prac assesment help (1 Viewer)

[benlar]

i need help with planning a first hand investigation to:
1. compare the reactivities of appropriate alkeses with corresponding alkanes and bromine water
2. compare the heat of combustion of propanol and ethanol

any help would be appreciated, thankyou

 

[Cobra]

O yeh, i need help with that prac too riviet, dreamerish, pLuvia, where are ya?

 

[pLuvia]

You maybe a little bit behind or that you have already finished another module but, here's my practical

Reaction of alkanes and alkenes with Br₂ and I₂

The aim of the experiment is to test whether a hydrocarbon is an alkane or alkene.

Method set up 4 test tubes, 2 with cyclohexane the other 2 with cyclohexene. Then drop about 1-2-3 drops in each of them until you see a reaction, if you don't then record it down

The observations you should be looking for is whether one reacts with the Bromine or/and Iodine. *hint* Alkenes have a double bond in the structure, knowing that they are more reactive because the double bond because it can open out to react with more molecules

Heat of combustion of propanol and ethanol

This one you have to determine the heat of combustion of ethanol and 1-propanol.

Please look at the attachment

1. Set up as shown
2. Weigh the exact mass of the spirit burners containing ethanol and 1-propanol, including the spirit burner itself and record
3. Measure out 100 mL of water using the measuring cylinder and pour into beaker
4. Record the initial temperature of the water
5. Start the stopwatch as the spirit burner’s wick is lit and combustion of the alkanol starts, time for 3 mins
6. After 3 mins, record the temperature of the water, and weigh the spirit burner straight after.
7. Repeat for the rest of the alkanols
8. Repeat steps 2 – 6 three times

ΔH = mCΔT using this formula you can find the heat of combustion

ΔH – Molar Enthalpy (kJ mol-1)
m – Mass of substance (grams)
C – Specific heat capacity (4.18 J kg-1K-1)
ΔT – Temperature change

The results will not match the exact values from a book, but you should notice the trend in the graph should be very similar. In your conclusion you should note the validity of the experiment, and the reasons for the inaccurate results eg loss of heat because of the surrounding environment. But also write down the ways of improving the experiment

For this experiment, you should do it in class

Hope this helps

 

[Dreamerish*~]

i need help with planning a first hand investigation to:
1. compare the reactivities of appropriate alkeses with corresponding alkanes and bromine water

Since Pluvia did a excellent job on the heat of combustion prac, I'll write up the alkane-alkene report.

Equipment:

• 4 test tubes
• Bromine water (Br_2(aq) or HOBr)
• Cyclohexane
• Cyclohexene
• Test tube rack
• Aluminium foil

Method:

• Add a small volume (5 mL) of cyclohexane to each of two test tubes.
• Add the same volume of cyclohexene to each of the other two.
• Label test tubes.
  
• Using the eyedropper, add several drops of bromine water into each of the four test tubes.
• Wrap one test tube containing cyclohexane, and one test tube containing cyclohexene in aluminium foil and store in a dark place.
• Place the other two test tubes on the test tube rack, and leave in a place where there is plenty of sunlight.
• After a few hours, place all four test tubes together and observe the macroscopic changes.

Results:

• Both test tubes containing cyclohexene would have decolourised the brown bromine water instantly.
• The test tube containing cyclohexane that was left in the sunlight slowly decolourised the bromine water.
• The test tube containing cyclohexane that was wrapped in foil and left in the dark did not decolourise the bromine water.

Conclusion:

• Alkenes are unsaturated compounds, which react with various molecules, undergoing addition reactions to form new compounds. Therefore when bromine water (Br_2(aq) or HOBr) was added to cyclohexene, it was decolourised. This is because the bromine water has reacted with the cyclohexene. The double bond of cyclohexene opened to join with the bromine atoms, forming dibromocyclohexane.
• Alkanes are saturated compounds which will undergo substitution reactions with substances such as bromine water when exposed to U.V. radiation. During substitution reactions, one hydrogen atom of the alkane is replaced by another atom, such as Br. Because of this, the cyclohexane that was left in the sunlight (i.e. U.V. light) reacted slowly to decolourise the bromine water while the cyclohexane left in the dark did not decolourise at all.

Hope that was clear enough.

 

[benlar]

hey thanks heaps, my chem teacher is a dud, and we have to do a prac assesment task on that on thursday, and we did the experiments once hell dodgy. thanks

 

[Riviet]

Hey, nice prac write-up Dreamerish and pLuvia!! Much more sophisticated than the 2 test tube version of the prac and great diagram! Leaves me with nothing else to add.

 

[Mountain.Dew]

Hey, nice prac write-up Dreamerish and pLuvia!! Much more sophisticated than the 2 test tube version of the prac and great diagram! Leaves me with nothing else to add.

the equations of the reactions occured would be nice...and thats about it.

 

[Floydy]

Remember to discuss validity, reliability and accuracy.

Also consider safety procedures as they are common questions in a test situation.