Moles Quiz

Q1 / 5

Calculate the M_r of Magnesium Hydroxide, Mg(OH)₂.
Give your answer to the nearest whole number.

Well Done!
M_r[Mg(OH)₂] = 24 + 16 + 16 + 1 + 1
= 58

Unlucky.
M_r[Mg(OH)₂] = 24 + 16 + 16 + 1 + 1
= 58

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Relative Atomic Mass, A_r

Moles Quiz

Q2 / 5

What is the mass (in grams) of 2 moles of potassium?
Give your answer to the nearest whole number.

Well Done!
A_r (K) = 39

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

Unlucky.
A_r (K) = 39

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

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The Formula

Moles Quiz

Q3 / 5

How many moles of NaOH are in 4g of pure NaOH?

Well Done!
M_r (NaOH) = 23 + 16 + 1
                = 40
n = m / M_r
   = 4/40
   = 0.1 mol

Unlucky.
M_r (NaOH) = 23 + 16 + 1
                = 40
n = m / M_r
   = 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.

Give your answer in the following format:

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, A_r	32	16
Mass / A_r	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, A_r	32	16
Mass / A_r	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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Empirical Formula

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, M_r	63.5 + 32 + (16 x 4) = 159.52	1 + 1 + 16 = 18
Mass / M_r	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, M_r	63.5 + 32 + (16 x 4) = 159.52	1 + 1 + 16 = 18
Mass / M_r	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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Empirical Formula

Moles Quiz

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