Chemical analysis

• What can you use to analyse chemically pure substances?

  The melting and boiling points.
• What is meant by purity?

  When only one compound or element is present.
• Name the techniques for testing for purity.

  Melting point analysis

  boiling point analysis
• Outline the process of melting point analysis.

  in this method, crystals of solid substances are added into a small vessel called a capillary tube. This tube is placed inside a melting point device. Gradually, this machine increases the samples temperature until it’s hot enough to melt. a small viewing window is available in the machine for observation. a pure substance will melt at exactly their melting point whilst impure ones melt below the melting point of the substance and at a range of temperatures.
• Outline the process of boiling point analysis.

  in this method the temperature of a liquid is increased and the temperature where it starts boiling is measured. Pure substances will melt at their exact melting point whilst impure ones boil at higher temperatures over a wider range.
• What is a formulation?

  A formulation is a mixture designed to be a useful product. They're made by mixing components in carefully measured quantities to ensure the product has the required properties.
• What can happen if the components of a formula are in the wrong ratio?

  They can potentially be dangerous

  They can be less useful.
• What is a common example of formulation?

  Paint: pigment, solvent, binder and additives. Medicines, soft / alcohol drinks, metal alloys, cleaning products.
• In paint what are the chemicals used for?

  Pigments: give colour mostly this is a metal oxide.

  solvent: dissolves other components producing a solution and alters the viscosity. this complement will evaporate off when paint is applied.

  Binder: makes the paint stick.

  Additives: give the paint desired properties- gloss / matte finish, glow in the dark.
• what is chromatography?

  A technique used to separate mixtures into their compounds. Paper chromatography can also be used to identify different compounds / chemicals present in the mixture.
• what is the stationary phase?

  where the molecules are stationary during chromatograph. it is a solid or a liquid supported on a solid. This is the chromatography paper.
• What is the mobile phase?

  Where the molecules can move during chromatography. It’s always liquid or gas. This is the solvent.
• What’s the analyte?

  The mixture of compounds being separated in a chromatography experiment.
• Paper chromatography

  1. Draw a straight line across a rectangle of chromatography paper 2cm in from the short edge

  2. Pour solvent into a beaker to a depth of 1cm

  3. Using a pipette drop a sample of ink on to the middle of the pencil line and draw a circle around it in pencil

  4. Place the chromatography paper into the beaker so that the starting line is just above the solvent

  5. Ensure the ink doesn't fall below the solvent surface

  6. Place a watch glass over the top of the beaker and let the solvent front move up the chromatography paper

  7. When it is about 1 cm from the top of the paper remove the paper from the beaker

  8. Using pencil draw a line across the solvent front and circle the spots left by the separation of the ink
• Paper chromatography is a *REQUIRED PRACTICAL*
• How do you analysis paper chromatograph?

  using a ruler measure the distance the solvent has travelled. Measure each ink spot. calculate the Rf value.
• How do you calculate the Rf value?

  Rf value is calculated by dividing the distance traveled by the solute by the distance traveled by the solvent.
• Explain what happens to the analyte in paper chromatography as it moves up the paper.

  The attraction between components and the stationary chroma paper separated them out. Compounds that are more polar will move a small distance up the paper before they become stuck others with weaker attractions will move a greater distance.
• How do you test for hydrogen?

  Squeaky pop test.
• Give the steps of the squeaky pop test.

  Collect the gas to be tested in a test tube. Take a pit split and hold it to the mouth of the test tube. If hydrogen is present a squeaky pop sound will occur.
• What’s the test for oxygen?

  Embering splint.
• What’s the test for oxygen?

  Glowing splint.
• Give the steps of the glowing splint test.

  Collect the gas wanting to be tested in a test tube. Take a lit split and blow out the flame. Put the glowing splint into the test tube. If oxygen is present the flame will reignite.
• What’s the test for carbon dioxide?

  Limewater.
• Give the steps in the lime water test.

  Pass the gas wanting to be tested through limewater. The limewater will become cloudy if carbon dioxide is present.
• how do you test for chlorine?


  damp litmus paper.
• What are the steps in using damp litmus paper?

  collect the gas wanting to be tested in a test tube. Take a piece of damp blue litmus paper and place it in the tube. If chlorine is present the litmus paper will become bleached; turn blue to white.
• How do you identify a metal ion?

  Flame test as the different metal ions produce different colour flames.
• What colour flame does lithium produce when burnt?

  crimson.
• What colour flame does sodium produce when burnt?

  Yellow.
• What colour flame does potassium produce when burnt?

  Lilac.
• What colour flame does calcium produce when burnt?

  Orange/red.
• What colour flame does copper produce when burnt?

  Green.
• Metal ions can be identified using ..?

  Sodium hydroxide.
• How does sodium hydroxide indicate metal ions.

  They form metal hydroxide precipitates. The chem oak behaviours of the precipitates and their colours will identify the presence of a given ion.
• Which metal ions form white precipitates?

  Calcium, magnesium and aluminium.
• Aluminium hydroxide can be identified using more sodium hydroxide. why?


  Aluminium oxide is the only precipitate that dissolves in excess sodium hydroxide.
• What Metal do blue precipitates indicate?

  Copper.
• What metal do green precipitates indicate?

  Iron (II)
• What metal do brown precipitates indicate?

  iron (III)