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Date May 2017 Marks available 3 Reference code 17M.3.sl.TZ1.7
Level SL Paper 3 Time zone TZ1
Command term Calculate Question number 7 Adapted from N/A

Question

Lanthanum metal may be produced by the electrolysis of molten LaBr3.

State why lanthanum cannot be produced by reducing its oxide with carbon.

[1]
a.

Calculate the current (I), in A, required to produce 1.00 kg of lanthanum metal per hour. Use the formula Q(C)=I(A)×t(s) and sections 2 and 6 of the data booklet.

[3]
b.

Markscheme

too high/higher than carbon in the reactivity series
OR
carbon/C is a weaker reducing agent than lanthanum/La

 

Accept “lanthanum is more reactive than carbon”.

Accept “lanthanum is a weaker oxidizing agent than carbon”.

Accept converse arguments.

[1 mark]

a.

amount of La «=1000 g138.91 gmol1» = 7.20 «mol»

«= 7.20 mol x 3 x 96500 Cmol–1» = 2.08 x 106 «C»

I «2.08×106 C60×60 s» = 579 «A»

 

Award [3] for “578 «A»” (from premature rounding) or “579 «A»”.

[3 marks]

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Options » A: Materials » A.2 Metals and inductively coupled plasma (ICP) spectroscopy
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