3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations

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Question 29

A student investigated the change in mass when hydrated magnesium sulfate was heated.

The word equation for the reaction is:

\text{hydrated magnesium sulfate} \rightleftharpoons \text{anhydrous magnesium sulfate} + \text{water}

This is the method used:

Add $g3.50\text{ g}$ of hydrated magnesium sulfate to an empty porcelain crucible.
Measure the mass of the crucible and contents.
Heat the crucible and contents strongly for 2 minutes.
Allow the crucible and contents to cool.
Measure the mass of the crucible and contents.
Repeat steps 3 to 5 until the mass of the crucible and contents does not change.

Table 1 shows the results.

Table 1

Total heating time in minutes	Mass of crucible and contents in grams
0	42.85
2	41.80
4	41.15
6	41.15

Questions:

Determine the mass of the empty porcelain crucible.

[2]

Explain why the mass of the crucible and contents decreased.

[2]

Suggest why the crucible and contents were heated until the mass did not change.

[1]

When $g246.5\text{ g}$ of hydrated magnesium sulfate is heated until the mass does not change, $kJ354\text{ kJ}$ of energy is taken in. The student heated $g3.50\text{ g}$ of hydrated magnesium sulfate until the mass did not change. Calculate the energy taken in during this reaction. Give your answer to 3 significant figures.

[2]

What type of reaction, in terms of energy transfer, takes place when hydrated magnesium sulfate is heated?

[1]

3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Question 29

A student investigated the change in mass when hydrated magnesium sulfate was heated.

The word equation for the reaction is:

\text{hydrated magnesium sulfate} \rightleftharpoons \text{anhydrous magnesium sulfate} + \text{water}

This is the method used:

Add $g3.50\text{ g}$ of hydrated magnesium sulfate to an empty porcelain crucible.
Measure the mass of the crucible and contents.
Heat the crucible and contents strongly for 2 minutes.
Allow the crucible and contents to cool.
Measure the mass of the crucible and contents.
Repeat steps 3 to 5 until the mass of the crucible and contents does not change.

Table 1 shows the results.

Table 1

Total heating time in minutes	Mass of crucible and contents in grams
0	42.85
2	41.80
4	41.15
6	41.15

Questions:

Determine the mass of the empty porcelain crucible.

[2]

Explain why the mass of the crucible and contents decreased.

[2]

Suggest why the crucible and contents were heated until the mass did not change.

[1]

[2]

What type of reaction, in terms of energy transfer, takes place when hydrated magnesium sulfate is heated?

[1]

3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations

Question 29

Table 1

Markscheme

3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations

Question 29

Table 1

Markscheme

3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations

Question 29

Table 1

3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations Questions

3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations

Question 29

Table 1

3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations Questions