Acids & Bases

This lesson covers:

  1. What the pH scale is
  2. How we can measure the pH of a solution
  3. The definitions of acids, alkalis, and bases
  4. Examples of neutralisation reactions

We measure the acidity or alkalinity of a solution using the scale. 

pH

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Illustration showing three flasks with coloured liquids representing different pH levels.

The pH scale ranges from:

0 to 14

0 to 7

-14 to 7

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Diagram of a pH scale highlighting the neutral point at pH 7.

What term can be used to describe solutions with a pH of 7?

Balanced

Acidic

Neutral

Alkaline

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Illustration of a pH scale highlighting the range from 0 to 7 indicating acidic solutions.

What term can be used to describe solutions with a pH lower than 7?

Alkaline

Neutral

Acidic

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Illustration of a pH scale showing values from 0 to 14 with colours ranging from red to purple.

What term can be used to describe solutions with a pH greater than 7?

Neutral

Acidic

Alkaline

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Illustration showing stomach acid with a pH level.

What pH does stomach acid typically have?

About 2

About 7

About 12

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Select two ways by which the pH of a solution can be measured.

pH probe

Distillation

Chemical indicator 

Reaction with water

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The pH of a solution can be measured using a type of chemical dye that changes colour, depending on the pH of the substance it's mixed with.


This chemical dye is usually referred to as:

pH dye

Acidity checker

Indicator solution

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indicator is made up of a several different indicator solutions. This means that it undergoes a smooth colour change over a wide range of pH values. 


It becomes more in colour in acidic solutions, but more bluey-purple in solutions.

Universal
red
alkaline

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What is the pH of pure water?

7

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A pH probe electronically measures the pH of a solution.


Select two reasons why using a probe may be more reliable than using an indicator.

Determining the colour of an indicator is subjective

A probe produces a more accurate result

A probe can be used in strongly acidic solutions

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A substance that forms an aqueous solution with a pH less than 7 is:

An ion

A base

An acid

An alkali

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pH scale highlighting the alkaline range from 8 to 14

Select the ion responsible for making an alkaline pH when dissolved in solution:

Na+

OH-

H+

H2O-

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Which of the following formulae represents nitric acid?

NaOH

HCl

H2SO4

HNO3

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Which of the following are acids?

(Select all that apply)

HNO3

CaCO3

HCl

H2SO4

NaOH

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Which of the following is represented by the formula CaCO3?

Calcium hydroxide

Carbon dioxide

Calcium carbonate

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