Chapter 1 - Some Basic Concepts of Chemistry

Define the law of multiple proportions. Explain it with two examples. How
does this law point to the existance of atoms?

A vessel contains 1.6 g of dioxygen at STP (273.15K, 1 atm pressure). The
gas is now transferred to another vessel at constant temperature, where
pressure becomes half of the original pressure. Calculate
(i) volume of the new vessel.
(ii) number of molecules of dioxygen.

Assertion (A) : Combustion of 16 g of methane gives 18 g of water.
Reason (R) : In the combustion of methane, water is one of the products.
(i) Both A and R are true but R is not the correct explanation of A.
(ii) A is true but R is false.
(iii) A is false but R is true.
(iv) Both A and R are false.

Assertion (A) : Significant figures for 0.200 is 3 where as for 200 it is 1.
Reason (R) : Zero at the end or right of a number are significant provided
they are not on the right side of the decimal point.
(i) Both A and R are true and R is correct explanation of A.
(ii) Both A and R are true but R is not a correct explanation of A.
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Exemplar Problems, Chemistry 8
(iii) A is true but R is false.
(iv) Both A and R are false.

Assertion (A) : One atomic mass unit is defined as one twelfth of the mass of
one carbon-12 atom.
Reason (R) : Carbon-12 isotope is the most abundunt isotope of carbon
and has been chosen as standard.
(i) Both A and R are true and R is the correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) Both A and R are false.

In the following questions a statement of Assertion (A) followed by a
statement of Reason (R) is given. Choose the correct option out of the
choices given below each question.
38. Assertion (A) : The empirical mass of ethene is half of its molecular mass.
Reason (R) : The empirical formula represents the simplest whole number
ratio of various atoms present in a compound.
(i) Both A and R are true and R is the correct explanation of A.
(ii) A is true but R is false.
(iii) A is false but R is true.
(iv) Both A and R are false.

The reactant which is entirely consumed in reaction is known as limiting reagent.
In the reaction 2A + 4B → 3C + 4D, when 5 moles of A react with 6 moles of B,
then
(i) which is the limiting reagent?
(ii) calculate the amount of C formed?

Volume of a solution changes with change in temperature, then, will the molality
of the solution be affected by temperature? Give reason for your answer.

Calculate the average atomic mass of hydrogen using the following data :
Isotope                               % Naturalabundance                                  Molar mass
1H                                      99.985                                                     1
2H                                       0.015                                                      2

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 whole
number ratio.
(a) Is this statement true?
(b) If yes, according to which law?
(c) Give one example related to this law.

What is the difference between molality and molarity?

What is the symbol for SI unit of mole? How is the mole defined?

What will be the mass of one atom of C-12 in grams?

What volume of 10M HCl and 3M HCl should be mixed to obtain 1L of
6M HCl solution?

4 litres of water are added to 2L of 6 molar HCl solutions.
What is the molarity of resulting solution?

What is 1molal solution?

The substance which gets used up in any reaction is called --------------

Calculate the weight of lime (CaO) obtained by heating 2000kg of 95% pure
lime stone (CaCO3)

Write an expression for molarity and molality of a solution.

How much potassium chlorate should be heated to produce 2.24L of
oxygen at NTP?

What is stoichiometry?

Vitamin C is essential for the prevention of scurvy.
Combustion of 0.2000g of vitamin C gives 0.2998g of CO2
and 0.819g of H2O. What is the empirical formula of vitamin C?

Calculate the number of moles in the following masses 
(i) 7.85g of Fe
(ii) 7.9mg of Ca

Write empirical formula of following 
CO, Na2CO3, KCl, C6H12, H2O2, H3PO4, Fe2O3, N2O4.

1L of a gas at STP weighs 1.97g. What is molecular mass?

Give one example each of a molecule in which empirical formula
and molecular formula are (i) same (ii) Different.

Calculate the number of molecules present in 0.5 moles of CO2?

At NTP, what will be the volume of molecules of 6.022 ´1023 H2?

What is the value of one mole?

What is formula mass?

Calculate molecular mass of 
C2H6, C12H22O11, H2SO4, H3PO4

Define one atomic mass unit (amu).

Write Postulates of Dalton’s atomic theory.

