Chemistry exam paper quesitons

test with whiteboard

Write the equation for the reaction of strontium with water

Sr + 2H₂O → Sr(OH)₂ + H₂

x = 5.8

Level 3 (5-6 marks)

• calculates correct mass of hydrous magnesium nitrate/anhydrous magnesium nitrate AND

• Explains preparation steps, with most fine detail

2Mg(NO₃)₂ → 2MgO + 4NO₂ +O₂

Using oxidation numbers, explain why this is a redox reaction

Both oxidation and reduction takes place

• Oxygen is oxidised because it goes from -2 in Mg(NO₃)₂ to 0 in O₂

• Nitrogen is reduced because it goes from +5 in Mg(NO₃)₂ to +4 in NO₂

1-iodopentane can be hydrolysed by water using aqueous silver nitrate, with ethanol as a solvent. A student uses this method to compare the rates of hydrolysis of 1-iodopentane and 1-bromopentane.

1-iodopentane reacted faster than 1-bromopentane. Explain why

• C-I bond is weaker than C-Br bond/C-I bond has lower bond enthalpy than C-Br bond

• carbon-halogen bond breaks (more easily)

A student reacts Zinc with hydrochloric acid. The rate of reaction decreases over time.

Explain why, in terms of collision theory

• acid concentration decreases

• fewer collisions per second/less frequent collisions

Level 3 (5-6 marks)

• Calculates correct mass of hexan-1-ol AND

• Explains purification steps, with most fine detail

Hex-1-ene can be polymerised to form poly(hex-1-ene).

Draw a section of poly(hex-1-ene) containing two repeat units

Calculate the number of barium ions in 1.50g of barium oxide.

Give your answer in standard form and to three significant figures

5.89 × 10²¹

Barium nitride is formed when barium is heated with nitrogen.

Write the electron configuration of a nitride ion.

1s²2s²2p⁶

Barium nitride reacts with water to form an alkaline solution and an alkali gas.

Write the equation for this reaction, including state symbols

Ba₃N_2(s) + 6H₂O_(l) → 3Ba(OH)_2(aq) + 2NH_3(g)

Level 3 (5-6 marks)

• All three scientific points are covered in detail and explained thoroughly

Describe the oxidation reactions of butan-1-ol forming an aldehyde and a carboxylic acid.

Explain, using a diagram, how the aldehyde can be produced in the laboratory by controlling the reaction conditions [6]

Level 3 (5-6 marks)

A comprehensive explanation with all three specific points covered thoroughly

A student carries out a titration to determine the mass of citric acid in one lime. The student follows the method:

• Squeeze the juice out of two limes

• transfer the juice onto a 250.0cm³ volumetric flask and make up to the mark with distilled water

• Pipette 25.0cm³ of the diluted lime juice into a conical flask and add a few drops of indicator

• Titrate solution with 0.8 mol dm^-3 NaOH_(aq)

They record and calculate a mean titre of 27.35cm³

Citric acid is neutralised by NaOH as shown by the equation below:

C₆H₈O₇ + 3NaOH → Na₃C₆H₅O₇ + 3H₂O

1. Calculate the mass, in g, of citric acid in one lime, assume that citric acid (M_r = 192.0) is the only acid in lime juice

2. Suggest how the student could modify the method to use an NaOH concentration of 0.2 mol dm^-3 instead of 0.8 mol dm^-3 . The student should aim to have the same titre as in the original method. Justify your answer

1. 7g

• use half a lime OR make up lime juice solution to 1 dm³ volumetric flask

• (Justification) 4 times less citric acid OR NaOH is 4 times more dilute (giving same titre) OR 1:4 ratio for NaOH concentration