Some Basic Concepts of Chemistry


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)  (Atomic masses: Au = 197, Na = 23, Li = 7, Cl = 35.5 amu)



Some Basic Concepts of Chemistry

Q 1.

Match the following prefixes with their multiples:

Q 2.

Calculate the atomic mass (average) of chlorine using the following data:

Q 3.

Give an example of a molecule in which the ratio of the molecular formula is six times the empirical formula.

Q 5.

What is one a.m.u. or one ‘u’?

Q 6.

How many oxygen atoms are there in 18 g of water?

Q 7.

Calculate the amount of carbon dioxide that could be produced when
(i) 1 mole of carbon is burnt in air.
(ii) 1 mole of carbon is burnt in 16 g of dioxygen.
(iii) 2 moles of carbon are burnt in 16 g of dioxygen.

Q 8.

What do you mean by significant figures?

Q 9.

What do you understand by stoichiometric coefficients in a chemical equation?

Q 10.

How much copper can be obtained from 100 g of copper sulphate (CuSO4  )? (Atomic mass of Cu= 63.5 amu)

Q 11.

Name two factors that introduce uncertainty into measured figures.

Q 12.

State Avogadro’s law.

Q 13.

Round up the following upto three significant figures:
(i) 34.216 (ii) 10.4107 (iii) 0.04597 (iv) 2808

Q 14.

The density of water at room temperature is 1.0 g/mL. How many molecules are there in a drop of water if its volume is 0.05 mL?

Q 15.

How are 0.50 mol  Na2C03  and 0.50 M  Na2C03  different?

Q 16.

Pressure is determined as force per unit area of the surface. The S.I. unit of pressure, pascal, is as shown below:1 Pa = 1  Nm-2.If mass of air at sea level is 1034 g  cm-2,calculate the pressure in pascal.

Q 17.

Q 18.

Define molality. How does molality depend on temperature?

Q 19.

In the reaction, A + B2——> AB2, identify the limiting reagent, if any, in the following  mixtures
(i) 300 atoms of A + 200 molecules ofB
(ii) 2 mol A + 3 mol B
(iii) 100 atoms of A + 100 molecules ofB
(iv) 5 mol A + 2.5 mol B
(v) 2.5 mol A + 5 mol B

Q 20.

Calculate the molecular mass of the following:
(i)  H20(ii)  C02(iii)  CH4

Q 21.

Express the following up to four significant figures.

Q 22.

Define the term ‘unit’ of measurement.

Q 23.

What is the molecular mass of a substance each molecule of which contains 9 atoms of carbon, 13 atoms of hydrogen and 2.33 x  10-23  g other component?

Q 24.

Use the data given in the following table to calculate the molar mass of naturally occurring argon.

Q 25.

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 percent of nitric acid in it is being 69%.

Q 26.

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

Q 27.

Determine the molecular formula of an oxide of iron in which the mass percent of iron and oxygen are 69.9 and 30.1 respectively. Given that the molar mass of the oxide is 159.8 g  mol-1(Atomic mass: Fe = 55.85, O = 16.00 amu)Calculation of Empirical Formula.

Q 28.

KCl03  on heating decomposes to give KCl and 02. What is the volume of  02 at N.T.P liberated by 0.1 mole of  KCl03?

Q 29.

Chlorine is prepared in the laboratory by treating manganese dioxide (Mn02) with aqueous hydrochloric acid according to the reaction.
4 HCl (aq) + Mn02 (s) ———–> 2 H2O (l) + MnCl2(aq) +Cl2(g)

How many grams of HCl react with 5.0 g of manganese dioxide? (Atomic mass of Mn = 55 u)

Q 30.

What is the SI unit of molarity?

Q 31.

Determine the empirical formula of an oxide of Iron which has 69.9 % iron and 30.1 % dioxygen by mass.

Q 32.

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040.

Q 33.

Express the following in scientific notation:
(i) 0.0048 (v) 6.0012 (ii) 234,000 (iii) 8008 (iv) 500.0

Q 34.

Calculate no. of carbon and oxygen atoms present in 11.2 litres of  C02  at N.T.P.

Q 35.

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?

Q 36.

What is the number of significant figures in 1.050 x 104?

Q 37.

The Vapour Density of a gaseous element is 5 times that of oxygen under similar conditions. If the molecule is triatomic, what will be its atomic mass?

Q 38.

What is an atom according to Dalton’s atomic theory?

Q 39.

A sample of drinking water was found to be severely contaminated with chloroform, CHCly 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.

Q 40.

What is the S.I. unit of mass?

Q 41.

If ten volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour could be produced?

Q 42.

Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation:(i)  N2 (g) + 3H2(g) —–> 2NH3 (g)
(ii) Will any of the two reactants remain unreacted?
(iii) If yes, which one and what would be its mass?

Q 43.

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

Q 44.

Convert the following into basic units:
(i) 28.7 pm (ii) 15.15 µs (iii) 25365 mg

Q 45.

How are 0.5 ml of NaOH differents from 0.5 M of NaOH?

Q 46.

Calcium carbonate reacts with aqueous HCl according to the reaction

CaC03 (s) + 2HCl (aq) ———->CaCl2  (aq) +C02(g) +H2O(l).

What mass of CaC03 is required to react completely with 25 mL of 0.75 M HCl?

Q 47.

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

Q 48.

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)  (Atomic masses: Au = 197, Na = 23, Li = 7, Cl = 35.5 amu)

Q 49.

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?

Q 50.

Define law of conservation of mass.