Acids and Alkalis (KS3)

(Sources: BBC Bitesize and my own lessons at school!)

Define ‘acid’

A substance with a pH of <7 which releases positive hydrogen ions when dissolved (H+). Physical properties include a sour taste.

Define ‘alkali’

A substance with a pH of >7 that releases negatively charged hydroxide ions (OH-); a base that dissolves in water. Physical properties include a soapy/slippery feeling. They can also be referred to as a base or basic substance.

Define ‘base’

A substance that neutralises an acid.

What is the pH range for weak acids?

6-4

What is the pH range for strong acids?

3-0

What is the pH range for weak alkalis?

8-10

What is the pH range for strong alkalis?

11-14

What does pH stand for?

Power of hydrogen

What is a salt?

A substance that is formed by the neutralisation of an acid using an alkali; it is soluble and often has a crystalline appearance.

What is the word equation for neutralisation?

Acid + Alkali → Salt + Water

What is the neutral pH?

7

What is an example of an indicator?

Litmus/Litmus paper

Define ‘indicator’

A substance which changes colour when exposed to an acid/base, revealing whether it is one of the two.

Define ‘universal indicator’

A substance which changes colour when exposed to an acid/base, revealing the exact pH based off of a chart.

What is saponification?

A fat or oil turned into a soap via alkaline reaction.

What is hydrolysis?

A chemical compound breaking down from a reaction with water or hydrogen-related compounds.

On the pH scale, metal oxides are…

Basic/Alkaline

On the pH scale, non-metal oxides are…

Acidic

What happens when there is too much of either an acid or a base?

The salt formed becomes either slightly acid or alkaline

Why is water produced alongside a salt?

Due to the positive hydrogen ions from the acid and and the negative hydrogen ions from the alkali forming bonds.

Is salt normally neutral?

Yuh huh bro, pH of 7

What are real-life examples of alkalis?

Cleaning products such as soap and drain cleaner. Baking soda can also be used to treat bee venom and they can be found in certain medications to alleviate stomach acid issues.

What are real life examples of acids?

Lemon juice (pH of 2), vinegar; sulphuric acid in labs.

How are salts named?

By combining the first name of the acid and the metal of the alkali

Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water

What is crystallisation?

Crystals forming from evaporated liquids (in the case of acids and alkalis, salt crystals are formed as the water evaporates from the mixture)

What is flavin?

A pigment that can act as a universal indicator.

Where can flavin commonly be found?

Apple skin, red cabbage, poppies, cornflowers, plums, grapes, etc.

What is flavin’s natural colour?

Purple

What is chemical weathering?

The process of chemicals, primarily acidic, causing erosion often by wet deposition.

Why are cleaning products alkaline?

Because the higher pH helps to break down acidic substances/oils/fats/bacteria. When paired with a disinfecting agent, alkalis make excellent and versatile cleaning products.