Number of molecules present in one gram molecular mass of a substance

Number of atoms in one gram of element

Number of millilitres which one mole of a gaseous substances occupies at $$NTP$$

MCQ Questions for Class 9 Chemistry Atoms And Molecules Quiz 11

Iron forms two oxides, in first oxide

$56$ grams of Iron is found to be combined with

$16$ gram oxygen and in second oxide

$112$ gram of Iron is found to be combined with

$48$ gram oxygen. This data satisfy the law of

0%
Conservation of mass
0%
Reciprocal proportion
0%
Multiple proportions
0%
Combining volume

Specific volume of cylindrical virus particle is

$6.02 \times {10^{ - 2}}\,\,cc/gm$ whose radius and length are 7 A and 10 A respectively. If

${N_A} = 6.02 \times {10^{23}}.$ Find molecular weight of virus.

0%
$15.4\,\,kg/mol$
0%
$1.54 \times {10^4}\,\,kg/mol$
0%
$3.08 \times {10^4}\,\,kg/mol$
0%
$3.08 \times {10^3}\,kg/mol$

The number of electrons in

$3.1\ mg\ NO_{3}^{-}$ is ______.

$(Given: N_{A}=6\times 10^{23})$

0%
$1.6\times 10^{-3}$
0%
$9.6 \times 10^{20}$
0%
$32$
0%
$9.6 \times 10^{23}$

Explanation

Given that

Mass of

$NO_{3}^{-}, W_{NO_{3}^{-}} = 3.1\ mg = 3.1\times 10^{-3} g$

Molar mass of

$NO_{3}^{-}, M_{NO_{3}^{-}} = 62\ g/mol$

$\therefore$ Moles of

$NO_{3}^{-}, n_{NO_{3}^{-}} = \dfrac {W_{NO_{3}^{-}}}{M_{NO_{3}^{-}}}$

$= \dfrac {3.1\times 10^{-3} g}{62g/mol} = 5\times 10^{-5} mol$

$1\ NO_{3}^{-}$ contain

$32$ electrons.

$\therefore$ Number of electron

$(N_{e}) = 32\times n_{NO_{3}^{-}} \times N_{A}$

$= 32 \times (5\times 10^{-5}) \times 6.022\times 10^{23}$

$= 9.6352 \times 10^{20}$

$= 9.6\times 10^{20} electrons$

Hence, option B is correct.

Arrange the following in order of decreasing masses:

0%
$10 ^ { 23 }$ molecules of $\mathrm { CO } _ { 2 }$ gas
0%
0.1 g atom of silver
0%
I gram of carbon
0%
0.1 mole of $\mathrm { H } _ { 2 } \mathrm { SO } _ { 4 }$
0%
$10 ^ { 23 }$ atoms of calcium.

The number of moles in

$1.6 \times 10^4$ grams of

$Ca(OH)_2$ are

0%
2.162
0%
21.62
0%
0.2162
0%
216.2

The weight of sulphuric acid needed for dissolving

$3 \mathrm { gm }$ magnesium carbonate is:

0%
$3.5 \mathrm { gm }$
0%
$7.0 \mathrm { gm }$
0%
$1.7 \mathrm { gm }$
0%
$17.0 \mathrm { gm }$

Explanation

The balanced equation is:

$H_2SO_4 + MgCO_3 \rightarrow MgSO_4 + H_2CO_3$

$98\ g$

$84 \ g$

Since,

$84 \ g \ MgCO_3 \ requires = 98 g \ H_2SO_4$

Therefore,

$3\ g$ of

$MgCO_3$ =

$\dfrac{98\times3}{84} = 3.5 \ g$

The present atomic weight scale is based on:

0%
$^{12}{ C }$
0%
$^{16}{ O }$
0%
$^{1}{ H }$
0%
$^{13}{ C }$

Explanation

The modern atomic weight scale is based on

$^{12}C$ . All the masses are measured relative to

$\text{carbon-12}$ . It is the standard unit for expressing the mass of an atom in amu (atomic mass unit). It is equal to the

$\cfrac {1}{12}$ of the mass of the atom of carbon-12.

Option

$A$ is correct.

