MOLE CONCEPT AND STOICHIOMETRY
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SHORT ANSWER QUESTIONS
1. What is the value of the avogadro’s number?
2. What is the value of molar volume of a gas at S.T.P?
3. What do you understand at S.T.P by the statement that ‘vapour density’ of carbon dioxide is 22?
4. Define vapour density. State the relationship between vapour density and molecular weight.
5. Explain the following statement: Relative atomic mass of sodium is 23.
LONG ANSWER QUESTIONS
1. State: a) Gay-Lussac’s law of combining volumes b) Avogadro’s law.
2. Define the terms: a) Vapour density b) Relative molecular weight , How are vapour density and molecular weight related?
3. Define a) Molar volume b) Avogadro’s number.
4. A) Define relative atomic mass. B) Ordinary chlorine has two isotopes Cl -35 and Cl-37 in the ratio of 3:1. Calculate the relative atomic mass of chlorine.
5. Explain the terms: a) Gram atom b) Gram mole.
6. A) What are the main applications of Avogadro’s law?
B) How does Avogadro’s law explain Gay Lussac’s law of combining volumes?
7. Explain the terms, empirical formula and molecular formula.
8. How is empirical formula related to molecular formula? If the molecular formula of the compound is C2H4O2, determine its empirical formula.
NUMERICALS
A. BASED ON GAY-LUSSAC’S LAW
1. Ammonia may be oxidized to nitrogen monoxide in the presence of a catalyst according to the equation: 4NH3 + 5O2 ---> 4NO + 6H2O. If 27 litres of reactants are consumed, what volume of nitrogen monoxide is produced at the same temperature and pressure?
2. Water can split into hydrogen and oxygen under suitable conditions. If a given experiment results in 2500 cm3 of hydrogen being produced, what volume of oxygen is liberated under the same conditions of temperature and pressure?
3. What volume of propane is burnt for every 100 cm3 of oxygen used in the combustion reaction at s.t.p?
4. 450 cm3 of CO and 200 cm3 of oxygen are mixed together and ignited. Calculate the composition of the resulting mixture.
5. 200 ml of C2H4 is burnt in just sufficient air (complete combustion). Calculate the resulting mixture composition at 100oC and 760mm of Hg.
B.BASED ON MOLE CONCEPT – AVOGADRO’S NUMBER
1. Calculate the mass of 0.2 moles of water.
2. How many moles of sodium hydroxide are contained in 160g of it?
3. Calculate the weight of 6.023 X 1023 molecules of NaCl.
4. What will be the number of atoms in 1 mole of N2?
5. Calculate the number of molecules in 11.2 litres of CO2 gas at S.T.P.
6. A piece of silver metal weighs 10.8g. How many atoms of Ag does it contain?
7. Calculate (a) weight in grams (b) number of moles (c) number of molecules in 44.8 dm3 of carbon dioxide at S.T.P.
8. Calculate the number of grams of oxygen in 0.1 mole of Na2CO3.10H2O.
9. A certain sample of nitrogen gas consists of 9.26 X 1022 nitrogen atoms.
a. How many moles of nitrogen atoms are present in this sample?
b. If the gas is entirely in molecular form, how many moles of N2 molecules are present in this sample?
c. What is the mass of the sample?
10. Calculate the number of oxygen atoms and its weight in 50g of CaCO3.
C. BASED ON AVOGADRO’S LAW
1. Under same conditions of temperature and pressure, you collect, 2 litres of CO2, 3 litres of Cl2, 5 litres of H2, 4 litres of N2 and 1 litre of SO2. In which gas sample will there be:
a. the greatest number of molecules? b. the least number of molecules?
2. a) A vessel contains N molecules of oxygen at certain temperature and pressure. How many molecules of SO2 can the vessel accommodate at the same temperature and pressure?
(b) Each of two flasks contains 2.0g of gas at the same temperature and pressure. One flask contains oxygen and the other hydrogen.
i. Which sample contains greater number of molecules?
ii. If the hydrogen sample contains N molecules, how many molecules are present in oxygen sample?
