Chemistry Problems based questions
Problems based on Gay Lussac’s Law:
(1) 4NH 3 + 5O 2 → 4NO + 6H 2 0 – If 27 litres of reactants are consumed, what
volume of nitrogen monoxide is produced at the same temperature and
pressure.
[1999]
(2) 4N 2 O + CH 4 → CO 2 + 2H 2 O + 4N 2 . If all volumes are measured at the same
temperature and pressure, calculate the volume of N 2 O required to give 150cm3
of steam.
[2001]
(3) What volume of oxygen would be required for the complete combustion of 100
litres of ethane according to the following equation. 2C 2 H 6 + 7O 2 →4CO 2 +
6H 2 O.
[2001]
3
(4) What volume of O 2 is required to burn completely a mixture of 22.4 dm of CH 4
& 11.2dm3 of H 2 . The reactions are: CH 4 + 2O 2 → CO 2 +2H 2 O ; 2H 2 +O 2 →
2H 2 O [All vols. At s.t.p.]
[2003]
(5) 560ml of carbon monoxide is mixed with 500ml of oxygen and ignited. The
chemical equation for the reaction is as follows: 2CO + O 2 → 2CO 2 . Calculate
the volume of oxygen used and carbon dioxide formed in the above reaction.
[2006]
3
(6) 200cm of acetylene is formed from a certain mass of calcium carbide. Find
the volume of oxygen required and carbon dioxide formed during its complete
combustion. The combustion reaction can be represented as :
[2009]
2C 2 H 2[g] + 5O 2[g] → 4CO 2[g] + 2H 2 O [g]
(7) 10 litres of a mixture of propane [60%] and butane [40%] is burnt. Calculate
the total volume of carbon dioxide formed. Combustion reactions of the
mixture represented as:
[2010]
C 3 H 8(g) + 5O 2(g) → 3CO 2(g) + 4H 2 O (g) ; 2C 4 H 10(g) + 13O 2(g) → 8CO 2(g) + 10H 2 O (g)
(8) 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 :
[2010]
𝐶3 𝐻8(𝑔) + 5𝑂2 (𝑔) → 3𝐶𝑂2(𝑔) + 4𝐻2 𝑂(𝑔)
2𝐶4 𝐻10(𝑔) + 13𝑂2(𝑔) → 8𝐶𝑂2(𝑔) + 10𝐻2 𝑂(𝑔)
(9) Calculate the volume of 320g of SO 2 at stp. (Atomic mass: S = 32 and O = 16).
[2011]
(10) State Gay Lussac’s Law of combining volumes.
[2011]
(11)Calculate the volume of oxygen required for the complete combustion of 8.8g of
propane (C 3 H 8 ). (Atomic mass: C = 14, O = 16, H = 1, Molar Volume = 22.4
dm3 at stp)
[2011]
(12)67.2 litres of hydrogen combines with 44.8 litres of nitrogen to form ammonia
under specific condition as:
𝑁2 (𝑔) + 3𝐻2 (𝑔) → 2𝑁𝐻3 (𝑔)
Calculate the volume of ammonia produced. What is the other substance, if
any, that remains in the resultant mixture?
[2012]
(13)The mass of 5.6 dm3 of a certain gas at STP is 12.0g. Calculate the relative
molecular mass of the gas.
[2012]
(14)What volume of oxygen is required to burn completely 90 dm3 of butane under
similar conditions of temperature and pressure?
[2013]
2𝐶4 𝑂10 + 13𝑂2 → 8𝐶𝑂2 + 10𝐻2 𝑂
(15)The vapour density of a gas is 8. What would be the volume occupied by 24.0
of the gas at STP?
[2013]
(16)A vessel contains X number of molecules of hydrogen gas at a certain
temperature and pressure. How many molecules of nitrogen gas would be
present in the same vessel under the same conditions of temperature and
pressure?
