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Question 18M.3.hl.TZ2.4

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Date May 2018 Marks available [Maximum mark: 10] Reference code 18M.3.hl.TZ2.4
Level hl Paper 3 Time zone TZ2
Command term Calculate, Deduce, Determine, State and explain Question number 4 Adapted from N/A
4.
[Maximum mark: 10]
18M.3.hl.TZ2.4

Vanadium forms a body centred cubic (BCC) crystal structure with an edge length of 303 pm, (303 × 10−12 m).

(a.i)

Deduce the number of atoms per unit cell in vanadium.

[1]

Markscheme

2

[1 mark]

(a.ii)

Calculate the expected first order diffraction pattern angle, in degrees, if x-rays of wavelength 150 pm are directed at a crystal of vanadium. Assume the edge length of the crystal to be the same as separation of layers of vanadium atoms found by x-ray diffraction. Use section 1 of the data booklet.

[2]

Markscheme

nλ = 2dsinθ

OR

θ = sin − 1 ( n λ 2 d )

 

θ = « sin − 1 ( 150 2 × 303 ) = » 14.3 «°»

 

Award [2] for correct final answer.

[2 marks]

(a.iii)

Calculate the average mass, in g, of a vanadium atom by using sections 2 and 6 of the data booklet.

[1]

Markscheme

m = « 50.94 6.02 × 10 23 =  » 8.46 × 10–23 «g»

[1 mark]

(a.iv)

Determine the volume, in cm3, of a vanadium unit cell.

[1]

Markscheme

«303 pm = 303 × 10–10 cm»

V = «(303 × 10–10)3 =» 2.78 × 10–23 «cm3 »

[1 mark]

(a.v)

Determine the density, in g cm−3, of vanadium by using your answers to (a)(i), (a)(iii) and (a)(iv).

[2]

Markscheme

«8.46 × 10–23 g × 2 =» 1.69 × 10–22 «g»

d = « 1.69 × 10 − 22  g 2.78 × 10 − 23  c m 3 = » 6.08 «g cm–3»

 

Accept any value in the range 6.07–6.09 «g cm–3».

Award [2] for correct final answer.

[2 marks]

(b.i)

Vanadium and other transition metals can interfere with cell metabolism.

State and explain one process, other than by creating free radicals, by which transition metals interfere with cell metabolism.

[2]

Markscheme

Any one of these alternatives:

ALTERNATIVE 1

disrupt enzyme binding sites

which can inhibit/over-stimulate enzymes

 

ALTERNATIVE 2

disrupt endocrine system

because they compete for active sites of enzymes/cellular receptors

 

ALTERNATIVE 3

form complexes/coordination compounds

which can bind to enzymes

 

ALTERNATIVE 4

act as oxidizing/reducing agents

OR

act as catalysts

 

which can initiate unwanted reactions

 

Accept “can undergo oxidation–reduction reactions” for M1 in Alternative 4.

[2 marks]

(b.ii)

Vanadium(IV) ions can create free radicals by a Fenton reaction.

Deduce the equation for the reaction of V4+ with hydrogen peroxide.

[1]

Markscheme

V4+(aq) + H2O2(aq) → V5+(aq) + OH–(aq) + •OH(aq)

 

Do not accept • on H.

Accept answer without •

[1 mark]

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