3. A gas cylinder can hold 1Kg of hydrogen at room temperature and pressure.
i. What mass of CO2 can it hold under similar conditions of temperature and pressure?
Ii. If the number of molecules of hydrogen in the cylinder. Give reasons for your answer.
4. The following gases collected under the same conditions of temperature and pressure occupy the volume as given below: Chlorine = 10 litres; Nitrogen = 20 litres ; NH3 = 15 litres; CO2 = 5 litres.
If nitrogen contains x molecules, find the number of molecules in chlorine, ammonia and carbon dioxide.
D.BASED ON VAPOUR DENSITY AND MOLECULAR WEIGHT
1. Atomic weight of chlorine is 35.5. What is its vapour density?
2. 2.8 dm3 of a gas ‘X’ at S.T.P is found to weigh 5.5g. Calculate
(a) Molecular mass (b) V.P of gas.
3.A gas cylinder filled with hydrogen holds 5g of a gas. The same cylinder holds 85g of a gas X under same temperature and pressure. Calculate the vapour desity and molecular weight of the gas X.
4. A gas cylinder can hold 5.6g of hydrogen at S.T.P. a. Calculate the amount of sulphur dioxide gas it can hold at S.T.P. b. If the number of molecules of hydrogen is X, Calculate the number of molecules of SO2 present in it.
5. 3g of a gas occupies a volume of 700ml at a temperature of 70oC and 700 mm of pressure. Give that 1 litre of hydrogen weighs 0.09g at S.T.P., find the vapour density and molecular weight of the gas.
E. BASED ON PERCENTAGE COMPOSITION
1. Calculate the percentage of nitrogen in ammonium nitrate.
2. Calculate the percentage of water of crystallization in washing soda.
3. Calculate the percentage of pure iron in 10 kg of Fe2O3 of 80% purity.
4. Urea [NH2 CONH2] and ammonium sulphate [(NH4)2 SO4] are fertilizers? Which of the above fertilisers is a better fertilizer? [At. Wt. of N=14, H=1, C=12, O=16, S=32]
5. Copper sulphate crystals (CuSO4.5H2O) lose the whole of their water of crystallization heating. Calculate the percentage loss in weight that will take place on heating a sample of crystals.[At. Wt. of Cu=63.5, S=32, O=16, H=1]
6. Percentage of water of crystallization in BaCl2.xH2O was found to be 14.73%. Find the number of molecules of water of crystallization, x in the compound.
7. Calculate the number of water of crystallization in hydrated copper sulphate crystals, if 10gm of hydrous copper sulphate crystals gives 6.4g anhydrous CuSO4 on heating.[ Cu = 64]
8. Calculate the total percentage of oxygen in magnesium nitrate crystals, Mg(NO3)2.6H2O.
9. What is the mass of nitrogen in 1000 kg of urea [CO(NH2)2]?
10. Calculate the percentage of boron in Borax Na2B4O7.10H2O
F. BASED ON EMPIRICAL AND MOLECULAR FORMULAE
1. A compound of Na, S and O has the following percentage composition: Na = 29.11%, O = 30.38% and S = 40.51%. Find its empirical formula.
2. Find the empirical formula and empirical formula of an acid of phosphorus which has the following composition: 2.47% of H, 38.27% of P and 59.26% of oxygen. The relative molecular mass is 162.
3. A compound contains 87.5% by mass of nitrogen and 12.5% by mass of hydrogen. Determine the empirical formula of the compound.
4. The empirical formula of a compound is C2H5. Its vapour density is 29. Determine the relative molecular mass of the compound and hence, its molecular formula.
5. The compound A has the percentage composition by following mass: Carbon 26.7%, Oxygen 71.1% and Hydrogen 2.2%. Determine the empirical and molecular formula of A, if its molecular weight is 90.
G. BASED ON CHEMICAL EQUATIONS
1. Aluminum carbide react with water according to the following equation: Al4C3 + 12H2O à 3CH4 + 4Al(OH)3. Calculate the volume of methane measured at S.T.P released from 14.4g of aluminum carbide by excess of water.
2. (a) Iron pyrites has the formula FeS2, what mass of sulphur is contained in 30g of pyrites?