(17)Oxygen oxidizes ethyne to carbon dioxide and water as shown by the equation:
2𝐶2 𝐻2 + 5𝑂2 → 4𝐶𝑂2 + 2𝐻2 𝑂
What volume of ethyne gas at s.t.p is required to produce 8.4 dm3 of carbon
dioxide at s.t.p? [H = 1, C = 12, O = 16]
[2014]
Problems based on Mole Concept – Avogadro’s Number:
(1) The gases H 2 , O 2 , CO 2 , SO 2 and Cl 2 are arranged in increasing relative
molecular mass. Given 8g. of each gas at s.t.p. Which gas will contain the least
number of molecules and which gas the most.
[2003]
(2) A flask contains 3.2g of sulphur dioxide. Calculate the following:
[2004]
(i)
The moles of sulphur dioxide present in the flask.
(ii)
The number of molecules of SO 2 present in the flask.
(iii)
The vlume occupied by 3.2g of sulphur dioxide at s.t.p. [S = 32, O = 16]
(3) 2KMnO 4 → K 2 MnO 4 + MnO 2 + O 2 . Given that the molecular mass of KMnO 4 is
158, what volume of oxygen [measured at room temperature] would be
obtained by complete decomposition of 15.8g of potassium permanganate.
[Molar volume at room temperature is 24 litres].
[2004]
(4) The volumes of gases A, B, C & D are in the ratio, 1:2, 2: 4 under the same
conditions of temperature and pressure.
(i)
Which sample of gas contains the maximum number of molecules?
(ii)
If the temperature and the pressure of gas A are kept constant, then
what will happen to the volume of A when the number of molecules is
doubled.
(iii)
If this ratio of gas volumes refers to reactants and products of reaction –
gas law observed is ______.
(iv)
If the volume of ‘A’ is actually 5.6dm3 at s.t.p., calculate the number of
molecules in the actual volume of ‘D’ at s.t.p [Avogadro’s number is
6x1023). Using your answer, state the mass of ‘D’ if the gas is dinitrogen
oxide [N 2 O]. [N = 14, O = 16]
[2005]
(5) Calculate the number of moles and the number of molecules present in 1.4g. of
ethylene gas [C 2 H 4 ]. What is the volume occupied by the same amount of
ethylene. [0.05 moles, 3x1022 molecules, 1.12 lit.] What is the vapour density
of ethylene.[Avogadro’s Number = 6 x 1023 ; Atomic weight of C = 12, H = 1;
Molar volume = 22.4 litres at s.t.p.]
[2006]
(6) The equation for the burning of octane is: 2C 8 H 18 + 25O 2 → 16CO 2 + 18H 2 O.
(i)
How many moles of carbon dioxide are produced when one mole of
octane burns?
(ii)
What volume, at s.t.p. is occupied by the number of moles determined in
(i).
(iii)
If the relative molecular mass of carbon dioxide is 44, what is the mass of
carbon dioxide produced by burning two moles of octane?
[2008]
(7) Define the term – Mole. A gas cylinder contains 24 x 1024 molecules of nitrogen
gas. If Avogadro’s number is 6 x 1023 and the relative atomic mass of nitrogen
is 14, calculate:
(i)
Mass of nitrogen gas in the cylinder.
(ii)
Volume of nitrogen at STP in dm3
[2009]
(8) Gas ‘X’ occupies a volume of 100cm3 at S.T.P. and weighs 0.5g.
relative molecular mass.
Find its
[2009]
(9) Dilute hydrochloric acid [HCl] is reacted with 4.5 moles of calcium carbonate.
Give the equation for the said reaction. Calculate (i) The mass of 4.5 moles of
CaCO 3 (ii) The volume of CO 2 liberated at stp. (iii) The mass of CaCl 2 formed
(iv) the number of moles of the acid HCl used in the reaction [relative molecular
mass of CaCO 3 is 100 and of CaCl 2 is 111].
[2010]
(10) Under the same conditions of temperature and pressure you collect 2 litres of
CO 2 , 3 litres of Cl 2 , 5 litres of H 2 , 4 litres of N 2 and 1 litre of SO 2 . In which gas
sample will there be the greatest number of molecules and the least number of
molecules. Justify your answer.
[1996]
(11) A vessel contains N molecules of oxygen at a certain temperature and pressure.
How many molecules of sulphur dioxide can the vessel accommodate at the
same temperature and pressure?
