ICP-OES/MS can be used to analyse alloys and composites. Distinguish between alloys and composites.

ICP-MS is a reference mode for analysis. The following correlation graphs between ICP-OES and ICP-MS were produced for yttrium and nickel.

Each y-axis shows concentrations calculated by ICP-OES; each x-axis shows concentrations for the same sample as found by ICP-MS.

The line in each graph is y = x.

Discuss the effectiveness of ICP-OES for yttrium and nickel.

Identify the purpose of each graph.

Calculate, to four significant figures, the concentration, in μg kg⁻¹, of vanadium in oil giving a signal intensity of 14 950.

Vanadium(V) oxide is used as the catalyst in the conversion of sulfur dioxide to sulfur trioxide.

SO₂(g) + V₂O₅(s) → SO₃(g) + 2VO₂(s)

$\frac{1}{2}$O₂(g) + 2VO₂(s) → V₂O₅(s)

Outline how vanadium(V) oxide acts as a catalyst.

Alloy:

mixture of metal with other metals/non-metals

OR

mixture of elements that retains the properties of a metal

Composite:

reinforcing phase embedded in matrix phase

Award [1 max] for implying “composites only have heterogeneous/nonhomogeneous compositions”.

[2 marks]

effective for yttrium «but less/not for nickel»

points on nickel graph do not lie on «y = x» line

OR

cannot be used for low concentrations of nickel

OR

concentration of nickel is lower than recorded value

Accept “ICP-OES is more accurate for lower yttrium concentrations than higher concentrations” for M1.

Accept [Ni] and [Y] for concentrations of nickel and yttrium.

Accept “detection limit for yttrium is lower than for nickel” for M2.

Award [1 max] for “more accurate for yttrium at lower concentrations AND nickel at higher concentrations”.

[2 marks]

Graph 1: determines wavelength of maximum absorption/maximum intensity «for vanadium»

Graph 2: determines absorption of known concentrations «at that wavelength»

OR

estimates [V]/concentration in a sample using «the signal» intensity

Do not accept just “determines maximum wavelength/λ_max” for M1.

Do not accept “calibration curve” for M2.

[2 marks]

«14 950 = 392.19x + 147.62»

x = 37.74 «μg kg^–1»

Answer must be given to four significant figures.

Do not accept values obtained directly from the graph.

[1 mark]

vanadium reduced in first reaction AND oxidized in second reaction

OR

V₂O₅ oxidizes SO₂ in first reaction AND VO₂ reduces O₂ in second reaction

OR

vanadium returns to original oxidation state «after reaction»

provides an alternative reaction pathway/mechanism «with a lower activation energy» ✔

Do not accept “reactants adsorb onto surface AND products desorb”.

Accept “oxidation number” for “oxidation state”.

[2 marks]