(b) When roasted, iron pyrites give sulphur dioxide according to the following equation:
4FeS2 + 11O2 ---> 2Fe2O3 + 8SO2. What volume of SO2 would be liberated by roasting 30g of pyrites? [Fe = 56]
3. a) What volume of hydrogen sulphide at S.T.P will burn in oxygen to yield 12.8g sulphur dioxide according to the equation: 2H2S + 3O2 ----> 2H2O + 2SO2?
(b) For the volume of hydrogen sulphide determined in (i) above, what volume of oxygen would be required for complete combustion?
4. Concentrated nitric acid oxidizes phosphorus to phosphoric acid according to the following equation: P + 5HNO3 ----> H3PO4 + H2O + 5NO2
a. What mass of Phosphoric acid can be prepared from 6.2g of phosphorus?
b. What mass of nitric acid will be consumed at the same time?
c. What would be the volume of steam produced at the same time if measured at 760mm and 273oC?
5. If a crop of wheat removes 20 kg of nitrogen per hectare of soil, what mass of the fertilizer calcium nitrate would be required to replace the nitrogen in a 10 hectare field?
6. Calcium hydroxide reacts with ammonium chloride to give ammonia, according to the following equation: Ca(OH)2 + 2NH4Cl --> CaCl2 + 2NH3 + 2H2O . If 5.35g of ammonium chloride are used, calculate: a. The mass of Calcium chloride formed and b. The volume, at S.T.P of NH3 liberated.
7. Calcium nitrate decomposes on heating according to the following equation:
2Ca(NO3)2 ---> 2CaO + 4NO2 +O2 The relative molecular mass of calcium nitrate is 164..
Calculate (a) The volume of nitrogen dioxide (NO2) obtained at S.T.P and
(b) The mass of calcium oxide obtained when 16.4 g of calcium nitrate is heated at constant mass.
8. Ammonia burns in oxygen. The combustion in the presence of a catalyst may be represented by:
4 NH3 + 5O2 --> 2NIO + 3H2O what mass of steam is produced when 1.5 g of nitrogen monoxide is formed
9. The equation for the reaction between carbon and sulphuric acid is given below:
C + 2H2SO4 à CO2 + 2H2O + 2SO2 Calculate:
a. The mass of carbon oxidized by 49g of sulphuric acid.
b. The volume of gases measured at S.T.P evolved at the same time.
CONCEPTUAL QUESTIONS
1. A sample of coal gas contained 45% H2, 30% CH4, 20% CO and 5% C2H2 by volume. 100ml of this gaseous mixture was mixed with 160 ml of oxygen and exploded. Calculate the volume and the composition of the resulting mixture, when cooled to room temperature and pressure.
2. A compound has O = 61.32%, S = 11.15%, H = 4.88% and Zn = 22.65%. The relative molecular mass of the compound is 287 amu. Find the molecular mass of the compound, assuming that all the hydrogen is present as water of crystallization. [ Zn = 65]
3. A 2.00 g sample containing Na2CO3 and NaHCO3 loses 0.248 g when heated to 300oC, the temperature at which NaHCO3 decomposes to Na2CO3, CO2 and water.
4. 1.84g of a mixture of CaCO3 and MgCO3 are heated strongly till no further loss of weight takes place. The residue weighs 0.96g. Find the percentage composition of the mixture.
5. 24ml of methane were mixes with 106 ml of oxygen and the mixture was exploded. The product, after cooling, measured 82ml, of which 58 ml were unused oxygen. Show that these results illustrate Gay-Lussac’s law.
PREVIOUS YEAR’S ICSE EXAMINATION QUESTIONS
1. Sate Gay-Lussac’s law of combining volumes.
2. What is the volume (measured in dm3 or liters) occupied by one molecule of a gas at S.T.P.?
3. When gases react together, their volumes bear a simple ratio to each other under the same conditions of temperature and pressure. Who proposed this law?
4. Define atomicity of a gas.
5. The relative atomic mass of Cl atom is 35.5 a.m.u. explain this statement.
6. Sate the term which defines the following: the mass of given volume of gas compared to the mass of an equal volume of hydrogen.
