Year 12 Chemistry Easter Revision Session

Learning Outcomes - CER:• Be aware of the key skills required in the AS

chemistry exams.• Pick up some useful exam tips.

Content (if time allows):• Mechanisms• Reactions of alcohols• Analysis• Enthalpy

Mechanisms - 1• You need to know 3 different mechanisms for this paper.

• The first one involves the reaction between alkenes and chemicals such as Br2

• Write a balanced equation (using displayed formulae) for the reaction between ethene and bromine, name the product formed and state what type of mechanism this is.

• Now draw out the mechanism.

Mechanisms - 1• Now redraw/adapt this mechanism for the reaction

between ethene and hydrogen chloride.

• What would be different about this reaction if you used propene as your organic starting material instead of ethene?

• Draw out the two products formed using skeletal formulae and structural formulae, and name both of them.

• Alkenes can also be used to form alcohols and alkanes. In each case state the conditions required for the reaction.

• Write a balanced symbol equation for the hydrogenation of but-1,3-diene.

Mechanisms – 1• An example PPQ from CER June 10 – definitely worth

attempting this question at some point during your revision (if we have time we’ll come back to it).

Mechanisms - 2• The second curly arrow mechanism you need to be aware of

is used for the reaction between halogenoalkanes and ____?

• What is the name of this type of mechanism?

• Write a balanced equation for the reaction between 1-iodopropane and sodium hydroxide.

• Now draw a mechanism for this reaction and name the product formed.

• What simple chemical test could you use to check that this reaction had occurred?

Mechanisms - 2• Would iodoethane hydrolyse faster or slower than

chloroethane? Explain your answer.

Iodoethane would hydrolyse faster because the C-I bond is weaker than the C-Cl bond.

Mechanisms - 3• Radical substitution.

• Attempt Q4 from CER Jan 10 – you have 9 mins max.

• The second page (part b) is included for those that finish quickly.

• The markscheme is printed on the back so that you can see it in detail later – DO NOT LOOK AT IT YET!!!

Reactions of alcohols:• There are two ways to make ethanol that you should know.

• For each method you need to be able to give the conditions and starting material(s), write balanced equations, and state advantages and disadvantages of each.

Reactions of alcohols:Divide your mini-whiteboard/page as shown below and see how many boxes you can complete.

Name of method 1, balanced equation and conditions.

Advantages of method 1

Disadvantages of method 1

Name of method 2, balanced equation and conditions.

Advantages of method 2

Disadvantages of method 2

Reactions of alcohols:• You’ve covered four different reactions of alcohols in this

course. What are they?

• Oxidation

• Esterification

• Combustion

• Dehydration

Reactions of alcohols:• You need to be able to write balanced equations for each

of these reactions. • We’ll come back to oxidation in a moment so instead write

balanced equations for:

• the esterification reaction between propan-1-ol and ethanoic acid (and name the product formed),

• the dehydration of butan-1-ol (stating the conditions required),

• and also the combustion of pentan-2-ol.

Reactions of alcohols:• the esterification reaction between propan-1-ol and

ethanoic acid (and name the product formed)

CH3COOH + CH3CH2CH2OH CH3COOCH2CH2CH3 + H2O propyl ethanoate

• the dehydration of butan-1-ol (stating the conditions required),

CH3CH2CH2CH2OH CH3CH2CH=CH2 + H2O

conditions required = conc. H2SO4 and heat

Reactions of alcohols:

• and also the combustion of pentan-2-ol.

CH3CH2CH2CH(OH)CH3 + 7.5 O2 5 CO2 + 6 H2O

Make sure you don’t forget about this oxygen when balancing the equation

Reactions of alcohols:

• Write down everything you can remember about the oxidation of alcohols on your mini-whiteboard – 1 min.

• Compare your efforts with the person sat next to you – 1 min.

• I’m now going to ask everyone to state one fact about the oxidation of alcohols.

Reactions of alcohols:• Students often find it difficult to write out the balanced

equations for these reactions.

• Have a go at writing balanced equations (using displayed formulae) for the oxidation of:

• Ethanol (distillation conditions)

• Propan-1-ol (reflux conditions)

• Propan-2-ol

We’ll come back to this section in a moment when we look at PPQ that combines oxidation of alcohols and analysis.

Analysis:• Infra-red spectroscopy and mass spectrometry.

• With regards to the analysis of organic molecules, what does each technique tell us about a molecule?

• IR – tells us the types of bonds that are present.

• MS – tells us the molar mass of the whole molecule and also of fragments of the molecule.

Analysis:• Infra-red spectroscopy:

• This spectra either represents propan-1-ol, propanal or propanoic acid.

• State which compound it is giving reasons for your answer.

Analysis:• Mass spectrometry:

• This spectra has been produced from pent-1-ene.• Identify the ions responsible for the peaks labelled A, B and

C.• What name is given to peak A?

Analysis:• Attempt the PPQ combining analysis and oxidation of

alcohols taken from the CER Jan 10 paper – you have 7 mins max.

• Once again the markscheme is on the back of your handout to make it easier for you to read it later - DO NOT LOOK AT IT YET!!

You also have this on the back of your handout so don’t worry if you can’t read this slide clearly.

Enthalpy:• There are three ways to determine the enthalpy change of

a reaction:

• Measure it directly

• Calculate it from bond enthalpies

• Calculate it from enthalpy of combustion or formation data via a Hess cycle.

Enthalpy:• Measuring enthalpy changes directly (CER Jan 10, Q3 a+b):

Enthalpy:• Calculate enthalpy changes from bond enthalpy data

(CER June 10, Q1 c):

Enthalpy:• Calculate from enthalpy of formation data via a Hess cycle

(CER June 10, Q1 d):

Enthalpy:• Calculate from enthalpy of combustion data via a Hess

cycle (CER Jan 10, Q3 c):