State Avogadro’s law.

Explain law of multiple proportions with an example.

State law of definite proportions.

How many significant figures are present in 
(a) 4.01 ´ 102
(b) 8.256
(c) 100

What do you understand by significant figures?

What is the difference between precision and accuracy?

What does the following prefixes stand for 
(a) pico (b) nano (c) centi (d) deci

What is the SI unit of volume? What is the other common unit which in not
an SI unit of volume.

What are the reference points in thermometer with Celsius scale?

Convert 350C to oF & K. 

What is the SI unit of density? 

How is volume measured in laboratory? Convent 0.5L into ml and
30cm3 to dm3

What is the difference between mass & weight? How is mass measured in
laboratory?

Write seven fundamental quantities & their units.

What are the two different system of measurement?

How are physical properties different from chemical properties?

How can we separate the components of a compound?

What is the difference between molecules and compounds?
Give examples of each.

Classify following as pure substances and mixtures – Air, glucose, gold,
sodium and milk.

Name the different methods that can be used for separation of components
of a mixture.

Classify following substances as element, compounds and mixtures – water,
tea, silver, steel, carbondioxide and platinum

How is matter classified at macroscopic level?

Differentiate solids, liquids & gases in terms of volume & shapes.

How can we say that sugar is solid and water is liquid?

How has chemistry contributed towards nation’s development?

What is chemistry? 

Give the two points of differences between homogeneous and heterogeneous
mixtures.

Chlorine is prepared in the laboratory by treating manganese dioxide (MnO₂) with aqueous hydrochloric acid according to the reaction

4HCl_(aq) + MnO_2(s) → 2H₂O_(l) + MnCl_2(aq) + Cl_2(g)

How many grams of HCl react with 5.0 g of manganese dioxide?

Calcium carbonate reacts with aqueous HCl to give CaCl₂ and CO₂ according to the reaction, CaCO_3(s) + 2 HCl_(aq) → CaCl_2(aq) + CO_2(g) + H₂O_(l)

What mass of CaCO₃ is required to react completely with 25 mL of 0.75 M HCl?

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.

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

How many significant figures should be present in the answer of the following calculations?

(i) 

(ii) 5 × 5.364

(iii) 0.0125 + 0.7864 + 0.0215

What will be the mass of one ¹²C atom in g?

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040 (assume the density of water to be one).

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)

Convert the following into basic units:

(i) 28.7 pm

(ii) 15.15 pm

(iii) 25365 mg

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

How are 0.50 mol Na₂CO₃and 0.50 M Na₂CO₃different?

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

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

If the speed of light is 3.0 x 10⁸ m s^-1, calculate the distance covered by light in 2.00 ns.

What is the concentration of sugar (C₁₂H₂₂O₁₁) in mol L^-1if its 20 g are dissolved in enough water to make a final volume up to 2 L?

The following data are obtained when dinitrogen and dioxygen react together to form different compounds:

     Mass of dinitrogen     Mass of dioxygen

(i)            14 g                            16 g

(ii)           14 g                            32 g

(iii)          28 g                            32 g

(iv)          28 g                            80 g

(a) Which law of chemical combination is obeyed by the 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

Round up the following upto three significant figures:

(i) 34.216

(ii) 10.4107

(iii) 0.04597

(iv) 2808

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

Express the following in the scientific notation:

(i) 0.0048

(ii) 234,000

(iii) 8008

(iv) 500.0

(v) 6.0012

A sample of drinking water was found to be severely contaminated with chloroform, CHCl₃, 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.

What do you mean by significant figures?

Match the following prefixes with their multiples:

What is the SI unit of mass? How is it defined?

Pressure is determined as force per unit area of the surface. The SI unit ofpressure, Pascal is as shown below:

1Pa = 1N m^-2

If mass of air at sea level is 1034 g cm^-2, calculate the pressure in Pascal.

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?

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.

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. Given that the molar mass of the oxide is 159.69 g mol^-1

How much copper can be obtained from 100 g of copper sulphate (CuSO₄)?

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%.

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

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.

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

Calculate the mass percent of different elements present in sodium sulphate (Na₂SO₄).

Calculate the molecular mass of the following:

(i) H₂O (ii) CO₂ (iii) CH₄