Question Paper Jan 2003 Unit-6A

7/29/2019 Question Paper Jan 2003 Unit-6A

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Winter 2003 C6A

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1. Part 1: you are required to carry out a series of tests on two organic compounds, B and C. You

are to use the information from the tests and spectroscopic data to propose identities for B andC.

Identification of two organic compounds

You have two liquid organic compounds labelled B and C. Each contains one functional group

and each may be prepared from the other in one synthetic step.Carry out the following tests, recording your observations and inferences in the spaces provided.In the inferences column record the functional group that may be suggested by your

observations.

(a) To 0.5 cm3 of liquid B add solid phosphorus pentachloride.

Observations Inferences

(2)

(b) Add 5 drops of liquid B to 2 cm2 of aqueous sodium carbonate.


(2)

(c) To 5 drops of liquid B add 5 cm3 of aqueous iodine. Add aqueous sodium hydroxide dropby drop, mixing well until the iodine colour is just discharged. Allow to stand.


(3)

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(d) Prepare a water bath by adding approximately 150 cm3 of tap water to a 250 cm3 beakerand heating it gently until it is almost boiling. To 1 cm3 of liquid C contained in a boiling

tube, add 5 cm3 of aqueous sodium hydroxide and warm gently in the water bath forapproximately 3 minutes. Add 6 cm3 of dilute nitric acid followed by five drops of

aqueous silver nitrate. The hot water bath will be used again in Part 4


(2)

(e) The mass spectrum of liquid C is given below.

100

80

60

40

20

0

25 50 75 100 125 150 175

m e

Relativeintensity

Identify the molecular ion on the mass spectrum, by marking it M+, and give itsm / e value.

.......

Draw the structure of the ion that gives rise to the peak with m / e = 43.

From the results of the tests identify C by giving its name.



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.......

Identify one other species with its m / e value that supports your conclusion.

.......(4)

(f) Suggest the identity of compound B.

.......(1)

(Total 14 marks)

2. Part 2: you are required to plan a procedure to determine the purity of one of theseorganic compounds.

Planning

The precipitation test described in Part 1 test (d) may be adapted to find the purity of liquid C

when prepared from the other compound in Part 1.

Describe an experiment that would provide information allowing the purity to be determined.

Include in your answer details of:

the apparatus; the procedure; how the experimental data would be used.Do not invent numbers to illustrate your plan.

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.........

.........(Total 8 marks)



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3. Part 3: you are required to carry out a series of tests on compound A in order to identify A.

Identification of compound A

You are provided with about 0.5 g of a salt labelled A. The compound contains one cation andone anion. Carry out the following tests on A, recording your observations and inferences in thespaces provided.

(a) Describe the appearance ofA.


(2)

(b) Add about half of the solid A to 10 cm3 of distilled water contained in a boiling tube.Stir until all or most of the solid has dissolved. Any undissolved solid will not interferewith subsequent tests. Use separate 2 cm3 portions of the solution for the tests (i), (ii), (iii)

and (iv).

(i) To 2 cm3 of the solution ofA add 2 cm3 of aqueous sodium carbonate.


(3)

(ii) To 2 cm3 of the solution ofA add 2 cm3 of dilute sulphuric acid and two pieces ofgranulated zinc. Warm the mixture gently.


(4)



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(iii) To 2 cm3 of the solution ofA add 2 cm3 of aqueous lead(II) nitrate.


(3)

(iv) To 2 cm3 of the solution ofA add 2 cm3 of aqueous barium nitrate solution.


(2)

(c) Add a few crystals of solid A to 1 cm3 of methanol.

Observation only required

(1)

(d) Comment on the bonding in compound A in light of your observation in test (c).

.......(1)

(Total 16 marks)

4. Part 4: you are required to find the crystallisation temperature of a solution of an inorganic salt.

Determination of crystallisation temperature

You are provided with a labelled boiling tube containing compound X. Use a burette to add 9.00cm3 of water to the solid, and then place a thermometer in the mixture.

Place the boiling tube in the hot water bath used for Part 1 (d) and stir its contents, with the

thermometer, until the solid has just dissolved.



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Immediately the solid has dissolved, remove the tube from the water bath and carefullywipe all traces of water from the outside. Stir gently with the thermometer and note the

temperature at which crystals begin to form. Record the temperature to 0.2 C and insertthe value into Table 1.

Replace the tube into the hot water bath and stir the contents until the crystals redissolve. Repeat

the cooling procedure to obtain a second estimate of the crystallisation temperature. Record thisalso in Table 1.

Calculate the mean crystallisation temperature, recording your value in the space below thetable, and then answer the questions that follow.

Table 1

1st crystallisation temperature reading,t1/C

2nd crystallisation temperature reading,t2/C

Mean temperature of crystallisation, t3 = .. C

(5)

The mean solubility of compound X is given on the graph below.

95

90

85

80

75

70

65

60

55

50

30 35 40 45 50Crystallisation temperature, T /C

Solubility,s/gper100cm

3

From the plot obtain a value for the solubility ofX at temperature t3 = .g/100 cm3



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Hence determine the mass, in g, ofX that the boiling tube contained originally.

(2)

Evaluation

Record, in the spaces below, the smallest volume printed on the burette scale, and the smallestdivision of temperature on the thermometer.

Burette ...

Thermometer .

Given that X was weighed to a precision of 0.01 g suggest which measurement: mass, volume

or temperature contributes most to the uncertainty in the value of solubility of compound X.

Justify your choice.

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Suggest how the accuracy ofeither the thermometer or the burette could be checked.

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.........(5)

(Total 12 marks)

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Question Paper Jan 2003 Unit-6A

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