A Level Chemistry B (Salters) H433/03 Practical skills in chemistry - Question Paper Monday 18 October 2021 Preview

Answer all the questions.

1 Alcohols are useful intermediates and react to give a variety of products.

For example, butan-1-ol can be oxidised to other useful products as shown below.

(a) Complete the flow diagram by writing on the dotted lines and drawing skeletal formulae in the

empty boxes.

Silver mirror

formed

skeletal formula

of organic product

skeletal formula

of organic product

butan-1-ol

What is seen when the reaction occurs?

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H

H

H

C

H

H

C

H

H

C

H

H

C O H

distil

with acidified

dichromate

solution

reflux

with acidified

dichromate

solution

warm with Fehling’s solution

reagent ............................................

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(b) Butan-2-ol is an isomer of butan-1-ol.

 Alcohols can be categorised as primary, secondary or tertiary.

 Which is the correct category for butan-2-ol?

 Explain your answer.

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(c) Alcohols can also undergo substitution reactions.

 The following sequence shows an incomplete mechanism for the reaction between

(CH3)

3COH and concentrated hydrochloric acid.

CH3

H+

CH3 C CH3

CH3

H

H

CH3 C CH3

CH3 –H2O

CH3 C CH3

+

OH

Cl –

O

CH3

CH3 C CH3

+ Cl

 The ‘curly arrow’ shows the movement of a pair of electrons.

 Complete this mechanism by drawing two more curly arrows in appropriate places. [2]

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(d)* A student prepares a pure sample of (CH3)

3CCl by the reaction from (c):

 (CH3)

3COH + HCl (CH3)

3CCl + H2O

 The preparation involves two parts.

 Part A The student shakes about 10cm3 of the alcohol with 20cm3 of concentrated hydrochloric

acid in a stoppered conical flask. The reaction occurs quickly at room temperature.

 Part B The student then separates the layers formed, removes the acid and dries and purifies

the organic product.

 The student uses data as shown in the table below.

Compound Does it mix

with water?

Density

/gcm–3

(CH3)

3COH yes 0.78

(CH3)

3CCl no 0.85

 Describe and explain the student’s procedure in part B. [6]

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 Additional answer space if required.

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2 Our bodies contain many proteins, including enzymes.

These proteins have individual molecular shapes.

(a) A protein can be described in terms of its primary, secondary and tertiary structure.

 Explain the terms primary, secondary and tertiary in this context.

Primary .....................................................................................................................................

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Secondary ................................................................................................................................

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Tertiary ......................................................................................................................................

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(b) Peptides and proteins are condensation polymers formed from amino acid monomers.

 The tripeptide glutathione is an antioxidant found in the body.

 The skeletal structure of glutathione is:

O O O

O

HO OH

NH2

N N

H

H

SH

 (i) Explain the significance of the dashed line and the wedge shown on the structure.

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