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Investigating the combustion of alcohol

Investigating the combustion of alcohol

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Summary

Investigating the combustion of alcohol

In a nutshell

By using a calorimeter you can investigate how efficient alcohols are as fuels. This can be done by measuring how much alcohol is required to raise the temperature of a fixed, known amount of water. 


Equations

These equations will be required for your analysis.     


WORD EQUATION

SYMBOL EQUATION

​enthalpy change=mass×specific heat capacity×change in temperatureenthalpy \, change = mass \times specific \, heat \, capacity \times change \,in \,temperatureenthalpychange=mass×specificheatcapacity×changeintemperature​​
​ Q=m×c×△TQ = m \times c \times \triangle TQ=m×c×△T​​
​mole=massmolecular massmole = \frac{mass}{molecular \,mass}mole=molecularmassmass​​​
​n=mMrn = \frac{m}{M_r}n=Mr​m​​​
​standard enthalpy change of combustion=enthalpy changemolestandard \, enthalpy \, change \, of \, combustion = \frac{enthalpy \, change}{mole}standardenthalpychangeofcombustion=moleenthalpychange​

​standard enthalpy change of combustion=enthalpy changemassstandard \, enthalpy \, change \, of \, combustion = \frac{enthalpy \, change}{mass}standardenthalpychangeofcombustion=massenthalpychange​​​
​E=QnE = \frac{Q}{n}E=nQ​

E=QmE = \frac{Q}{m}E=mQ​​​


Variable definitions 

QUANTITY NAME​​

SYMBOL

UNIT NAME

UNIT

​enthalpy changeenthalpy \,changeenthalpychange​​
​QQQ​​
​kilo joule per gram or kilo joule per molekilo \, joule \, per \space gram \, or \, kilo \, joule\, per \space molekilojouleper gramorkilojouleper mole​​
​kJ g−1 or kJ mol−1kJ \, g^{-1} \, or \, \\ kJ \, mol^{-1}kJg−1orkJmol−1​​
​massmassmass​​
​mmm​​
​gramgramgram​​
​ggg​​
​specific heat capacityspecific \,heat\,capacityspecificheatcapacity​​
​CCC​​
​joule per gram per degrees celsiusjoule \space per \space gram \space per \space degrees \, celsiusjoule per gram per degreescelsius​​
​J g−1 °C−1J \, g^{-1} \, \degree C^{-1}Jg−1°C−1​​
​ molemolemole​​
​nnn​​
​molemolemole​​
​molmolmol​​
​ standard enthalpy changestandard \, enthalpy \, changestandardenthalpychange​​
​EEE​​
​kilo joule per mole or kilo joule per gramkilo\,joule\,per\,mole \, \text{or}\, kilo\,joule\,per\,gramkilojoulepermoleorkilojoulepergram​​
​kJ mol−1or kJ g−1kJ\,mol^{-1} or \\ \, kJ\,g^{-1}kJmol−1orkJg−1​​


Equipment list 

The following equipment list can be used to conduct an experiment to evaluate the relationship between different alcohols and the amount of energy released.


EQUIPMENT

USE

Copper calorimeter with lid
This is where water will be heated. A lid is required to ensure energy loss to the environment is kept to a minimum.
Thermometer
To measure the temperature.
Water
The temperature of water will be measured to identify how much energy the alcohol releases.
Spirit burner
To burn the alcohol.
Measuring cylinder
To measure out the amount of water.
Balance
To measure the mass of the spirit burner.
Clamp stand
To hold the calorimeter.
Methanol, ethanol, propan-111​-ol 
They will be used as fuels for the investigation.
Matches and splint
To light the wick of the spirit burner.

​


Experiment: Investigating the combustion of different alcohols and the amount of fuel released


Experimental variables

The independent variable is the one you change. The dependent variable is the one which depends on what has been changed, therefore it is the one you measure. The constant variable is the one which is kept constant.


Independent variable
​AlcoholAlcoholAlcohol​​
Dependent variable
​Enthalpy changeEnthalpy \, changeEnthalpychange​​
Control variable
​Volume of waterVolume \, of \, waterVolumeofwater​​


Safety precautions

When performing experiments, it is very important you consider safety precautions. This is so you and others do not get hurt.


​​HAZARD

RISK

SAFETY MEASURE

Methanol, ethanol, propan-111​-ol
Toxic and can cause skin irritation/health issues if absorbed by the skin.
Avoid contact with skin. Wear suitable gloves. Wash hands after use.
Alcohols
They are flammable and easily catch fire.

