Paper 2 - (A few practicals)

Question 1

Describe a method where magnesium can react with HCL to produce H2 gas

Answer 1

• add a set volume of dilute hydrochloric acid to a conical flask and carefully placed on a balance
• next, add some magnesium ribbon to the acid and quickly plug the flask with a cotton wool
• start the stopwatch and record the mass on the balance. Take readings of the mass at regular intervals
• plot the results in a table and work out the mass lost for each reading
• plot a graph with time on the x-axis and loss of mass on the y-axis
• repeat experiment but with more concentrated acid solutions

Question 2

Describe the method for the disappearing cross practical

Answer 2

• measure a set volume of dilute sodium thiosulfate solution using a measuring cylinder and pour it into a conical flask
• place the flask on a piece of paper with a black cross drawn on it
• add some dilute HCL to the flask and start the stopwatch
• now watch the black cross disappear through the cloudy sulfur and time how long it takes to disappear
• the reaction can be repeated with solutions of either reactant at different concentrations

Question 3

Portable water practical - seawater / salt water

Answer 3

• measure the mass of the evaporating basin using a balance
• add measured volume of water
• measure the mass of the evaporating basin using a balance
• heat the evaporating basin using a Bunsen burner to evaporate the water
• measure the mass of the evaporating basin again using a balance
• subtract mass of evaporating basin from mass
• repeat and calculate a mean, discarding anomalous results
• calculate the mass in 100cm^3 water if necessary