MCQ Questions for Class 9 Chemistry Atoms And Molecules Quiz 4

A neutral atom of an element has a nucleus with a nuclear charge 13 times and mass 27 times that of hydrogen nucleus. What is the ratio of electrons to protons in its stable positively charged ion?

0%
27 : 13
0%
10 : 19
0%
10 : 13
0%
10 : 14

Explanation

Let the neutral atom of the element be

$X$ .

Given, the nuclear charge of

$X$ is 13 times that of the hydrogen nucleus.

$\Rightarrow$ Atomic number

$=13$

Mass of X is 27 times that of hydrogen nucleus

$\Rightarrow$ Mass number

$=27$ .

Since

$_{13}X^{27}, EC=2, 8, 3$

If X forms stable positively charged ion i.e.,

$X^{+3}$ (as it has 3 valence electrons in its valence shell)

$X^{+3}\rightarrow$ Atomic number

$=13-3=10.$ This implies number of electrons

$=10$ . Number of protons

$=13$ .

$Ratio=10 : 13$

When hydrogen burns in oxygen, _________ is produced.

0%
water
0%
hydrogen peroxide
0%
both A and B
0%
none of these

Explanation

When hydrogen burns in oxygen, water is produced.

The reaction is as follow:

$2H_2 + O_2 \rightarrow 2H_2O$

The percentage by mole of

${ NO }_{ 2 }$ in a mixture of

${ NO }_{ 2 }(g)$ and

$NO(g)$ having average molecular mass 34 is :

0%
25%
0%
20%
0%
40%
0%
75%

Explanation

Let

$x$ represent the percentage by mole of

${ NO }_{ 2 }$ in the mixture.

The molecular masses of

${ NO }_{ 2 }$ and

$NO$ are

$46$ g/mol and

$30$ g/mol respectively.

The average molecular mass of the mixture is

$\dfrac {46\times x +30\times (100-x)}{100}=34$ .

Hence,

$x= 25$ %.

The symbol for SI unit of mole is:

0%
mol
0%
mole
0%
M
0%
$m$

$N_2O$ is heavier than

$O_2$ .

0%
True
0%
False

Explanation

$N_2O (molar\ mass\ 44)$ is heavier than

$O_2 (molar\ mass\ 32)$ .

Various theories were put forward to study the nature of atom. The main postulates of Dalton's atomic theory are:

0%
Dalton's atomic theory proposed that all matter was composed of atoms.
0%
Dalton's atomic theory proposed that all matter was composed of molecules.
0%
All atoms of an element are identical.
0%
The atoms of different elements vary in size and mass.

According to Dalton's atomic theory, the smallest particle from which matter is made up of is called as:

0%
atom
0%
ion
0%
electron
0%
molecule

$1$ amu is equal to

$1.66\times 10^{-24}$ g.

0%
True
0%
False

Explanation

The atomic mass unit (amu) is equal to

$\frac{1}{12}$ of the mass of one atom of the carbon-12 isotope.

1 mole carbon-12 atoms weigh 12 g.

$6.022 \times 10^{-23}$ carbon -12 atoms weigh

$12g$ .

1 carbon-12 atom weighs

$\dfrac {12}{6.022 \times 10^{-23}} \ g$

$\therefore 1\ amu = \dfrac{1}{12} \times$ mass of one C-12 atom

$= \dfrac {1}{12}$

$\times \dfrac {12}{6.022 \times 10^{-23}}$

$= 1.66 \times 10^{-24} g$ or

$1.66 \times 10^{-27} kg$ .

The number of moles of '

$X$ ' atoms in

$93$ gm of 'X' are:

(Molecular Weight of

$X =31$ g/mole)

0%
$3$
0%
$3.5$
0%
$4$
0%
$2$

Explanation

As we know,
Number of moles of

$X$

$=w/Molecular \ Weight$
So the number of moles of

$X$

$= \dfrac{93}{31} = 3$

The number of atoms in

$60$ g of neon

$[Ne]$ are:

(Molar mass of

$Ne=20$ g/mole)

0%
$6 \times 6.022 \times 10 ^{23}$ atoms
0%
$2 \times 6.022 \times 10 ^{23}$ atoms
0%
$5 \times 6.022 \times 10 ^{23}$ atoms
0%
$3 \times 6.022 \times 10 ^{23}$ atoms

What mass of

$Na$ will contain

$6.023 \times 10^{23}$ number of atoms?

