Test: Acidity and indicators - Year 7 MCQ

Citric acid is an acid found in citrus fruits like lemons. Sodium hydroxide and potassium hydroxide are alkalis, and soap is typically made with alkalis.

Tea is an example of a weak acid, with a pH close to neutral. Hydrochloric acid and sulfuric acid are strong acids, and citric acid, though weaker than the other two, is still stronger than tea.

A universal indicator turns purple when it comes into contact with a strong alkali, indicating a high pH value (towards 14 on the pH scale).

A universal indicator turns green when it comes into contact with a solution that has a pH close to 7, indicating a neutral or slightly alkaline substance.

When handling strong acids and alkalis, it is important to use protective equipment such as safety goggles, lab coats, and gloves to prevent injury from corrosive or irritant substances.

Acids typically start with hydrogen in their chemical formulas, such as HCl for hydrochloric acid and H₂SO₄ for sulfuric acid. Alkalis often end with hydroxide, and the presence of carbon is more indicative of organic compounds.

Hydrangea flowers can be blue or pink depending on the pH of the soil

The acid kills bacteria and helps to begin the process of digesting proteins

Vinegar, being a weak acid with a pH around 2-3, would turn a universal indicator yellow. Soap and potassium hydroxide are alkalis, and bleach is a strong alkali, all of which would turn the indicator blue or purple.