mixtures

• What is the definition of a pure substance in chemistry?

  A pure substance consists only of one element or one compound.
• How does the everyday meaning of 'pure' differ from its chemical meaning?

  In chemistry, 'pure' means only one element or compound, not mixed with others.
• What is a mixture in chemistry?

  A mixture consists of two or more different substances that are not chemically joined together.
• What happens to the chemical properties of substances in a mixture?

  Being part of a mixture does not change the chemical properties of the substances.
• How can mixtures be separated?

  Mixtures can be separated by physical processes.
• What is the principle behind filtration?

  Filtration separates an insoluble solid from a liquid using filter paper.
• What is an example of filtration in practice?

  Separating sand from a mixture of sand and water.
• Why does filtration work?

  Filtration works because filter paper has tiny holes that allow small molecules and dissolved ions to pass through.
• What is crystallisation used for?

  Crystallisation is used to produce solid crystals from a solution.
• How does crystallisation work?

  Crystallisation works by warming a solution to evaporate some solvent, leaving crystals behind.
• What is the process to obtain large, regularly shaped crystals from crystallisation?

  Warm the solution, stop heating when crystals form, then cool and filter the excess liquid.
• What is simple distillation used for?

  Simple distillation is used to separate a solvent from a solution.
• How does simple distillation work?

  Simple distillation works because the dissolved solute has a higher boiling point than the solvent.
• What is an example of simple distillation?

  Producing pure water from seawater.
• What is fractional distillation used for?

  Fractional distillation is used to separate different liquids from a mixture of liquids.
• How does fractional distillation work?

  Fractional distillation works because different liquids have different boiling points.
• What happens to vapours during fractional distillation?

  Vapours rise through a column that is hot at the bottom and cooler at the top.
• How are different liquids collected during fractional distillation?

  Different liquids are collected from different parts of the column based on their boiling points.
• What is paper chromatography used for?

  Paper chromatography is used to separate mixtures of soluble substances.
• What are the two phases in chromatography?

  The stationary phase is absorbent paper, and the mobile phase is the solvent.
• How does chromatography separate substances in a mixture?

  Different dissolved substances are attracted to the two phases in different proportions, causing them to move at different rates.
• What does a chromatogram indicate about a pure substance?

  A pure substance produces one spot on the chromatogram.
• How can a chromatogram be used to identify substances?

  Two substances are likely the same if they produce the same number of spots that match in color and travel the same distance.