MCQ Questions for Class 9 Chemistry Atoms And Molecules Quiz 7

When mass is enclosed in a system and no transfer of material and energy is allowed in or out, it's _____ will never change.

0%
quality
0%
quantity
0%
temperature
0%
shape

During any chemical change, the total mass of the products is equal to the total mass of reactants. This is a statement according to:

0%
Law of conservation of mass
0%
Law of constant composition
0%
Law of multiple proportion
0%
Law of reciprocal proportion

$AgNO_3+NaCl\rightarrow AgCl+NaNO_3$ . In this reaction, mass of

$AgNO_3$ and

$NaCl$ is equal to the mass of

$AgCl$ and

$NaNO_3$ . Then this chemical reaction satisfies:

0%
Law of constant composition
0%
Law of conservation of mass
0%
Gay Lussac's law
0%
Law of multiple proportion

When magnesium is burnt in air, the weight of magnesium :

0%
increases
0%
decreases
0%
remains same
0%
Depends on the atmosphere

Explanation

When magnesium is burnt in air, the weight of magnesium increases due to the formation of

$MgO$ .

$2Mg+O_2\rightarrow 2MgO$

Magnesium + Oxygen

$\longrightarrow$ Magnesium Oxide + Oxygen

48.6 g + 50.0 g

$\longrightarrow$ 80.6 g + ?

Predict the mass of oxygen that will be left over after the reaction of 48.6 grams of magnesium with 50.0 grams of oxygen.

0%
20.6
0%
19.6
0%
18
0%
17.6

Explanation

According to law of conservation of mass, the total mass of reactants must equal the total mass of products
If we assume the mass of oxygen as

$X$ g then,

Total mass of reactants = Total mass of products

$48.6+50=80.6+X$

$X = 18\ g$

The chemical equation is balanced to satisfy one of the following laws in chemical reactions. This law is known as the:

0%
law of conservation of mass.
0%
law of multiple proportions
0%
law of chemical equilibrium.
0%
none of these

The matter is neither created nor destroyed during any physical or chemical change. This statement is of the :

0%
Law of constant proportion
0%
Law of conservation of mass
0%
Law of reciprocal proportion
0%
Law of multiple proportion

Explanation

The law of conservation of mass states that "the matter is neither created nor destroyed during any physical or chemical change".

The Law of conservation of Mass states that matter can be changed from one form into another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass remains constant. The total mass of the universe is constant within measurable limits.

Option

$B$ is correct.

Calculate the mass (in grams) of one molecule of

$CH_{3}COOH$ .

(Molar mass of

$CH_{3}COOH = 60.06\ g/ mol$ )

0%
$9.97\times 10^{-23}$
0%
$60.06$
0%
$9.97\times 10^{23}$
0%
None of above

Explanation

The molar mass of

$CH_3COOH$ is given as

$60.06\ g/mol$

We need to find the mass of 1 molecule of

$CH_3COOH$

We can use this formula:

$Number\ of\ atoms = \dfrac {mass} {molar\ mass} \times Avogadro\ number$

We can substitute the following values in the formula:

$Number\ of\ atoms = 1$

$Molar\ mass = 60.06\ g/mol$

$Avogadro\ no. = 6.022 \times 10^{23}$

$Number\ of\ atoms = \dfrac {mass} {molar\ mass} \times Avogadro\ number$

$\therefore 1 = \dfrac {mass} {60.06} \times 6.022 \times 10^{23}$

$mass = \dfrac {60.06} {6.022 \times 10^{23}}$

$= 9.973 \times 10^{-23}\ g$

What are the merits of Dalton's atomic theory?

0%
Explains laws of chemical combination
0%
Explains the law of conservation of mass
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Both A and B
0%
Atoms can not be rearranged, combined or separated in a chemical reaction.

In a compound, the ratio of the atoms or element by mass remains always the same irrespective of :

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temperature
0%
nature of compound
0%
source of compound
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size of compound

Explanation

Compounds are formed by the combination of two or more elements. In a compound, the ratio of the atoms or element by mass remains always the same irrespective of the source of the compound. This means a certain compound always formed by the combination of atoms in the same ratio by mass. If the ratio of the mass of constituent atoms will be altered the new compound is formed.

Hence, option

$C$ is correct.

A solution of copper oxide was prepared by heating, igniting and precipitation. Which of the following method will give higher ratio of copper oxide?

