Required practicals

Question 1

Required practical 8: Water purification

Answer 1

1. Pour around 1 cm depth of the salt water into a test tube in the rack
2. Dip the nichrome wire into this solution, and then hold the tip of the wire in a blue Bunsen burner flame
3. Record observation in a table - a yellow flame test confirms the presence of sodium ions
4. Add a few drops of dilute nitric acid to this solution. Then add 1cm depth of silver nitrate solution
5. Record observations in the table - a white precipitate with nitric acid and silver nitrate solution confirms the presence of chloride ions
6. Place the remaining salt water in the conical flask and set up the apparatus for distillation

Question 2

Plan an investigation to show how the concentration of the sodium thiosulfate solution affects the rate of the reaction with dilute hydrochloric acid

Answer 2

• Measure indicated volume of sodium thiosulfate and place this into a conical flask
• Measure indicated volume of hydrochloric acid
• Place the conical flask on a cross
• Add hydrochloric acid to the conical flask and swirl
• Start the stopwatch and measure the time it takes for the cross to be no longer visible
• Repeat and calculate a mean
• Repeat for different concentrations of sodium thiosulfate
• Control variables: concentration and volume of hydrochloric acid, volume of thiosulfate solution