Chemical Analysis (purity, formulations & chromatography, identification of common gases, methods of identifying ions)

• What's a pure substance?

  May consist of a single element or compound which contains no other substance
• What's a mixture?

  Consists of two or more elements or compounds that are not chemically combined
• How do you know if something is a pure substance?

  Melt and boil at specific and sharp temps e.g. pure water has a boiling point of 100 degrees Celsius and a melting point of 0 degrees Celsius
• How can you tell if it's a mixture?

  Mixture have a range of melting and boiling points as they consist of different substances that tend to lower the melting and broaden the melting point range
• What can melting and boiling point data be used for?

  distinguish pure substances from mixtures
• Cooling curve for a pure substance

  
• Cooling curve for an impure substance

  
• What's a formulation

  A mixture that has been designed for a specific purpose to deliver a commercial product
• What is chromatography used for?

  To separate substance and provide info to help identify them
• Why must the pencil line be drawn and not ink?

  Ink would run into chromatogram along with the samples
• Why must the pencil line sit about the level of the solvent?

  So the samples don't wash into the solvent container
• Chromatography practical diagram

  
• What is the mobile phase in paper chromatography?

  The solvent in which the sample molecules can move, which in paper chromatography is liquid
• What is the stationary phase in paper chromatography?

  The actual chromatography paper itself
• How can you disguise pure substances in chromatography?

  It will only produce one spot
• What's the calculate for Rf value?

  Distance moved by substance/distance moved by solvent
• Required practical: Investigating Chromatography diagram

  
• Method for this practical

  1. Use a ruler to draw a horizontal pencil a one 2cm from the end of the chromatography paper

  2. Use a different capillary tube to put a tiny spot of each colouring A,B,C and D on the line

  3. Use the fifth tube to put a small spot on the unknown mixture U on the line

  4. Make sure each spot is no more than 2-3 m in diameter and label each spot in pencil

  5. Pour water into beaker to a depth of no more than 1cm and clip the top of the chromatography paper to the wooden spill. Top end is the furthest from the spots

  6. Remove the paper and draw a pencil a line on dry part of paper

  7. Measure the distance between two pencil lines

  8. Measure each food colour distance
• Test for hydrogen

  -Hold burning split held at the open end of a test tube of gas

  -If hydrogen present and loud "squeaky pop" should be heard
• Test for oxygen


  -Place a glowing splint inside a test tube of gas

  -If oxygen present the splint will relight
• Test for carbon dioxide

  -Bubble gas through lime water

  -If carbon dioxide present, limewater turns cloudy
• Test for chlorine


  -Use of litmus paper

  -If chlorine gas present, damp blue litmus paper will be bleached white
• When is the flame test used?

  To identify the metal ions by the colour of the flame they produce
• Why must you use a nichrome wire?

  It doesn't have a flame colour and a high M.P and it's unreactive
• Why must you use a blue flame?

  Can see colour better with a blue flame
• Why ions do you use a flame test for?

  Cations (positive ions)
• What colour are lithium ions in a blue flame?

  Crimson red
• What colour are sodium ions in a blue flame?

  Yellow
• What colour are potassium ions in a blue flame?


  Lilac
• What colour are calcium ions in a blue flame?

  Brick red
• What colour are copper ions in a blue flame?

  Green
• What colour are magnesium and aluminium ions in a blue flame?

  Bright white
• What test can you do to get magnesium ions and what is the positive result?

  Add NaOH

  Add NaOH in excess

  A white precipitate should form
• What test can you do to get copper ions and what is the positive result?

  Add NaOH

  Add NaOH

  Blue preciptate should form
• What test can you do to get iron (II) ions and what is the positive result?


  Add NaOH

  Add NaOH in excess

  Green precipitate
• What test can you do to get iron (III) ions and what is the positive result?

  Add NaOH

  Add NaOH in excess

  Brown precipitate
• What test can you do for a pure substance and what is the result

  Test its boiling point if a liquid and melting point if solid

  Should be close to the data book value
• How can you test for water?

  cobalt chloride paper turns from blue to red in the presence of water

  Anhydrous copper (II) sulphate turns from a white powder to blue in presence of water
• What are anions?

  negatively charged ions
• How to test for chloride ions and what is the result?

  Add Nitric acid (to remove carbonate)

  Add few cm3 of silver nitrate

  White precipitate should form