​Keep away from naked flames. Close the lids of any bottles containing alcohol and store them way safely when not in use. 

Spirit burner
Spirit burners can cause a fire.
Keep flammable items away from the flame and tuck away loose items of clothing.
Do not walk around with the spirit burner when it is lit.
Do not leave the flame unattended.


Note: As a general rule, eye protection must be worn for all chemistry related practicals.


Method

This is your instructions for how to complete the experiment. 

Chemistry; Chemistry practicals; KS4 Year 10; Investigating the combustion of alcohol
1.
Thermometer
2.
Calorimeter
3.
Alcohol
4.
Spirit burner
5.
Clamp stand


1.
Use a measuring cylinder to measure 100 cm3100 \, cm^3100cm3 of water​
2.
Transfer 100 cm3100 \, cm^3100cm3 of water to the calorimeter.​
3.
Place the calorimeter on a clamp stand and adjust the height so that it is just above the flame of the spirit burner.
4.
Record the initial temperature of the water and the mass of the empty spirit burner.
5.
Fill the spirit burner with methanol and record the mass of the spirit burner.
6.
Place the spirit burner under the calorimeter.
7.
Place the lid on the calorimeter and light the wick.
8.
Heat the water until the temperature rises to 25 °C25 \, \degree C25°C. Extinguish the flame immediately once the temperature has been reached.​

Note: Stir the water constantly whilst you are waiting for the temperature to rise.
9. 
Record the mass of the spirit burner after the experiment and the final temperature. Record all results in a table.
10. 

Repeat steps 1-9 for ethanol and propan-111​-ol.


Analysis  

This is how you will use your data to be able to form conclusions.


1.
Firstly, calculate the change in mass for each alcohol.

​change in mass=(mass of spirit burner with alcohol)−(mass of empty spirit burner)change \, in \, mass = (mass \,of \,spirit \,burner \,with \,alcohol) - (mass \,of \,empty \,spirit \,burner)changeinmass=(massofspiritburnerwithalcohol)−(massofemptyspiritburner)​​
2.
Calculate the enthalpy change for each alcohol using the following equation.  

enthalpy change=mass×specific heat capacity×change in temperatureenthalpy \, change = mass \times specific \, heat \, capacity \times change \,in \,temperatureenthalpychange=mass×specificheatcapacity×changeintemperature

Tip: Specific heat capacity for water is 4.2 J g−1 °C−14.2 \,J \, g^{-1} \, \degree C^{-1}4.2Jg−1°C−1​ .
3.
Calculate the amount of energy released per gram. To do this, use the following equation.

​standard enthalpy change of combustion=enthalpy changemassstandard \, enthalpy \, change \, of \, combustion = \frac{enthalpy \, change}{mass}standardenthalpychangeofcombustion=massenthalpychange​​​

You may be asked to calculate the amount of energy per mole. In this instance you will need to first work out the number of moles using the equation.

​mole=massmolecular massmole = \frac{mass}{molecular \,mass}mole=molecularmassmass​​​

Then use the following equation.

​standard enthalpy change of combustion=enthalpy changemolestandard \, enthalpy \, change \, of \, combustion = \frac{enthalpy \, change}{mole}standardenthalpychangeofcombustion=moleenthalpychange​​​
4.
Finally you should comment on what your results show and the relationship between the alcohols, the temperature change and energy released.


Conclusion

The greater the length of the alcohol chain, the greater the temperature rise. This is because the more carbon atoms there are, the more energy is released.


Evaluation

Once you have completed your experiment, it will be important to consider how well your results fit the theoretical values. You should make sure you identify any anomalies and not include them in your final results. If you did have anomalous results, you will need to think about why. Further evaluate how you could improve your experiment.


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Investigating the combustion of alcohol

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FAQs - Frequently Asked Questions

How can you ensure you use the alcohol safely?

​Keep the alcohol away from naked flames. Close the lids of any bottles containing alcohol and store them way safely when not in use.

How does the chain length of the alcohol impact the results?

The greater the length of the alcohol chain the greater the temperature rise. This is because the more carbon atoms there are, the more energy is released.

How can you investigate the combustion of alcohols?

You can investigate the combustion of alcohols by measuring how much alcohol is required to raise the temperature of a fixed, known amount of water.

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