Acids and bases (A-level only)

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Question 34

This question is about an experiment to determine the solubility of strontium hydroxide, $Sr(OH)2\text{Sr(OH)}_2$ , in water at $∘C20\ ^\circ\text{C}$ .

Strontium hydroxide is slightly soluble in water.

Solid strontium hydroxide is added to approximately $dm31\text{ dm}^3$ of distilled water in a stoppered flask.
The mixture is kept at $∘C20\ ^\circ\text{C}$ and shaken until no more solid dissolves.
The mixture is filtered into another flask and stoppered.
A $cm320.0\text{ cm}^3$ sample of the filtrate is transferred to a conical flask with a pipette and a few drops of indicator added.
This sample is titrated with $dm−30.100\text{ mol dm}^{-3}$ nitric acid.
The titration is repeated several times.

Suggest why the mixture must be kept in a stoppered flask with excess solid until no more solid dissolves.

[1]

Suggest why it is important to completely remove any undissolved strontium hydroxide by filtration before the titration.

[2]

Give the chemical equation for the reaction between strontium hydroxide and nitric acid.

[1]

Table 1 shows the results of the titrations with $dm−30.100\text{ mol dm}^{-3}$ nitric acid ( $HNO3\text{HNO}_3$ ).

Table 1

Titration	Rough	1	2	3
Final burette reading / $cm3\text{cm}^3$	$27.50$	$26.35$	$31.85$	$27.55$
Initial burette reading / $cm3\text{cm}^3$	$0.00$	$0.10$	$5.00$	$1.20$
Titre / $cm3\text{cm}^3$	$27.50$	$26.25$	$26.85$	$26.35$

Use the results in Table 1 to calculate the mean titre. Then, use your mean titre to calculate the solubility of strontium hydroxide, in $g\text{g}$ per $cm3100\text{ cm}^3$ of solution at $∘C20\ ^\circ\text{C}$ . Give your answer to 3 significant figures. (Assume $Mr(Sr(OH)2)=121.6M_r(\text{Sr(OH)}_2) = 121.6$ )

[5]

Acids and bases (A-level only)

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 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59

Question 34

This question is about an experiment to determine the solubility of strontium hydroxide, $Sr(OH)2\text{Sr(OH)}_2$ , in water at $∘C20\ ^\circ\text{C}$ .

Strontium hydroxide is slightly soluble in water.

Solid strontium hydroxide is added to approximately $dm31\text{ dm}^3$ of distilled water in a stoppered flask.
The mixture is kept at $∘C20\ ^\circ\text{C}$ and shaken until no more solid dissolves.
The mixture is filtered into another flask and stoppered.
A $cm320.0\text{ cm}^3$ sample of the filtrate is transferred to a conical flask with a pipette and a few drops of indicator added.
This sample is titrated with $dm−30.100\text{ mol dm}^{-3}$ nitric acid.
The titration is repeated several times.

Suggest why the mixture must be kept in a stoppered flask with excess solid until no more solid dissolves.

[1]

Suggest why it is important to completely remove any undissolved strontium hydroxide by filtration before the titration.

[2]

Give the chemical equation for the reaction between strontium hydroxide and nitric acid.

[1]

Table 1 shows the results of the titrations with $dm−30.100\text{ mol dm}^{-3}$ nitric acid ( $HNO3\text{HNO}_3$ ).

Table 1

Titration	Rough	1	2	3
Final burette reading / $cm3\text{cm}^3$	$27.50$	$26.35$	$31.85$	$27.55$
Initial burette reading / $cm3\text{cm}^3$	$0.00$	$0.10$	$5.00$	$1.20$
Titre / $cm3\text{cm}^3$	$27.50$	$26.25$	$26.85$	$26.35$

[5]

Acids and bases (A-level only)

Question 34

Acids and bases (A-level only) Questions

Acids and bases (A-level only)

Question 34

Acids and bases (A-level only) Questions