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Year 10
AQA
Higher

Change in pH: practical

I can investigate the change in pH on adding base to a fixed volume of acid.

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New
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Year 10
AQA
Higher

Change in pH: practical

I can investigate the change in pH on adding base to a fixed volume of acid.

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Lesson details

Key learning points

  1. When powdered hydroxide/oxide (base) is added to an acidic solution there is an increase in pH.
  2. pH changes quickly around the neutralisation point.
  3. Indicators, such as Universal Indicator paper, can be used to collect quantitative data on pH.
  4. pH can be plotted on a graph to find the quantity of base required to neutralise an acid.

Keywords

  • PH - A measure of the hydrogen ion (H⁺) concentration in a solution.

  • Neutralisation - A chemical reaction between an acid and base to produce a neutral solution of a metal salt and water.

  • Base - A substance that neutralises an acid to form a salt and water.

  • Quantitative - Refers to a measurement of quantity. A numerical value.

Common misconception

All added calcium hydroxide dissolves completely, and the pH readings are accurate without consistent mixing.

Calcium hydroxide has low solubility in water, so not all of it dissolves readily. Consistent mixing ensures uniform pH readings. Without proper mixing, pH readings can be inaccurate, leading to incorrect conclusions about the neutralisation point.

Emphasise consistent mixing and accurate measurements. Encourage students to stir thoroughly after each addition of calcium hydroxide for uniformity. Use a pH meter for precision and record data systematically to understand the importance of accuracy in experiments.
Teacher tip

Equipment

UI paper, white tiles, dilute HCl, measuring cylinders, beakers, glass rods, top-pan balance, weighing boats, spatulas, calcium hydroxide powder, graph paper, rulers, UI pH scales.

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
What happens to the pH when a base is added to an acidic solution?
the pH decreases
Correct answer: the pH increases
the pH stays the same
the pH becomes negative
Q2.
What is the purpose of Universal Indicator paper?
to measure the temperature of a solution
to detect whether a substance contains metal ions
Correct answer: to determine the pH of a solution by showing a range of colours
to identify whether a gas is being produced
Q3.
What does plotting pH changes on a graph help determine?
the rate of temperature change
Correct answer: the point at which neutralisation occurs
the volume of liquid in a beaker
the exact amount of gas released
Q4.
Why is accurate data collection important?
to ensure safety in the laboratory
to save time during an experiment
Correct answer: to ensure reliable and reproducible results
to make sure equipment is clean
Q5.
What is observed when pH changes around the neutralisation point?
the temperature of the solution increases
the pH remains constant
a gas is produced
Correct answer: the indicator changes colour suddenly
Q6.
What does a colour change on the Universal Indicator paper indicate?
the temperature of the solution has increased
a chemical reaction has finished
Correct answer: the pH of the solution has changed
the solution has become saturated

Exit quiz

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6 Questions

Q1.
Match each of the following key terms to the correct definitions.
Correct Answer:pH,a measure of hydrogen ion concentration

a measure of hydrogen ion concentration

Correct Answer:neutralisation,a reaction between an acid and a base

a reaction between an acid and a base

Correct Answer:base,increases pH when added to an acid

increases pH when added to an acid

Correct Answer:quantitative,data represented as numerical values

data represented as numerical values

Correct Answer:hydrogen ion (H⁺),responsible for acidity in a solution

responsible for acidity in a solution

Q2.
What happens to the pH of a basic solution when an acid is added?
Correct answer: the pH decreases
the pH increases
the pH stays the same
the pH becomes negative
Q3.
What is neutralisation?
A reaction that lowers the pH of a solution.
Correct answer: A reaction between an acid and a base to form salt and water.
The process of dissolving a solid in water.
The reaction between an acid and a metal.
Q4.
How does pH change near the neutralisation point?
the pH remains constant
the pH decreases slowly
Correct answer: the pH increases or decreases rapidly
the pH slowly increases then levels off
Q5.
What can be determined by plotting pH on a graph during neutralisation?
the rate of temperature change
Correct answer: the amount of acid required to neutralise the base
the concentration of the base
the speed of the reaction
Q6.
Which of the following is an example of a base?
hydrochloric acid
Correct answer: sodium hydroxide
sulfuric acid
carbon dioxide