Chapter 1 – Some Basic Concepts of Chemistry Exercise 25
Calculate the molecular mass of the following :
- (i) H2o
- (ii) CO2
- (iii) CH4
- (i) Molecular mass of H2O :2 × 1 + 1 × 16 = 18u
- (ii) Molecular mass of CO2 :1 × 12 + 2× 16 = 44 u
- (iii) Molecular mass of CH4 : 12 + 4 × 1 = 16 u
Calculate the mass percent of different elements present in sodium sulphate (Na2SO4).
Molecular mass of Na2SO4
= 2 × Atomic mass of Na + Atomic mass of S + 4 × Atomic mass of O
= 2 × 23 + 32 + 4 × 16
= 46 + 32 + 64
= 142 u.
Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1% oxygen by mass.
Hence, the empirical formula is Fe2CO3
Calculate the amount of carbon dioxide that could be produced when
(1) 1 mole of carbon is burnt in air.
(2) 1 mole of carbon is burnt in 16 g of dioxygen.
(3) 2 moles of carbon are burnt in 16 g of dioxygen.
- Hence, 1 mole of C produces 44 g of CO2
- Hence, O2 is the limiting reagent.
∵ 32 g O2 reacts with C to produce 44 g of CO2
∵ 16 g O2 reacts with C to produce
∵ 64 g O2 reacts with C to produce 88 g of CO2
∵ 16 g O2 reacts with C to produce =
Calculate the mass of sodium acetate (CH3COONa) required to make 500 mL of 0.375 molar aqueous solution. Molar mass of sodium acetate is 82.0245 g mol-1.
Chapter 1 – Some Basic Concepts of Chemistry Exercise 26
Calculate the concentration of nitric acid in moles per litre in a sample which has a density 1-41 g mL-1 and the mass per cent of nitric acid in it being 69%.
Mass percent 69 means that 69 g of HNO3 are dissolved in 100 g of the solution.
How much copper can be obtained from 100 g of copper sulphate (CuS04) ?
Molar mass of CuSO4
= 63.5 + 32 + 4 × 16
=63.5 + 32 + 64
= 159.5 amu or u
159.5 g of CuSO4 contains copper = 63.5 g
100 g of CuSO4 contains copper = = 39.81 g
Determine the molecular formula of an oxide of iron in which the mass per cent of iron and oxygen are 69.9 and 30.1 respectively.
For empirical formula, Fe2O3.
Molecular mass of Fe2O3 x 1
= 2 x 56 + 3 x 16
= 112 + 48
Molecular formula = u (Empirical formula)
∴ Molecular formula = (Fe2O3) x 1 = (Fe2O3)
Calculate the average atomic mass of chlorine using the following data.
In three moles of ethane (C2H6), calculate the following:
- (i) Number of moles of carbon atoms.
- (ii) Number of moles of hydrogen atoms.
- (iii) Number of molecules of ethane.
(i) 1 mole of C2H6 contains 2 moles of carbon atoms.
Number of moles of carbon atoms in 3 moles of C2H6 = 3 x 2 = 6
(ii) 1 mole of C2H6 contains 6 moles of hydrogen atoms.
Number of moles of hydrogen atoms in 3 moles of C2H6 = 3 x 6 = 18
(iii) 1 mole of C2H6 = 6.022 x 1023 molecules Number of molecules in 3 moles of C2H6
= 3 x 6.022 x 1023 = 1.807 x 1024 molecules
What is the concentration of sugar (C12H22O11) in mol L -1 if its 20 g are dissolved in enough water to make a final volume up to 2 L?
The molecular mass of sugar ((C12H22O11)
= 12 x 12 + 1 x 22 + 11 x 16
= 144 + 22 + 176
If the density of methanol is 0.793 kg L-1 what is its volume needed for making 2.5 L of its 0.25 M solution?
Moles of methanol present in 2.5 L of 0.25 M solution
Pressure is determined as force per unit area of the surface. The SI unit of pressure, pascal is 1 Pa = 1 Nm-2. If mass of air at sea level is 1034 g cm-2, calculate the pressure in pascal.
Mass of air at sea level = 1034 g cm-2
Acceleration due to gravity, g = 9.8 m s-2
What is the S.I. unit of mass? How is it defined?
The S I. unit of mass is kilogram. The amount of matter present in a substance is called mass. The unit of mass kilogram is defined as being equal to the mass of international prototype of the kilogram.
Match the following prefixes with their multiplies
- (i) micro 106
- (ii) deca 109
- (iii) mega 10-6
- (iv) giga 10-15
- (v) femto 10
- (i) micro → 10-6
- (ii) deca → 10
- (iii) mega → 106
- (iv) giga → 109
- (v) femto → 10-15
What do you mean by significant figures?
Significant figures : The significant figures in a number are all the certain digits plus one doubtful digit, e.g., 2005 has four significant figures.
A sample of drinking water was found to be severely contaminated with chloroform, CHCI3, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
- (i) Express this in percent by mass.
- (ii) Determine the molality of chloroform in the water sample.
(i) 15 ppm means 15 parts in million (106) parts
Express the following in the scientific notation:
- (i) 0.0048
- (ii) 234,000
- (iii) 8008
- (iv) 500.0
- (v) 6.0012
- (i) 4.8 x 106
- (ii) 2.34 x 105
- (iii) 8.008 x 103
- (iv) 5.00 x 102
- (v) 6.0012 x 100 or 6.0012
How many significant figures are present in the following?
