Acids are substances turn litmus paper red and have a pH of less than 7.

Alkalis are substances that turn litmus paper blue and have a pH more than 7. Alkalis are soluble bases.

Acids and Bases can cancel each other out to become neutral. Neutral substances have a pH of 7.

The pH scale measured using Universal Indicator shows the strength of acids and alkalis from 1 to 14.

Pure water is neutral.

The pH of soil affects flower colour.

•Hydrangea flowers are blue in acidic soil with a pH of 5.5 or lower. Blooms are pink if soil pH is 7 or higher.

Indicators

Indicators are substances that change colour in solutions of different acidity and alkalinity.

Examples are:

•natural pH indicators include: Beets: A very basic solution (high pH) will change the color of beets or beet juice from red to purple. Blackberries: Blackberries, black currants, and black raspberries change from red in an acidic environment to blue or violet in a basic environment

•Red cabbage

•Litmus

•Phenolphthalein

•Methyl orange

•Universal indicator

•Litmus, phenolphthalein, methyl orange etc do not show how strong or weak an acid or alkali is, but Universal indicator does.

•Universal indicator is a mixture of indicators that give a range of colours which correspond to the pH of a solution.

•Using a pH meter is a more accurate way of measuring the pH numerically.

•Using pH paper and Univeral Indicator solution shows the colour change and is a simpler way to measure pH.

Neutralisation reactions

This is a chemical reaction where an acid and base react together to form a salt and water.

Acid + Base → Salt + Water

Alkalis are bases that are soluble in water.

Acid + Alkali → Salt + Water

Acids and Alkalis cancel each other out (neutralize)

Neutralization produces substances called salts.

•Hydrochloric acid produce ‘chloride’ salts

•Sulphuric acid produces ‘sulphate’ Salts

•Nitric acid produces ‘nitrate’ salts

Examples of neutralisation reactions:

hydrochloric acid + sodium hydroxide → sodium chloride + water

sulphuric acid + lithium hydroxide → lithium sulphate + water

nitric acid  + potassium hydroxide → potassium nitrate + water

Titration

Titrations are often carried out by using a neutralization reaction between an acid and an alkali. <!–

Titrations can tell you the volume of acid needed to neutralise a fixed volume of alkali.

Neutralisation in daily life

Examples of neutralisation reactions in daily life:

•If soil is too acidic, farmers add lime (an alkali) to cancel out the acid and make soil neutral.

•If soil is too alkaline, farmers add manure (acidic) to make soil neutral

•Nitric acid and Ammonium hydroxide (alkali) react to form Ammonium nitrate which is used to fertilize soil (allow plants to grow healthy.)

•Too much acid in the stomach causing heartburn and indigestion can be neutralized by an antacid such as Milk of Magnesia containing magnesium hydroxide (base)

•Toothpaste contains bases like magnesium hydroxide and calcium hydroxide which react with acids in your mouth to reduce acidity.

•Bee stings are acidic and can be neutralized with weak alkalis such as baking soda.

•Wasp stings are alkaline and can be neutralized with a weak acid like vinegar.

•Rust is a base called iron oxide. It can be removed by neutralization with sulphuric acid.

•Acidic waste gases from industries are neutralized by sprays of calcium hydroxide to prevent acid rain.

Hazard Symbols

•A Hazard is something that can cause harm.

•Acids and Alkalis may cause harm. They can be corrosive when concentrated and when dilute can be irritants.