MCQ Questions for Class 9 Chemistry Atoms And Molecules Quiz 8

Greek philosophers, ______and _______suggested that matter is made up of tiny indivisible particles called atoms.

0%
Democritus and Leucippus
0%
Dalton and Rutherford
0%
Einstein and Kanad
0%
Democritus and Dalton

Democritus' atomic theory states that:

0%
atoms are homogeneous
0%
atoms are indestructible
0%
atoms are solid but invisible
0%
all of the above

Explanation

According to Democritus, atoms were minuscule quantities of matter. He stated that
1. All matter consists of invisible particles called atoms
2. Atoms are indestructible
3. Atoms are solid but invisible
4. Atoms are homogeneous
5. Atoms differ in size, shape, mass, position, and arrangement.

Hence, option

$D$ is correct.

Which of the following is the unit of molar mass?

0%
u/mole
0%
g/mole
0%
g/litre
0%
None of above.

Dalton's theory fails to determine the existence of:

0%
molecules
0%
compounds
0%
allotropes
0%
All of the above

According to Democritus, matter is made up of:

0%
small, indivisible particles
0%
large particles
0%
large, divisible particles
0%
None of above

Which of the following scientist did not believe in atomic theory at all?

0%
Aristotle
0%
Democritus
0%
Rutherford
0%
Proust

Who thought that all materials were made of the four elements, earth, fire, water, and air?

0%
Dalton
0%
Aristotle
0%
Thomson
0%
Chadwick

The theory that the universe is composed of two elements, the atoms, and the void, in which they exist and move was given by:

0%
Bohr
0%
Dalton
0%
Leucippus
0%
Werner

Which of the following is a postulate of Dalton's atomic theory?

0%
All matter consists of indivisible particles called atoms.
0%
The atom is the smallest unit of matter that can take part in a chemical reaction.
0%
Atoms of the same element can combine in the same ratio to form compounds.
0%
All of the above

Explanation

Postulates of Dalton's atomic theory:

(i) All matter consists of indivisible particles called atoms.

(ii) Atoms of the same element are similar in shape and mass but differ from the atoms of the other elements.

(iii) Atoms can not be created or destroyed.

(iv) Atoms of different elements may combine in a fixed simple whole-number ratio to form compound atoms.

(v) Atoms of the same element can combine in the same ratio to form compounds.

(vi) Atoms are the smallest unit of matter that can take part in a chemical reaction.

So, option

$D$ is correct.

Which of the following is a merit of Dalton's atomic theory?

0%
Laws of chemical combination
0%
The distinction between the fundamental particle of an element (atom) and that of a compound (molecule)
0%
Both A and B
0%
None of the above

Explanation

Dalton's theory explains the laws of chemical combinations. Dalton was the first person to recognize a workable difference between the fundamental particle of an element (atom) and that of a compound (molecule).

So both the statements are correct.

Option

$C$ is correct.

Dalton's theory of same element have same mass and properties was proved wrong with the invention of:

0%
molecules
0%
isotopes
0%
neutrons
0%
compounds

Explanation

According to Dalton's atomic theory, atoms of an element are identical in mass, size and many other chemicals or physical properties.

But, practically we observe that atoms of several elements differ in their densities and masses.

These atoms with the different masses are known as isotopes. For example, Chlorine (Cl) has 2 isotopes with the mass numbers of 35 and 37.

Hence, correct option is

$\text{B}$ .

Which of the following explains Democritus' atomic model?

0%
0%
0%
0%
None of the above

Dalton had suggested that an atom is indivisible.

0%
True
0%
False

Which of the following is a wrong representation of atom and it's ion?

0%
$Rb/ Rb^{-}$
0%
$Mg/ Mg^{2+}$
0%
$F/F^{-}$
0%
$Li/Li^{+}$
0%
$Br/ Br^{-}$

Explanation

$Rb$ is a alkali metal that has tendency to release one electron and form mono-positive ion. It can not hold negative charge. So, the correct representation of atom and its ion is

$Rb/Rb^+$ .

What is the approximate mass of

$Ca(NO_3)_2$ ?

(Given- Atomic mass of

$Ca = 40, N = 14, O = 16$ )

0%
$70$
0%
$82$
0%
$102$
0%
$150$
0%
$164$

Explanation

The approximate mass of

$\displaystyle Ca(NO_3)_2$

$=\displaystyle 40 + 2 \times [14 + (3 \times 16)] = 40 + 2 \times (14+48) = 40 + 2 \times 62 = 40+124=164$ .

Among the following, which one can not be further broken down by chemical means?