- (i) 0.0025
- (ii) 208
- (iii) 5005
- (iv) 126,000
- (v) 500.0
- (vi) 2.0034
- (i) 2
- (ii) 3
- (iii) 4
- (iv) 3
- (v) 4
- (vi) 5
Chapter 1 – Some Basic Concepts of Chemistry Exercise 27
Round up the following upto three significant figures:
- (i) 34.216
- (ii) 10.4107
- (iii) 0.04597
- (iv) 2808
- (i) 34.2
- (ii) 10.4
- (iii) 0.0460
- (iv) 2810 or 2.81 x 103
The following data are obtained when dinitrogen and dioxygen react together to form different compounds:
Mass of dinitrogen Mass of dioxygen
- (i) 14 g 16g
- (ii) 14 g 32 g
- (iii) 28 g 32 g
- (iv) 28 g 80 g
(a) Which law of chemical combination is obeyed bythe above experimental data? Give its statement.
(b) Fill in the blanks in the following conversions:
- (i) 1 km = ……….. mm = ……….. pm
- (ii) 1 mg = ……….. kg = ………….. ng
- (iii) 1 mL = ………… L = ……………. dm3
(a) Law of multiple proportions : This law was proposed by Dalton in 1803. It states that “If two elements can combine to form more than one compound the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers.
Fixing the mass of dinitrogen as 28 g, masses of dioxygen combined will be 32, 64, 32 and 80 g in the given four oxides. These are in the ratio of 2 : 4 : 2 : 5 which is a simple whole number ratio. Hence, the given data obeys the law of multiple proportions.
- (i) 106mm, 1015pm
- (ii) 10-6 kg, 106ng
- (iii) 10-3 L, 10-3 dm3
If the speed of light is 3.0 x 108 m s-1, calculate the distance covered by light in 2.00 ns.
Speed of light = 3.0 x 108 m s-1
Distance covered by light in 2.00 ns = 3.0 x 108 x 2 x 10-9 = 6.00 x 10-1 m = 0.600 m
In a reaction :A + B2 → AB2
Identify the limiting reagent, if any, in the following reaction mixtures.
- (i) 300 atoms of A + 200 molecules of B
- (ii) 2 mol A + 3 mol B
- (iii) 100 atoms of A + 100 molecules of B
- (iv) 5 mol A + 2.5 mol B
- (v) 2.5 mol A + 5 mol B
According to the equation, one mole of A reacts with one mole of B and one atom of A reacts with one molecule of B.
- (i) B is limiting reagent because 200 molecules of B will react with 200 atoms of A and 100 atoms of A will be left in excess.
- (ii) A
- (iii) Both will react completely because it is stoichiometric mixture. No limiting reagent.
- (iv) B
- (v) A
Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation:
N2(g) + H2(g) → 2NH3(g)
(i) Calculate the mass of ammonia produced if 2.00 x 103 g dinitrogen reacts with 1.00 x 103 g of dihydrogen.
(ii) Will any of the two reactants remain unreacted?
(iii) If yes, which one and what would be its mass?
The balanced chemical equation is N3 + 3H3 → 2NH3
How are 0.50 mol Na2CO3 and 0.50 M Na2CO3different?
1 mol Na2CO3 2 x 23 + 12 + 3 x 16 = 106 g mol-1
0.50 mol Na2CO3 0.50 x 106= 53 g
0.50 M Na2CO3 solution means that 0.50 moles
or 53 g of Na2CO3 are dissolved in 1000 mL of solution.
lf ten volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced?
Convert the following into basic units :
- (i) 28.7 pm
- (ii) 15.15pm
- (iii) 25365 mg
Chapter 1 – Some Basic Concepts of Chemistry Exercise 28
Which one of the following will have largest number of atoms?
- (i) 1 g Au(s)
- (ii) 1 g Na(s)
- (iii) 1 g Li(s)
- (iv) 1 g of Cl2(g)
Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040.
What will be the mass of one 12C atom in g?
How many significant figures should be present in the answer of the following calculations?
- (ii) 5×5.364
- (iii) 0.0125 + 0.7864 + 0.0215
Use the data given in the following table to calculate the molar mass of naturally occurring argon isotopes:
Calculate the number of atoms in each of the following:
- (i) 52 moles of Ar
- (ii) 52 u of He
- (iii) 52 g of He.
A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide, 0.690 g of water and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate
- (i) empirical formula,
- (ii) molar mass of the gas, and
- (iii) molecular formula.
Calcium carbonate reacts with aqueous HCI to give CaCI2 and CO2 according to the reaction,
CaC03(s) + 2HCI(aq) —> CaCI2(aq)+ CO2(g) + H2(s)O(I).
What mass of CaC03 is required to react completely with 25 mL of 0.75 M HCI?
Chlorine is prepared in the laboratory by treating manganese dioxide (Mn02) with aqueous hydrochloric acid according to the reaction
4HCI(aq) + MnO2(s) → 2H2O(I) + MnCI2(aq) + Cl2(g)
How many grams of HCI react with 5.0 g of manganese dioxide?