Chemistry paper two

• Disappearing cross-method

  1. Measure out 10cm³ of sodium thiosulphate solution into the 50cm³ measuring cylinder

  2. Dilute this by adding 40cm³ of water to the same 50cm³ measuring cylinder. Add this to the conical flask.

  3. Put the conical flask on the laminated card with the black cross

  4. Using the 10cm³ measuring cylinder measure out 10cm³ of dilute hydrochloric acid.

  Add the hydrochloric acid to the sodium thiosulphate, start the stopwatch and give the flask a swirl.

  5. Stop the clock when you can no longer see the cross

  6. Record the time taken

  7. Repeat using different concentrations

  8. Repeat the whole experiment and calculate a mean for each concentration
• Rates of reaction (hydrogen test)-method

  1. Measure 50cm³ of hydrochloric acid in a conical flask

  2. Attach the conical flask to a bung and delivery tube which leads into a tray of water

  3. Place an upturned measuring cylinder filled with water over the end of the delivery tube

  4. Add a strip of magnesium to the acid and start a stopwatch

  5. Measure the volume of hydrogen produced every 10 seconds

  6. Repeat with different concentrations of acid
• Chromatography-method

  1. Draw a horizontal pencil line 2cm from a short edge of the chromatography paper.

  2. Use a glass capillary tube to put a small spot of each known colouring and the unknown one on the five pencil spots.

  2. Pour water into the beaker to a depth of no more than 1cm.

  3. Ensure that the pencil line is above the water surface, and that the sides of the paper do not touch the beaker wall.

  4. Wait for the water solvent to travel at least three quarters of the way up the paper. Carefully remove it and draw another pencil line on the dry part of the paper as close to the wet edge as possible.

  5. Calculate RF values
• Potassium

  Lilac (purple) flame

  
• Calcium

  Brick red / orange red flame

  
• Testing water purity-method

  1. Pour some water into a beaker

  2. Add universal indicator to establish if the water has a pH of 7

  3. Record the mass of a empty evaporating basin

  4. Fill the basin with water and place on a tripod

  4. Heat the basin with a bunsen burner until all the water has evaporated

  5. Weigh the basin again, if the mass has increased then the water isn't pure
• Distillation-method

  1. Place a conical flask of water on to of a tripod

  2. Connect the top of the conical flask to a delivery tube that feeds into a test tube surrounded by ice and water

  3. Heat the flask until the water boils

  4. Allow the steam to travel into the test tube where it will condense into pure water