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Chemical formula and equation Mole concept f4 2011

CHEMICAL FORMULA AND EQUATION

1. Write the chemical formula of the compound in the table below.

Ion Chloride Nitrate Hydroxide Sulphate Carbonate oxide

SodiumMagnesium

Lead(II)

Copper (II)

Iron (II)

Iron (III)

Aluminium

2. Write balanced chemical equation for the following chemical reactions.

(a) Heat solid of copper (II) carbonate

………………………………………………………………………………………….

(b) Nitric acid reacts with sodium hydroxide

………………………………………………………………………………………….

(c) Hydrochloric acid reacts with zinc metal

………………………………………………………………………………………….

(d) Copper(II)nitrate reacts with magnesium

………………………………………………………………………………………….

(e) Chlorine gas reacts with lithium hydroxide

………………………………………………………………………………………….

(f) Hydrogen gas reacts with lead(II) oxide

………………………………………………………………………………………….

3. Avogadro constant, NA is defined as the number of particles in one mole of a substance

[1 Mol any substance consist of 6.02 X 1023 particles].

Calculate the number of particles in:

(a) 0.1 mol of calcium

(b) 1.5 mol of iron

(c) 2.0 mol of oxygen gas

(d) 1.5 mol of helium




(e) 2.0 mol hydrogen chloride

4. Calculate the number of moles of the following substances.(a) 6.0 x 1023 aluminium

(b) 1.8 x 1021 argon

(c) 1.2 x 1023 bromine gas

(d) 2.4 x 1020 carbon dioxide

(e) 3.0 x 1023 ammonia

5. Calculate the mass of following substances.

a) 1.5 mol of chlorine gas b) 2.5 moles of oxygen gas

c) 2.0 moles of sulphuric acid d) 0.5 moles of ammonia, NH3

e) 2.5 moles of lead (II) carbonate f) 0.5 moles copper(II) nitrate, Cu(NO3)2

Molar volume: The volume of one mole of the gas[22.4 dm3 mol-1 at STP, standard temperature and pressure]

[24 dm3 mol-1 at Room condition]




6. Calculate the volume of gases below.

(a) 0.5 mol of chlorine at STP.

(b) 0.2 mol of carbon dioxide at Room condition.

(c) 1.5 mol of methane at room condition.

(d) 0.5 mol of helium at room condition.

(e) 2.5 mol of ammonia at STP

7. Calculate the number of moles of the gases below.

(a) 250 cm3 of carbon dioxide in room temperature.

(b) 500 cm3 of hydrogen sulfide at STP.

(c) 200 cm3 of hydrogen chloride in room temperature.

(d) 750 cm3 of neon in room temperature.

(e) 300 cm3of ammonia at STP.

8. Magnesium powder reacts with hydrochloric acid to produce salt and hydrogen gas.

(a) Write the balance chemical equation for this reaction.

………………………………………………………………………………………….

(b) If 2.4 g of magnesium powder is added into excess hydrochloric acid, calculate,

(i) The mass of salt formed.

(ii) The volume of hydrogen gas liberated at room temperature.

9. Lead is extracted according to the following equation.

C + PbO CO2 + Pb




(a) Write the balanced chemical equation for the reaction.

………………………………………………………………………………………….

(b) Determine the number of moles of lead extracted from 0.5 mole of lead (II) oxide.

(c) Calculate the number of moles of carbon required to extracts 0.5 mole of

lead(II) oxide.

(d) What is the mass of lead are produced if 44.6 g of lead (II) oxide is heated with

excess carbon.

[ RAM : Pb = 207, O = 16, C = 12 ]

10. Excess sodium carbonates is added into 50 cm3 of 0.5 mol dm-3 copper(II) chloride.

The chemical equation for the reaction is as follows:

CuCl2 + Na2CO3 NaCl + CaCO3

(a) Balance the chemical equation for the reaction.

(b) Calculate the mass of copper(II)carbonate.

11. A hydrocarbon is burnt completely in air to form 17.6 g of carbon dioxide gas and 7.2 g of

water. What is the molecular formula of the hydrocarbon compound?