The relative formula mass

$(M_{r})$ of calcium carbonate

$(CaCO_{3})$ is

$100$ . What is the mass of carbon present in

$100\ g$ of calcium carbonate?

0%
$12\ g$
0%
$36\ g$
0%
$40\ g$
0%
$60\ g$

Explanation

Solution:- (A)

$12 \ g$

The relative formula masses

$\left( {M}_{r} \right)$ of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.

Mass of

$1$ mole of carbon

$= 12 \; g$

$CaC{O}_{3}$ contains only

$1$ mole of carbon, thus the mass of carbon present in

$100 \; g$ calcium carbonate, i.e.,

$1$ mole

$CaC{O}_{3}$ is

$12 \; g$ .

A compound contains

$7$ carbon atoms,

$2$ oxygen atoms and

$9.96\times 10^{-24}\,g$ of other elements. The molecular mass of compound is

$(N_A =6\times 10^{23})$

0%
$122$
0%
$116$
0%
$148$
0%
$154$

Explanation

Molecular mass

$=(7\times 12)+(2\times 16)+(9.96\times 10^{-24})\times 6.02\times 10^{23}$

$=84+32+6$

$=$

$122\ gm$
option

$(a)$

The volume of one mole of water at

$277\ K$ is

$18\ ml$ . One

$ml$ of water contains

$20$ drops. The number of molecules in one drop of water will be

$(N_{A}=6\times 10^{23})$

0%
$1.07\times 10^{21}$
0%
$1.67\times 10^{21}$
0%
$2.67\times 10^{21}$
0%
$1.67\times 10^{20}$

Explanation

$1$ mole

$=185\ ml$ (given)

$1\ ml=20\ drops$

$\therefore 1$ mole

$=18\times 20$

$=3360\ drops$ .

$1$ mole

$=6.022\times 10^{23}$ molecules

$\Rrightarrow 360\ drops=6.022\times 10^{23}$ molecules

$\therefore 1\ drops=x$ molecules

$360\times x=1\times 6.022\times 10^{23}$

$x=1.67\times 10^{21}$ molecules

Hence, Option

$B$ is the correct answer.

For

$CuSO_4.5H_2O,$ which is the correct mole relationship?

0%
mole of $Cu= 9 \times mole\ of\ O$
0%
mole of $Cu= 4 \times mole\ of\ O$
0%
mole of $Cu= 5 \times mole\ of\ O$
0%
mole of $O= 9 \times mole\ of\ Cu$

Molecular mass of dry air is ________________.

0%
less than moist air
0%
greater than moist air
0%
equal to moist air
0%
may be greater or less than moist air

Explanation

The molecular mass of dry ice is greater than moist air.

As dry air consists of nitrogen and oxygen while moist air contains water vapour which less mass than that of oxygen and nitrogen making the mass of moist air lower.

$M.M$ of dry air

$\simeq 28.9\ gm$

$M.M$ of moist air

$< 28.9\ gm$

Cortisone is a molecular substance containing

$21$ atoms of carbon per molecule. The mass percentage of carbon in cortisone is

$69.98$ %. What is the molecular mass of cortisone?

0%
$180.05$
0%
$360.1$
0%
$312.8$
0%
$205.8$

Explanation

Here $69.98$ % of carbon.

i.e $100$ gram of cortisone $\equiv 69.98\ gram\$ Carbon

As $21$ atoms of carbon per molecules

$\therefore 21\times 12=252\ gram$ Carbon

$100\ gram$ Cortisone $\equiv 69.98\ gram$ Carbon

$x\ gram$ cortisone $\equiv 252\ gram$ Carbon

$\therefore x=\dfrac{100\times 252}{69.98}$

$=360.1\ gram/mole$

$\therefore$ Option $B$ correct

Equivalent mass of a bivalent metal is

$32.7$ Molecular mass of its chloride is _____________.

