MCQ Questions for Class 9 Chemistry Atoms And Molecules Quiz 3

The mass of one oxygen molecule is:

0%
$2.656\times 10^{-23}\ gm$
0%
$5.312\times 10^{-23}\ gm$
0%
$1.66\times 10^{24}\ gm$
0%
$32\ gm$

Explanation

$\bf{Hint-}$ One mole of any gas has Avogadro's number of molecules.

$\bf{STEP-1}$ To find the mass of one-mole oxygen gas molecules.

One mole contains

$6.02\times 10^{ 23 } \ molecules$ of oxygen.

$1\ mole$ of oxygen weighs

$32\ g$ .

Thus, weight of

$1$ oxygen molecule is

$\dfrac { 32 }{ 6.023\times 10^{ 23 } } =5.312\times10^{ -23 }\ gm$ .

$\bf{Final answer-}$ Option B

The formula and molecular mass of common salt is :

0%
$NaCl, 58.5$
0%
$MgCl_2, 46$
0%
$CaCl_2, 62$
0%
$FeCl_3, 54$

Explanation

Molecular formula of common salt (sodium chloride) is

$NaCl.$ Its molar mass is

$23 + 35.5 = 58.5 g mol^{-1}$

The formula and molecular mass of ethanol is:

0%
$C_3H_6O = 34 g mol^{-1}$
0%
$C_2H_6O_2 = 62 g mol^{-1}$
0%
$C_2H_5O = 45 g mol^{-1}$
0%
$C_2H_6O = 46 g mol^{-1}$

Explanation

Molecular formula of ethanol is

$C_2H_5OH$ .

Molar mass of

$= C_2H_6O = 2 \times 12 + (6 \times 1) + 16 = 46 g mol^{-1}$

Which of the following contain maximum number of molecules?

0%
1g $CO_2$
0%
1g $N_2$
0%
1g $H_2$
0%
1g $CH_4$

Explanation

For a molecule,

molecular weight in grams

$=$ Avogadro's number

$({ N }_{ A }) = 6.023 \times { 10 }^{ 23 }$
(A) 1g

$CO_2$

44 gram of

${ CO }_{ 2 }$ =

${ N }_{ A }$ molecules

$\therefore$ 1 gram of

$CO_2$ contains

$\dfrac{1}{44} \times N_A$ molecules

(B) 1g

${ N }_{ 2 }$
28 gram of

${ N }_{ 2 } ={ N }_{ A }$ molecules

$\therefore$ 1 gram of

${ N }_{ 2 }$ contains

$\dfrac{1}{28} \times N_A$ molecules

(C) 1g

$H_2$

2 gram of

$H_2$ contains

$N_A$ molecules

$\therefore$ 1 gram of

$H_2$ contains

$\dfrac {1}{2} \times N_A$ molecules

(D) 1g

${ CH }_{ 4 }$
16 gram of

${ CH }_{ 4 }$ =

${ N }_{ A }$ molecules

$\therefore$ 1 gram of

${ CH }_{ 4 }$ =

${ N }_{ A }/16$

Maximum number of molecules are found in 1 gram hydrogen.

The number of atoms present in

$10$ gms of

$CaCO_{3}$ is:

0%
$5N_{A}$
0%
$0.5N_{A}$
0%
$5$
0%
$N_{A}$

Explanation

The molecular weight of calcium carbonate is

$100$ g.

$10$ g of calcium carbonate corresponds to

$0.1$ mole.

One molecule of calcuim carbonate contains

$5$ atoms. Hence,

$0.1$ mole of calcium carbonate will contain

$0.5N_A$ atoms. Here,

$N_A$ is the Avogadro number.

Assertion: 1 mole

$O_{3} (ozone)=N$ molecule of

$O_{3} (ozone)=3N$ atoms of

$O (oxygen)=48g$

Reason: A mole is the amount of matter that contains as many as objects as the number of atoms exactly in 12 g C-12 (

$N$ = Avogadro number).

0%
Assertion is correct but Reason is incorrect.
0%
Assertion is incorrect but Reason is correct.
0%
Both Assertion and Reason are correct and Reason is correct explanation of Assertion
0%
Both Assertion and Reason are correct but Reason is not correct explanation of Assertion

Explanation

$1$ mole of ozone weighs

$48$ g (molecular weight). It contains Avogadro number (

$N$ ) of molecules. Each ozone molecule contains

$3$ oxygen atoms. Hence,

$1$ mole of ozone contains

$3N$ atoms of oxygen.