0%
$23$ g
0%
$46$ g
0%
$6.023$ g
0%
$11.5$ g

Explanation

One mole of each substance contains

$N_A = 6.023\times10^{23}$ atoms. Here

$N_A$ = Avogadro number.

Mass of one mole of atoms = Molar mass

So, the mass of one mole of

$Na$ =

$23$ g =

$6.023 \times 10^{23}$ number of atoms. (Atomic mass of

$Na$ =

$23$ u and molar mass is numerically equal to the atomic mass)
Hence, option A is correct.

Atomic number (Z) of a neutral atom and mass number (A) of an atom are equal to:

(Here n = number of neutrons and p = number of protons):

0%
Z = n and A = n+p
0%
Z = e and A = n+e
0%
Z = p and A = n+p
0%
Z = n and A = p+e

The number of potassium atoms present in

$117$ g of potassium sample (Molecular Weight

$= 39$ g/mole) is:

0%
$9 \times 6.023 \times 10 ^{23}$ atoms
0%
$7 \times 6.023 \times 10 ^{23}$ atoms
0%
$4 \times 6.023 \times 10 ^{23}$ atoms
0%
$3 \times 6.023 \times 10 ^{23}$ atoms

Explanation

As we know, one mole of each substance contains

$N_A = 6.023\times10^{23}$ atoms.

Here, moles of

$K$

$=\dfrac{117}{39} = 3$

$\therefore$ atoms of

$K$

$=3 N_A = 3\times6.023\times10^{23}$ atoms

Hence, option D is correct.

A/An______ is the smallest particle of a substance which can take part in a chemical reaction.

0%
atom
0%
molecule
0%
both A and B
0%
none of the above

The mass of one molecule of compound

${C}_{60}{H}_{122}$ is :

0%
$1.3\times {10}^{-20}g$
0%
$5.01\times {10}^{-21}g$
0%
$3.72\times {10}^{-23}g$
0%
$1.4\times {10}^{-21}g$

Explanation

Mass of one molecule of

${C}_{60}{H}_{122} =60\times C+122\times H= (12\times 60)+122\quad amu$

$=842\ amu$ (

$1amu = 1.66\times {10}^{-24}g$ )
(Atomic Mass Unit (amu): The atomic mass unit (amu) is equal to one twelfth of the mass of one atom of carbon-12 isotope.)

$=842\times 1.66\times {10}^{-24}g$

$=1.4\times {10}^{-21}g$

The number of nitrogen atoms in

$21$ g of nitrogen are:

(Molecular Weight of Nitrogen

$=14$ g/mole)

0%
$0.75$ $N_A$
0%
$1.5$ $N_A$
0%
$21$ $N_A$
0%
$14$ $N_A$

Explanation

Number of moles of nitrogen

$= \dfrac{21}{28} = 0.75$
So, the number molecules of nitrogen

$0.75 N_A$
The number of atoms of nitrogen

$\Rightarrow \ 2\times0.75 N_A = 1.5 N_A$

Which of the following is a suitable example for illustrating the law of conservation of mass? (Atomic mass of O = 16 u; H = 1 u)

0%
18g of water is formed by the combination of 16g oxygen with 2g of hydrogen.
0%
18g of water in liquid state is obtained by heating 18g of ice.
0%
18g of water is completely converted into vapour state on heating.
0%
18g of water freezes at $4^{o}C$ to give same mass of ice.

Explanation

According to law of conservation of mass
Mass of reactants

$=$ Mass of products

$H_2 + O_2\rightarrow 2H_2O$

$4 g$

$32 g$

$36 g$

$2 g$

$16 g$

$18 g$

$2g + 16g = 18 g$

Therefore, correct option is

$A$ .

The molecular mass of

$CuSO_4.5H_2O$ is:

(Atomic mass of

$Cu$

$=$ 63.5,

$H$

$=$ 1,

$O$

$=$ 16,

$S$

$=$ 32)

0%
233.5 gm/mole
0%
249.5 gm/mole
0%
251.5 gm/mole
0%
247.5 gm/mole

Explanation

The molecular mass of a compound is the sum of atomic masses of each element present in the molecule.

