Atom and State Symbols Essay

Submitted By taraiz
Words: 937
Pages: 4

Subject: Chemistry Foundation Code: 2811

Session: January Year: 2003 Final Mark Scheme
25/1/2003

MAXIMUM MARK

60

Page 1 of 8

/ ; NOT () ecf AW ora

= alternative and acceptable answers for the same marking point = separates marking points = answers which are not worthy of credit = words which are not essential to gain credit = (underlining) key words which must be used to gain credit = error carried forward = alternative wording = or reverse argument

Abbreviations, annotations and conventions used in the Mark Scheme

1.

(a) isotope
69 71

protons 31 31

number of neutrons 38 40

electrons 31 31 [2]

Ga Ga

(b)

deflection/ acceleration/ accelerator ignore ‘atoms’ beyond 1st stage ionisation/ electron bombardment/ ioniser not electron gun detection/ detector deflector ignore ‘what deflects’

[4]
(c) (i) average mass/weighted mean/average mass of an atom / the isotopes

compared with carbon-12 1/12th of mass of carbon-12/on a scale where carbon-12 is 12

not 12 g or... mass of 1 mole of atoms compared with carbon-12 1/12th of mass of 1 mol of carbon-12/on a scale where carbon-12 is 12 g
(ii)
69

[3]

Ga: 61%;

71

Ga: 39%

(allow 62/38 → 69.76 below) [1] = 69.8 ignore g / grammes

(iii) Ar = 69 x 61/100 + 71 x 39/100 = 69.78

[2] [Total: 12 marks]

Page 3 of 8

2

(a) 1s22s22p63s2 [1]
(b) (i)

Mg: 0 [1]

(ii) MgO: +2 / 2 / II

[1]
(c) (i) 3Mg(s) + N2(g) → Mg3N2(s) 1 for correct formulae and balancing; 1 for correct state symbols

[2]
(ii) N2 is less reactive than O2 /

bond between N atoms is stronger than bond between O atoms / nitrogen has a triple bond and oxygen has a double bond activation energy of N > activation energy of O

The emphasis here should be a comparison for the mark
[1]
(d) MgO has a giant structure

MgO is ionic / charged magnesium and oxide ions shown strong forces [3]
(e) (i) MgO dissolves/disappears

[1]
(ii) m(MgO) = 24.3 + 16 = 40.3 (g mol )
−1

(accept 40)

mass MgO = 0.0500 x 40.3 = 2.015 g / 2.02 g / 2.01 g / 2 g g is needed here

[2]
(iii) moles HNO3 = 2 x 0.0500 = 0.100 mol

right or wrong for 1st mark volume HNO3 = 0.25 dm3 / 250 cm3
i.e. moles HNO3/0.400 dm3 / 1000 x moles HNO3/0.400 cm3 0.05/0.400 → 0.125 dm3 / 125 cm3 would score 1 mark as molar ratio not used

[2]
(f) (i) ions move / free ions

[1]
(ii) Mg2+ /NO3− / H+/OH−

2 max [2] [Total: 17 marks]

Page 4 of 8

3.

(a)

(i) purification/sterilisation/kills or removes germs/disinfects

not ‘to make bleach’

not ‘cleans the water’
[1]

(ii) turns red / yellow / orange

then colourless / bleaches colourless then ‘nothing’ scores 1 mark colourless then ‘red’ does not score because overall bleaching is not implied.

[2]
(b) reagent silver nitrate/Ag+ ions observation white (precipitate) / goes white equation

mark independently

Ag+(aq) + Cl−(aq) → AgCl(s) / NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)
(state symbols not required) Fluorine for reagent + ‘correct’ displacement equation scores 1 mark)

[3]
(c) (i)

Cl : C = 85.6/35.5 : 14.4/12 =2:1

= 2.4 : 1.2

Cl2C has mass of 83. 166 = 2 x 83 molecular formula = Cl4C2
Cl : C = 85.6/17 : 14.4/12 → Cl4C scores 1 mark / Cl : C = 85.6/17 : 14.4/6 → Cl2C scores 1 mark Cl : C = 85.6/35.5 : 14.4/6 → ClC scores 1 mark

[3]
(ii) perc is covalent / perc is not ionic / C−Cl bond in perc is covalent

/…