Exercises: Elements and compounds

Define an element and a compound, and give one example of each.

Classify each substance as an element or a compound: oxygen, water, iron, carbon dioxide, sodium chloride, gold.

Name the elements present in each compound:

1. a) water ($\text{H}_2\text{O}$)

1. b) carbon dioxide ($\text{CO}_2$)

1. c) sodium chloride (NaCl)

Iron filings and sulfur powder are mixed in a dish. A magnet removes the iron. The mixture is then heated strongly, and a dark grey solid, iron sulfide, forms. The magnet no longer attracts it.

1. a) Was the first stage forming a mixture or a compound?

1. b) Explain the evidence that iron sulfide is a compound.

1. c) Why can the iron not be separated using a magnet after heating?

Copper is used in electrical wiring in Irish homes, and sulfur is a yellow, brittle solid.

1. a) Classify each as a metal or a non-metal.

1. b) Give three physical properties that distinguish metals from non-metals.

1. c) Explain why copper is suitable for wiring.

The table gives properties of four elements.

1. a) Which elements are metals?

1. b) Which elements are non-metals?

1. c) Explain how you decided.

Sodium is a soft, reactive metal and chlorine is a poisonous green gas. Together they form sodium chloride, which is table salt.

1. a) Is sodium chloride an element, a compound or a mixture? Justify.

1. b) Compare the properties of sodium chloride with those of its elements and explain what this shows about compounds.

1. c) Describe how the composition of sea salt dissolved in water differs from that of sodium chloride.

Air is a mixture of nitrogen, oxygen, argon and carbon dioxide.

1. a) Classify each gas as an element or a compound.

1. b) Explain why air is a mixture and not a compound. Give two reasons.

1. c) A student says: "Water is a mixture of hydrogen and oxygen." Evaluate this statement.

A scientist is given a grey shiny solid. It conducts electricity, can be hammered into sheets and does not break down when heated.

1. a) What kind of substance is it most likely to be? Justify with evidence.

1. b) Which further test or observation could help show that it is a single element rather than a compound?

1. c) Explain why a non-metal is generally unsuitable for making cooking pots, whereas a metal is suitable.