1) Chemists play an important role in developing fuels for the future. One area of interest has been in the ‘hydrogen economy’ where chemists have been looking at the possibilities of using hydrogen as a fuel, either directly or indirectly. (a) (i) Hydrogen can be burnt as a fuel in an internal combustion engine. Give one advantage of hydrogen over petrol. Hydrogen is used as fuel as it is pollution free. Combustion of petrol produces carbon monoxide and carbon dioxide as a pollutant[1] (ii) Describe one way in which hydrogen can be produced. It can be produced from cracking of hydrocarbon/ It can be produced from electrolysis of water.[1] (iii) Why might your method of production in (ii) not save fossil fuels? Fossil fuel is needed to crack hydrogen/ Fossil fuel is needed to produce electrical energy needed in electrolysis. [1] (b) One novel way of producing hydrogen is to use ‘Powerballs’. These contain the ionic compound sodium hydride, NaH, encapsulated inside poly(ethene) spheres. The Powerballs are stored in water and are cut open automatically to allow the sodium hydride to react with the water and produce hydrogen when required. (i) The hydride ion is H–. Draw a dot-cross diagram to represent both of the ions in sodium hydride. You should show outer electrons only.

[2] (ii) The reaction of the sodium hydride with water produces sodium hydroxide solution as well as hydrogen. Write a balanced equation for this reaction.

2 22NaH H O NaOH H+ → +

[2]

X X

X X

X X

X X

Na + X

O

H - O rep electrons of

hydrogen atom.

X rep electrons of

sodium atom.

2) Since the time of Mendeleev and Lothar Meyer many more elements have been discovered. Sir William Ramsey discovered argon in 1894. He removed oxygen and nitrogen from air and found he was left with about one percent which was the gas argon. (i) The oxygen can be removed by passing air over hot copper. Copper oxide, CuO, is formed. Write a balanced equation for this reaction. Include state symbols.

22 ( ) ( ) 2 ( )C u s O g C u O s+ →

[2] (ii) The nitrogen was removed by passing it over hot magnesium. This produced a white solid called magnesium nitride, Mg3N2. The balanced equation for this reaction is given below.

3Mg(s) + N2(g) � Mg3N2(s)

Calculate the number of moles of nitrogen gas in 1 dm3 of air at room temperature and Assume air to be 80% nitrogen gas by volume and that one mole of gas occupies 24dm3

at room temperature and pressure. 24dm3 of air���� 1 mole of air

No of mole of N2����( 78

100x

1

24) mol= 0.0325mol

[2] (iii) Use equation 3.1 and your answer to (ii) to calculate the mass of magnesium that would react with the nitrogen in 1 dm3 of air, at room temperature and pressure. Ar: Mg, 24 Ratio of Mg:N2 = 3:1

No of mol of Mg=3x( 78

100x

1

24) mol

Mass of Mg ����3x( 78

100x

1

24) x 24g= 0.234g

[2] 3) Caesium is stored under oil because it reacts rapidly with oxygen to form a highly dangerous ‘superoxide’. Analysis of a sample of the superoxide showed the compound to obtain 80.6% caesium by mass, the rest being oxygen. Calculate the empirical formula for the superoxide. Show your working.

[3]

Cs O

Percentage 80.6 19.4

No of Moles 80.6

133=0.6060

19.4

16=1.212

Finding Ratio 0.6060

0.6060=1

1.212

0.6060=2

Ratio 2:1

Formula CsO2

4) Baking powder is used in the manufacture of foodstuffs that require a honeycomb structure, such as bread. Baking powder contains sodium hydrogencarbonate, NaHCO3. This decomposes on heating as shown below.

2NaHCO3(s) � Na2CO3(s) + CO2(g) + H2O(l)

10g of sodium hydrogencarbonate were needed in the manufacture of a sponge cake. Calculate the maximum volume (in dm3) of carbon dioxide that could be produced, at room temperature and pressure, by decomposing this mass of sodium hydrogencarbonate. One mole of any gas has a volume of 24 dm3 at room temperature and pressure.

