Acids, Bases & pH — Drills · Grade 8 Science

Chapter: Chemistry

What these drills covers

By the end of Acids, Bases & pH you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: acid, base, pH scale, indicator, neutralization, model, evidence, system boundary, assumption.

Problem 1

A solution with pH 3 is
  1. strongly basic
  2. weakly basic
  3. acidic
  4. neutral
Answer and explanation

acidic

Below 7 is acidic; 7 is neutral; above 7 is basic.

Problem 2

What is the pH of a neutral solution at room temperature?
Answer and explanation

7

Pure water at room temperature has pH 7.

Problem 3

Moving from pH 5 to pH 3 means the hydrogen-ion concentration has become
  1. 2 times larger
  2. 20 times larger
  3. 100 times larger
  4. half as large
Answer and explanation

100 times larger

Each pH unit is a factor of ten, so two units is 10 × 10 = 100.

Problem 4

A solution of pH 9 is how many pH units from neutral?
Answer and explanation

2

9 − 7 = 2 units above neutral, so it is basic.

Problem 5

Mixing an acid with a base produces
  1. a stronger acid
  2. a salt and water
  3. only gas
  4. no change
Answer and explanation

a salt and water

Neutralisation forms a salt and water, moving the pH toward 7.

Problem 6

An indicator is useful because it
  1. changes the pH
  2. shows the pH by changing colour
  3. neutralises the solution
  4. measures temperature
Answer and explanation

shows the pH by changing colour

Indicators report pH through a colour change without altering what is being measured appreciably.

Problem 7

Explain why pH 4 and pH 6 are not 'almost the same' even though the numbers are close.
Answer and explanation

The scale is logarithmic, so each unit is a tenfold change in hydrogen-ion concentration. pH 4 therefore has a hundred times the hydrogen-ion concentration of pH 6, which is a large difference in how the solution behaves — in how fast it corrodes a metal, for instance, or how it affects living things. Close numbers on this scale do not mean close concentrations.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Describe how you would compare the acidity of three household liquids fairly.
Answer and explanation

Use the same measuring method on all three — the same indicator paper or the same calibrated meter — at the same temperature, with clean equipment rinsed between samples so one liquid does not contaminate the next. Use equal volumes, record each reading, and repeat each measurement so a single misreading is visible. Report the readings with the method used, since paper gives a coarser value than a meter.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Browse all courses