Given that the relative atomic mass of C = 12, H=1, O =16]

12. 5g of calcium carbonate is added to excess hydrochloric acid.(a) Write balanced chemical equation for the reaction.

………………………………………………………………………………………….




(b) Determine the volume of carbon dioxide gas evolved at room temperature

13. When sodium bicarbonate is heated, it decomposed to sodium carbonate, carbon dioxide and

water.

(a) Write a balanced chemical equation for the decomposition of sodium bicarbonate on

heating.

………………………………………………………………………………………….

(b) If 8.4 g of sodium bicarbonate decomposes, calculate

(i) The volume of carbon dioxide gas evolved at room temperature.

(ii) The mass of sodium carbonate formed.

Concentration of acids and alkalis.(STOICHEIOMETRY)

The concentration of a solution is the mass (in gram) or the number of mole of solute

dissolved in a solvent to form 1.00 dm3 of solution.

Concentration, g dm-3 Mass of solute, g

Volume of solution , dm3

Concentration, mol dm-3 /

molarity

Number of mole of solute, mol

Volume of solution , dm3

Ma = Concentration of the acid, M b = Concentration of the alkali

Va = Volume of used acid, V b = Volume of used alkali

a = the number of mole of acid, b = the number of mole of alkali

1. 100cm3 of HCl 2.0 mol dm-3 reacts completely with excessive zinc powder. Calculate thevolume of gas released at room temperature? (Molar volume = 24 dm 3 at room temperature).

Titration

Formula MaV2 = a

MbVb b

Dilution

M1V1 = M2V2




2. 5 g of Calcium carbonates dissolves in 100 cm3 of nitric acid 0.5 mol dm-3 to produce salt,

carbon dioxide gas and water.

(i) Write out the equation.

………………………………………………………………………………

(ii) Calculate the moles of calcium carbonates used. (RAM Ca =40, C = 12, O = 16).

(iii) Calculate the moles of acid.

(iv) Calculate the volume of gas produced.

3. X g sodium carbonate reacts completely with 100 cm3 hydrochloric acid

1.0 moldm-3 to produce sodium chloride, carbon dioxide and water. Find X.

(relative atomic mass: Na =23, C = 12, O = 16)

4. 10 g of copper(II) oxide reacts completely with 100 cm

3

hydrochloric acid to formcopper(II) chloride and water. Calculate the molarity of acid used.

(JAR Cu =64, O = 16 )

5. The concentration of sodium hydroxide solution is 8.0 g dm-3.

(a) What is the molarity of the solution?




(b) What is the molarity of the solution produced when 100 cm3 of distilled water is added

to 50 cm3 of this solution?

6. In the titration experiment, 25.0 cm3 of 2.0 mol dm-3 sodium hydroxide solution is titrated

with sulphuric acid from a burette. 18.50 cm3 of sulphuric acid is needed for complete

neutralization.

(a) Write a balanced chemical equation for the neutralization.

………………………………………………………………………………

(b) Calculate the number of mole of sodium hydroxide used in this experiment.

(c) Calculate the number of moles of sulfphuric acid needed to exactly neutralize 25.0 cm3

of 2.0 mol dm-3sodium hydroxide.

(d) Calculate the molarity of sulphuric acid.

7. 1.25 mol dm-3 hydrochloric acid reacts completely with 25.0 cm3 of 1.0 mol dm-3 sodium

carbonate.

(a) Write a balanced chemical equation for this reaction.

………………………………………………………………………………

(b) Calculate the number of mole of sodium carbonate used in this experiment.

(c) Calculate the volume of hydrochloric acid needed to exactly neutralize 25.0 cm3 of 1.0

mol dm-3 sodium carbonate.

PAPER 2: STRUCTURE

1.

2. Diagram 1 shows the set-up of the apparatus for an experiment to determine the




empirical formula of an oxide of copper.

Table 1 shows the results of an experiment after heating, cooling and weighing are

repeated until a constant weight is obtained.