7. A vessel contains N molecule of oxygen at a certain temperature and pressure. How many molecules of sulphates of sulphur dioxide can the vessel accommodate at the same temperature state the law used in the above deduction.
8. If 100 cm3 of oxygen contains Y molecules, how many molecules of nitrogen will be present in 50 cm3 of nitrogen under the same conditions of temperature and pressure?
9. The number of atoms in one mole of hydrogen is twice the number of in mole of helium at the same temperature and pressure.
A. Based on Gay-Lussac’s Law
1. LPG stands for liquefied petroleum gas. Varieties of LPG are marketed including a mixture of propane (60%) and butane(40%). If 10 litre of this mixture is burnt, find the total volume of carbon dioxide gas added to the atmosphere. Combustion reactions can be represented as:
C3H8(g) + 5O2 (g) --> 3CO2(g) + 4H2O (g) 2C4H10(g) + 13O2 (g) --> 8CO2 (g) + 10 H2O
2. Calcium carbide is used for the artificial ripening of fruits. Actually the fruit ripens because of the heat evolved while calcium carbide reacts with moisture. During this reaction, calcium hydroxide and acetylene gas is fromed. If 200 cm3 of acetylene gas is formed form a certain mass of calcium carbide, find the volume of oxygen required and carbon dioxide formed during the complete combustion. The combustion reaction can be represented as given below: 2C2H2(g) + 5O2(g) --> 4CO2(g) + 2H2O(g)
3. 560ml of carbon monoxide is mixed with 500 ml of oxygen and ignited. The chemical equation for the reaction is as follows 2CO + O2 --> 2CO2
Calculate the volume of oxygen used and carbon dioxide formed in the above reaction.
4. What volume of oxygen is required to burn completely a mixture of 22.4 dm3 of methane and 11.2 dm3 of hydrogen into carbon dioxide an steam?
CH4 + O2 --> CO2 + 2H2O 2H2 + O2 --> 2H2O
5. The reaction 4N2O + CH4 --. CO2 + 2H2O + 4N2 takes place in the gaseous state. If all volumes are measured at the same temperature and pressure, calculate the volume of dinitrogen oxide (N2O) required to give 150cm3 of steam.
6. What volume of oxygen would be required for the complete combustion of 100 litres of ethane according to the following equation: 2C2H6 + 7O2 --> 4CO2 + 6H2O
B.BASED ON MOLE CONCEPT – AVOGADRO’S NUMBER
1. Calculate the mass of (a) 1022 atoms of sulphur. (b) 0.1 mole of carbon dioxide.
2. Calculate the volume of 320g of SO2 at S.T.P.
3. A gas cylinder contains 24X1024 molecules of nitrogen gas. If Avogadro’s number is 6 X 1023. Calculate a. mass of nitrogen gas in the cylinder. b. Volume of nitrogen gas at S.T.P in dm3
4. The equation for the burning of octane is 2C8H18 + 5CO2 --> 16 CO2 + 18H2O.
a. How many moles of carbon dioxide are produced when one mole of octane burns?
b. What volume at S.T.P is occupied b the number of moles determined in (a)?
c. What is the mass of the CO2 produced by burning two moles of octane?
d. What is the empirical formula of octane?
5. Calculate the number of moles and the number of molecules present in 1.4g of ethylene gas. What is the volume occupied by the same amount of ethylene gas?
6. The volumes of gas A, B, C and D are in the ratio 1:2:2:4, under the same conditions of temperature and pressure.
a. Which sample of gas contains the maximum number of molecules?
b. If the temperature and the pressure of gas A are kept constant, what will happen to the volume of a gas A when the number of molecules are doubled?
c. If this ratio of gas volumes refers to the reactants and products of a reaction, which gas law is being observed?
d. If the volume of gas is actually 5.6dm3 at S.T.P., calculate the number of molecules in the actual volume of gas D at S.T.P.
e. Using your answer from (d) state the mass of gas D, if the gas is dinitrogen oxide (N2O)
7. A flask contains 3.2g of sulphur. Calculate the following
a. The number of moles of sulphur dioxide present in the flask.
b. The number of molecules of SO2 present in the flask.
c.The volume occupied by 3.2g of sulphur dioxide at S.T.P.
