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# Concentration and moles for SQA Higher Chemistry 1. Moles
2. Mole ratios

Avogadro's constant: 1 mole = 6.02 x 10²³ 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 × 10²³ atoms of a substance?

n = N/Nₐ = 4.515 × 10²³ ÷ (6.02 × 10²³) = 0.75 mol

0.75 mol # 2

What is the mole ratio between FeS and Fe₂O₃ in the following reaction: 4 FeS + 7 O₂ → 2 Fe₂O₃ + 4 SO₂?

2:1 # 3

What is the moles of 2g of calcium carbonate (CaCO₃)?

2 / 100 = 0.02 mol # 4

If 0.3 moles of KClO₃ are used in the following reaction: KClO₃ + P₄ → P₄O₁₀ + KCl, how many moles of P₄O₁₀ are produced? (This equation isn't balanced, you will need to balance it).

Balanced: 10 KClO₃ + 3 P₄ → 3 P₄O₁₀ + 10 KCl ratio 10:3 therefore mol P₄O₁₀ = 0.3/(10/3) = 0.09 mol # 5

What is the mole ratio between CaCl₂ and NaCl in the following reaction?

3CaCl₂ + 2Na₃PO₄ → Ca₃(PO₄)₂ + NaCl

The coefficient in front of CaCl₂ is 3, while the coefficient in front of NaCl is 1.
Thus, the CaCl₂ to NaCl ratio is 3 : 1.

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