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Zinc nitrate thermally decomposes to give two gases - OCR Gateway - GCSE Chemistry - Question 7 - 2019 - Paper 4

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Zinc nitrate thermally decomposes to give two gases. 2Zn(NO₃)₂(s) → 2ZnO(s) + 4NO₂(g) + O₂(g) A student heats 1.89 g of zinc nitrate until there is no further reac... show full transcript

Worked Solution & Example Answer:Zinc nitrate thermally decomposes to give two gases - OCR Gateway - GCSE Chemistry - Question 7 - 2019 - Paper 4

Step 1

Calculate the moles of zinc nitrate

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Answer

To find the moles of zinc nitrate, we can use the formula:

Moles=massmolar mass\text{Moles} = \frac{\text{mass}}{\text{molar mass}}

Substituting the known values:

Moles=1.89 g189 g/mol=0.01 moles\text{Moles} = \frac{1.89 \text{ g}}{189 \text{ g/mol}} = 0.01 \text{ moles}

Step 2

Identify the total moles of gas produced

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Answer

From the balanced equation:

2Zn(NO₃)₂(s) → 2ZnO(s) + 4NO₂(g) + O₂(g)

For every 2 moles of zinc nitrate decomposed, 5 moles of gas (4 moles of NO₂ and 1 mole of O₂) are produced. Therefore, the total gas produced per mole of zinc nitrate is:

Gas moles=52×0.01=0.025 moles\text{Gas moles} = \frac{5}{2} \times 0.01 = 0.025 \text{ moles}

Step 3

Calculate the total volume of gas produced

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Answer

Using the ideal gas law, where 1 mole of gas occupies 24 dm³:

Volume=moles×24 dm³/mole\text{Volume} = \text{moles} \times 24 \text{ dm³/mole}

Thus,

Volume=0.025 moles×24 dm³/mole=0.60 dm³\text{Volume} = 0.025 \text{ moles} \times 24 \text{ dm³/mole} = 0.60 \text{ dm³}

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