The mole is a unit of measurement used in chemistry for the amount of a substance. It is defined as the amount of substance that contains the same number of atoms or entities as there are in 12 g of carbon-12. Iron, Fe, reacts with steam, H2O. An oxide of iron and hydrogen, H2, are made. The oxide of iron has the formula Fe_xO_y where x and y are whole numbers. In a reaction 1.67 g of iron, Fe, reacts with 0.72 g of steam, H2O. 0.08 g of hydrogen, H2, are made. (i) Calculate the number of moles of iron, steam and hydrogen. Give your answers to 2 decimal places. The relative atomic mass, A_r, of H is 1.0, of O is 16.0 and of Fe is 55.8. Moles of iron = Moles of steam = Moles of hydrogen = (ii) Look at the reaction equation. It shows the formation of 1 mole of the oxide of iron, Fe_xO_y. Use your answers to (b)(i) to balance the reaction equation and work out the formula of the oxide of iron, Fe_xO_y.

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The mole is a unit of measurement used in chemistry for the amount of a substance - OCR Gateway - GCSE Chemistry: Combined Science - Question 16 - 2021 - Paper 9

Question 16

The mole is a unit of measurement used in chemistry for the amount of a substance. It is defined as the amount of substance that contains the same number of atoms or... show full transcript

Worked Solution & Example Answer:The mole is a unit of measurement used in chemistry for the amount of a substance - OCR Gateway - GCSE Chemistry: Combined Science - Question 16 - 2021 - Paper 9

Step 1

Define the term mole.

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Answer

The mole is defined as the amount of a substance that contains exactly 6.02 x 10^23 elementary entities. This number, known as Avogadro's number, signifies how many atoms or molecules are present in one mole of any substance.

Step 2

(i) Calculate the number of moles of iron, steam and hydrogen.

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To find the number of moles, we use the formula:

ext{Number of moles} = rac{ ext{mass (g)}}{ ext{molar mass (g/mol)} }

Moles of Iron (Fe):
- Mass of Fe = 1.67 g
- Molar mass of Fe = 55.8 g/mol
- Moles of Fe = (rac{1.67}{55.8} \approx 0.03) (to 2 decimal places)
Moles of Steam (H2O):
- Mass of H2O = 0.72 g
- Molar mass of H2O = 18.0 g/mol
- Moles of H2O = (rac{0.72}{18.0} \approx 0.04) (to 2 decimal places)
Moles of Hydrogen (H2):
- Mass of H2 = 0.08 g
- Molar mass of H2 = 2.0 g/mol
- Moles of H2 = (rac{0.08}{2.0} \approx 0.04) (to 2 decimal places)

Step 3

(ii) Look at the reaction equation.

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The balanced reaction involving iron and steam to form the oxide of iron can be formulated as:

3 ext{Fe}(s) + 4 ext{H}_2 ext{O}(g) \rightarrow ext{Fe}_3 ext{O}_4(s) + 4 ext{H}_2(g)

Thus, the formula for the oxide of iron is ( ext{Fe}_3 ext{O}_4).

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