloric acid + sodium hydroxide
Sulphuric acid + potassium hydroxide
Nitric acid + Lithium hydroxide
Hydrochloric acid + potassium hydroxide
Sulphuric acid + sodium hydroxide