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Cation
0%
Inert Gas
0%
Crystal
0%
Anion
0%
Element

Ionic species with a positive charge called as :

0%
cation
0%
inert Gas
0%
crystal
0%
anion
0%
element

Explanation

Ionic species with a positive charge are called cations.
Cations form when an element or group of elements(compounds) lose one or more electrons. Cations can be formed from metal elements, as well as nonmetal elements. If a metal element forms an ion, it always forms a cation. Some metals always form the same type of cation. For example, sodium always forms a

$+1$ cation (

$Na^+$ ) and magnesium always forms a

$+2$ cation

$(Mg^{2+})$ .

Find the best option among the following about the simplest unit of water that retains its properties :

0%
A molecule
0%
A mixture of compounds
0%
An isotope
0%
An isomer
0%
An acid salt

Explanation

A molecule is a group of two or more atoms that form the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of that substance.

Thus, from a structural point of view, a molecule consists of an aggregation of atoms held together by valence forces. So, the simplest unit of water that retains its properties is a molecule.

Hence option

$A$ is correct.

All of the following are compounds except :

0%
copper sulfate
0%
carbon dioxide
0%
washing soda
0%
air
0%
lime

Explanation

All are compounds except Air which is a mixture of various gases in definite proportion.

Hence, the correct option is

$D$ .

The molar mass of

$\displaystyle Al{ Cl }_{ 3 }$ is:

0%
$67.9$ g/mol
0%
$106.5$ g/mol
0%
$62.5$ g/mol
0%
$133.5$ g/mol

Explanation

Atomic mass of Al =

$27\ u$

Atomic mass of Cl =

$35.5\ u$

Molar mass of

$AlCl_3$ =

$27+3 (35.5)=133.5$ g/mol

Hence, the correct option is

$\text{D}$ .

One atomic mass unit is equal to?

(Given, mass of one carbon-12 atom

$= 1.992 \times 10^{-23}$ )

0%
$1.66\times 10^{-27}g$
0%
$1.66\times 10^{-24}g$
0%
$1.66\times 10^{-23}g$
0%
$1.66\times 10^{-25}g$

Explanation

One atomic mass unit (amu or u) is equal to 1/12th of the mass of an atom of carbon-12.

Mass of an atom of carbon-12

$= 1.992 \times 10^{-23}\ g$

1 amu

$=$ 1/12 mass of carbon-12 atom

$= \dfrac {1}{12} \times 1.992 \times 10^{-23}$

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

Statement 1: One mole of

$CO_2$ has a greater mass than

$1$ mole of

$H_2O$ .
Statement 2: The molecular mass of

$CO_2$ is greater than the molecular mass of

$H_2O$ .

0%

Both Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1
0%

Both Statement 1 and Statement 2 are correct and Statement 2 is not the correct explanation of Statement 1
0%

Statement 1 is correct but Statement 2 is not correct
0%

Statement 1 is not correct but Statement 2 is correct
0%
Both statements are incorrect

Explanation

Statement 1: One mole of

$CO_2$ has a greater mass than

$1$ mole of

$H_2O$ .

Statement 2: The molecular mass of

$CO_2$ is greater than the molecular mass of

$H_2O$ .

The molecular masses of

$CO_2$ and

$H_2O$ are

$44\ g/mol$ and

$18 \ g/mol$ respectively.

The mass of

$1$ mole of a substance is equal to its molecular mass.
Both Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1.

Hence, option

$A$ is correct.

Find the accurate statement for the significance of Avogadro's number ?

0%
It is the conversion factor between grams and pounds.
0%
It is a universal physical constant just as the speed of light.
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It is the number of particles that is required to fill a 1-liter container.
0%
It is the inverse diameter of an H atom.
0%
It is the number of electrons in the universe.

All atoms of the same element have :

0%
different numbers of electrons.
0%
equal number of protons.
0%
different numbers of neutrons.
0%
different numbers of protons.
0%
equal number of neutrons.

Molar mass of ethanol

$(C_2H_5OH)$ is:

(Atomic masses: C = 12 u, H = 1 u, O = 16 u)

0%
$34$
0%
$38.9$
0%
$46$
0%
$45.1$
0%
$62.1$

Explanation

Molar mass of ethanol (

$C_2H_5OH$ )

$=\displaystyle ( 2 \times atomic\ mass\ of\ carbon) + (6 \times atomic\ mass\ of\ hydrogen) + (1 \times atomic\ mass\ oxygen)$

$=\displaystyle 2(12) + 6(1) + 1(16) = 46\ g/mol$

An atom differs from its ion in:

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Nuclear charge
0%
Mass number
0%
Number of electrons
0%
Number of neutrons

Explanation

An atom differs from its ion in number of electrons. For example,

$\displaystyle H$ atom has 1 electron. Whereas

$\displaystyle H^+$ ion has 0 electrons. On the other hand,

$\displaystyle H^-$ ion has 2 electrons.

