Frequently Asked Questions: Mixtures

Q. When substances dissolve, is it always a solid dissolved in a liquid?
A. No.

• Solids can dissolve in solids (e.g. In alloys of metals such as stainless steel, the three metals, iron nickel and chromium, are melted and mixed as if they dissolve in each other).
• Liquids can dissolve in liquids (e.g. cordial dissolves in water).
• Gases can dissolve in gases (e.g. The air around us is a mixture of many gases such as nitrogen and oxygen).
• Gases can dissolve in liquids (e.g. Carbon dioxide dissolves in soft drink).

Q. Why do soft drinks left opened go 'flatter' faster on a hot day?
A. Solids such as sugar dissolve better in hotter water. However, it is the opposite effect with gases. Gases dissolve better in colder water, and will evaporate out of the water (e.g. when soft drink goes 'flat') when it is hotter.

Q. Why is the ocean getting saltier?
A. Salt in rocks on land washes down to the oceans after rain. The pure water in the oceans is constantly evaporating so the ocean water is becoming more salty.

Q. How do they get the bubbles in soft drink?
A. Carbon dioxide gas is forced under pressure to dissolve in the cold coloured flavoured water.