RP2 - measurement of an enthalpy change

Question 1

what’s the calorimetric method

Answer 1

• wash the equipment with the solutions to be used
• dry cup after washing
• put polystyrene cup in a beaker for insulation and support
• measure out desired volumes of solutions with volumetric pipettes and transfer to insulated cup
• clamp thermometer into place making sure the thermometer bulb is immersed into solution
• measure initial temp of solution . Do this every min for 2-3 min
• at minute 3 transfer second reagent to cup . If solid reagent is used then add the solution to the cup first and then add the solid weighed out on a balance
• stir mixture ( ensures that all of the solution is same temp )
• record temp every minute after addition for several mins

Question 2

what are some errors in the calorimetric method

Answer 2

• energy transfer from surroundings
• approximation in specific heat capacity of solution . Method assumes all solutions have the heat capacity of water
• neglecting the specific heat capacity of the calorimeter - we ignore any energy absorbed by apparatus
• reaction or dissolving may be incomplete or slow
• density of solution is taken to be the same as water

Question 3

what is the flame calorimeter used for

Answer 3

measuring enthalpy of combustion
- the fuel is burnt and the flame is used to heat up water in a metal cup
Need to measure :
- mass of spirit burner before and after
- temperature change of water
- volume of water in cup

Question 4

what are some errors in using flame calorimetry

Answer 4

• energy losses from calorimeter
• incomplete combustion of fuel
• incomplete transfer of energy
• evaporation of fuel after weighing
• heat capacity of calorimeter not included
• measurements not carried out under standard conditions as H2O is gas , not liquid in this experiment