Substance Mass(g)

Mass of combustion tube + porcelain dish 18.75 g

Mass of combustion tube + porcelain dish + oxide of copper 20.75 g

Mass of combustion tube + porcelain dish + copper 20.35 g

(a) What is meant by empirical formula?

………………………………………………………………………………………….

[1 mark](b) Based on Table 5 results,

(i) Calculate the mass of copper and the mass of oxygen used in the experiment.

[2 marks]

(ii) Calculate the mole ratio of copper atoms to oxygen atoms.

Given that the relative atomic mass of Cu, 64; O ,16.

[2 marks]

(iii) State the empirical formula of this oxide of copper.

………………………………………………………………………………………

[1 mark]

(iv) Write the chemical equation for the reaction in this experiment.

Oxide of copper

Dry hydrogengas

Heat

Diagram 1

Table 1




………………………………………………………………………………………

[1 mark]

(c) Describe the steps that should be taken to ensure that all the air in the combustion

tube has been expelled , before any heating is carried out.

…………………………………………………………………………………………

…………………………………………………………………………………………

…………………………………………………………………………………………

[3 marks]

2. (a) Culculate the relative molecular or formula masses of the following substances.

(i) Ethanol, C2H5OH.

Given that relative atomic mass of H = 1, C = 12, O = 16.

[1 mark]

(ii) Zinc nitrate, Zn(NO3)2

Given that relative atomic mass of O = 16 , N = 14, Zn = 65 .

[1 mark]

(b) A closed glass bottle contains 4 mol molecules of oxygen, O2.

(i) What is the number of oxygen molecules in the bottle?

[1 mark]

(ii) How many oxygen atoms are there in the bottle?

[1 mark]

(c) Find the number of moles of atoms in a sample containing 9.03 × 1020 atoms of copper.




[1 mark]

(d) Calculate the mass, in gram, of 3.5 moles of copper(II) carbonate, CuCO3.Given that relative formula mass of CuCO3 = 124

[1 mark]

(e) When silver carbonate, Ag2CO3 is heated, it will decompose to produce silver

metal, carbon dioxide gas and oxygen gas as shown in the equation below.

2Ag2CO3(s) 4Ag(s) + 2CO2(g) + O2(g)

A student heats 8.28 g silver carbonate. Calculate the volume of carbon dioxide gas,

CO2 collected at room temperature.

Given that relative atomic mass of C = 12, O =16, Ag = 108,

[3 marks]

3. Diagram 3 shows 3.1 g of copper (II) carbonate being heated strongly in attest tube. The gas

given out is passed into limewater in a test tube through a delivery tube.

(a) State the observation made when copper(II)carbonate powder is heated until thereaction is complete.

…………………………………………………………………………………………

Copper(II)

carbonate

Heat

stronglyLime water

Diagram 3




[1 mark]

(b) Write the chemical equation to represent the reaction that takes place.

…………………………………………………………………………………………

[1 mark](c) Calculate the number of moles of copper(II)oxide produced.

[2 marks]

(d) Calculate the volume of gas produced at STP.

[2 marks]

(e) (i) What can be observed if the product is heated in a stream of hydrogen gas?

…………………………………………………………………………………………

[1 mark]

(ii) Calculate the mass of the substance produced.

[2 marks]

PAPER 2 : ESSAY4.

(a) The information below is regarding substance X




(i) Determine the empirical formula of substance X.

[Given that the relative atomic mass of C = 12 , H = 1]

(ii) Determine the molecular formula of substance X.

(iii) Based on the answers in (a)(i) and (a)(ii) , compare andcontrast the empirical formula and the molecular formula.

[ 8 marks]

(b) Magnesium can react actively with oxygen to form magnesium oxide.

Describe an activity that can be carried out in the laboratory to determine the

empirical formula of magnesium oxide.

Include the calculations involved in your answer.

Given that the relative atomic mass for O = 16, Mg = 24.

[11 marks]

• Carbon 85.70%

• Hydrogen 14.30%

• Relative molecular mass = 56

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