Which of the following is not part of the atomic theory?

0%
Compounds are made up of combinations of atoms.
0%
All atoms of a given element are alike.
0%
All matter is composed of atoms.
0%
A chemical reaction involves the rearrangement of atoms.
0%
The atom is mainly empty space.

Explanation

Main postulates of Dalton's atomic theory

All matter is made of atoms. Atoms are indivisible and indestructible.
All atoms of a given element are identical in mass and properties
Compounds are formed by a combination of two or more different kinds of atoms.
A chemical reaction is a rearrangement of atoms

option

$E$ is not a part of Atomic theory.

The size of the nucleus is measured in _______ units.

0%
$amu$
0%
angstrom
0%
fermi
0%
$cm$

Explanation

The size of the nucleus is measured in fermi units.

$\displaystyle \ 1 \ fermi = 10^{-15} \ m$ .

Who first coined the term 'atomos' meaning indivisible?

0%
Rutherford
0%
Thomson
0%
Aristotle
0%
Democritus
0%
Dalton

The molar mass of

$CaCO_3$ is :

0%
$68$ g $/$ mol
0%
$75$ g $/$ mol
0%
$82$ g $/$ mol
0%
$100$ g $/$ mol
0%
$116$ g $/$ mol

Explanation

Molar mass of

$Ca$ is

$40 \ g/mole$
Molar mass of

$C$ is

$12 \ g/mole$
Molar mass of

$O$ is

$16 \ g/mole$
Total molar mass is

$40+12+16 \times 3 =100\ g/mol$

Which of the following will not be affected by changes in temperature and pressure?

0%
Density
0%
Equilibrium constant
0%
Molar mass
0%
Freezing point
0%
Molarity

Explanation

Properties are affected by a change in temperature and pressure.

For example, the phase of a substance is determined by its temperature and pressure, the density of fluid changes with temperature and pressure. Molarity is defined as the number of moles of solute dissolved per liter of solution. It is expressed in units as

$mol/L$ . Molar mass is the mass of one mole of substances. It does not change with temperature and pressure. All other properties like density, melting point, the equilibrium constant are temperature or pressure-dependent.

Which of the groups below represents the correct relationship in order from smallest (or simplest) to largest (or more complex)?

0%
Matter - element - compound - electron - atom
0%
Electron - element - atom - compound - matter
0%
Electron - atom - element - matter - compound
0%
Electron - atom - element - compound - matter
0%
Atom - electron - element - compound - matter

Which law states that in a chemical reaction, the total mass of the products is equal to the total mass of the reactants?

0%
Law of constant proportions
0%
Law of conservation of energy
0%
Law of conservation of mass
0%
Law of multiple proportions

A symbol of an element does not convey information about :

0%
Atomic number
0%
Atomic weight
0%
Mass number
0%
All the above

Barium chloride reacts with sodium sulfate to form barium sulfate and sodium chloride. Then, according to the law of conservation of mass:

0%
The total mass of reactants, barium chloride, and sodium sulfate taken is greater than the total mass of products, barium sulfate, sodium chloride formed.
0%
The total mass of reactants, barium chloride, and sodium sulfate taken is less than the total mass of products, barium sulfate, sodium chloride formed.
0%
The total mass of the reactants is equal to the total mass of products.
0%
None of the above

Explanation

$BaCl_2 + Na_2SO_4 \rightarrow BaSO_4 + 2NaCl$

The total mass of the reactants is equal to the total mass of products.

Hence, option C is correct.

The symbols of lead and mercury are _________ respectively.

0%
$Hg, Pb$
0%
$Pb, Hg$
0%
$Le, Me$
0%
$Ld, My$

Explanation

Lead is a chemical element with atomic number 82 and symbol Pb comes from the Latin word $plumbum$ . It is a soft and malleable metal with a density exceeding that of most common materials. Mercury is a chemical element with symbol Hg and atomic number 80. It is commonly known as quicksilver and was formerly named $hydrargyrum$ .

A balanced chemical equation supports

0%
Law of chemical equilibrium
0%
Law of conservation of energy
0%
Law of conservation of mass
0%
None of these

$1\ amu = \dfrac{1}{12}$ the mass of one:

0%
$C-12$ atom
0%
$N$ atom
0%
$O$ atom
0%
$H$ atom

Explanation

An atomic mass unit (symbolized amu) is defined as precisely 1/12 the mass of an atom of carbon-12. The carbon-12 ( $C-12$ ) atom has six protons and six neutrons in its nucleus. In imprecise terms, one amu is the average of the proton rest mass and the neutron rest mass.