0%
Heating
0%
Precipitation
0%
Ignition
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All of the above will give the same ratio

Dalton’s atomic theory was based on:

0%
Law of chemical combination
0%
Mass theory
0%
Periodic table
0%
None of the above

Explanation

When substances react, they do so by following certain laws. These laws are called the laws of chemical combination. Law of conservation of mass, the law of definite proportions, the law of multiple proportions, Gay lussac's law of gaseous volumes, Avogadro's law. These formed the basis of Dalton's atomic theory of matter.

Dalton explained about atoms on the basis of the Laws of Chemical Combinations.

So, the correct option is

$A$ .

______ are the smallest unit of matter that can take part in a chemical reaction.

0%
Molecules
0%
Compounds
0%
Atoms
0%
Electrons

Explanation

Dalton's atomic theory states that atoms are the smallest unit of matter that can participate in a chemical reaction. Chemical reactions involve the combination, separation, or rearrangement of atoms, but atoms are neither created, destroyed, divided into parts, or converted into atoms of any other kind.

Option

$C$ is correct.

If the ratio of the atoms by mass is altered then:

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new compound formed
0%
same compounds are formed
0%
no reaction takes place
0%
state of compounds are changed

Combustion of a piece of paper to form ash, water vapour and carbon dioxide follows law of conservation of mass.

0%
True
0%
False

The ratio of mass of nitrogen and oxygen in nitric oxide is:

0%
$7:16$
0%
$1:8$
0%
$7:8$
0%
$7:15$

The concept of atom based on experimental observation first came from:

0%
Dalton's atomic theory
0%
Law of conservation of mass
0%
Law of mass theory
0%
Law of chemical combination

Which of the following is polyatomic element?

0%
Sulphur
0%
Phosphorous
0%
Argon
0%
Helium

Explanation

Sulphur

$(S_8)$ and phosphorous

$(P_4)$ are polyatomic elements. Argon and helium are noble gases or are monoatomic elements.

Hence, options A and B are correct.

What is the molecular mass of

$C_2H_4?$

0%
$26$
0%
$14$
0%
$28$
0%
$16$

Explanation

Molecular mass of

$C_2H_4 = (2\times atomic\ mass\ of\ carbon )$

$+ (4\times atomic\ mass\ of\ hydrogen)$

$=(2\times 12)+(4\times 1)$

$=28$

Option

$C$ is correct.

Formula unit mass of magnesium chloride is :

0%
94
0%
95
0%
96
0%
24

Explanation

Formula unit mass of magnesium chloride (

$MgCl_2$ ) is

$24+35.5+35.5=95$

Which of the following is true with respect to law of conservation of matter?

0%
It is also called as law of conservation of mass.
0%
Mass of products in a chemical reaction is equal to the mass of reactants.
0%
Matter is not perfectly conserved
0%
All of the above

Dalton's atomic theory was not accepted fully :

0%
when atoms combine it must be presumed to be a binary one, unless some cause appear to the contrary.
0%
when elements react, their atoms sometimes combine in more than one simple, whole-number ratio.
0%
elements are characterized by the mass of their atoms.
0%
None of the above

Explanation

According to Dalton, When atoms combine in only one ratio, ".. it must be presumed to be a binary one unless some cause appears to the contrary".

There was no experimental evidence to support this postulate, and it leads him to mistakenly assume that the formula of water was OH and the formula of ammonia was NH. As a result, Dalton's atomic weights for oxygen and nitrogen were incorrect and his experimental data did not support many of the conclusions he drew from it.

Hence, option

$A$ is correct choice.

Atoms of different elements combine in:

0%
unequal ratios.
0%
prime number ratios.
0%
equal ratios.
0%
whole number ratios.

Find the mass of

$4.12\times 10^{24}$ molecules of

$NH_3$ ?

0%
$110\ g$
0%
$116.3\ g$
0%
$120\ g$
0%
$100\ g$

Explanation

Number of Moles

$= \dfrac{Given \ number \ of \ molecules}{N_A}$

Number of Moles of

$NH_3=\dfrac{4.12\times 10^{24}}{6.022\times 10^{23}}=6.84$

Mass of one mole of

$NH_3 = 17 \ g\ (molar \ mass)$

Mass of

$6.84 \ moles \ of\ NH_3=6.84\times 17\ g=116.3\ g\ (approximately)$

Atomic mass of which of the following element is $24$ ?

