Science - Unit 5 - Acids And Alkalis

What is an indicator?

Acidic and alkaline solutions may be compared using the pH scale. pH is a measure of the concentration of hydrogen ions in a solution.

A colour change will indicate the presence of an acid or an alkali.

A natural indicator can be made from red cabbage.

Litmus paper can determine whether a solution is an acid or alkali. Red litmus paper will turn blue in the presence of an alkaline, blue litmus paper will turn red in the presence of an acid.

Universal indictor (UI) is a scientific indicator used to determine the pH of a solution. Acids appear orange/red, neutral appears green and alkaline solutions appear blue/purple depending on whether they are strong or weak.

How does the pH scale work?

Acidic and alkaline solutions may be compared using the pH scale. pH is a measure of the concentration of hydrogen ions in a solution.

A colour change will indicate the presence of an acid or an alkali.

A natural indicator can be made from red cabbage.

Litmus paper can determine whether a solution is an acid or alkali. Red litmus paper will turn blue in the presence of an alkaline, blue litmus paper will turn red in the presence of an acid.

Universal indictor (UI) is a scientific indicator used to determine the pH of a solution. Acids appear orange/red, neutral appears green and alkaline solutions appear blue/purple depending on whether they are strong or weak.

What are the noticeable differences between alkali and acidic reactions?

Students will know that an acid and alkali will neutralise each other and produce a salt and water. This is called a neutralisation reaction.

The name of the salt produced can be worked out from the names of the acid and the alkali.

Chemical equations can be written to describe a neutralisation reaction.

Metals can react with acids to form a new product. Students will know that a salt made from hydrochloric acid will end in chloride. A salt made from nitric acid will end in nitrate. A salt made from sulfuric acid will end in sulfate.

How is data interpreted in a practical situation?

Students will know that a strong acid can be neutralised by a strong alkali. Weak acids are neutralised by a weak alkali. Students will know that a strong acid cannot be neutralised by a weak alkali.

What is acid rain?

Students will know that chemical reactions between sulphur dioxide and water in the atmosphere may cause a decrease in the pH of rainwater. This is called acid rain. The sulphur compounds released into the atmosphere from burning fossil fuels.

Students will know that acid rain damages the waxy layer on the leaves of trees. This makes it more difficult for trees to absorb the minerals they need for healthy growth and they may die. Acid rain also makes rivers and lakes too acidic for some aquatic life to survive.