energetics practical

Question 1

practical 2a
enthalpy change of anhydrous copper(II) sulfate
step 1

Answer 1

Accurately weigh out approximately 5g of anhydrous copper(II) sulfate (Mr = 159.5) using a weighing bottle

Question 2

practical 2a
enthalpy change of anhydrous copper(II) sulfate
step 2

Answer 2

Measure out 50 ml water into a weighed polystyrene beaker,

re-weigh the beaker + water and record the temperature of the water in equal intervals up to 4 minutes

Question 3

practical 2a
enthalpy change of anhydrous copper(II) sulfate
step 3

Answer 3

Quickly add the anhydrous copper(II) sulfate to the water and stir until dissolved. cover with lid

Record temperature in equal intervals.
measure the highest temperature reached and, hence, the temperature change

Question 4

practical 2b
enthalphy change of copper(II) sulfate pentahydrate
step1

Answer 4

Accurately weigh out approximately 7.8 g of copper(II) sulfate pentahydrate (Mr = 249.5)

Question 5

practical 2b
enthalphy change of copper(II) sulfate pentahydrate
step 2

Answer 5

Measure out 50 ml water into a weighed polystyrene beaker, re-weigh the beaker + water and record the temperature of the water over a couple of minutes

Question 6

practical 2b
enthalphy change of copper(II) sulfate pentahydrate
step 3

Answer 6

Quickly add the copper(II) sulfate pentahydrate to the water and stir until dissolved. Record the final temperature reached and, hence, the temperature change

Question 7

2 – Measuring an enthalpy change

Answer 7

• Put polystyrene cup in a beaker for insulation and support.
• Clamp thermometer into place making sure the thermometer bulb is immersed in liquid.
• Measure the initial temperatures of the solution (or both solutions if 2 are used)
• Transfer reagents to cup. If a solid reagent is used then add the solution to the cup first and then add the solid weighed out on a balance.
• Stir mixture.
• Measure highest/lowest temperature reached.

Question 8

practical errors

Answer 8

• Errors include:
heat loss/gain,
approximation of specific heat capacity of solution,
neglecting specific heat capacity of calorimeter,
reaction incomplete,
assuming density of solution the same as water

Question 9

slow reactions

Answer 9

Notes •
If reaction is slow then then exact temperature rise can be hard to obtain as cooling occurs at the same time as the reaction takes place – to counteract this, take readings at regular intervals, plot, and extrapolate the temperature curve back