Mass of one atom of oxygen is:

0%
$\frac {16}{6.023 \times 10^{23}}g$
0%
$\frac {32}{6.023 \times 10^{23}}g$
0%
$\frac {1}{6.023 \times 10^{23}}g$
0%
$8\ u$

Explanation

Mass of

$6.023 \times 10^{23}$ atoms of oxygen = Atomic mass of oxygen = 16 g

Mass of one atom of oxygen =

$\dfrac{16}{6.023\times 10^{23}}$ g

Cation and anion present (if any) in

$CH_3COONa$ are :

0%
Cation; $CH_3 COO^-$ Anion; $Na^+$
0%
Anion; $CH_3 COO^-$ Cation; $Na^+$
0%
Cation; $CH_3 COO^{2-}$ Anion; $Na^+$
0%
Anion; $CH_3 COO^{2-}$ Cation; $Na^+$

Explanation

The cation and anion is

$CH_3COONa$ are
Cation

$\rightarrow Na^+$
Anion

$\rightarrow CH_3COO^-$

Which of the following statements is not true about an atom?

0%
Atoms are not able to exist independently.
0%
Atoms are the basic units from which molecules and ions are formed.
0%
Atoms are always neutral in nature.
0%
Atoms aggregate in large numbers to form the matter that we can see, feel or touch.

Which has maximum number of atoms?

0%
24 g of C (12)
0%
56 g of Fe (56)
0%
27 g of Al (27)
0%
108 g of Ag (108)

Explanation

12 g of C contains

$N_A$ number of atoms.
Therefore, 24 g of C contains 2

$N_A$ number of atoms.

Similarly, 56 g of Fe, 27 g of Al and 108 g of Ag contain

$N_A$ number of atoms.

Therefore, maximum number of atoms is present in 24 g of C.

Which of the following compounds contains maximum number of atoms?

0%
18gm of $H_2O$
0%
18gm of $O_2$
0%
18gm of $CO_2$
0%
18gm of $CH_4$

Explanation

$No. of\ atoms= \dfrac{Mass \times atomicity}{Molar\ Mass}\times N_{A}$

Using the above formula:
a) In 18gm of

$H_{2}O$ :
No. of atoms=

$\dfrac{18\times 3}{18}\times N_{A} = 3N_{A}$

b) In 18gm of

$O_{2}$ :
No of atoms=

$\dfrac{18\times 2}{32}\times N_{A} = 1.12N_{A}$

c) In 18gm of

$CO_{2}$ :
No. of atoms=

$\dfrac{18\times 3}{44}\times N_{A} = 1.23N_{A}$

d) In 18gm of

$CH_{4}$ :
No. of atoms=

$\dfrac{18\times 5}{16}\times N_{A} = 5.63N_{A}$
Therefore, 18gm

$CH_{4}$ has a maximum number of atoms.

The number of atoms in 0.1 mol of a triatomic gas is:

0%
6.026 x 10 $^{22}$
0%
1.806 x 10 $^{23}$
0%
3.600 x 10 $^{23}$
0%
1.800 x 10 $^{22}$

Explanation

A number of atoms

$=$ No. of moles x Avagadro's Number

$=0.1 \times 6.022\times 10^{23}$

$= 6.02\times 10^{22}$

Now since we have the number of molecules of the gas. And also we know that there are 3 atoms present in one molecule.

So the number of atoms present in 0.1 moles of the gas is:

$=3×6.02×10^{22}$

$=18.06×10^{22}$

$=1.806×10^{23}$

Avogadro's number is ?

0%
$6.023 \times 10^{23}$
0%
$6.066 \times 10^{-19}$
0%
$6.032 \times 10^{24}$
0%
$6.203 \times 10^{18}$

Explanation

Correct option: $A$

Explanation:

Avagadro’s number is a number of particles(electrons, protons, etc.) found in a mole of a substance.
Conversion between moles and grams depends on Avogadro's number.
Avogadro's number has value $6.022 \times10^{23}$ .
For example: $1$ mole of $C =$ $12 \ g =$ $6.022 \times 10^{23}$ molecules

Which of the following would weigh the highest?

0%
0.2 mole of sucrose $(C_{12} H_{22} O_{11})$
0%
2 moles of carbon dioxide $(CO_2)$
0%
2 moles of calcium carbonate $(CaCO_3)$
0%
10 moles of water $(H_2O)$

Explanation

Applying mole concept,

1 mole

$=$ molecular weight in gram.