[1999]
(12) The gases chlorine, nitrogen, ammonia and sulphur dioxide are collected under
the same conditions of temperature and pressure. If 20 litres of nitrogen
contain ‘X’ no. of molecules state the number of molecules in 10 litres of
chlorine, 20 litres of ammonia and 5 litres of sulphur dioxide.
[2001]
(13) Samples of O 2 , N 2 , CO and CO 2 under the same conditions of temperature and
pressure contain the same number of molecules represented by X. The
molecules of oxygen occupy V litres and have a mass of 8g. Under the same
conditions of temperature and pressure, what is the volume occupied by: (i) X
molecules of N 2 (ii) 3X molecules of CO. (III) What is the mass of CO 2 in
grams? (iv) In answer the above questions, whose law has been used. [2002]
(14) Define the term ‘atomic weight’.
[2005]
(15) The gas law which relates the volume of a gas to the number of molecules of
the gas is
[2008]
(a) Avogadro’s Law
(b) Gay-Lussac’s Law
(c) Boyle’s Law (d) Charles’ Law
(16) Correct the following statement – Equal masses of all gases under identical
conditions contain the same number of molecules.
(17) Calculate the mass of :
(i)
1022 atoms of sulphur.
(ii)
0.1 mole of carbon dioxide
[2011]
[Atomic mass: S = 32, C = 12 and O = 16 and Avogadro’s Number = 6 x 1023]
(18) Concentrated nitric acid oxidizes phosphorus to phosphoric acid according to
the following equation:
𝑃 + 5𝐻𝑁𝑂3 (𝑐𝑜𝑛𝑐. ) → 𝐻3 𝑃𝑂4 + 𝐻2 𝑂 + 5𝑁𝑂2
If 9.3g of phosphorus was used in the reaction, calculate:
(i)
Number of moles of phosphorus taken.
(ii)
The mass of phosphoric acid formed.
(iii)
The volume of nitrogen dioxide produced at STP.
[H = 1, N = 14, P = 31, O = 16]
[2012]
(19) O 2 is evolved by heating KClO 3 using MnO 2 as a catalyst
𝑀𝑛𝑂2
2𝐾𝐶𝑙𝑂3 �⎯⎯⎯⎯� 2𝐾𝐶𝑙 + 3 𝑂2
(i)
Calculate the mass of 𝐾𝐶𝑙𝑂3 required to produce 6.72 litre of O 2 at STP.
[atomic masses of K = 39, Cl = 35.5, O = 16]
(ii)
Calculate the number of moles of oxygen present in the above volume
and also the number of molecules.
(iii)
Calculate the volume occupied by 0.01 mole of CO 2 at STP.
[2013]
(20) State Avogadro’s Law.
[2014]
(21) A cylinder contains 68g of ammonia gas at s.t.p.
[2014]
(i)
What is the volume occupied by this gas?
(ii)
How many moles of ammonia are present in the cylinder?
(iii)
How many molecules of ammonia are present in the cylinder? [N-14, H-1]
Problems based on – Vapour Density and Molecular Weight:
(1) Find the relative molecular mass of a gas, 0.546g of which occupies 360 cm3 at
87°C and 380mm Hg pressure. [1 litre of hydrogen at s.t.p. weighs 0.09g][1996]
(2) Mention the term defined by the following: The mass of a given volume of gas
compared to the mass of an equal volume of hydrogen.
[2001]
(3) 2KMnO 4 → K 2 MnO 4 + MnO 2 + O 2 [K 2 MnO 4 + MnO 2 is the 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 had undergone a
loss in mass of 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.
[2004]
(4) A gas cylinder of capacity of 20 dm3 is filled with gas X the mass of which is
10g. When the same cylinder is filled with hydrogen gas at the same
temperature and pressure the mass of the hydrogen is 2g, hence the relative
mass of the gas is (a) 5 (b) 10 (c) 15 (d) 20.
[2009]
(5) An organic compound with vapour density = 94 contains C = 12.67%,
H = 2.13% and Br = 85.11%. Find the molecular formula. [Atomic mass:
C = 12, H = 1, Br = 80]
[2011]