Acids, alkalis and titrations

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Question 17

The formula for hydrated sodium carbonate is $Na2CO3⋅xH2O\text{Na}_2\text{CO}_3\cdot x\text{H}_2\text{O}$ .

The value of $x$ is a whole number between 1 and 12. It can be determined by carrying out a titration with $mol/dm30.200\text{ mol/dm}^3$ hydrochloric acid ( $HCl\text{HCl}$ ) solution as follows:

dissolve a sample of $Na2CO3⋅xH2O\text{Na}_2\text{CO}_3\cdot x\text{H}_2\text{O}$ in water to make $cm3250\text{ cm}^3$ of solution
measure out $cm325.0\text{ cm}^3$ of this solution into a conical flask
add the $HCl\text{HCl}$ solution using a burette until the end point is reached
record the volume of solution added
repeat the titration three more times

The table shows the results:

Titration number	1	2	3	4
Volume in $cm3\text{cm}^3$ of $HCl\text{HCl}$ solution added	25.80	24.95	25.30	25.05
Concordant titration results ( $✓\checkmark$ )

Concordant results are those within $cm30.20\text{ cm}^3$ of each other. Identify the concordant results in the table.

[1]

Using the concordant results, calculate the average (mean) volume of $HCl\text{HCl}$ solution added. Give your answer to 2 decimal places.

[2]

Which is the most suitable piece of apparatus to measure out $cm325.0\text{ cm}^3$ of $Na2CO3\text{Na}_2\text{CO}_3$ solution?

A beaker
B gas syringe
C measuring cylinder
D pipette

[1]

These results were obtained in another titration:

parameter	value
mass of $Na2CO3⋅xH2O\text{Na}_2\text{CO}_3\cdot x\text{H}_2\text{O}$ in $cm3250\text{ cm}^3$ of the $Na2CO3\text{Na}_2\text{CO}_3$ solution	$g7.15\text{ g}$
average volume of $HCl\text{HCl}$ solution added to $cm325.0\text{ cm}^3$ of solution	$cm325.00\text{ cm}^3$
concentration of the $HCl\text{HCl}$ solution	$mol/dm30.200\text{ mol/dm}^3$

Calculate the amount, in moles, of $HCl\text{HCl}$ in $cm325.00\text{ cm}^3$ of solution.

[1]

In this reaction, two moles of $HCl\text{HCl}$ react with one mole of $Na2CO3\text{Na}_2\text{CO}_3$ . Calculate the amount, in moles, of $Na2CO3\text{Na}_2\text{CO}_3$ in $cm325.0\text{ cm}^3$ of the $Na2CO3\text{Na}_2\text{CO}_3$ solution.

[1]

Calculate the amount, in moles, of $Na2CO3\text{Na}_2\text{CO}_3$ in $cm3250\text{ cm}^3$ of this $Na2CO3\text{Na}_2\text{CO}_3$ solution.

[1]

Using your answer from (d)(iii), calculate the mass, in grams, of $Na2CO3\text{Na}_2\text{CO}_3$ in the $g7.15\text{ g}$ of $Na2CO3⋅xH2O\text{Na}_2\text{CO}_3\cdot x\text{H}_2\text{O}$ . [ $MrM_{\text{r}}$ of $Na2CO3=106\text{Na}_2\text{CO}_3 = 106$ ]

[1]

In another experiment it is found that $g14.3\text{ g}$ of $Na2CO3⋅xH2O\text{Na}_2\text{CO}_3\cdot x\text{H}_2\text{O}$ contains $g5.3\text{ g}$ of sodium carbonate ( $Na2CO3\text{Na}_2\text{CO}_3$ ).

Calculate the mass of water in $g14.3\text{ g}$ of $Na2CO3⋅xH2O\text{Na}_2\text{CO}_3\cdot x\text{H}_2\text{O}$ .

[1]

Calculate the amount, in moles, of $H2O\text{H}_2\text{O}$ in this mass of water.

[1]

Calculate the amount, in moles, of $Na2CO3\text{Na}_2\text{CO}_3$ in $g5.3\text{ g}$ of sodium carbonate. [ $MrM_{\text{r}}$ of $Na2CO3=106\text{Na}_2\text{CO}_3 = 106$ ]

[1]

Using your answers to parts (ii) and (iii), calculate the value of $x$ in $Na2CO3⋅xH2O\text{Na}_2\text{CO}_3\cdot x\text{H}_2\text{O}$ .

[1]

Titration number

Volume in

cm3\text{cm}^3

HCl\text{HCl}

solution added

25.80

24.95

25.30

25.05

Concordant titration results (

✓\checkmark

)

parameter

value

mass of

Na2CO3⋅xH2O\text{Na}_2\text{CO}_3\cdot x\text{H}_2\text{O}

cm3250\text{ cm}^3

of the

Na2CO3\text{Na}_2\text{CO}_3

solution

g7.15\text{ g}

average volume of

HCl\text{HCl}

solution added to

cm325.0\text{ cm}^3

of solution

cm325.00\text{ cm}^3

concentration of the

HCl\text{HCl}

solution

mol/dm30.200\text{ mol/dm}^3

Acids, alkalis and titrations

Question 17

Acids, alkalis and titrations Questions

Acids, alkalis and titrations

Question 17

Acids, alkalis and titrations Questions