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WORKSHEET MOLE By Sir Shah Murtaza

Q1. Potassium reacts with water as shown in the equation.

a. Describe what you would see when potassium reacts with water.
b. A sample of 0.195 g of potassium was added to 500 cm3 of cold water. When the reaction was finished, 100 cm3 of 0.100mol/dm3 hydrochloric acid was added to form solution X.

(i) Calculate the number of moles of hydroxide ions formed when the potassium was added to water.
(ii) Calculate the number of moles of hydrogen ions in 100 cm3 of 0.100mol/dm3 hydrochloric acid.
(ii) Give an ionic equation to represent the neutralization reaction.
Q2. Manganese (IV) oxide catalyses the decomposition of aqueous hydrogen peroxides. In an experiment 50.0 cm3 of aqueous hydrogen peroxide was mixed with 0.50 g of manganese (IV) oxide. The total volume of oxygen formed was measured every 10 seconds.
The results of the experiment are shown in the graph.

(i) After how many seconds did the decomposition of hydrogen peroxide finish?
(ii) How many moles of oxygen were produced at the end of the decomposition? [At room temperature and pressure one mole of oxygen occupies 24000 cm3.]
(iii) Use your answer to (ii) to calculate the concentration, in mol/dm3, of the 50.0 cm3 of aqueous hydrogen peroxide used in the experiment.
Q3. Nickel is a transition element. It is manufactured in a four-stage process from nickel (II) sulphide, NiS.
• Stage 1 – nickel (II) sulphide is heated in air to form nickel (II) oxide and sulphur dioxide.
• Stage 2 – nickel (II) oxide is heated with carbon to give impure nickel.
• Stage 3 – impure nickel is reacted with carbon monoxide to make nickel tetracarbonyl, Ni (CO)4.
• Stage 4 – nickel tetracarbonyl is decomposed to give pure nickel. (i) Construct the balanced equation for the reaction in stage 1.
(ii) Calculate the mass of sulphur dioxide that is formed when 182 kg of nickel sulphide is heated in air.

Q4. Ethene can also be converted into a compound that contains carbon, hydrogen and oxygen. A sample of the compound was analyzed and found to contain 0.72 g of carbon, 0.18 g of hydrogen and 0.96 g of oxygen.
Show that the empirical formula of the compound is CH3O.

Q5. A sample of a compound of iron is analyzed. The sample contains 0.547 g of potassium, 0.195 g of iron, 0.252 g of carbon and 0.294 g of nitrogen.
Calculate the empirical formula of this compound.

Q6. At room temperature ozone decomposes slowly to form oxygen, O2.
The decomposition can be represented by the equation below. The reaction is exothermic. One mole of ozone will release 143 kJ when it is fully decomposed.
2O3 → 3O2

Calculate the energy released when 16 g of ozone is decomposed.

Q7. In the presence of bright light, silver chloride decomposes into silver atoms which make the glass go dark, and into chlorine atoms.
AgCl → Ag + Cl

Calculate the maximum mass of silver that can be formed when 0.287 g of silver chloride decomposes.

Q8. Magnesium reacts with ethanoic acid to make magnesium ethanoate and hydrogen.
(a) Write the equation for this reaction. Use the equation to calculate the mass of magnesium needed to react completely with 50 cm3 of 1.0mol/dm3 of ethanoic acid.
(b) Suggest why the reaction between magnesium and 1.0mol/dm3 ethanoic acid is much slower than the reaction between magnesium and 1.0mol/dm3 hydrochloric acid.

Q9. The mass of iron (II) ions in a sample of fertilizer can be determined by the reaction between iron (II) ions and acidified potassium manganate (VII), KMnO4.
A student analyzed a sample of the fertilizer. He dissolved the sample in 25.0 cm3 of dilute sulphuric acid and titrated the solution formed with 0.0200 mol / dm3 potassium manganate (VII). The student used 22.5 cm3 of potassium manganate (VII) to reach the end-point.
(i) Calculate the number of moles of potassium manganate(VII) used in the titration.
(ii) One mole of potassium manganate (VII) reacts with five moles of iron (II) ions. Calculate the mass, in grams, of iron (II) ions in the sample analyzed.

Q10. The nitrates of metallic elements also decompose when heated. Calcium nitrate decomposes to form calcium oxide, nitrogen dioxide and oxygen.

A 0.010 mol sample of calcium nitrate is heated. Calculate the number of moles of gas produced when this sample is completely decomposed.

Q11. The exhaust system of a motor car is fitted with a catalytic converter. When nitrogen monoxide passes through the converter it reacts with carbon monoxide. (i) During the course of a journey 2.4 dm3 of nitrogen monoxide was produced by the engine. Calculate the volume of nitrogen gas produced if all the nitrogen monoxide reacted in the converter. (ii) In reality, only 1.0 dm3 of nitrogen was produced after the gases had passed over the catalytic converter. Calculate the percentage of nitrogen monoxide that had reacted.

Q12. The fermentation of glucose can be represented by the following equation.

Calculate the maximum mass of ethanol that could be made from 36 tones of glucose.

Q13. Iron (II) sulphate, FeSO4, is easily oxidized to iron (III) sulphate.
(a) Calculate the percentage by mass of iron in iron (II) sulphate.
(b) An impure sample of iron (II) sulphate was analyzed by titration. The sample was dissolved in 25.0 cm3 of dilute sulphuric acid and then titrated against 0.0400 mol/dm3 potassium dichromate (VI) solution. 19.0 cm3 of potassium dichromate (VI) solution was required to reach the end-point. (i) Calculate the number of moles of potassium dichromate(VI) used in the titration.

Q14. Dilute ethanoic acid and dilute hydrochloric acid both react with magnesium ribbon to form hydrogen. (a) Give the formula of one ion found in both of these dilute acids. (b) Magnesium ribbon reacts with hydrochloric acid as shown in the equation. A 0.24 g sample of magnesium ribbon is added to 5.0 cm3 of 2.0 mol/dm3 hydrochloric acid. (i) Which reactant, magnesium or hydrochloric acid, is in excess? Use calculations to explain your answer.
(ii) Calculate the maximum mass of magnesium chloride that can be formed in this reaction.
(iii) A 0.24 g sample of magnesium ribbon is added to 5.0 cm3 of 2.0 mol/dm3 ethanoic acid.
Explain why this reaction forms the same volume of hydrogen but takes place much more slowly than the reaction of the same mass of magnesium with 5.0 cm3 of 2.0 mol/dm3 hydrochloric acid.
Q15. Octane burns in air. A petrol-powered motor car travels at a constant speed of 80 km/h. For every kilometer traveled 108 g of carbon dioxide are formed.
When the motor car travels 100 km calculate (i) the mass of carbon dioxide emitted by the car, (ii) the mass of petrol burned by the car assuming that petrol is 100% octane.

Q16. Ethanol can also be manufactured from glucose, C6H12O6. A solution containing 18 kg of glucose makes only 0.92 kg of ethanol. Calculate the percentage yield of ethanol

Q17. Fertilizers supply the essential elements, nitrogen, phosphorus and potassium for plant growth. A bag of fertilizer contains 500 g of ammonium sulfate, (NH4)
2SO4, and 500 g of potassium nitrate, KNO3.
(a) Calculate the percentage by mass of nitrogen in the bag of fertilizer.