Chemistry

Some Basic Concepts of Chemistry

Question:

How is empirical formula of a compound related to its molecular formula?

Answer:

Molecular formula = (Empirical formula)n where n is positive integer.

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Some Basic Concepts of Chemistry

Q 1.

Match the following prefixes with their multiples:
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-15

Q 2.

Calculate the atomic mass (average) of chlorine using the following data:
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-9

Q 4.

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

Q 7.

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

Q 8.

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

Q 9.

Name two factors that introduce uncertainty into measured figures.

Q 10.

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 11.

What do you mean by significant 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.

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 16.

How are 0.50 mol  Na2C03  and 0.50 M  Na2C03  different?

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.
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-38

Q 22.

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 23.

Define the term ‘unit’ of measurement.

Q 24.

Use the data given in the following table to calculate the molar mass of naturally occurring argon.
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-30

Q 25.

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 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 percent of nitric acid in it is being 69%.

Q 27.

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 28.

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 29.

What is the SI unit of molarity?

Q 30.

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 31.

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

Q 32.

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

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

Q 35.

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

Q 36.

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 37.

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 38.

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 39.

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 40.

What is the S.I. unit of mass?

Q 41.

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 42.

Define law of conservation of mass.

Q 43.

Calculate the number of moles in each of the following.

Q 44.

How many significant figures should be present in the answer of the following?
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-29

Q 45.

Calculate the number of atoms in each of the following:
(i) 52 moles of He (ii) 52 u of He (iii) 52 g of He

Q 46.

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

Q 47.

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 48.

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

Q 49.

Why air is not always regarded as homogeneous mixture?

Q 50.

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