UNIT 3 – CHEMICAL WORLD


Summary questions 1. What is the difference between an alkali and a base?


2. What is an indicator?


3. a. State the colour change observed when litmus paper is dipped in: i. an acid ii. a base


b. Give one advantage of using universal indicator instead of litmus indicator.


4. Draw the pH scale and add as many examples as you can for each pH. You may need to research additional examples online.


5. Describe how you would carry out an investigation to measure the pH of different substances in the laboratory.


6. The soil in Claire’s garden has a pH of 4.5. Claire really wants to grow an apple tree, which needs a pH of approximately 5.0–6.8 to grow.


:Fig. 22.14 a. Describe how Claire tested the pH of her soil. b. How can Claire adjust the pH of the soil to ensure that the tree grows? c. Research other plants she can grow in her garden if the soil is to remain at pH 4.5.


7. a. What is the purpose of a titration? b. State how the following pieces of equipment are used during a titration: i. burette


ii. pipette iii. conical flask


8. A group of students carried out an investigation to find out how much hydrochloric acid was required to neutralise sodium hydroxide base. Their results were recorded in the following table:


Trial Volume of acid (cm3 1 2 3


Average a. Calculate the average volume of acid (cm3 ) required to neutralise the base.


b. Do you think these results are precise? Justify your answer. c. Name the products produced in this neutralisation reaction.


d. Describe how you would separate the salt and water at the end of this investigation. Use a diagram to support your answer.


220 Elements of Science


) required to neutralise the base 19.6 20.5 20.6


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