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Concentration and moles for Edexcel GCSE Chemistry

Concentration and moles

This page covers the following topics:

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).

Moles

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.

Mole ratios

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

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

2

What is the mole ratio between FeS and Feโ‚‚Oโ‚ƒ in the following reaction: 4 FeS + 7 Oโ‚‚ โ†’ 2 Feโ‚‚Oโ‚ƒ + 4 SOโ‚‚?

2:1

What is the mole ratio between FeS and Feโ‚‚Oโ‚ƒ in the following reaction: 4 FeS + 7 Oโ‚‚ โ†’ 2 Feโ‚‚Oโ‚ƒ + 4 SOโ‚‚?

3

What is the moles of 2g of calcium carbonate (CaCOโ‚ƒ)?

2 / 100 = 0.02 mol

What is the moles of 2g of calcium carbonate (CaCOโ‚ƒ)?

4

If 0.3 moles of KClOโ‚ƒ are used in the following reaction: KClOโ‚ƒ + 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‚ƒ + 3 Pโ‚„ โ†’ 3 Pโ‚„Oโ‚โ‚€ + 10 KCl ratio 10:3 therefore mol Pโ‚„Oโ‚โ‚€ = 0.3/(10/3) = 0.09 mol

If 0.3 moles of KClOโ‚ƒ are used in the following reaction: KClOโ‚ƒ + 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).

5

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

3CaClโ‚‚ + 2Naโ‚ƒPOโ‚„ โ†’ Caโ‚ƒ(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

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

3CaClโ‚‚ + 2Naโ‚ƒPOโ‚„ โ†’ Caโ‚ƒ(POโ‚„)โ‚‚ + NaCl

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