If Avogadro number N A , is changed from 6.022 × 10 23 m o l - 1 to 6.022 × 10 20 m o l - 1 , this would change:

The definition of mass in units of grams

The ratio of chemical species to each other in a balanced equation.

The ratio of elements to each other in a compound.

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If two compounds have the same empirical formula but different molecular formulae, they must have

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Important Questions on Some Basic Concepts of Chemistry

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

In Carius method of estimation of halogens,

250 mg

of an organic compound gave

141 mg AgBr

. What is the percentage of bromine in the compound (atomic mass of

Ag = 108

and atomic number of

Br = 80

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

An organic compound contains

80 %

(by wt.) carbon and remaining percentage of hydrogen. The right option for the empirical formula of this compound is: [Atomic wt. of

C

12

and of

H

1

]

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

Compound $A$ contains $8.7 %$ Hydrogen, $74 %$ Carbon and $17.3 %$ Nitrogen. The molecular formula of the compound is, Given : Atomic masses of $C, H$ and $N$ are $12, 1$ and $14$ amu respectively.

The molar mass of the compound $A$ is $162 g {mol}^{- 1}$ .

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

A sample of a hydrate of barium chloride weighing 61 g was heated until all the water of hydration is removed. The dried sample weighed 52 g. The formula of the hydrated salt is: (atomic mass, Ba = 137 amu, Cl = 35.5 amu)

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

An organic compound contains

24 %

carbon,

4 %

hydrogen and remaining chlorine. Its empirical formula is

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

If Avogadro number

N_{A}

, is changed from

6.022 \times 10^{23} m o l^{- 1}

6.022 \times 10^{20} m o l^{- 1}

, this would change:

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

An organic compound contains

60 % C; 4.48 % H

and

35.5 % O .

Its empirical formula is

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

The percentage of nitrogen by mass in ammonium sulphate is closest to (atomic masses H = 1, N = 14, O = 16, S = 32)

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

The empirical formula and molecular mass of a compound are

{CH}_{2} O

and

180 g

respectively. The molecular formula of the compound will be

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

In a compound

C, H

and

N

are present in

9 : 1 : 3.5

by weight. If molecular weight of compound is

108

, the molecular formula of compound is

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

A mixture of gases contains

H_{2}

and

O_{2}

gases in the ratio of

1 : 4

(w/w). What is the molar ratio of the two gases in the mixture?

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

1.25 g of a metal (M) reacts with oxygen completely to produce 1.68 g of metal oxide. The empirical formula of the metal oxide is [Molar mass of M and O are

69.7 g m o l^{- 1}

and

16.0 g m o l^{- 1}

, respectively]

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

Suppose the elements

X

and

Y

combine to form two compounds

X Y_{2}

and

X_{3} Y_{2}

. When

0.1 mole

X Y_{2}

weighs

10 g

and

0.05 mole

X_{3} Y_{2}

weighs

9 g

, the atomic weights of

X

and

Y

are

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

The number of water molecules is maximum in

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

An unknown chlorohydrocarbon has 3.55 % of chlorine. If each molecule of the hydrocarbon has one chlorine atom only; chlorine atoms present in 1 g of chlorohydrocarbon are :(Atomic wt. of

Cl = 35 .5 u;

Avogadro constant

= 6 .023 \times 10^{23} {mol}^{- 1}

)

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

Mass % of carbon in ethanol is

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

The volume of oxygen at STP required to burn 2.4 g of carbon completely is:

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

A pure compound contains

2.4 g

C, 1.2 \times 10^{23}

atoms of

H, 0.2

moles of oxygen atoms. Its empirical formula is

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

The ratio of mass percent of

C and H

of an organic compound

(C_{X} H_{Y} O_{Z})

6 : 1 .

If one molecule of the above compound

(C_{X} H_{Y} O_{Z})

contains half as much oxygen as required to burn one molecule of compound

C_{X} H_{Y}

completely to

{CO}_{2}

and

H_{2} O .

The empirical formula of the compound

C_{X} H_{Y} O_{Z}

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Chemistry>Physical Chemistry>Some Basic Concepts of Chemistry>Empirical and Molecular Formulae

A compound has the following composition by weight;

N a = 18.60 %, S = 25.80 %, H = 4.02 %

and

O = 51.58 %

Assuming that all the hydrogen atoms in the compound are part of water of crystallization, the correct molecular formula of the compound is

If two compounds have the same empirical formula but different molecular formulae, they must have

Important Questions on Some Basic Concepts of Chemistry

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