Amount of Substance (OCR AS Chemistry)

A synthetic carbohydrate was isotopically labelled with carbon-13.

Analysis of a 12 g sample of the carbohydrate found it to contain 6.93 g carbon, 0.80 g hydrogen and the remainder was oxygen. 

Determine the empirical formulae of the carbohydrate.

The fermentation of glucose, C₆H₁₂O₆, is one method scientists can use to produce ethanol.  

Write a balanced symbol equation for this reaction.

During the fermentation process in the reaction in part (b), 312 g of ethanol was produced from 1.5 kg of glucose. 

Calculate the percentage yield of this reaction to 3 significant figures.

Ethanol can also be produced by the hydration of ethene, as shown in the following equation: 

C₂H₄ (g) + H₂O (g) → C₂H₅OH (g)

A student predicts that the production of ethanol from the fermentation of glucose will have a higher atom economy than from the hydration of ethene. 

Concrete is one of the most common building materials and also one of the top three producers of carbon dioxide in the world. One of the main components of concrete is cement which is made by the thermal decomposition of limestone with other materials such as clay in a kiln at temperatures around 1450 ^oC. 

Calculate the mass, in kg, of carbon dioxide produced when 1 tonne of limestone is thermally decomposed.

‘Asbestos’ is a generic, commercial term used to describe a number of mineral fibres, which were once commonly found in most buildings.

The most common type of asbestos, chrysotile, makes up the vast majority of all asbestos products. Its chemical composition is 28.03% magnesium, 21.60% silicon, 1.16% hydrogen and the rest is oxygen. 

Calculate the empirical formula for chrysotile asbestos.

The M_r of chrysotile is 520.2. 

Use your answer to part (b) to calculate the molecular formula of chrysotile.

Another industrial mineral, belite, is used in the manufacture of cement. It’s main component is dicalcium silicate, Ca₂SiO₄, which reacts with water to form Ca₃Si₂O₄(OH)₆ and calcium hydroxide. 

Write an equation for this reaction.

A sample of hydrated copper sulphate, CuSO₄.xH₂O, has a relative formula mass of 285.6. 

Calculate a value for ‘x’. Give your answer to 2 decimal places.

A student completed an experiment to determine the value of ‘x’ in a hydrated salt. They heated a solid sample of the salt, CuSO₄.xH₂O, in a crucible for 60 seconds and recorded the following set of results.

Use the data obtained by the student to calculate a value for ‘x’. Give your answer to 2 decimal places.

The actual value for x in CuSO₄.xH₂O is 5.

Copper(II) sulfate undergoes a displacement reaction with magnesium, because magnesium is a more reactive metal than copper.

Strong heating of calcium nitrate will cause a thermal decomposition reaction to occur. During the reaction, calcium oxide, nitrogen dioxide and another gas are formed.

Write a balanced chemical equation, with state symbols, for this reaction

A sample of 0.655 g of calcium nitrate was thermally decomposed.  

Calculate the amount, in moles, of the calcium oxide which was produced. Give your answer to the appropriate number of significant figures.

Calculate the amount, in moles, of gas which was produced during the thermal decomposition of the 0.655 g sample of calcium nitrate. Give your answer to the appropriate number of significant figures.

In a different experiment, a 1.23 g sample of pure lead nitrate, Pb(NO₃)₂, was heated until it had completely decomposed, in the same way as calcium nitrate in part (a).

Calculate the total volume, in cm³, of nitrogen dioxide gas produced at 50.0 ^oC and 101 kPa.

The gas constant, R, = 8.31 J mol^-1 K^-1.

Record your answer to the appropriate number of significant figures.

When magnesium reacts with hydrochloric acid, the following reaction occurs:

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)  

During the reaction, the hydrogen produced occupies 103 cm³ at 25.0 ^oC and 100 kPa. 

Calculate the amount, in moles, of hydrogen gas produced during the reaction. 

The gas constant, R, is 8.31 J mol^-1 K^-1.

Using your answer to part (a), calculate the exact volume in cm³ of 0.15 mol dm^-3 HCl, which would be needed to produce that amount of hydrogen gas. Give your answer to 1 decimal place.
 

