[Maximum number: 8]

A student needed to make $500.0 \mathrm{~cm}^{3}$ of a $0.2500 \mathrm{~mol} \mathrm{dm}^{-3}$ solution of sodium hydroxide, NaOH , from the solid for a titration.

(a)

Calculate the mass of sodium hydroxide needed.

[ 1 ]

(b)

Describe the process of preparing a standard solution from a solid using a volumetric flask.

[ 3 ]

(c)

A $10.00 \mathrm{~cm}^{3}$ sample of the sodium hydroxide solution was titrated with $0.2000 \mathrm{~mol} \mathrm{dm}^{-3}$ solution of hydrochloric acid, HCl(aq).

Determine the actual concentration of the sodium hydroxide solution for this titration trial. Record the initial and final volume in the data table to the correct number of significant figures.

Concentration:

[ 2 ]

(d)

Explain why the sodium hydroxide solution must be standardized. Assume there are no systematic errors.

[ 2 ]

[Maximum number: 1]

Nitrogen dioxide, $\mathrm{NO}_{2}$ , is a brown, toxic and corrosive gas. It can be made in a school laboratory by heating a group II metal nitrate or by the reaction of copper, Cu , with concentrated nitric acid, $\mathrm{HNO}_{3}$ .

(a)

(i)

Calculate the mass, in g , of Cu required to make 0.0100 moles of $\mathrm{NO}_{2}$ . Use section 7 of the data booklet.

[ 1 ]

[Maximum number: 1]

Water contaminated with mercury contains methylmercury ions, $\mathrm{CH}_{3} \mathrm{Hg}^{+}$ . These ions are absorbed by living organisms, then slowly metabolized and excreted.

Young fish were taken at regular intervals from a mercury contaminated lake and tested to determine mercury ion content.

Mercury ion content in muscle tissue of fish

(a)

The concentration of mercury ion in a sample of the fish is $0.0052 \pm 0.0001 \mu \mathrm{~g} \mathrm{Hg} \mathrm{g}^{-1}$ .

[ 1 ]

(i)

Calculate the mass of Hg , in $\mu \mathrm{g}$ , in 3.723 g of the sample.

[ 1 ]

[Maximum number: 1]

How many moles of phosphate ions, $\mathrm{PO}_{4}{ }^{3-}$ , are there in 103.39 g of $\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}$ ?
$M_{r}=310.18$

A

0.11

B

0.33

C

0.67

D

2.00

[Maximum number: 2]

Phenol red, bromocresol green and phenolphthalein are acid-base indicators.

Phenol red

Bromoscresol green

Phenolphthalein

(a)

(i)

Determine the molecular and empirical formulas of phenolphthalein.

Molecular formula:
Empirical formula:

[ 2 ]

[Maximum number: 4]

A powder has the following percentage composition by mass:
30.0 % sucrose, $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}$
45.0 % citric acid, $\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7}$
25.0 \% sodium hydrogencarbonate, $\mathrm{NaHCO}_{3}$

In the presence of water, the powder effervesces as the citric acid reacts with the sodium hydrogencarbonate:

$3 \mathrm{NaHCO}_{3}(\mathrm{~s})+\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7}(\mathrm{aq}) \rightarrow \mathrm{Na}_{3}\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}_{7}\right)(\mathrm{aq})+3 \mathrm{CO}_{2}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})$

(a)

(i)

Determine the limiting reactant when 1.00 g of this powder reacts.

[ 3 ]

(ii)

Calculate the percentage yield obtained by a student who collected $0.043 \mathrm{dm}^{3}$ of carbon dioxide from 1.00 g of the powder.

If you did not obtain an answer to (a)(ii), use $0.068 \mathrm{dm}^{3}$ , but this is not the correct value.

[ 1 ]

[Maximum number: 5]

Phosphorus is an element that is an essential part of the biological molecules involved in both respiration and photosynthesis.

(a)

7.75 g of phosphorus was combusted in a limited supply of oxygen, the mass of the oxide produced was 13.75 g .

[ 5 ]

(i)

Calculate the number of atoms in 7.75 g of phosphorus. Use sections 2 and 7 of the data booklet.

[ 1 ]

(ii)

Determine the empirical formula of the oxide formed, show your working. Use section 7 of the data booklet.

[ 3 ]

(iii)

The $M_{r}$ of the oxide formed in (b)(ii) was known to be $219.88 \mathrm{gmol}^{-1}$ .

Determine the molecular formula of the oxide formed, showing your working. Use section 7 of the data booklet.

[ 1 ]

[Maximum number: 2]

An organic compound, A, has the following composition by mass when its only combustion products, carbon dioxide and water, are analysed.

(a)

Determine the empirical formula of A.

[ 2 ]

[Maximum number: 2]

Phenolphthalein is an acid-base indicator.

(a)

Determine the molecular and empirical formulas of phenolphthalein.

Molecular formula:

Empirical formula:

[ 2 ]

[Maximum number: 5]

A student needed to make $500.0 \mathrm{~cm}^{3}$ of a $0.2500 \mathrm{~mol} \mathrm{dm}^{-3}$ solution of sodium hydroxide, NaOH , from the solid for a titration.

(a)

Calculate the mass of sodium hydroxide needed.

[ 1 ]

(b)

Describe the process of preparing a standard solution from a solid using a volumetric flask.

[ 3 ]

(c)

The standardized sodium hydroxide solution from (c) was used to titrate a propanoic acid solution of unknown concentration.

[ 1 ]

(i)

Calculate the concentration of the propanoic acid if $15.00 \mathrm{~cm}^{3}$ of its solution was neutralized with $20.00 \mathrm{~cm}^{3}$ of standardized sodium hydroxide.

If you did not determine the concentration of sodium hydroxide in part (c), use $0.2155 \mathrm{~mol} \mathrm{dm}^{-3}$ although this is not the correct answer.

[ 1 ]