0%
Magnesium
0%
Sodium
0%
Chlorine
0%
Sulphur

Explanation

Atomic mass of magnesium is

$24$ .

Who believed that atoms could not be split?

0%
Thomson
0%
Rutherford
0%
Dalton
0%
Both A and B

Who postulated that matter is made up of very small particles in 430 BC?

0%
Democritus
0%
Aristotle
0%
Dalton
0%
Robert Brown

When two molecules of hydrogen react with one molecule of oxygen, the mass of reactants is

$36$ , what is the mass of products?

0%
$18$
0%
$36$
0%
$9$
0%
$32$

Explanation

The Law of conservation of mass states that the total mass of reactants is equal to the total mass of products. In any chemical reaction, the total mass of the substance before and after the reaction is the same although its matter undergoes a physical change.

$2H_2+O_2 \longrightarrow 2H_2O$

Hence, the mass of the product i.e., water is

$36$ .

Who proposed the earliest views on the shapes and connectivity of atoms?

0%
Leucippus
0%
Rutherford
0%
Thomson
0%
Both B and C

J.J. Thomson discovered _________ at the end of 19th century.

0%
Electrons
0%
Nuclei
0%
Atoms
0%
Molecules

The theory of Democritus state that:

0%
everything is composed of "atoms", which are physically, but not geometrically, indivisible
0%
between atoms, there lies empty space
0%
there are an infinite number of atoms
0%
All of the above

Which of the following structural feature of an atom was proposed by Rutherford?

0%
The positively charged particle is called a proton.
0%
The size of the nucleus is very small as compared to the size of the atom.
0%
An atom consists of a positively charged sphere and the electrons are embedded in it.
0%
All of above

Which law is not applicable for a nuclear reaction where large amount of energy is released?

0%
Law of conservation of mass
0%
Law of definite proportion
0%
Law of multiple proportion
0%
Avagrado's law

Formula unit mass for

$K_2CO_3$ is :

0%
140u
0%
138u
0%
120u
0%
125u

Explanation

Formula unit mass of

$K_2CO_3 =$

$2\times Atomic \ mass \ of \ K + 1 \times Atomic\ mass\ of\ C + 3\times Atomic\ mass\ of\ O$
=

$2\times 39u + 1 \times 12u + 3\times 16u$
= 138 u.

A formula unit indicates :

0%
the highest whole number ratio of ions in a compound.
0%
only the lowest whole number ratio of uncharged molecules in a compound.
0%
the lowest whole number ratio of ions in a compound.
0%
both A and B.

The formula unit mass of a substance is the:

0%
sum of the atomic masses of all atoms in a formula unit of a compound
0%
relative atomic masses of atoms
0%
double the numerical value of the atomic mass
0%
None of above

Explanation

The formula mass of a substance is defined as the sum of the atomic masses of constituent atoms in a compound. This is generally used for compounds which do not contain discrete molecules, but ions as their constituent units. Example: NaCl (sodium chloride) made of sodium and chlorine ions. Formula unit mass of NaCl = (1

$\times$ 23) + (1

$\times$ 35.5) = 58.5 u

Molecules made up of two or more elements are called:

0%
ions
0%
compounds
0%
mixture
0%
both a and c

Which of the following element is represented by the chemical symbol

$P$ ?

0%
Sulphur
0%
Phosphorus
0%
Oxygen
0%
Hydrogen

Explanation

The symbol,

$\ P$ , represents the element Phosphorus.
Sulphur is represented by the symbol

$\ S$ .
Oxygen is represented by the symbol

$\ O$ .
Hydrogen is represented by the symbol

$\ H$ .

Which of the following is not a property of a molecule?

0%
Molecules of any given substance are similar.
0%
Molecules are represented by chemical formula.
0%
The properties of a substance are the properties of the molecule.
0%
None of above.

A molecule is _________ .

0%
Positive
0%
Negative
0%
Neutral
0%
Both A and C

Explanation

A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction is known as a molecule. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are made up of atoms that are held together by chemical bonds. These bonds are formed by sharing or exchange of electrons among atoms.

So, the correct option is

$C$

Formula unit mass is used for :

0%
molecules
0%
ionic compound
0%
uncharged compounds
0%
all of above

Which of the following is not a molecule?

