Moles Quiz
Moles Quiz
Q1 / 5
Calculate the Mr of Magnesium Hydroxide, Mg(OH)2.
Well Done!
Mr [Mg(OH)2] = 24 + 16 + 16 + 1 + 1
= 58
Unlucky.
Mr [Mg(OH)2] = 24 + 16 + 16 + 1 + 1
= 58

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Moles Quiz
Q2 / 5
What is the mass (in grams) of 2 moles of potassium?
Well Done!
Ar (K) = 39

m = n x Mr
= 2 x 39
= 78g
Unlucky.
Ar (K) = 39

m = n x Mr
= 2 x 39
= 78g

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Moles Quiz
Q3 / 5
How many moles of NaOH are in 4g of pure NaOH?
Well Done!
Mr (NaOH) = 23 + 16 + 1
= 40
n = m / Mr
= 4/40
= 0.1 mol
Unlucky.
Mr (NaOH) = 23 + 16 + 1
= 40
n = m / Mr
= 4/40
= 0.1 mol

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Moles Quiz
Q4 / 5
1.6g of sulphur was heated in oxygen. Its mass increased to 4.0g. Calculate the empirical formula of this oxide of sulphur.

CO2 = CO2
Fe2O3 = Fe2O3
Ca(OH)2 = Ca(OH)2
etc.

Well Done!

Sulphur Oxygen
Mass (g) 1.6 4.0 - 1.6 = 2.4
Relative Atomic Mass, Ar 32 16
Mass / Ar 1.6 / 32 = 0.05 2.4 / 16 = 0.15
Amount / Smallest Amount 0.05 / 0.05 = 1 0.15 / 0.05 = 3
Ratio of Amounts 1 3

EMPIRICAL FORMULA: SO3

Unlucky.

Sulphur Oxygen
Mass (g) 1.6 4.0 - 1.6 = 2.4
Relative Atomic Mass, Ar 32 16
Mass / Ar 1.6 / 32 = 0.05 2.4 / 16 = 0.15
Amount / Smallest Amount 0.05 / 0.05 = 1 0.15 / 0.05 = 3
Ratio of Amounts 1 3

EMPIRICAL FORMULA: SO3

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Moles Quiz
Q5 / 5
HARD: Copper sulphate crystals contain water of crystallisation (water in its crystal structure) and have the formula CuSO4.xH2O, where x is a whole number. 49.9g of a sample of copper sulphate was found to have 18g of water of crystallisation. Calculate x.

Well Done!

CuSO4 H2O
Mass (g) 49.9 - 18 = 31.9 18
Relative Molecular Mass, Mr 63.5 + 32 + (16 x 4) = 159.52 1 + 1 + 16 = 18
Mass / Mr 31.9 / 159.5 = 0.2 18 / 18 = 1
Amount / Smallest Amount 0.2 / 0.2 = 1 1 / 0.2 = 5
Ratio of Amounts 1 5

x = 5
EMPIRICAL FORMULA: CuSO4.5H2O

Unlucky.

CuSO4 H2O
Mass (g) 49.9 - 18 = 31.9 18
Relative Molecular Mass, Mr 63.5 + 32 + (16 x 4) = 159.52 1 + 1 + 16 = 18
Mass / Mr 31.9 / 159.5 = 0.2 18 / 18 = 1
Amount / Smallest Amount 0.2 / 0.2 = 1 1 / 0.2 = 5
Ratio of Amounts 1 5

x = 5
EMPIRICAL FORMULA: CuSO4.5H2O

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Moles Quiz
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