Magnesium nitrate, Mg(NO₃)₂, will decompose when heated to give a white solid and a mixture of gases. One of the gases released is an oxide of nitrogen, X. 7.4 g of anhydrous magnesium nitrate is heated until no further reaction takes place. What mass of X is produced? A. 1.5 g B. 2.3 g C. 3.0 g D. 4.6 g

A-Level CIE Chemistry 1.2 Formulae, Equations & Calculations: Magnesium nitrate, Mg(NO₃)₂, wil

Magnesium nitrate, Mg(NO₃)₂, will decompose when heated to give a white solid and a mixture of gases - CIE - A-Level Chemistry - Question 16 - 2016 - Paper 1

Question 16

Magnesium nitrate, Mg(NO₃)₂, will decompose when heated to give a white solid and a mixture of gases. One of the gases released is an oxide of nitrogen, X. 7.4 g of... show full transcript

Worked Solution & Example Answer:Magnesium nitrate, Mg(NO₃)₂, will decompose when heated to give a white solid and a mixture of gases - CIE - A-Level Chemistry - Question 16 - 2016 - Paper 1

Step 1

Calculate the molar mass of magnesium nitrate (Mg(NO₃)₂)

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Answer

The molar mass of magnesium nitrate can be calculated as follows:

Magnesium (Mg): 24.31 g/mol
Nitrogen (N): 14.01 g/mol (2 nitrogen atoms)
Oxygen (O): 16.00 g/mol (6 oxygen atoms)

So, $Molar ext{ mass} = 24.31 + 2(14.01) + 6(16.00) = 24.31 + 28.02 + 96.00 = 148.33 ext{ g/mol}$

Step 2

Determine the number of moles of magnesium nitrate used

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Answer

To find the number of moles of magnesium nitrate:

$ext{Number of moles} = rac{ ext{mass}}{ ext{molar mass}} = rac{7.4 ext{ g}}{148.33 ext{ g/mol}} \approx 0.050 ext{ moles}$

Step 3

Write the balanced decomposition equation

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Answer

The decomposition of magnesium nitrate can be represented as:

ightarrow 2 ext{MgO} + 4 ext{NO}_2 + ext{O}_2$$ From this equation, 2 moles of magnesium nitrate produce 4 moles of nitrogen dioxide (NO₂).

Step 4

Calculate the mass of nitrogen oxides produced

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Answer

According to the equation, for every 2 moles of magnesium nitrate, 4 moles of NO₂ are produced.

Using the mole ratio:

1 mole of Mg(NO₃)₂ produces 2 moles of NO₂, thus:

Moles of NO₂ produced from 0.050 moles of Mg(NO₃)₂: $ext{Moles of NO}_2 = 0.050 imes 2 = 0.1 ext{ moles}$

The molar mass of NO₂ is:

Nitrogen (N): 14.01 g/mol
Oxygen (O): 16.00 g/mol (2 oxygen atoms) $Molar ext{ mass of NO}_2 = 14.01 + 2(16.00) = 14.01 + 32.00 = 46.01 ext{ g/mol}$

Now calculate the mass of NO₂ produced: $ext{Mass of NO}_2 = ext{moles} imes ext{molar mass} = 0.1 imes 46.01 = 4.601 ext{ g}$

Step 5

Final mass of gas X produced

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Answer

Since one of the produced gases is NO₂ and matches with the provided options, we round the mass to:

$ext{Mass of X} ext{ is approximately } 4.6 ext{ g}$ .

Thus, the answer is option D: 4.6 g.

Magnesium nitrate, Mg(NO₃)₂, will decompose when heated to give a white solid and a mixture of gases - CIE - A-Level Chemistry - Question 16 - 2016 - Paper 1

Worked Solution & Example Answer:Magnesium nitrate, Mg(NO₃)₂, will decompose when heated to give a white solid and a mixture of gases - CIE - A-Level Chemistry - Question 16 - 2016 - Paper 1

Calculate the molar mass of magnesium nitrate (Mg(NO₃)₂)

Determine the number of moles of magnesium nitrate used

Write the balanced decomposition equation

Calculate the mass of nitrogen oxides produced

Final mass of gas X produced

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