Molecular mass

$=$ Atomic mass of

$Cu$ + atomic mass of

$S$ + (9

$\times$ atomic mass of

$O$ ) + (10

$\times$ atomic mass of

$H$ )

$= 63.5+32+ 9 \times 16+10 \times 1 = 249.5\ gm/mole$

Which has a higher mass : 1 mole of

$CO_2$ or 1 mole of

$CO?$ (Mass of

$C=12,$ Mass of

$O=16$ )

0%
$CO_2$
0%
$CO$
0%
Both $CO_2$ and $CO$ have same mass
0%
None of the above

Explanation

As we know,
mass of one mole

$CO_2 = 44gm$ i.e.

$( 12+ (2\times 16)$
mass of one mole

$CO = 28gm$ i.e.

$( 12+ 16)$

Two elements always combine together in a fixed ratio by weight.

0%
True
0%
False

Explanation

The statement, "Two elements always combine in a fixed ratio by weight." is false. In a compound, their ratio of masses can remain fixed. But two elements can combine in different ratios to form different compounds.
For example, consider C and O. They combine to form

$CO$ and

$CO_2$ .
12 g of C combine with 16 g of O to form

$CO$ . The ratio by weight of C to O is

$12:16$ or

$3:4$ .
12 g of C combine with 32 g of O to form

$CO_2$ . The ratio by weight of C to O is

$12:32$ or

$3:8$ .
Thus, elements can combine in different ratios to form different compounds but the ratio remains fixed for a particular compound.

Consider the following statements:
(a) Molecular mass of

$CH_3OH$ is

$32\ u.$
(b) In

$NH_3$ , the ratio of

$N$ and

$H$ by mass is

$14: 3.$
(c) The formula mass of

$CaCl_2$ is

$111\ u.$
(d) Isotopes have same mass number.

Which of the above statements are correct?

0%
$\text {(a) and (c)}$
0%
$\text {(a), (b) and (d)}$
0%
$\text {(a), (b) and (c)}$
0%
$\text {(a), (c) and (d)}$

Explanation

a) Molecular mass of

$CH_3OH = 12 + 4 \times 1 + 16 = 32\ u$ . This is correct statement.

b) In

$NH_3$ , the ratio of

$N$ and

$H$ by mass is

$14:3.$ , This is correct statement.

c) Formula mass of

$CaCl_2 = 40 + 2 \times 35.5 = 111\ u$ . This is correct statement.

d) Isotopes have the same atomic number but different mass numbers. For example

$^{12}_6C$ and

$^{14}_6C.$ Hence given statement is incorrect.

Hence, option

$C$ is correct.

The molecular mass of

$(NH_4)_2CO_3$ is:

Given atomic mass of H = 1, O = 16, C = 12, N = 14.

0%
96 gm/mole
0%
98 gm/mole
0%
94 gm/mole
0%
80 gm/mole

Explanation

Molar mass

$(NH_4)_2CO_3 = 2\times18+12+3\times16 = 96 gm/mole$

Sodium chloride (

$NaCl$ ) reacts with silver nitrate (

$AgNO_3$ ) to produce silver chloride (

$AgCl$ ) and sodium nitrate (

$NaNO_3$ ). The law which satisfies this equation is ___________________ .

0%
conservation of mass
0%
conservation of energy
0%
newton's law
0%
dalton's law

Explanation

Reaction:

$NaCl+AgNO_3 \rightarrow AgCl+NaNO_3$

Mol : 1 mol 1 mol 1 mol 1 mol

Mass : 58.5 g 170 g 143.5 g 85 g

Total mass of reactants is equal to the total mass of products. This is the law of conservation of mass.

Two chemical species

$X$ and

$Y$ combine together to form a product

$P$ which contains both

$X$ and

$Y$

$X + Y \rightarrow P$

$X$ and

$Y$ cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning the species

$X, Y$ and

$P$ are correct?

(i)

$P$ is a compound
(ii)

$X$ and

$Y$ are compounds
(iii)

$X$ and

$Y$ are elements
(iv)

$P$ has a fixed composition

0%
(i), (ii) and (iii)
0%
(i), (ii) and (iv)
0%
(ii), (iii) and (iv)
0%
(i), (iii) and (iv)

State whether the given statement is true or false.

An atom is electrically neutral though it contains charged particles.

0%
True
0%
False

$1.2\, \times\, 10^{24}$ atoms of iron weighs ______ grams.