0%
$68.2$
0%
$103.7$
0%
$136.4$
0%
$4166.3$

Explanation

Given that,

Equivalent weight of metal

$= 32.7$

As the given metal is bivalent, so charge on metal

$= 2$

Molar mass of metal

$= 2 \times 32.7$

$=65.4$

The chloride of given metals

$= MCl_{2}$

$= 65.4 +( 2 \times 35.5$ )

$= 65.4 + 71$

$= 136.4 \, gm^{-1}$

So, the correct option is

$C$

What is the definition of relative atomic mass,

$A_{r}$ ?

0%
$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C}\right )\times 12$
0%
$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C \times 12}\right )$
0%
$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C}\right )$
0%
$\left (\dfrac {\text {mass of one atom of}^{12}C}{\text {average mass of naturally occurring atoms of an element}}\right )$

Explanation

It is the ratio of the average mass per atom of an element from a given sample to

$\cfrac{1}{12}$ the mass of a carbon-

$12$ atom.

Relative atomic mass,

${A}_{r} = \left( \cfrac{\text{average mass of naturally occurring atoms of an element}}{\text{mass of one atom of } {^{12}{C}}} \right) \times 12$

Hence, option A is correct.

The molecular mass of a compound containing only one nitrogen atom can be

0%
$73$
0%
$74$
0%
$146$
0%
$148$

Explanation

Compounds containing one

$N$ atom always have odd molecular weights, i.e.

$73$ here.

The minimum mass of water needed to slake

$1\ kg$ of quicklime, assuming no loss by evaporation, is:

0%
$243.2\ g$
0%
$642.8\ g$
0%
$160.7\ g$
0%
$321.4\ g$

Explanation

$CaO+H_2O\longrightarrow Ca(OH)_2$

moles of

$CaO=\dfrac {1000}{56}=17.85$ moles

$1$ mole

$CaO\equiv 1$ mole

$H_2O$

mass of

$H_2O\equiv 17.85\times 18$

$=321.42$ gram

So, the correct option is

$D$

A sample of ozone gas is found to be

$40\%$ dissociated into oxygen. The average mass of sample should be

0%
$41.60$
0%
$40$
0%
$42.35$
0%
$38.40$

Explanation

Given that,

$\alpha = 40\% = 0.4$

$2O_{3} \longrightarrow 3O_{2}$

$O_{3} \longrightarrow \dfrac {3}{2} O_{2}$
We know that,

$\alpha = \dfrac {D-d}{(n-1)d}$

$D=\dfrac {48}{2} =24,\ d = ?,\ n = \dfrac {3}{2} = 1.5$

$0.4 = \dfrac {24-d}{(1.5-1)d} = \dfrac {24-d}{0.5d}$

$0.2d=24$

$d= \dfrac {24}{12} = 20$
Molar mass

$= 2 \times 20 = 40$

The number of hydrogen atoms in

$0.9\ g$ glucose

$C_{6}H_{12}O_{6}$ , is same as

0%
$0.48\ g$ hydrazine, $N_{2}H_{4}$ `
0%
$0.17\ g$ ammonia, $NH_{3}$
0%
$0.30\ g$ ethane, $C_{2}H_{6}$
0%
$0.03\ g$ hydrogen $H_{2}$

Explanation

$C_{5}H_{12}O_{6}\longrightarrow 12\ H$

$180\ gm\longrightarrow 12$ moles

$0.9\ gm\longrightarrow x$ moles

$x=\dfrac{12\times 0.9}{180}=\dfrac{0.3}{5}=0.06$
No.of hydrogen atom

$=0.06\times r\times 10^{23}$

$=3.6\times 10^{22}$ atoms

(a)

$M_{2}H_{2}\rightarrow 4H$

$32\ gm$

$4$ moles

$0.48\ gm \rightarrow x$ mol.

$x=\dfrac{4\times 0.48}{32}=0.06\ moles\Rightarrow 3.6\times 10^{22}$ atoms

(b)

$NH_{3}\rightarrow 3H$

$17\ gm$

$3$ moles

$0.17\ gm$

$0.03\ moles$

(c)

$C_{2}H_{6}\rightarrow 6H$

$30\ gm$

$6\ mole$

$0.30$

$0.06\ mole$

(d)

$H_{2}\rightarrow 2H$

$2\ gm\longrightarrow 2$ moles

$0.03$

$0.03$ mole

The percentage of copper and oxygen in samples of

$CuO$ obtained by different methods were found to be the same. This illustrates the law of

0%
Constant proportions
0%
Conservation of mass
0%
Multiple proportions
0%
Reciprocal proportions

Explanation

In chemistry, the law of constant proportions, or the law of definite composition, states that a chemical compound always contains exactly the same proportion of elements by mass and this law further says that, in any particular chemical compound, all samples of that compound will be made up of the same elements in the same proportion or ratio. For example, any water molecule is always made up of two hydrogen atoms and one oxygen atom in a ratio.