A student completed the same reaction as in part (a), using 3.75 g of magnesium.

Calculate the mass of magnesium chloride produced by the student during this reaction.  

Calculate the number of atoms of hydrogen produced during the students reaction in part (c).

The Avogadro constant, L = 6.022 x 10²³.

Magnesium carbonate is a common antacid that is used to react with and neutralise excess stomach acid, HCl, with the following equation:

MgCO₃ (s) + 2HCl (aq) MgCl₂ (aq) + CO₂ (g) + H₂O (l)

The total mass of the reactants is 9.91 g.

What volume of CO₂ is produced at RTP?

Another magnesium salt, magnesium sulfate, can exist in hydrated or anhydrous forms. 

6.31 g of a sample of magnesium sulphate, MgSO₄.xH₂O, was strongly heated until no further change in mass was recorded. 

Calculate the number of moles of water of crystallisation in the magnesium sulphate sample given that 3.61 g of solid remained.

Another sample of hydrated magnesium sulphate, MgSO₄.xH₂O, is found to contain 51.1% water by mass.

Calculate the value of x in this hydrated salt.

Describe the effect on the value of x obtained if the salt was not heated strongly to a constant mass.

Carvone is an organic compound containing carbon hydrogen and oxygen.

Complete combustion of 0.1526 g carvone produces 0.4470 g of carbon dioxide and 0.1281 g of water.

Determine the empirical formula of carvone, showing your working.

0.146 g sample of carvone, when vaporised, had a volume of 0.0341 dm³ at 150 ^oC and 100.2 kPa.
Calculate its molar mass showing your working.

Using your answer to part b), determine the number of molecules of carvone in 0.146 g.

Fireworks contain elements to give them their colour, as well as oxygen-containing compounds to facilitate speedy combustion.

In a firework, solid potassium nitrate, KNO₃, decomposes to form solid potassium nitrite, KNO₂, and oxygen, O₂. 

Calculate the mass, in g, of potassium nitrate, KNO₃, required to make 1.5 g of oxygen.

Give your answer to 2 significant figures. 

Calculate the volume of gas at RTP, in dm³, that is produced in the reaction outlined in part (a).
Give your answer to 2 significant figures. 

Potassium can form a superoxide, KO₂ (s), which will react with carbon dioxide, CO₂ (g), to produce potassium carbonate, K₂CO₃ (s) and oxygen, O₂ (g).

Calculate the volume, in dm³, of carbon dioxide which will react with 5.00 g of the superoxide.

Give your answer to 3 significant figures. 

During the reaction outlined in part (c), 2.61 g of potassium carbonate, K₂CO₃, was produced when the experiment was carried out.

Calculate the percentage yield for the production of potassium carbonate. Give your answer to 2 decimal places. 

Salts are commonly made during neutralisation reactions.

3.75 g of zinc oxide, ZnO (s), was added to 75.0 cm³ of 1.00 mol dm^-3 of hydrochloric acid (aq) producing a salt. 

Calculate the limiting reagent in the reaction. Give your answer to 2 significant figures. 

During the reaction, 4.35 g of the salt was produced.

Calculate the percentage yield of the reaction. Give your answer to 3 significant figures.

Calculate the atom economy of the reaction, why a high atom economy is beneficial and what could be done to improve the atom economy to this reaction.

Evaluate which of ZnO and HCl should ideally be in excess when the aim is to produce a pure, dry salt and explain your answer.

Ammonia can be oxidised by bacteria to N₂O, or by an inorganic catalyst to NO.

90 cm³ ammonia gas, NH₃ (g), is combusted in oxygen, O₂ (g) in a closed system to produce nitrogen monoxide and water, H₂O (l).

What is the total volume of gas remaining in the system when 90 cm³ of ammonia is combusted completely with 50 cm³ of oxygen?

The temperature of the reaction is kept constant.

Sketch a line on the graph below that shows the correct relationship between pressure and .

At 25 ^oC and 100 kPa, a gas occupies a volume of 35 dm³.

Calculate the new temperature, in ^oC, of the gas if the volume is decreased to 15 dm³ at constant pressure.