Hence, the correct option is $\text{A}$

Identify the correct statement(s) from the following:

0%
The shorthand representation of a molecule of a substance (element or compound) in terms of symbols and subscript numbers is known as the chemical formula.
0%
Atoms of different elements combine in a certain fixed ratio to form a compound.
0%
All chemical compounds are represented by their respective chemical formulae.
0%
Symbols of all elements are derived from their Latin names.

Explanation

(A) The molecules of substances (elements or compounds) are represented by their chemical formulae. For example, a molecule of sodium chloride is represented as

$NaCl$ , a molecule of water is represented as

$H_2O$ .

(B) Different elements always combine in a fixed ratio form a compound. For example, hydrogen and water always combine in

$2:1$ ratio to form water.

$HCl$ and water as

$H_2O$ .

(D) Not all symbols of elements are derived from their Latin names. For example, the symbols of Hydrogen is H, Helium is He.

Au is an example of a symbol that is derived from the Latin name, Aurum, for gold.

Nitrogen reaction with oxygen to form nitrous oxide.

What will be the volume ratio of the reactants and products of the given reaction?

$2N_{2}+O_{2}\rightarrow 2N_{2}O$

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

Explanation

$2N_{2}+O_{2}\rightarrow 2N_{2}O$

The Law of chemical combination states that the Ratio of reactants & products are Reactions coefficients or stoichiometry coefficients.

Ratio

$= 2:1:2$

Hence, the correct option is

$(D)$ .

The mass of 5 moles of

$H_2SO_4$ is:

0%
$180\ g$
0%
$250\ g$
0%
$300\ g$
0%
$490\ g$

Explanation

The molar mass of hydrogen ( $H$ ) is $1$

Molar mass of sulphur ( $S$ ) is $32$

Molar mass of oxygen ( $O$ ) is $16$

We can calculate the molar mass of $H_2SO_4$ by adding the molar masses of all the atoms in the molecule.

So,

$molar\ mass\ of\ H_2SO_4 = (2 \times molar\ mass\ of\ H) + (molar\ mass\ of\ S) + (4 \times molar\ mass\ of\ O)$

= $(2 \times 1) + (32) + (4 \times 16)$

= $98$

We know that molar mass of a substance is defined as the mass of $1$ mol of that substance. So, we can write it as follows:

Mass of $1$ mol of $H_2SO_4$ = Molar mass of $H_2SO_4$ = $98$

Hence, mass of $5$ moles of $H_2SO_4$ = $5 \times 98$ = $490$

Which of the following is a quantity necessary to determine the molecular formula of a compound?

0%
Boiling point
0%
Rate of reaction
0%
Molecular mass
0%
Molarity (moles per litre)
0%
Density

What weight of calcium contains the same number of atoms as those in

$3 g$ of carbon?

0%
$10 g$
0%
$20 g$
0%
$30 g$
0%
$40 g$

Explanation

Atomic weights of

$C$ and

$Ca$ are 12 g/mol and 40 g/mol respectively.

3 g

$C \displaystyle = \dfrac {3 \ g}{12 \ g/mol}= 0.25 \ mol C$ .

Number of moles of

$Ca \displaystyle =$ number of moles of

$C \displaystyle =$ 0.25.
Weight of

$Ca \displaystyle = 3 \ mol \times 40 \ g/mol = 10 \ g$ .
Note: Since

$C$ and

$Ca$ samples have same number of atoms, they will have same number of moles.

Which of the following contains the least number of molecules?

0%
52 g of $N_2O_5$
0%
36 g of $H_2O$
0%
28 g of $CO$
0%
51 g $NH_3$

Explanation

Let N be the Avogadro's number.
Mass is divided with molar mass to obtain the number of moles.

The number of moles are multiplied with Avogadro's number to obtain number of molecules.

(A) Number of molecules in 52 g of

$\displaystyle N_2O_5 = \dfrac {52 \: g}{(28+80) \: g/mol} \times N = 0.48N$

(B) Number of molecules in 36 g of

$\displaystyle H_2O = \dfrac {36 \: g}{18 \: g/mol} \times N = 2N$

$\displaystyle = \dfrac {28 \: g}{28 \: g/mol} \times N = N$

(D) Number of molecules in 51 g

$\displaystyle NH_3 \: = \dfrac {51 \: g}{17 \: g/mol} \times N = 3N$

Hence, 52 g of

$\displaystyle N_2O_5$ contains least number of molecules.