Here the percentage of copper and oxygen obtained by the different methods are the same in

$CuO$ which indicates that it illustrates the law of constant proportion.

Option

$A$ is correct.

Which phrase would be incorrect to use:

0%
A molecule of a compound
0%
An atom of an element
0%
An atom of a molecule
0%
None of these

Which of the following statement (s) is/are correct about the Avogadro's number ?

0%
It is the number of atoms contained in one mole of any element.
0%
It is the number of electrons required to deposit one mole of atoms of any metallic element from a solution of its salt.
0%
It is the number of grams of any element that contains its $6.022\times 10^{23}$ atoms.
0%
It is the number of particles (atoms, molecules or ions) required to make one gram of the substance under consideration

Pressure of

$1$ g of an ideal gas A at

$27^o$ C is found to be

$2$ bar. When

$2$ g of another ideal gas B is introduced in the same flask at same temperature the pressure becomes

$3$ bar. What is the relationship between their molecular masses?

0%
$2M_B=M_A$
0%
$M_B=M_A$
0%
$M_B=4M_A$
0%
$M_B=2M_A$

Explanation

Let, the molecular masses of

$A$ and

$B$ be

$M_A$ and

$M_B$

$(2)\times(V)=\left(\dfrac{1}{M_A}\right)\times(R)\times(300)$

$(3)\times(V)=\left(\dfrac{1}{M_A}+\dfrac{2}{M_B}\right)\times(R)\times(300)$

$\therefore \dfrac{2}{3}=\dfrac{\dfrac{1}{M_A}}{\dfrac{1}{M_A}+\dfrac{2}{M_B}}$

$\therefore \dfrac{2}{M_A}+\dfrac{4}{M_B}=\dfrac{3}{M_A}$

$\therefore \dfrac{4}{M_B}=\dfrac{1}{M_A}$

$\therefore \dfrac{M_A}{M_B}=\dfrac{1}{4}$

$\therefore M_B=4M_A$

So, the correct option is

$C.$

Avogadro number is

0%
Number of atoms in one gram of element
0%
Number of millilitres which one mole of a gaseous substances occupies at $NTP$
0%
Number of molecules present in one gram molecular mass of a substance
0%
All of these

Explanation

Avogadro number is the Number of molecules present in one mole (gram molecular mass)of a substance

and is equal to

$6.02\times 10^{23}.$

The composition of universe is approximately

$90\%$ hydrogen and

$10\%$ helium, by mass. It represented that

0%
there are $18$ hydrogen atoms in the universe per atom of helium.
0%
there are $9$ hydrogen atoms in the universe per atom of helium.
0%
there are $36$ hydrogen atoms in the universe per atom of helium
0%
the average molar of universe is $2.20\ g$ per mole

Explanation

$9\% H=90\ am\ H$ in

$100\ am$ universe

$10\% He=10\ am\ He$ in

$100\ am$ universe
No. of gram atoms of

$H=\dfrac{90}{1}=90$
No. of gram atoms of

$He=\dfrac{10}{4}=2.5$

$\dfrac{no.of\ H\ atom}{No.of\ He\ atoms}=\dfrac{40}{2.5}=36$

So ans is option

$c$

$ave.ml.mass=\dfrac{\% of H\times of +\%\ of\ He\times at}{100}$

$=\dfrac{90\times 2+10\times 4}{100}$

$=\dfrac{220}{100}=2.2\ gm/mole$
So ans option

$d$

If the atomic weight of carbon were set at 24 amu, the value of the Avogadro constant would be:

0%
$6.022 \times 10^{23}$
0%
$12.044 \times 10^{23}$
0%
$3.011 \times 10^{23}$
0%
None of these

Explanation

1 amu

$\times N_A = 1g$ [ from general definition ]

Wt of 1 mole of

$C^{12} = 12 g$

If mass of one atom of

$C^{12}$ is set to be 24 amu then ( mass of one atom

$\times$ avogadro's no = mass of 1 mole of

$C^{12}$ )

$24 amu \times N_A = 12 g$

$N_A =\dfrac {12 g}{24 amu}= \dfrac {12g}{ 224 \times \dfrac {1}{6.023 \times 10^{23} g } }$

$= \dfrac {6.023}{2} \times 10^{23} = 3.011 \times 10^{23}$

Hence, Option "C" is the

1 amu is equal to

0%
$\dfrac{1}{12}$ of C-12
0%
$\dfrac{1}{14}$ of O-16
0%
$1\,g$ of hydrogen
0%
$1.66 \times 10^{-23} kg$

The modern atomic weight scale is based on

0%
$C^{12}$
0%
$O^{16}$
0%
$H^1$
0%
$C^{13}$

Explanation

Modern atomic weight scale is based on

$C^{12}$ . The standard unit for expressing the mass of atom is amu (atomic mass unit). It is equal to 1/12 of the mass of an atom of carbon-12.

In water, the proportion of oxygen and hydrogen by mass is:

0%
$1: 4$
0%
$1 : 8$
0%
$4 : 1$
0%
$8 : 1$

Explanation

The chemical formula of water is

$H_2O$ . The molar mass of oxygen and hydrogen is

$16$ and

$1 \ g/mol$ respectively. Water has

$2H$ and one oxygen atom.

In water, the ratio of oxygen to hydrogen is

$8:1$ by mass.

Hence, option D is correct.

Which of the following postulates of Dalton's atomic theory is challenged by the next generation's scientists?

0%
All matter is made of very tiny particles called atoms,
0%
Atoms are particles, which cannot be created or destroyed in a chemical reaction.
0%
Atoms of a given elements are identical in mass, shape and chemical properties
0%
None of the above

Explanation

According to the postulate of Dalton's atomic theory that 'atoms of a given element are identical in mass, shape and chemical properties' was challenged after the discovery of isotopes by the next-generation scientist. After the discovery of mass spectrometry, it was found that some elements have the same atomic number but a different mass number (isotopes).

For example, there are two types of chlorine atoms

$^{35}Cl$ and

$^{37}Cl$ having mass

$35$ amu and

$37$ amu.

After the discovery of isotopes, it was concluded that atoms of all elements may not be similar in all respect.

A molecule can be defined as the:

0%
A group of two or more atoms that are chemically bonded together
0%
The smallest particle of an element or a compound that is capable of independent existence and shows all the properties of that substance
0%
The substance which is formed by the combination of atoms of the same element or of different elements
0%
All these are correct.

Explanation

A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound. A molecule is formed by the combination of atoms of the same element or of different elements.

So, all the statements are correct.

Thus option

$D$ is correct.

Write true or false for the following statements:
A compound is a substance composed of two or more elements, chemically combined in a fixed proportion.

0%
True
0%
False

Which of the following is not an element?

0%
Oxygen gas
0%
Carbon dioxide gas
0%
Sulphur dioxide gas
0%
Nitrogen dioxide gas
0%
All of the above

Explanation

Elements are pure substances that cannot be further broken down into simpler substances.

Oxygen gas, Carbon dioxide gas, sulphur dioxide gas, nitrogen dioxide gas are examples of compounds and they can be further broken down into elements by chemical reactions. There is no element in the given options.

Hence, option

$E$ i.e. All of the above is the correct answer.

Which of the following represents amu?

0%
Mass of 1 hydrogen atom
0%
Mass of C-12 atom
0%
mass of O-16 atom
0%
1/12th of mass of C-12 atom

Explanation

An atomic mass unit (symbolized amu) is defined as precisely

$\frac{1}{12}th$ the mass of an atom of carbon-12. The carbon-12 (C-12) atom has six protons and six neutrons in its nucleus.