0%
$O$
0%
$O_2$
0%
$CO_2$
0%
$N_2$

Explanation

A molecule may be homonuclear, that is, it consists of atoms of a single chemical element, as with oxygen (

$O_2 \ or\ N_2$ ), or, it may be heteronuclear, a chemical compound composed of more than one element, as with water (

$H_2O \ or \ CO_2$ ). Out of all the options,

$O$ represents a single oxygen atom and not a molecule.

Which of the following is Dalton's symbol for carbon?

0%
0%
0%
0%
None of above

Formula mass unit of

$Na_2CO_3.10H_2O$ is :

0%
290
0%
286
0%
180.02
0%
105.97

Explanation

Formula unit mass of

$Na_2CO_3$
=

$2\times atomic\ mass\ of\ Na + 1\times atomic\ mass\ of\ C + 3\times atomic\ mass\ of\ O$

$= 2\times 22.98 + 1\times 12.01 + 3\times 16$

$=105.97 u$
Formula unit mass of

$10H_2O = 10\times atomic\ mass\ of\ H_2O$

$= 10\times 18.02$

$=180.02 u$
Formula unit mass of

$Na_2CO_3.10H_2O = 105.97 + 180.02$

$= 285.99 u$

Formula unit mass of

$ZnO$ is :

0%
$85$
0%
$90$
0%
$81$
0%
$89$

Explanation

Formula unit mass of

$ZnO$ is

$=(1\times atomic\ mass\ of\ Zn) + (1\times atomic\ mass\ of\ O)$

$= 1\times 65 + 1\times 16$

$= 81 u.$

Option

$C$ is correct.

What is the formula mass of

$Ba(HSO_3)_2$ ?
Atomic mass of Ba is 137 u

0%
299 u
0%
250 u
0%
290 u
0%
260 u

Explanation

Formula mass of

$Ba(HSO_3)_2$

$= 1\times atomic\ mass\ of\ Ba + 2\times atomic\ mass\ of\ H + 2\times atomic\ mass\ of\ S$

$\\\\\\\\\\ + 6\times atomic\ mass\ of\ O$

$= (1\times 137 + 2\times 1 + 2\times 32 + 6\times 16)$ u

$= (137 + 2 + 64 + 96)$ u

$=299$ u

Hence, the correct option is

$A$

The formula unit mass of

$CuSO_4.5H_2O$ is

0%
159.62
0%
90.10
0%
249.72
0%
240

Explanation

Formula unit mass of

$CuSO_4 = 1\times Atomic\ mass\ of\ Cu + 1\times Atomic\ mass\ of\ S + 4\times Atomic\ mass\ of\ O$
=

$1\times 63.55 + 1\times 32.07 + 4\times 16$

$= 159.62\ u$

Formula unit mass of 5

$H_2O = 5\times Molecular\ mass\ of\ H_2O$
=

$5\times 18$

$= 90\ u$

Formula unit mass of

$CuSO_4.5H_2O = 159.62 + 90 = 249.70\ u$

Kanad called the tiniest of tiny particles of matter as:

0%
Parman
0%
Parmounu
0%
Anu
0%
Parmanu

Explanation

One of the earliest attempts to understand the structure of matter was made by Maharishi Kanad, an Indian sage who lived around the

$6th$ century BC. According to him, if the matter is broken into smaller and smaller pieces, a stage will come when the matter cannot be broken further. Kanad called these tiniest of tiny particles Parmanu.

One atomic mass is equal to

0%
$1.66\times10^{-27}$ g
0%
$1.66\times10^{-24}$ g
0%
$1.66\times10^{-23}$ g
0%
$1.66\times10^{-25}$ g

Explanation

One atomic mass unit is equal to

$1.66 \times 10^{-24} g.$ It is equal to 1/12th of mass of atom of Carbon-12. It is abbreviated as

$\text{u.}$

Formula unit mass for

$(NH_{4})_{2}SO_{4}$ is :

0%
142 u
0%
129 u
0%
137 u
0%
132 u

Explanation

Formula unit mass for

$(NH_{4})_{2}SO_{4}$

$= 2\times atomic\ mass\ of\ N + 8\times atomic\ mass\ of\ H + 1\times atomic\ mass\ of\ S$

$\\\\\\\\\ + 4\times atomic\ mass\ of\ O$

$= 2\times 14 + 8\times 1 + 1\times 32 + 4\times 16$

$= 28 + 8 + 32 + 64$

$= 132\ u$ .

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 7 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 7 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

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