topic 2

• What is the definition of a mixture in chemistry?

  A mixture consists of 2 or more elements or compounds not chemically combined together.
• How do the chemical properties of substances in a mixture compare to those in a pure substance?

  The chemical properties of each substance in a mixture are unchanged.
• What is a pure substance in chemistry?

  A pure substance is a single element or compound, not mixed with any other substance.
• How does the everyday use of 'pure' differ from its use in chemistry?

  In everyday language, a pure substance is one that has had nothing added to it, making it unadulterated.
• What distinguishes pure substances from mixtures based on melting point data?

  Pure substances have a sharp melting point, while mixtures melt over a range of temperatures.
• How can melting and boiling point data be used in chemistry?

  Melting and boiling point data can be used to distinguish pure substances from mixtures.
• What are the experimental techniques for separating mixtures?

  • Simple distillation
  • Fractional distillation
  • Filtration
  • Crystallisation
  • Paper chromatography
• What is the purpose of simple distillation?

  Simple distillation is used to separate a solvent from a solution.
• Why is simple distillation effective for separating a solvent from a solution?

  It works because the dissolved solute has a much higher boiling point than the solvent.
• What happens to the solution during simple distillation?

  The remaining solution becomes more concentrated in solute as the amount of solvent decreases.
• What is fractional distillation used for?

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

  It works when the liquids have different boiling points.
• What is an example of fractional distillation in practice?

  It is commonly used to separate ethanol from water.
• What happens to ethanol during fractional distillation?

  Ethanol has a lower boiling point than water, so it evaporates first.
• What is the sequence of events in fractional distillation?

  The sequence is heating -> evaporating -> cooling -> condensing.
• How does fractional distillation separate hydrocarbons in crude oil?

  It separates hydrocarbons into fractions, each containing molecules with a similar number of carbon atoms.
• What is the purpose of filtration in separating mixtures?

  Filtration is used to separate an insoluble precipitate from a solution.
• How does the fractionating column work in fractional distillation?

  The fractionating column works continuously, with vaporized oil rising and condensing at different temperatures.
• What is the process of crystallisation used for?

  Crystallisation is used to separate a soluble salt from the solution it is dissolved in.
• What are the steps involved in crystallisation?

  1. Warm the solution to evaporate the solvent, 2. Allow the solution to cool, 3. Collect and dry the crystals.
• What is the purpose of paper chromatography?

  Paper chromatography is used to separate mixtures and identify substances.
• What are the two phases involved in chromatography?

  Chromatography involves a stationary phase and a mobile phase.
• How does separation occur in chromatography?

  Separation depends on the distribution of substances between the stationary and mobile phases.
• What is the Rf value in chromatography?

  The Rf value is calculated as the distance moved by the substance divided by the distance moved by the solvent.
• How do Rf values help in identifying compounds?

  Different compounds have different Rf values in different solvents, aiding in identification.
• What does a pure compound produce on a chromatogram?

  A pure compound will produce a single spot in all solvents.
• What do impure substances show on a chromatogram?

  Impure substances will show more than one spot on a chromatogram.
• How can substances be identified using paper chromatography?

  By comparing the height of spots with known substances on the same paper.
• How can Rf values be used for identification?

  Rf values can be calculated and compared to known values for different substances.
• What is the core practical for investigating the composition of inks?

  • Use simple distillation
  • Use paper chromatography
• What is potable water?

  Potable water is suitable for drinking and must have low levels of microbes and contaminants.
• What are the steps to make waste and ground water potable?

  1. Sedimentation, 2. Filtration, 3. Chlorination.
• What occurs during sedimentation in water treatment?

  Large insoluble particles sink to the bottom of the water.
• What is the purpose of chlorination in water treatment?

  Chlorination is used to kill microbes in the water.
• How does filtration work in making water potable?

  Water is filtered through beds of sand to remove small insoluble particles.
• How can seawater be made potable using distillation?

  1. Filter the seawater, 2. Boil it, 3. Cool and condense the water vapor.
• Why must water used in analysis be pure?

  It must be pure because dissolved salts could react with the substances being analyzed, leading to false results.
• What are the three states of matter?

  Solid, liquid, and gas
• What are the processes of melting and freezing?

  • Melting: solid → liquid at the melting point
  • Freezing: liquid → solid at the melting point
• What are the processes of boiling and condensing?

  • Boiling: liquid → gas at the boiling point
  • Condensing: gas → liquid at the boiling point