Hence, option

$D$ is correct.

Write true or false for the following statement:
One atomic mass unit is a mass unit equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12.

0%
True
0%
False

In water, the ratio of the mass of hydrogen to the mass of oxygen is always

$1 : 8$ , whatever is the source of water.

0%
True
0%
False

Explanation

Law of constant proportions states that "In a chemical substance, the elements are always present in definite proportions by mass”.
Water, being a chemical substance, the ratio of the mass of hydrogen to the mass of oxygen will always be

$1: 8$ . Whatever be the source of water.

Hence, the above statement is true.

One of the statements of Dalton's atomic theory is given below:
Compounds are formed when atoms of different elements combine in a fixed ratio.
Which of the following laws is/are not related to this statement?

0%
Law of conservation of mass
0%
Law of definite proportions
0%
Law of multiple proportions
0%
Avogadro law

Which of the following reactions is not according to the law of conservation of mass?

0%
$2Mg(s)+O_2(g)\to 2MgO(s)$
0%
$C_3H_3(g)+O_2(g)\to CO_2(g)+H_2O(g)$
0%
$P_4(s)+5O_2(g)\to P_4O_{10}(s)$
0%
$CH_4(g)+2O_2(g)\to CO_2(g)+2H_2O(g)$

Mass is measure of the amount of matter.

0%
True
0%
False

Fill in the blanks:-

The formula unit mass of

$Ca_3(PO_4)_2$ is_______.

0%
310
0%
270
0%
330
0%
410

Explanation

Formula unit mass of

$Ca_3{(PO_4)}_2$

$= (3 \times atomic \ mass \ of \ Ca) + (2 \times atomic \ mass \ of \ P) + (8 \times atomic \ mass \ of \ oxygen)$

$=(3 \times 40) + (2 \times 31) + (8 \times 16)$

$=310$

$\therefore$ The formula unit mass of

$Ca_3{(PO_4)}_2$ is

$310$

Hence, option A is correct.

The smallest part of an element capable of independent existence is called an atom.

0%
True
0%
False

The smallest part of the matter, capable of independent existence is called an atom.

0%
True
0%
False

The central part of the atom is called the nucleus.

0%
True
0%
False

Explanation

$\text{True}$

The central part of the atom is called the nucleus. It contains protons and neutrons which are collectively called nucleons.

The outermost shell of an atom is known as

0%
valency
0%
valence electrons
0%
nucleus
0%
valence shell

Write 'true' or 'false' for the following statement:
An atom on the whole has a positive charge.

0%
True
0%
False

Choose the correct answer from the options given below.
In water, the hydrogen-to-oxygen mass ratio is:

0%
$1 : 8$
0%
$1 : 16$
0%
$1 : 32$
0%
$1 : 64$

Explanation

The molecular formula of water is

$H_2O$

Mass of H

$= 1$

Mass of O

$= 16$

Ratio of mass

$= (2 \times H):O$

$=(2\times1):16$

$=2:16$

$=1:8$

Which of the following substance is made up of only one type of particle?

0%
compound
0%
element
0%
mixture
0%
mixed metal

Explanation

$\text{Element}$ is the substance made up of only one type of particle.

Sugar, salt, water, ammonia are:

0%
elements
0%
compounds
0%
mixtures
0%
All of the above

According to Daltons atomic theory atoms are indestructible.

0%
True
0%
False

Explanation

$True$

According to Dalton's atomic theory atoms are indestructible. But further studies revealed that atoms can also be broken down. There is a nucleus present at the center of the atom. The nucleus has a proton, neutron, fermion, and many other subatomic particles. Electrons are revolving around the nucleus in some specific orbits. So this aspect of Dalton's atomic theory that atoms are indestructible was not correct.

Which one of the following is the standard for atomic mass?

0%
${ }_{1}^{1} \mathrm{H}$
0%
${ }_{6}^{12} \mathrm{C}$
0%
${ }_{6}^{14} \mathrm{C}$
0%
${ }_{8}^{16} \mathrm{O}$

Explanation

${ }_{6}^{12} \mathrm{C}$ is the standard for atomic mass.

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 11 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 11 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

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