0%
$90$
0%
$111.5$
0%
$80$
0%
$70$

Explanation

For Fe atomic mass

$= 56$ g

$= 6.023 \times (10 )^{ 23 }$ atoms

$1.2 \times { 10 }^{ 24 }$ atoms

$=\quad \dfrac { 56 }{ 6.023\times { 10 }^{ 23 } } \times 1.2\times { 10 }^{ 24 }= 111.5$ g

An element A (atomic weight

$=12$ ) and B (atomic weight

$=35.5$ ) combines to form a compound X. If

$4$ mol of B combines with

$1$ mol of A to give

$1$ mol of X. The weight of

$1$ mol of X would be :

0%
47.5 g
0%
74.0 g
0%
154.0 g
0%
148.8 g

Explanation

Given:

Atomic weight of A= 12 and B= 35.5

A and B combine to form a compound X and the reaction can be given as:

$\begin{array}{l}\;\;\;\:\:\:4B\;\;\;\;+\;\;A\;\rightarrow X\\4\times35.5\;+\;12\rightarrow\;?\end{array}$

Weight of X = (

$4\times35.5$ ) +

$12$ = 154 g

So the correct option is C.

The number of electrons and protons are always equal in all atoms.

0%
True
0%
False

Which of the following options contains only elements?

0%
Air, water, oxygen
0%
Hydrogen, oxygen, brass
0%
Air, water, iron
0%
Calcium, sulphur, carbon

State True or False.

There is no difference between one mole and one gram molecule.

0%
True
0%
False

Explanation

The statement, "There is no difference between one mole and one gram molecule." is false.

One mole of any molecule corresponds to Avogadro's number of molecules, i.e,

$6.023 \times 10^{23}$ molecules.

One gram of any molecule is not equal to Avogadro's number of molecules. It is defined as the molar mass of any molecule equal to Avogadro's number of molecules.

State True or False.

Mass of reactants is always equal to the mass of the products. (Don't consider nuclear reaction)

0%
True
0%
False

Explanation

The statement, "Mass of reactants is always equal to the mass of the products. (Don't consider nuclear reaction)" is true. This is the statement of the law of conservation of mass.
For example, consider the combustion of

$C$ .

$C+O_2 \rightarrow CO_2$
The molar masses of

$C$ ,

$O_2$ and

$CO_2$ are 12 g/mol, 16 g/mol and 44 g/mol respectively.
Total mass of reactants for combustion of 1 mole of

$C$ is

$12+32=44 \: g$ .
The total mass of products for combustion of 1 mole of

$C$ is

$44 \: g$ .

Hence the mass of the reactants is equal to the mass of the products.

Law of conservation of mass was put forward by :

0%
Lavoisier
0%
Dalton
0%
Priestly
0%
Thomson

A compound was found to contain

$5.37\ \%$ of Nitrogen. What is the minimum molecular weight of the compound?

0%
26.07 g
0%
2.607
0%
260.7
0%
None

Explanation

$100$ g of compound contains

$5.37$ g of nitrogen.

$\therefore$ The number of moles of nitrogen is

$\dfrac {5.37}{14}=0.3835$ moles.
Hence, the minimum molecular weight of the compound is

$\dfrac {100}{0.3835}=260.7$ g/mol.

Option

$C$ is correct.

Atomic mass of an element is:

0%
actual mass of one atom of the element
0%
average mass of an atom of different atoms of the element
0%
always a whole number
0%
None of these

All samples of carbon dioxide contain carbon and oxygen in the mass ratio of

$3 : 8$ . This is in agreement with the law of :

0%
conservation of mass
0%
constant proportion
0%
multiple proportions
0%
gaseous volumes

An organic compound contains

$4$ % sulphur. Its minimum molecular weight is :

0%
200
0%
400
0%
800
0%
1600

Explanation

$4$ g sulphur is in

$100$ g compound, hence

$32$ g sulphur is in

$=\left (\frac {100}{4}\times 32\right )=800 g$ compound.

Which of the following is not a compound?

0%
Oxygen
0%
Water
0%
Sugar
0%
Common salt

Explanation

Oxygen is an element and not a compound as its molecule is made up of only one kind of atom,

$O_2$ . Whereas, water(

$H_2O$ ), sugar(

$C_{12}H_{22}O_{11}$ ) and common salt (

$NaCl$ ), are all made up of two more different kinds of atoms, hence they are all known as compounds.

