States of matter

• What is the difference between 'pure' in chemistry and everyday use?

  In chemistry, 'pure' means a single substance.
• What defines a mixture in chemistry?

  Consists of 2 or more substances not chemically combined.
• How do the chemical properties of substances in a mixture behave?

  They remain unchanged in a mixture.
• What is a pure substance in chemistry?

  A single element or compound, not mixed.
• How is 'pure' defined in everyday language?

  A substance that is unadulterated and natural.
• What is the melting point characteristic of pure substances?

  They have a sharp melting point.
• How do mixtures behave in terms of melting and boiling points?

  They melt over a range of temperatures.
• What technique is used to separate a pure liquid from a mixture of liquids?

  Fractional distillation.
• What is the principle behind fractional distillation?

  It separates liquids with different boiling points.
• What is a common application of fractional distillation?

  Separating ethanol from water.
• What happens to ethanol during fractional distillation?

  Ethanol evaporates first due to lower boiling point.
• What is the sequence of events in distillation?

  Heating -> evaporating -> cooling -> condensing.
• What is the purpose of simple distillation?

  To separate a solvent from a solution.
• Why is simple distillation effective for salt solutions?

  The solute has a higher boiling point than the solvent.
• What happens to the solution during simple distillation?

  The remaining solution becomes more concentrated in solute.
• What is the purpose of filtration in separating mixtures?

  To separate insoluble particles from a solution.
• What is the process of crystallisation used for?

  To separate soluble salts from a solution.
• What is the first step in crystallisation?

  Warm the solution to evaporate the solvent.
• What happens after warming the solution in crystallisation?

  Allow the solution to cool to form crystals.
• What does paper chromatography separate?

  Mixtures of soluble substances.
• What are the two phases involved in chromatography?

  The stationary phase and the mobile phase.
• What does the Rf value represent in chromatography?

  Distance moved by substance / distance moved by solvent.
• How do Rf values help in identifying compounds?

  Different compounds have different Rf values.
• What indicates a pure compound on a chromatogram?

  It produces a single spot in all solvents.
• What indicates an impure substance on a chromatogram?

  It shows more than one spot on the chromatogram.
• How can substances be identified using known substances in chromatography?

  Compare heights of spots on the same paper.
• How can Rf values be used for identification?

  Calculate Rf values and compare with known values.
• What is the purpose of investigating ink composition using chromatography?

  To separate and identify different pigments.
• What is potable water?

  Water suitable for drinking.
• What are the requirements for water to be considered potable?

  Low levels of microbes and contaminants.
• What is the first step in making waste water potable?

  Sedimentation to remove large particles.
• What is the purpose of filtration in making water potable?

  To remove small insoluble particles.
• What is the role of chlorination in water treatment?

  To kill microbes in the water.
• What is the process of making sea water potable using distillation?

  Boil, then cool and condense the vapor.
• What is the process for investigating color dyes in an ink sample using chromatography?

  1. Draw a starting line 2 cm above the bottom.
  2. Place a drop of ink on the starting line.
  3. Place the bottom of the paper into water.
  4. Leave until water reaches the top.
  5. Observe the distances traveled by each dye.
  6. Calculate Rf values.
• What is the purpose of the investigation described?

  To determine the Rf value for a dye
• What is the first step in the method for the investigation?

  Draw a pencil start line on chromatography paper
• How far from the bottom should the start line be drawn on the chromatography paper?

  1-2 cm from the bottom
• Where should the spot of food coloring be placed?

  On the start line
• What is the role of the solvent in this investigation?

  To carry the dye up the chromatography paper