chemistry unit 1

chapter 2--amount of substance

exam style questions answers

HideShow resource information
  • Created by: madeha
  • Created on: 08-07-13 19:09
Preview of chemistry unit 1

First 182 words of the document:

AS Chemistry Chapter 2
Extension
Answers to teacher notes questions
examination-style
Answers Marks Examiner's tips
1 (a) (i) 75.0 × 10­3 × 0.500 = 0.0375 (mol) 1
(ii) 21.6 × 10­3 × 0.500 = 0.0108 (mol) 1
(iii)0.0375 ­ 0.0108 = 0.0267 (mol) 1
(iv) m
oles of MgCO3 = 0.0267/2 = 0.01335 (mol) 1 0.0133 to 0.0134 would be allowed.
mass of MgCO3 = 0.01335 × 84.3 1
= 1.125 g 1
percentage MgCO3 = 1.125/1.25 × 100 1 Keep going through the calculation.
= 90% 1 You can score consequential marks
even if you have made an arithmetic
error.
(b) (i) % oxygen = 38.0 1 If no % of oxygen, maximum 1 mark.
Na= 36.5/23 S= 25.5/32.1 O = 38.0/16 1
= 1.587 = 0.794 = 2.375
= 2:1:3 1
(ii) Na2SO3 + 2HCl ­ 2NaCl + H2O + SO2 1 You can also have multiples when
balancing your equation.
2 (a) (i) 100 × l0­3 × 0.500 = 5.00 × 10­2 (mol) 1 accept 5 × 10­2 / 0.05
7.3 × 10­3 × 0.600 = 1.64 × 10­2 or
(ii) 2 1
1.638 × 10­2 (mol) only
(iii)1.64 × 10­2 (mol) 1
(iv) 5.00 × 10­2 ­ 1.64 × 10­2 = 3.36 × 10­2 (mol) 1
(v) 3.36 × 10­2 × ½ = 1.68 × 10­2 (mol) 1 if 2.78 × 10­2 used 1.39 × 10­2
1.68 × 10­2 × 132.1 or 1.39 × 10­2 × 132.1 1
= 2.22 g or 1.83 g 1
(b) pV = nRT 1 If you get the moles wrong you will
get consequential marks if you use
n = 0.143 = 8.41 × 10­3 (mol) 1 your mole value correctly.
17
pV
T = 10­4
= 100 000 × 2.86 × ­3 1
nR 8.31 × 8.4 × 10
= 408.5 ­ 410.5 (K) 1
AQA Chemistry AS Level © Nelson Thornes Ltd 2008

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

AS Chemistry Chapter 2
Extension
Answers to teacher notes questions
examination-style
Answers Marks Examiner's tips
3 (a) moles HNO3 = 175 × 10­3 × 1.5 = 0.2625 mol 1
moles Pb(NO3)2 = ½ × 0.2625 = 0.131 mol 1 You must use the ratio from the
equation, i.e. 2 : 1
Mr Pb(NO3)2 = 331.2 1
mass Pb(NO3)2 = 331.2 × 0.131= 43.3 g 1
(b) (i) pV = nRT 1 Don't forget p in Pa, V in m3 and T in K.…read more

Page 3

Preview of page 3

Here's a taster:

AS Chemistry Chapter 2
Extension
Answers to teacher notes questions
examination-style
Answers Marks Examiner's tips
5 (a) (i) moles KNO3 = 1.00/101.1 = 9.89 × 10­3 1
(mol)
(ii) p
V = nRT or n = pV/RT 1
pV
moles O2 = n = 1
RT
­4
100 000
= × 1.22 × 10 1
8.31 × 298
= 4.93 × 10­3 (mol) 1
(b) (i) s implest ratio of atoms of each element 1 You must learn this definition exactly.…read more

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »