DP Chemistry: 8.2 Properties of acids & bases

8.2 Properties of acids & bases

Written specifically for students to provide help and support for the IB Diploma chemistry programme this page provides full coverage of the syllabus content of Topic 8.2 Properties of acids & bases. It encourages you to think critically and provides many questions with full worked answers so that you can monitor and improve your knowledge and understanding.

Learning outcomes

After studying this topic you should be able to:

Understand:

  • Most acids react with reactive metals, metal oxides, metal hydroxides, hydrogen carbonates and carbonates in an observable and characteristic way.
  • Neutralisation reactions are exothermic and produce salt and water.

Apply your knowledge to:

  • Balance chemical equations for the reaction of acids.
  • Identify the acid and base required to make different salts.
  • Perform acid-base titrations with different indicators.

Relationships & vocabulary

Nature of science

This sub-topic is an example of how obtaining evidence for theories arises from experimental work. The modification of acid–base theories has developed from the observable properties of the reactions of acids and bases.

International-mindedness

For examples and links to International mindedness, Theory of knowledge, utilization etc. see separate page which covers all of Topics 8 & 18: Acids & bases.

Vocabulary

neutralisationnitric acidsulfuric acidsodium hydrogencarbonate

Learning slides

You can use this slide gallery for learning or for reviewing concepts and information. It covers all the key points in the syllabus for this sub-topic.

  

Something to think about

The characteristic properties of acids are generally well known. Reactions of acids with reactive metals, metal oxides, hydroxides, carbonates and hydrogencarbonates are all obvious examples. Other less obvious examples which are not technically on the IB programme are reactions with sulfides and sulfites. You should also know their characteristic reaction with acid-base indicators such as litmus, phenolphthalein, methyl orange and universal indicator. It is less obvious to list the characteristic properties of bases. Firstly a base needs to be defined and although the previous sub-topic, 8.1 Theories of acids & bases covered the Brønsted-Lowry definition I think what is meant here by a base is simply a substance that neutralises an acid. Consequently there are only three characteristic properties of bases:

1. They neutralize acids.

2. If they are soluble in water they give a characteristic colour with acid-base indicators indicating a pH value greater than 7.

3. Hydroxides react with ammonium salts when heated to form ammonia.

e.g. NH4Cl(s) + NaOH(aq) → NH3(g) + NaCl(aq) + H2O(l)

Ionically the ammonium ion is behaving as a Brønsted-Lowry acid and the hydroxide ion is behaving as a Brønsted-Lowry base:

NH4+(s) + OH–(aq) → NH3(g) + H2O(l)

Utilization of the reverse of this reaction is made in Option D: Medicinal chemistry as many drugs contain an basic amine (substituted ammonia) functional group and can be made much more polar and hence more soluble in aqueous solution by reacting them with hydrochloric acid to convert them into a salt.

One toy from the past is a baking powder submarine. These were once given away in cereal packets. Baking powder or bicarbonate of soda is essentially sodium hydrogencarbonate. In water or slightly acidic solution the hydrogencarbonate ion behaves as a base and reacts to form carbon dioxide.

HCO3–(s) + H3O+(l) → CO2(g) + 2H2O(l)

When the submarine containing a small amount of baking powder was placed in water the gas evolved caused the submarine to surface then it would dive as the gas was expelled and then rise up again - magic! - and a really nice way to show a characteristic reaction of a particular type of base.

 

Test your understanding of this topic

(Note that your teacher may have restricted your access to some or all of these questions and worked answers if they are going to use them as a class test or set them as an assignment.)

For ten 'quiz' multiple choice questions with the answers explained see MC test: Properties of acids & bases.

For short-answer questions see Properties of acids & bases questions.

More resources

1. A demonstration of acid-base neutralization reactions from Jonathan Bergmann and Aaron Sams.

Acid-base neutralization  

2. A simple video by Manipal K-12 Technologies on how ammonia can be prepared by heating solid calcium hydroxide with ammonium chloride.

Preparation of ammonia  

3. A video showing the baking powder submarine in action.

Baking powder submarine  

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