So, option A is correct.

The smallest particle of a substance (element or compound) which has the properties of that substance and can exist independently is called a ..............

0%
Molecule
0%
Atom
0%
Nucleus
0%
Neutrons

Explanation

The smallest particle of a substance (element or compound) which has the properties of that substance and can exist independently is called a

$molecule$ .

.............. is the smallest unit of an element that maintains the properties of that element.

0%
electron
0%
atom
0%
proton
0%
ions

Explanation

An atom is the smallest particle which consists of electros, protons and neutrons in it.

$\therefore$ Option

$B$ is correct.

Calculate the molecular mass of

$H_2O$ (Water)

0%
$18$
0%
$36$
0%
$20$
0%
$16$

Explanation

Molecular mass of

$H_2O$ is

${2+16=18}$

$\therefore$ Option

$A$ is correct.

An atom which is deficient of electrons is called a ________ .

0%
positive ion
0%
proton
0%
negative ion
0%
none of these

Molecules are the components of:

0%
Solutions
0%
Gases
0%
Solids
0%
All of the above

State True or False.
The smallest particle of an element is molecule.

0%
True
0%
False

Explanation

Smallest particle of element is atom.

Hence the statement is False.

Hence

$B$ is correct option.

When hydrogen and oxygen combine to form water, they form:

0%
an unstable compound
0%
a stable mixture
0%
an unstable mixture
0%
an extremely stable compound

Explanation

When hydrogen and oxygen combine to form water, they form water an extremely stable compound. We can say water is a stable compound because tremendous energy is released is a signal that it is very hard to break water molecules into the original components.

$2H_2+O_2\longrightarrow 2H_2O$

3 g of a hydrocarbon on combustion in excess of oxygen produces 8.8 g of

$CO_2$ and 5.4 g of

$H_2O$ .

The data illustrates the law of :

0%
Conservation of mass
0%
Multiple proportions
0%
Constant proportions
0%
None of the above

Explanation

Mass of carbon in 8.8 g

$CO_2 = \dfrac {12}{44} \times 8.8 = 2.4 \ g$

Mass of hydrogen in 5.4 g

$H_2O = \dfrac{2}{18} \times5.4 = 0.6 \ g$

Total mass

$( C + H )= 2.4 + 0.6 = 3.0 \ g$

Mass of hydrocarbon = 3.0 g (given)

These data illustrate the law of conservation of mass.

Option (A) is correct.

The weights of two elements which combines with one another are in the ratio of their:

0%
atomic weight
0%
molecular weight
0%
equivalent weight
0%
none of the above

Explanation

According to the law of multiple proportions, when two elements combine to form more than one compound, the weight of one element combined with a fixed weight of the other is in a ratio of small whole numbers.

Hence, the weight of two elements that combine is in the ratio of their atomic weight.

So, the correct option is

$A$ .

Weight of oxygen in

$32.2$ g

$\displaystyle Na_{2}SO_{4}$ .

$\displaystyle 10H_{2}O$ is:

0%
20.8 gm
0%
22.4 gm
0%
2.24 gm
0%
2.08 gm

Explanation

Moles of the given compound =

$\displaystyle \frac{32.2}{322}=0.1 \ mol$

Each molecule contains

$14 \ O \ atoms$

Moles of oxygen

$= 14\times0.1 = 1.4\ moles$

Weight of oxygen=

$1.4\times16 = 22.4 \ g$

Modern atomic mass scale is based on the mass of:

0%
$H - 1$
0%
$C - 12$
0%
$C - 14$
0%
$C - 16$

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 equal to

$1.6605 \times 10^{-19} \: g$ .
amu is also called as avogram.
Avogram is a unit of mass and weight equal to one gram divided by the Avogadro's number.

Weight of oxygen in

$Fe_2O_3$ and FeO is in the ratio of :

0%
$3 : 2$
0%
$1 : 2$
0%
$2 : 1$
0%
$3 : 1$

Explanation

$Fe_2O_3$ =

$48g$ oxygen

$FeO = 16g$ oxygen
ratio of oxygen in

$Fe_2O_3$ :oxygen in

$FeO = 3:1$

The percentage of copper and oxygen in a sample of CuO obtained from different methods were found to be same. This proves the law of :

0%
Constant proportion
0%
Multiple proportion
0%
Reciprocal proportion
0%
None of these

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 4 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 4 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

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