8. When heated, potassium permanganate decomposes according to the following equation: 2KMnO4 --> (K2MnO4 + MnO2) + O2
Solid residue. Given that the molecular mass of potassium permanganate is 158. What volume of oxygen would be obtained by the complete decomposition of 15.8g of KMnO4?
9. The gases H2, O2, CO2, SO2 and Cl2 are arranged in increasing relative molecular mass. Given 8 g of each gas at S.T.P. which gas will contain the least number of molecules and which gas the most?
C. BASED ON AVOGADRO’S LAW
1. Sample of gases O2, N2, CO2 and CO under the same conditions of temperature and pressure contain the same number of molecules represented by X. The molecules of O2 occupy V litres and have a mass of 8g.
a. What is the volume occupied by (i) X molecules of N2? (iii) 3X molecules of CO?
b. What is the mass of CO2 in grams?
c. In answering the above questions, which law have you used?
2. Complete the following table where the gases have been collected under the same conditions of temperature and pressure:
Gas
|
Volume (in litres)
|
No. of moleucles
|
Chlorine
|
10
| |
Nitrogen
|
20
| |
Ammonia
|
20
| |
Sulphur dioxide
|
5
|
D. BASED ON VAPOUR DENSITY AND MOLECULAR WEIGHT
1. When heated, potassium permanganate decomposes according to the following equation: 2KMnO4 --> (K2MnO4 + MnO2) + O2 Solid residue
Some potassium permanganate was heated in a test tube. After collecting one litre of oxygen at room temperature it was found that the test tube has undergone a loss in mass 1.32g. if one litre of hydrogen under the same conditions of temperature and pressure has a mass of 0.0825g. Calculate the relative molecular mass of oxygen.
E. BASED ON PERCENTAGE COMPOSITION
1. Calculate the percentage of nitrogen and oxygen in ammonium nitrate.
2. Calculate the percentage of oxygen in ammonium nitrate.
3. Calculate the percentage of sodium in sodium aluminium fluoride.
4. Calculate the percentage of nitrogen in aluminium nitride.
5. Calculate the percentage of platinum in ammonium chloroplatinate, (NH4)2PtCl6.
6. Calculate the percentage of phosphorus in the fertilizer super phosphate, Ca(h2PO4)2
F. BASED ON EMPIRICAL FORMULA AND MOLECULAR FORMULA
1. An organic compound with vapour density = 94 contains C = 12.67%, H = 2013% amd Br = 85.11%. Find its molecular formula.
2. A gaseous compound of nitrogen and hydrogen contains 12.5% hydrogen by mass. Find the molecular formula of the compound, if its relative molecular mass is 37.
3. What is the empirical formula of octane?
4. A compound has the following percentage composition by mass carbon 14.4%, hydrogen 1.2% and chlorine 84.5%. Determine the empirical formula of this compound. Work correct to one decimal place. The relative molecular mass of this compound is 168. So what is its molecular formula?
5. A compound X consists of 4.8% carbon and 95.2% bromide by mass.\
a. Determine the empirical formula of this compound working correct to one decimal place.
b. If the vapour density of the compound is 252, what is the molecular formula of the compound?
c. Name the type of chemical reaction by which X can be prepared from ethane.
6. Determine the empirical formula of a compound containing 47.9% potassium, 5.5% beryllium and 46.6% fluorine by mass.
7. An experiment showed that in a lead chloride, 6.21g of lead combined with 4.26g of chlorine . what is the empirical formula of this chloride?
8. The percentage composition of sodium phosphate as determined by analysis is 42.1% sodium, 18.9% phosphorus and 39% oxygen. Find the empirical formula of the compound.
9. A metal M forms a volatile chloride containing 65.5% chlorine. If the density of the chloride relative to hydrogen is 162.5, find the molecular formula of the chloride.