What is the mass of one molecule of oxygen?

0%
$5.31\times { 10 }^{ -23 }g$
0%
$5.33\times { 10 }^{ 23 }g$
0%
$5.25\times { 10 }^{ 23 }g$
0%
$5.02\times { 10 }^{ -23 }g$

Explanation

Explanation:

The molecular mass of oxygen ( $O_2$ ) is $32\ grams$ .

$\therefore$ $6.023 \times 10^{23}$ molecules of oxygen ( $O_2$ ) have mass $=32\ grams$ .

$\therefore$ One molecule of oxygen ( $O_2$ ) will have mass $=\dfrac{32}{6.023\times 10^{23}}=5.31\times 10^{-23}\ grams$ .

Final Answer: One molecule of oxygen ( $O_2$ ) have mass $=5.31\times 10^{-23}\ grams$ . Hence option $A$ is correct.

Identify the pair of substances having the same formula unit mass.

0%
Calcium chloride, potassium carbonate
0%
Calcium oxide, hydrochloric acid
0%
Carbon monoxide, ammonia
0%
Carbon dioxide, nitrous oxide

Explanation

Carbon dioxide and nitrous oxide have the same formula unit mass.
Formula unit mass for carbon dioxide

$\displaystyle CO_2 = 12 +2(16)=12+32=44\ u$
Formula unit mass for nitrous oxide

$\displaystyle N_2O = 2(14)+16=28+16=44\ u$

Let's look at the formula unit mass of the other given compounds:
Formula unit mass for calcium chloride

$\displaystyle CaCl_2 = 40+2(35.5)=40+71=111\ u$
Formula unit mass for potassium carbonate

$\displaystyle K_2CO_3 = 2(39)+12+3(16)=78+12+48=138\ u$
Formula unit mass for calcium oxide

$\displaystyle CaO = 40+16=56\ u$
Formula unit mass for hydrochloric acid

$\displaystyle HCl = 1+35.5=36.5\ u$
Formula unit mass for carbon monoxide

$\displaystyle CO = 12+16=28\ u$
Formula unit mass for ammonia

$\displaystyle NH_3 = 14+3(1)=17\ u$

The heaviest among the following is:

0%
$50\ g$ of $Fe$
0%
$5\ moles$ of $N_2$
0%
$0.1\ g \ atom$ of $Ag$
0%
$0.1\ g$ of $Ca$

Explanation

(A)

$50$ g of

$\displaystyle Fe$

(B) 5 moles of

$\displaystyle N_2 = 5 \: mol \times 28 \: g/mol = 140$ g.

$Ag$

$\displaystyle = 0.1 \: g \: atom \times 108 \: g/ \: atom = 10.8$ g

(D)

$0.1$ g

$\displaystyle Ca$

Hence, 5 moles of

$\displaystyle N_2$ are heaviest.

What is the approximate molecular mass of dry air containing 78%

$N_2$ and 22%

$O_2$ ?

0%
28.88
0%
27
0%
30
0%
34

Explanation

The molecular mass of dry air is given by-

$\displaystyle = \dfrac { [ \text { Molecular mass of }N_2 \times \text { Percentage of }N_2 ] + [ \text { Molecular mass of }O_2 \times \text { Percentage of }O_2 ] } { \text { Percentage of }N_2 + \text { Percentage of }O_2 }$

$\displaystyle = \dfrac { [ \text { 28 } \times \text { 78 } ] + [ \text { 32 } \times \text { 22 } ] } { \text { 78 } + \text {22 } }$

$\displaystyle = \text {28.88 g/mol}$

Hence, option

$A$ is correct.

Who was the first scientist to propose that all matter was made of small spheres called atoms?

0%
John Dalton (early 1800's)
0%
Ernest Rutherford (1911)
0%
Niel's Bohr (1913)
0%
Joseph John Thomson (1897)

Explanation

John Dalton was the first scientist to propose that all matter was made of small spheres called atoms. The main points of Dalton's Atomic theory given by John Dalton are:-

(a) Elements are extremely small particles called atoms.

(b) Atoms of a given element are identical in size, mass, and other properties,

(d) Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

(e) In chemical reactions, atoms are combined, separated, or rearranged.

Option

$A$ is correct.

A smallest particle of a compound that can have the independence existence and that can retain all the properties of that compound is called as:

0%
molecule
0%
ion
0%
atom
0%
element

Explanation

A smallest part of the compound that can have the independence existence and that can retain all the properties of that compound is called as molecule. Ex:

$H_2,Cl_2$

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 8 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 8 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

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