Sample exam 2 Organic Chemistry Module 7

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(30 marks) 50 mins

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Multiple Choice

1)

What is the isomer of C₇H₁₄  which undergoes an addition reaction with Br₂?

• a) Cycloheptane
• b) 1-ethyl -2 -methylpentane
• c) Ethylcyclopentane
• d) 2,3- dimethylpent-1-ene

2)

What is the correct K_a expression for the ionisation of propanoic acid?

• a) [H₃O+][CH₃CH₂COO-]/[CH₃CH₂OOH]
• b) [CH₃CH₂OOH]/[H₃O+][CH₃CH₂COO-]
• c) [CH₃OOH]/[H₃O+][CH₃COO-]
• d) [H₃O+][CH₃COO-]/[CH₃OOH]

3)

2,2,4-trimethylpentane is a component of petrol with an enthalpy of combustion of -5460 KJ mol^-1

Calculate the mass of 2,2,4-trimethylpentane needed to heat 1L of water by 75 degrees celsius?

• a) 172.41g
• b) 4.50g
• c) 6.5g
• d) 71.25g

4) 

Which test would not be sufficient to distinguish between propan-1-ol and propanoic acid?

• a) Measurement of pH
• b) Addition of sodium hydrogen carbonate
• c) Addition of hydrogen bromide
• d) Addition of acidified potassium dichromate solution

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Short answer section

5) [2 marks]

Describe, with the aid of a diagram below, how soap is used to remove stains from clothes.

6) [1 mark]

Name the following:

7) [3 marks]

Identify and name compounds W, X and Y for the following series of reactions

Question 8) [6 marks]

The below graph shows the trend for boiling point of three functional groups – alkanes, alcohols and amines. Identify X, Y and Z and explain the trend in the data provided.

Question 9) [5 Marks]

Compare and contrast to addition polymers with respect to their chemical properties, their structure and uses. 

Question 10) [3 marks]

Determine the pH of 1 M citric acid with a pK_a value of 2.79.

Question 11) [6 marks]

Outline the method you used for the esterification reaction and propose ways to increase the safety and efficiency of this reaction.

ANSWERS

Multiple Choice

1) D

2) A

3) C

2,2,4-trimethylpentane molar mass = (18*1.008+ 8*12.01)g/mol

Q = mc(delta)T

Q = 1 * 4.18* 75

 = -313.5 KJ

Mol of 2,2,4-trimethylpentane -313.5 KJ/ -5460 KJ mol^-1 = .057 mol

.057 mol*(18*1.008+ 8*12.01)g/mol

= 6.5 g

4) C

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Short Answers

5) Hydrophilic head of the soap molecule is polar hence it will be attracted to water. The hydrophobic tail is non-polar so it will be attracted to the oil. This will form a micelle that will allow the oil to dissolve in water with agitation removing it from clothes.

7) Buta-2-one

8) W = But-1-ene, X = Buta-1-ol, Z = Batanal

9)

Marking rubric:

• Identify what x, y and z are – 2 marks
• Describing the trend – 2 marks 
• Explaining why – 2 marks

Trend:

• As the length of the carbon chain increases the boiling point also increases.
• As the carbon chain gets longer the lines begin to converge making the boiling points closer together.

z = alkane – dispersion forces, y = amine – dispersion and weaker hydrogen bond, x= alcohols – strongest hydrogen bonds and dispersion bonds

Answer:

As the length of the carbon chain increases the boiling point also increases because dispersion forces become larger as the carbon chains increase. This occurs due to the number of carbons increasing so there is a greater area for dispersion forces to interact with other molecules increasing the energy required to separate them, hence a higher boiling point. 

The reason the boiling points converge as the molecules get larger is due to the dispersion forces becoming stronger hence making the hydrogen bonding from the function groups become negligible to the total intramolecular forces. 

z = alkane – dispersion forces, y = amine – dispersion and weaker hydrogen bond, x= alcohols – strongest hydrogen bonds and dispersion bonds

The alkane has the lowest boiling point since it has the same dispersion forces but no hydrogen bonding.

Nitrogen is less electronegative than oxygen hence it doesn’t pull the hydrogen’s electrons in as much. This means the nucleus in the alcohol is more exposed hence it has stronger hydrogen bonding accounting for it having a higher boiling point then the amine.

10)

Mention Alcohol and organic carboxylic acid, 1 mark

Concentrated sulfuric acid and heat, 2 marks

Heat in reflux apparatus for 30 mins, 1 mark

Use heating mat instead of Bunsen burner since organic volatile flammable chemical are being used, 1 mark