Required practical 2 -Calorimetry

Question 1

Describe general method for calorimetry of solutions(10)

Answer 1

1- washes the equipment (cup and pipettes etc) with the solutions to be used

2-dry the cup after washing

3-put polystyrene cup in a beaker for insulation and support

4-Measure out desired volumes of solutions with volumetric pipettes, transfer to insulated cup

5-clamp thermometer into place making sure the thermometer bulb is immersed in solution

6- measure the initial temperatures of the solution or both solutions if 2 are used. Do this
every minute for 2-3 minutes

7- At minute 3 transfer second reagent 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.

8- If using a solid reagent then use ‘before and after’ weighing method

9-stirs mixture

10- Record temperature every minute after addition for several minutes

Question 2

Why do you stir the mixture in step 9

Answer 2

ensures that all of the solution is at the same temperature

Question 3

How do you prevent heat loss to surroundings(3)

Answer 3

• ensure there isn’t a high temp. diff. between surrounding and calorimeter
• insulate using polystyrene cup and lid
• use bomb calorimeter

Question 4

How can the accuracy be improved(4)

Answer 4

• read thermometer at eye level
• stir solution so temp is evenly distributed
• use digital thermometer for faster + accurate readings
• use larger masses+conc. leading to larger changes and smaller uncertainties.

Question 5

how to reduce uncertainties

Answer 5

-use larger masses leading to larger changes and smaller uncertainties.

0weighing balance with greater resolution

Question 6

How is enthalpy change calc experimentally

Answer 6

Q= mc∆T
ΔH=Q/mol
m=mass of solution that changes temp.1g=1cm3
c=specific heat capacity(usually water)
Q=energy taken in/out

Question 7

what should you do to get a better temp average

Answer 7

take temp of the reactants for a few
minutes before they are added together

If reactants are solutions, measure temp of both solutions.

Question 8

Why can the exact temperature rise be

difficult to obtain as

Answer 8

cooling occurs simultaneously with the reaction,

Question 9

how do you counteracts this.

Answer 9

we take readings at regular time intervals and extrapolate temp curve/line back to when the reactants were added together.

Question 10

what are Errors that could arise from method

Answer 10

• energy transfer from surroundings usually lost
• approximating specific heat capacity of solution.Method assumes all solutions have heat capacity of water

–neglecting heat capacity of calorimeter-ignored any energy absorbed by the apparatus

• reaction/dissolving may be incomplete/ slow
• density of solution is taken as the same as h2o

Question 11

why can’t enthalpy change directly calculated from calorimetry

Answer 11

Not possible to prevent some dissolving

there will difficulty of measuring T (change) of a
solid-if reactant is solid