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# Concentration and moles for Edexcel GCSE Chemistry

1. Moles
2. Mole ratios

Avogadro's constant: 1 mole = 6.02 x 10ยฒยณ atoms/molecules/protons. To convert from moles to atoms (or reverse) use Avogadro's constant. Moles can also be calculated by using the pyramid (mass = moles x RFM).

The mole ratio is the ratio between the amount of moles in the compounds of a reaction. The mole ratio can be used as a conversion factor between reactants and products, and can be worked out by looking at the coefficients in front of the formulae of the compounds.

# 1

How many moles is 4.515 ร 10ยฒยณ atoms of a substance?

n = N/Nโ = 4.515 ร 10ยฒยณ รท (6.02 ร 10ยฒยณ) = 0.75 mol

0.75 mol

# 2

What is the mole ratio between FeS and FeโOโ in the following reaction: 4 FeS + 7 Oโ โ 2 FeโOโ + 4 SOโ?

2:1

# 3

What is the moles of 2g of calcium carbonate (CaCOโ)?

2 / 100 = 0.02 mol

# 4

If 0.3 moles of KClOโ are used in the following reaction: KClOโ + Pโ โ PโOโโ + KCl, how many moles of PโOโโ are produced? (This equation isn't balanced, you will need to balance it).

Balanced: 10 KClOโ + 3 Pโ โ 3 PโOโโ + 10 KCl ratio 10:3 therefore mol PโOโโ = 0.3/(10/3) = 0.09 mol

# 5

What is the mole ratio between CaClโ and NaCl in the following reaction?

3CaClโ + 2NaโPOโ โ Caโ(POโ)โ + NaCl

The coefficient in front of CaClโ is 3, while the coefficient in front of NaCl is 1.
Thus, the CaClโ to NaCl ratio is 3 : 1.

3 : 1

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