CP 8 - Combustion of Alcohols

Question 1

What is the functional group in alcohols

Answer 1

-OH

Question 2

What are the molecular formulae of methanol, ethanol, propanol and butanol?

Answer 2

Methanol - CH4O
Ethanol - C2H6O
Propanol - C3H8O
Butanol - C4H10O

Question 3

Describe an experiment to investigate

the combustion of alcohols

Answer 3

Heat a copper can containing 100cm3 water using a spirit burner

Record the temperature of the water and the mass of the spirit burner before and after the experiment

Repeat with different alcohols

Question 4

Different alcohols in spirit burners are
burnt to heat water in a copper can.
What are possible errors in this
experiment?

Answer 4

Heat lost to surroundings
Not all flames are the same height from different spirit burners
Incomplete combustion
Evaporation of alcohols while weighing

Question 5

What safety precautions should be taken when investigating the combustion of alcohols?

Answer 5

Light the wick of the spirit burner with a splint

Don’t move a lit burner
Ensure the room is well ventilated
Tie back long hair
Don’t leave flame unattended

Question 6

When combusting alcohols to heat water, what is the
effect on temperature change if the number of
carbons in each alcohol molecule increases?

Answer 6

More carbons in a molecule means a

greater increase in temperature

Question 7

How could you measure the temperature of the water more precisely than using a thermometer?

Answer 7

Use a digital temperature probe to record

temperatures to 2 decimal places

Question 8

Different alcohols are being combusted to heat a copper can of water. State 3 factors which must be controlled to allow a fair comparison

Answer 8

• Mass or volume of water
• Height of copper can above wick
• Height of flame
• Shape of copper container
• Number of moles of alcohol

Question 9

Write an chemical equation for the combustion of ethanol

Answer 9

C2H5OH + 3O2 → 2CO2 + 3H2O

Or

2C2H5OH + 6O2 → 4CO2 + 6H2O