A-LevelChemistryAtoms, molecules and stoichiometry9701/23 · May/June 2020 · Q213 Marks

Explain what is meant by the term relative isotopic mass.

(a)Explain what is meant by the term relative isotopic mass.[2]
(b)A sample of copper contains two isotopes, 63Cu and 65Cu. The relative atomic mass of the copper in this sample is 63.55. Calculate the percentage abundance of each of these isotopes. Show your working. percentage abundance of 63Cu = ................................... % percentage abundance of 65Cu = ................................... %[2]
(c)(i)Name the type of bonding within a sample of solid copper.[1]
(c)(ii)Draw a labelled diagram to show the bonding within a sample of solid copper.[2]
(c)(iii)State the electronic configuration of a copper atom. 1s²...................................................................................................................................[1]
(d)A student is provided with a sample of hydrated copper(II) sulfate, CuSO4•xH2O, and is asked to determine the value of x. The student dissolves a sample of the hydrated copper(II) sulfate in water and adds it to an excess of aqueous potassium iodide to make a total volume of 250.0 cm³ of solution. 2CuSO4 + 4KI → 2CuI + I2 + K2SO4 The amount of iodine produced during this reaction is found by titrating a sample of this solution with sodium thiosulfate solution. 25.0 cm³ of the iodine-containing solution requires 20.0 cm³ of 0.10 moldm-³ sodium thiosulfate solution. I2 + 2S2O3²- → S4O6²- + 2I-
(d)(i)Calculate the amount, in mol, of copper(II) sulfate present in the original sample of hydrated copper(II) sulfate. Show your working. amount of copper(II) sulfate = .............................................. mol[2]
(d)(ii)A total of 7.98 g of CuSO4 is present in 10.68 g of CuSO4•xH2O. Complete each row of the table to calculate the value of x, where x is an integer. [Mr: CuSO4,159.6] amount of CuSO4 in 10.68 g of CuSO4•xH2O | .............................................. mol --- amount of H2O in 10.68 g of CuSO4•xH2O | .............................................. mol --- value of x | x = ..............................................[3]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[2] EITHER M1 mass of an atom / isotope M2 relative / compared to 1/12 (the mass) of (an atom of) C-12 OR on a scale in which a C-12 (atom / isotope) has (a mass of exactly) 12 (units) OR M1 mass of one mol (of atoms) of an isotope M2 relative / compared to 1/12 (the mass) of 1 mol of C-12 OR in which one mol C-12 (atom / isotope) has a mass of (exactly) 12 g
[2] % abundance of 63Cu = 72.5% % abundance of 65Cu = 27.5% M1 correct algebraic expression AND correct calculation of x for one isotope % ab of 63Cu = x (x/100 × 63) + ((1- x)/100 × 65) = 63.55 so x =72.5 OR % ab of 65Cu = x (1-x)/100 × 63) + x/100 × 65) = 63.55 so x = 27.5 M2 calculation of abundance of other isotope by 100- x
[1] metallic
[2] diagram showing the bonding in a sample of copper M1 diagram shows regular arrangement of spheres labelled as positively charged ions / +2 or +1 / cations M2 diagram shows surrounded by electrons and clearly labelled as 'delocalised electrons'
[1] (1s²2) 2s2 2p6 3s2 3p6 3d10 4s1 OR (1s²) 2s2 2p6 3s2 3p6 4s1 3d10
[2] M1 calculate the number mol S2O3 2-added 20/1000 x 0.10 = 2x10-3 = 0.002 (mol S2O3 2-) M2 calculate number mol CuSO4 in 250cm³ (1mol S2O3 2-: 1 mol CuSO4) = 0.002 mol CuSO4 in 25cm³ so 0.02 mol CuSO4 in 250cm³
[3] M1 amount of CuSO4 in 10.68 g of CuSO4·XH2O 7.98 / (159.6) = 0.05 (mol) M2 amount of H2O in 10.68 g of CuSO4·XH2O (10.68 -7.98) / 18 = 2.7 / 18 =) 0.15 (mol) M3 value of x (mol H2O ÷ mol CuSO4 =) 3