Ar: Na, 23; H,1.0; C,12; O,16

5) Aqueous silver nitrate can be used as a test for halide ions. A student decided to carry out this test on a solution of magnesium chloride. The bottle of magnesium chloride that the student used showed the formula MgCl2.6H20. The student dissolved a small amount of MgCl2.6H20 in water and added aqueous silver nitrate to the aqueous solution.

i) What is the molar mass of MgCl2.6H20?

Mr= 24+(35.5 x2) +(6x18)=203

ii) What would the student see after adding the aqueous silver nitrate, AgNo3(aq)?

A colourless solution and a white PPt would be observed

iii) Write an ionic equation for this reaction. Include the state symbols. Ag+ (aq) + Cl- (aq) ���� AgCl (s)

vol

7) This question looks at the reaction of sodium with water and with oxygen. (a) A chemist reacted 0.0500 mol of sodium with water to form 50.0 cm3 of aqueous sodium hydroxide.

2Na(s) + 2H2O(l)� 2NaOH(aq) + H2(g)

(i) What mass of Na was reacted?

No of mole= Mass

Mr

Mass of Na= 0.0500x 23

= 1.15g (ii) Calculate the volume of H2, in dm3, that would be produced at room temperature and pressure, r.t.p.

1 mol of gas molecules occupies 24.0 dm3 at r.t.p. Ratio of Na: H2 = 2:1 1 mol H2���� 24dm3

12x 0.0500 mol ���� 24 x 1

2 x 0.0500=0.6dm3

(iii) Calculate the concentration, in mol dm–3, of NaOH that was formed.

Na: NaOH= 1:1 No of mole of NaOH= 0.0500mol

0.0500= molarity x 50.0

1000

Molarity= 0.0500 x 1000

50.0

=1.00mol/dm3

(b) Sodium reacts with oxygen to form sodium oxide, Na2O. Draw a ‘dot-and-cross’ diagram for Na2O. Show outer electrons only.

[2]

X rep electrons of sodium

O rep electrons of oxygen

8) Barium reacts with water in a redox reaction.

Ba(s) + 2H2O(l) �Ba(OH)2(aq) + H2(g) (ai) Explain, in terms of electrons, what is meant by oxidation. Oxidation is defined as the loss of electrons from a substance[1] (ii) Which element has been oxidised in this reaction? Deduce the change in its oxidation number. Element: Barium oxidation number changes from 0 to +2 [2] (iii) Sulphuric acid was added to aqueous barium hydroxide until the solution was just � eutralized, forming the insoluble salt, BaSO4, and water.

Ba(OH)2(aq) + H2SO4(aq)� BaSO4(s) + 2H2O(l) The electrical conductivity of the solution steadily decreased as the sulphuric acid was added. Explain why the electrical conductivity decreased. Barium Hydroxide is an electrolyte containint Ba2+ and OH- ions. As sulphuric acid is added. Ba2+ ions react with SO4

2- ions to form Barium sulphate PPT. OH- ions react with H+ ions to form water[2] (b) Barium metal can be extracted from barium oxide, BaO, by reduction with aluminium.

6BaO + 2Al� 3Ba + Ba3Al 2O6

Calculate the mass of barium metal that could be produced from reduction of 500 g of barium oxide using this method.

No of mol of BaO= 500

153mol.

Mole ratio: BaO:Ba=2:1

No of moles of Ba= 1

2x

500

153 mol

Mass= 1

2x

500

153x137

= 223.8g

=224g

9) Sodium reacts with excess oxygen to form sodium peroxide, Na2O2.

Na2O2 is used in laundry bleaches. When added to water a reaction takes place forming an alkaline solution and hydrogen peroxide, H2O2.

(i) Construct a balanced equation for the formation of sodium peroxide from sodium.

2Na+O2���� Na2O2[1] (ii) Construct a balanced equation for the reaction of sodium peroxide with water.

Na2O2 +2H2O ���� 2NaOH + H2O2 [1]

Describe the trend in colour. As you move down group VII of periodic table, the halogen

becomes darker. Chlorine is a yellowish-green gas, bromine is a reddish-brown liquid and iodine is a purplish-black solid

Add aqueous silver nitrate to a sample of drinking water, a white PPT of silver chloride and a colourless solution is obtained. The presence of the white PPT confirms the

presence of chloride ions.

Ag+(aq) + Cl-(aq) ���� AgCl(s)