Chemistry · JEE

Important Questions: Mole concept, molar mass, percentage composition, empirical and molecular formulae for JEE

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The most important Mole concept, molar mass, percentage composition, empirical and molecular formulae questions for JEE cover conceptual traps, standard results, and numerical patterns from Mole concept, molar mass, percentage composition, empirical and molecular formulae. Goodmarks provides 7+ high-yield MCQs with full solutions.

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Q1ChemistryUnit 1: Some Basic Concepts in Chemistry

What is the density of wet air with

75 \%

relative humidity at 1 atm and

300 \mathrm{K}

? Given : vapour pressure of

H_{2} O

is 30 torr and average molar mass of air is

29 g / m o l

Q2ChemistryUnit 1: Some Basic Concepts in Chemistry

Calculate the volume occupied by 40 g. of a

C H_{4}

\mathrm{S.T.P}

if its

\mathrm{V} . \mathrm{D}

. is 8

Q3ChemistryUnit 1: Some Basic Concepts in Chemistry

1.00 \mathrm{g}

of a hydrated salt contains

0.2014 \mathrm{g}

of iron,

0.1153 \mathrm{g}

of sulphur

0.2301 \mathrm{g}

of oxygen and 0.4532 g of water of crystallisation. If its empirical formula

(\boldsymbol{F e}=\mathbf{5 6} ; \boldsymbol{S}=\mathbf{3 2} ; \mathbf{0}=\mathbf{1 6})

F e S O_{x} \cdot y H_{z} O,

then find the value of

x, y

and

z

Q4ChemistryUnit 1: Some Basic Concepts in Chemistry

The formula that gives the symbolic representation of the actual number of atoms of various elements present in one molecule of the compound, is called:

Q5ChemistryUnit 1: Some Basic Concepts in Chemistry

A compound of sodium does not give

C O_{2}

when heated but it gives

C O_{2}

when treated with dilute acids. A crystalline compound is found to have 37.1\% Na and 14.52\%

\boldsymbol{H}_{\mathbf{2}} \boldsymbol{O}

. Hence, the compound is :

Q6ChemistryUnit 1: Some Basic Concepts in Chemistry

The composition of a sample of Wustite is

F e_{0.93}

O. What is the percentage of iron present as

F e^{3+}

in total iron?

Q7ChemistryUnit 1: Some Basic Concepts in Chemistry

A solution is prepared by adding 2 g of substance

A

to 18 g of water. The mass percent of the solute is:

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Important questions test core concepts that appear frequently across JEE Main and Advanced papers — definitions, standard formulas, and classic problem types.

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Key areas include Mole concept, molar mass, percentage composition, empirical and molecular formulae. Prioritise these before moving to edge cases.

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