Comparing the enthalpy changes of combustion of different alcohols

Aldehydes are colourless, mobile and very volatile liquids. They are an intermediate between alcohols and acids; they differ in the sense that they have two less hydrogen atoms in their molecule.

I predict that the enthalpy change of combustion will increase following this pattern: Methanol?Ethanol?Propan-1-ol?Butan-1-ol. It is possible to see from the table I displayed at the start of the investigation that the number of carbon atoms in the molecule increases from Methanol to Butan-1-ol. If there's a bigger number of carbon atoms more energy will be required to break the initial bonds between the molecules. Therefore a more elevate temperature will be required, and less of the mass of the fuel will be lost during the reaction. In terms of my experiment I predict that the longer-chain alcohols will lose less mass during the combustion than the short-chain ones. Consequently more energy will be given off when the new bonds of the products will be formed; therefore the combustions in which the fuels lose less mass will be the more exothermic ones.

Constant variables:

* The volume of each liquid fuel (Methanol, Ethanol, Propan-1-ol and Butan-1-ol) used during the experiment has to be constant. If different volumes are used, it will be harder to compare the enthalpy change of combustion by looking at the mass lost. It wouldn't make the experiment a fair test.

* The temperature of the water, which is heated by the combustion of each fuel, has to be constant. (Around room temperature 20 ?C). Even though we are only interested in the temperature rise, and the mass lost for it to rise, we have to take into account that at different temperatures the particles have different kinetic energies. If the starting temperature of the water is too high, the particles will have more kinetic energy, and it will take less time for the water to rise to a certain temperature. As a result, we have to make sure that the starting temperatures of the water are all constant.

* The material that we are going to use as draught shielding has to be the same for each phase of the experiment. Different materials have isolating capacities. To make the experiment a fair test the same material will have to be used.

Apparatus descriptions:

Apparatus nomenclature

Apparatus use

Reason for using it

Small metal container

Used as a calorimeter. It will contain water, which will be heated as a result of the fuel combustion.

Metals have an elevate heat conductivity. More heat energy will be transferred to the water.

0-110 ?C or 0-50 ?C thermometer

Used to measure the temperature of the water at the different stages of the experiment.

To be able to monitor the change in temperatures. The latter will be maintained constant, so that I will eventually be able to calculate how much fuel has been burnt to be able to make the temperature of the water rise by 20?

00cm3 measuring cylinder

Used to measure the quantities of each fuel used in the reaction

To make sure that the quantity of each fuel being combusted remains constant, hence assuring a fair test.

Spirit burners

These are the containers in which the combustion reaction will be happening.

To make sure that the water in the calorimeter is heated in a safe manner in which the fuel is safely contained into the spirit burner.

Balance

To weigh the amounts of fuel during the different stages of the experiment

To evaluate the mass of the fuel being burnt during the experiment

Draught shielding

It will be placed around the spirit burner and the calorimeter during the course of the reaction

To minimize the heat losses during the reaction. This will be ensuring a fair test

Protective eyewear (goggles)

To protect are eyes from entering in contact with any of the fuels

The fuels we will be using, such as ethanol and methanol are toxic and harmful.

Lab coat

To protect our clothes from entering in contact with any of the fuels

It would be dangerous to have any of the fuels on your clothes, because it would increase the flammability of the material.

Clamp

To hold the calorimeter over the spirit burner

To make sure the calorimeter is maintained in an up right position

Method:

I will now annotate the procedure, which I will use to carry out my experiment:

* I will put 200 cm3 of water at room temperature in the metal calorimeter.

* I will clamp the calorimeter so that it is maintained up right on top of the spirit burner.

* I will arrange a glass protection around the calorimeter and spirit burner. The latter will function as a protective barrier as well as a draught exclusion system.

* I will measure out each amount of fuel (Methanol, Ethanol, Propan-1-ol and Butan-1-ol) with the aid of the measuring cylinder, and make sure the quantities are constant.

* I will weigh the fuel and note down the value, before the combustion reaction starts

* I will replace the spirit burner under the calorimeter and light the wick.

* I will keep stirring the water with the thermometer until its temperature will have risen by 20?. The stirring will favour the movement of particles, and will give more kinetic energy to the particles.

* After the water has risen by the desired temperature I will extinguish the burner and keep stirring the water. I will then note the highest temperature reached.

* I will then weigh the fuel, and subtract this value to the value I had noted regarding the weight of the fuel before the combustion. The result will represent the mass of fuel that has burnt during the course of the combustion.

* I will repeat this experiment for each of the fuels that I have decided to use.

* I will display my results in a table, in order to represent them graphically, which will aid me into drawing a conclusion.

Risk assessment:

Title of the experiment:

Comparing the enthalpy change of combustion of 4 chosen fuels

Outline of procedures:

Equal amounts of Methanol, Ethanol, Propan-1-ol and Butan-1-ol will be burned in a spirit burner.

Hazardous substance being used.

Nature of the hazard (e.g. toxic, flammable, harmful etc.)

Quan

Used

(ml)

Control measures and precautions.

Methanol

Highly flammable and toxic.

If swallowed: wash mouth give 1-2 glasses of water and seek medical attention if victim shows drunken symptoms.

If vapour inhaled: remove victim to fresh air and keep warm.

If spilt on skin or clothes: remove contaminated clothing. Wash affected area with cold water to reduce flammability if over 10 ml.

If spilt in lab: Shut all sources of ignition. Open all windows. Cover with mineral absorbent and clear up into a bucket. Rinse area with a cloth. Wash absorbent with dispersing agent and pour liquid down foul water drain

Ethanol

Highly flammable

Propan-1-ol

Highly flammable and harmful

Butan-1-ol

Highly flammable and harmful

Non-chemical hazards and precautions to be taken:

* Wearing goggles and lab coat is essential to prevent the substance from entering in contact with the eyes and clothes

* Keeping the fuels in safely sealed bottles, away from ignition sources, the maximum quantity in one bottle should not exceed 500 ml. The more reactive alcohols should be kept in dark bottles isolated from light energy.

* Make sure that glass containers are wisely positioned throughout the workstation, so to avoid any of them falling on the floor and creating a source of danger.

* Non-synthetic clothes should be worn under the lab coat, which have a lower flammability.

Disposal of residues:

Methanol & Ethanol:

For the disposal of 500 ml of the any of the two alcohols I will have to add the alcohol to 10 litres of water and I would have to pour this down the foul-water drain.

Propanol and Butanol:

For the disposal of 100 ml of any of these two alcohols I would first have to check whether Propan-1-ol and Butan-1-ol are water soluble or not. Tendentially alcohols going up to propan-1-ol are fairly soluble in water, therefore to dispose of them I would only need to wash them down a foul-water drain with plenty of water.

As the carbon chain increases, the water solubility decreases a lot. Hence it would be safer to dispose of longer carbon chain alcohols such as Butan-1-ol with the water-insoluble alcohols procedure. An authorised waste contractor should become in charge of the disposal of such alcohols.

Chemistry coursework