10. Determine the empirical formula of a compound whose composition by mass is 42% nitrogen 48% oxygen and 9% hydrogen.
G. BASED ON CHEMICAL EQUATIONS
1. Calculate the volume of oxygen required for the complete combustion of 8.8g of Propane.
2. 4.5 moles of calcium carbonate are reacted with dilute HCl.
a. Write the equation for the reaction.
b. What is the mass of 4.5 moles of calcium carbonate?
c. What is the volume of carbon dioxide liberated at S.T.P?
d. How many moles of HCl are used in this reaction?
3. Commercial sodium hydroxide weighing 30g has some sodium chloride in it. The mixture on dissolving in water and subsequent treatment with excess of silver nitrate solution formed a precipitate weighing 14.3g. what is the percentage of sodium hydroxide? The equation for the reaction is given below: NaCl + AgNO3 ---> AgCl + NaNO3
4. From the equation: C + 2H2SO4 ---> CO2 + 2H2O + 2SO2. Calculate:
a. The mass of carbon oxidized by 49g of sulphuric acid.
b. The volume of sulphur dioxide measured at S.T.P., liberated at the same time.
5. A sample of ammonium nitrate when heated yields 8.96 litres of steam. NH4NO3 --> N2O + H2O
a. What volume of dinitrogen oxide is produced at same time as 8.96 litres of steam?
b. What mass of ammonium nitrate should be heated to produce 8.96 litres of steam?
6. Given the relative molecular mass of copper oxide is 80. What volume of ammonia is required to completely reduce 120g of copper oxide? The equation: 3CuO + 2NH3 --> 3Cu + 2H2O +N2
7. The equations given below relate to the manufacture of sodium carbonate:
i. NaCl + NH3 + CO2 + H2O --> NaHCO3 + NH4Cl
ii. 2NaHCO3 --> Na2CO3 + H2O + CO2
Question a and b are based on the production of 21.2g of sodium carbonate.
a. What mass of sodium hydrogen carbonate must be heated to give 21.2g of sodium carbonate?
b. To produce the mass of sodium hydrogen carbonate calculated in (a), what volume of carbon dioxide, measured at S.T.P would be required?
8. The reaction of potassium permanganate with acidified iron (ii) sulphate is given below:
2KMnO4 + 10FeSO4 + 8H2SO4 --> K2SO4 + 2MnSO4 + 5Fe(SO4)3 + 8H2O
If 15.8g of potassium permanganate was used in the reaction, calculate the mass of iron(II)sulphate used in the above reaction. [At.wt of Mn = 55, Fe = 56]
9. 10g of mixture of sodium chloride and anhydrous sodium sulphate is dissolved in water. An excess of barium chloride solution is added and 6.99g of barium sulphate is precipitated according to the equation: Na2SO4 + BaCl2 --> BaSO4 + 2NaCl. Calculate the percentage of sodium sulpahte in the original mixture. [ At. Wts. Of O = 16, Na = 23, S = 32, Ba = 137.]
10. Solid ammonium dichromate on heating decomposes to form products. The reaction is given below: (NH4)2Cr2O7 --> N2 + Cr2O3 + 4H2O [Cr = 52]
a. Calculate the volume of nitrogen gas at S.T.P that will be evolved when 31.5g of ammonium dichromate is heated.
b. Calculate the mass of chromium (III)oxide formed at the same time.
c. What will be the loss of mass if 31.5g of ammonium dichromate is heated above 1000C?
11. When excess of lead nitrate was added to a solution of sodium sulphate, 15.15g of lead sulphate was precipitated. What mass of sodium sulphate was present in the original solution?
12. What mass of anhydrous sodium carbonate is left when all the water of crystallization of washing soda is expelled by heating 57.2g of washing soda?
13. 112cm3 of a gaseous fluoride of phosphorus has a mass of 0.63g. calculate the relative molecular mass of the fluoride. If the molecule of the fluoride contains only one atom of phosphorus, then determine the formula of the phosphorus fluoride.
14. If 112cm3 of hydrogen sulphide is mixed with 120cm3 of chlorine at S.T.P., what mass of sulphur is formed? H2S + Cl2 --> 2HCl + S
