Exercises: Indicators, pH and neutralisation

State whether each solution is acidic, neutral or alkaline:

1. a) pH 2

1. b) pH 7

1. c) pH 11

1. d) pH 6

State the colour of each indicator in an acidic solution and in an alkaline solution:

1. a) Litmus

1. b) Universal indicator (approximate colours)

Name the products formed when an acid reacts with an alkali, and write the general word equation for neutralisation.

Write word equations and balanced symbol equations for:

1. a) Hydrochloric acid reacting with sodium hydroxide.

1. b) Sulfuric acid reacting with sodium hydroxide, giving sodium sulfate and water.

A farmer in Co. Meath finds that the soil in a field has a pH of $4.5$. Crops grow poorly.

1. a) State whether the soil is acidic or alkaline.

1. b) Name a substance, such as lime (calcium hydroxide or calcium carbonate), that can be added to the soil, and explain what happens.

1. c) Predict whether the pH after treatment would be higher or lower than $4.5$.

A student adds dilute sodium hydroxide, a little at a time, to $25$ cm³ of dilute hydrochloric acid containing a few drops of universal indicator, and records the colour.

1. a) Describe the colour changes expected from start to finish.

1. b) State the pH and colour at the point of neutralisation.

1. c) Explain why the pH rises as alkali is added.

Antacid tablets containing magnesium hydroxide are taken to relieve indigestion caused by excess hydrochloric acid in the stomach.

1. a) Write a balanced symbol equation for the reaction.

1. b) Explain why the tablet is a better choice than a strong alkali such as sodium hydroxide.

1. c) Explain why the pH of the stomach should not become too high.

Solution A has a pH of $3$ and solution B has a pH of $5$.

1. a) State which is more acidic.

1. b) Given that each decrease of one pH unit means a tenfold increase in hydrogen ion concentration, calculate how many times greater the hydrogen ion concentration is in A than in B.

1. c) A student says "solution B has a pH of $5$, so it is neutral". Explain why the student is wrong.

A lake in Co. Wicklow is affected by acid rain, with a measured pH of $4.8$.

1. a) Describe the sources of the gases that cause acid rain.

1. b) Explain how adding powdered limestone, calcium carbonate, to the lake would help, and write a word equation for the reaction between calcium carbonate and an acid.

1. c) Explain two effects on aquatic life of the lake's low pH.