Determination of enthalpy change of combustion

Question 1

first step for determination of /\HC of methanol?

Answer 1

1) using a measuring cyliner, measure out 150 cm^3 of water, pour water into beaker, record initial temp. of water to the NEAREST 0.5 degrees c,

Question 2

2nd step

Answer 2

2) add methanol to spirit burner, weigh spirit burner containing the methanol

Question 3

3rd step

Answer 3

3) place spirit burner under the beaker with clamp holding beaker and thermometer in beaker.

Question 4

4th step

Answer 4

4) after 3 mins extinguish flame and immediately record max. temp reached by the water

Question 5

5th step

Answer 5

5) re-weigh the spirit burner containing methanol and assume that the wick has not been burnt

Question 6

how may the experimental enthalpy change of combustion value be inaccurate?

Answer 6

• heat loss to surroundings other than water, (includes beaker but mainly air surrounding)
• incomplete comb. of methanol (CO and C being produced instead of CO2)
• evaporation of methanol from the wick (therefore burner should be weighed as soon as possible after extinguishing the flame spirit burners usually hve a cover to reduce error)
• non-standard conditions.

Question 7

what can be used to minimise errors from heat loss and incomplete combustion ?

Answer 7

use of draught screens and input of oxygen gas