Molecular weight of

$C_{12}H_{22}O_{11} = 12\times12 + 22\times 1 + 11\times 16 = 342$

Molecular weight of

$CO_2 = 12 + 2\times 16 = 44$

Molecular weight of

$CaCO_3 = 40 + 12 + 3\times 16 = 100$

Molecular weight of

$H_2O = 16 + 2\times 1 = 18$

The results can be calculated as:

Weight of a sample in gram

$=$ number of moles

$\times$ molar mass

(a) 0.2 moles of

$C_{12}H_{22}O_{11} = 0.2 \times 342 = 68.4\ gm$

(b) 2 moles of

$CO_2 = 2 \times 44 = 88\ gm$

$CaCO_3 = 2 \times 100 = 200\ gm$

(d) 10 moles of

$H_2O = 10 \times 18 = 180\ gm$

Hence, 2 moles of

$CaCO_3$ weighs more than other compounds.

0%
Assertion and reason both are correct statements and reason is correct explanation for assertion.
0%
Assertion and reason both are correct statements but reason is not correct explanation for assertion.
0%
Assertion is correct statement but reason is wrong statement.
0%
Assertion is wrong statement but reason is correct statement.

The mass of one steel screw is 4.11gm. Find the mass of one mole of these steel screws.

0%
$2.475 \times 10^{21} kg$
0%
$3.56 \times 10^{21} kg$
0%
$4.2 \times 10^{21} kg$
0%
$4.2 \times 10^{20} kg$

Explanation

Mass of one steel screw is 4.11 gm, so mass of one mole is

$= 4.11*6.023*10^{23} = 2.475 \times 10^{24} g = 2.475 \times 10^{21} kg$

A sample of vitamic C is known to contain

$2.58 \times10^{24}$ oxygen atoms. How many moles of oxygen atoms are present in the sample?

0%
2.28 moles
0%
2.14 moles
0%
1 moles
0%
4.28 moles

Explanation

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

$1$ mole of oxygen atoms

$\therefore$ Number of moles of oxygen atoms in

$2.58 \times 10^{24}$ atoms

$= \dfrac {2.58 \times 10^{24}}{6.023\times 10^{23}} = 4.28\ mol$

$\therefore 4.28$ moles of oxygen atoms are present in the sample.

Hence, the correct answer is option

$D$ .

Which has more number of atoms:

$100$ g of

$N_2$ or

$100$ g of

$NH_3$ ?

0%
$NH_3$
0%
$N_2$
0%
Both have same number of atoms
0%
Cannot be determined

Explanation

Atomic mass of N = 14 u

Atomic mass of H = 1 u

Number of moles =

$\dfrac {Mass}{Molar\ Mass}$

$(i) \ 100 g \ N_2$

$= \dfrac {100}{(14 \times 2)}$ moles

$= \dfrac {100}{28}$ moles

Number of

$N_2$ molecules

$= \dfrac {100}{28} \times 6.022 \times 10^{23}$

1 molecule of

$N_2$ has 2 atoms. So, number of

$N$ atoms

$= \dfrac {100}{28} \times 6.022 \times 10^{23}\times 2 = 43.01 \times 10^{23}$ atoms

$(ii) \ 100 g \ NH_3 = \dfrac {100}{14 + (3 \times 1)} = \dfrac {100}{17}$ moles

$= \dfrac {100}{17} \times 6.022 \times 10^{23}$ molecules

$= \dfrac {100}{17} \times 6.022 \times 10^{23} \times 4$ atoms (since one molecule of

$NH_3$ has 4 atoms.)

$= 141.69 \times 10^{23}$ atoms

$\therefore$

$NH_3$ would have more atoms

The formula unit mass of

$Ca_3 (PO_4)_2$ is :

0%
$360$
0%
$240$
0%
$118$
0%
$310$

Explanation

Mass of

$Ca_3 (PO_4)_2$

$= (3 \times$ atomic mass of Ca

$) + (2 \times$ atomic mass of phosphorus

$) + (8 \times$ atomic mass of oxygen)

$= 3\times 40+2\times31+8\times16 = 310$

Raunak took 5 moles of carbon atoms in a container and Krish also took 5 moles of sodium atoms in another container of same weight. Whose container has more number of atoms?

0%
Raunak
0%
Krish
0%
Both have same
0%
None of these

Explanation

Equal moles of different atoms contain the same number of atoms.

1 mole has

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

Both have 5 moles of atoms.

Therefore, the number of atoms

$= 5\times 6.023\times 10^{23}$ .

Hence the correct option is C.

The visible universe is estimated to contain

$10^{22}$ stars. How many moles of stars are present in the visible universe?

0%
$6.023 \times 10^{23}$ moles
0%
$6.023$ moles
0%
$1.5$ moles
0%
$0.0166$ moles

Explanation

1 mole of stars equals

$6.023 \times 10^{23}$ stars

$\therefore$ Number of moles of stars

$= \dfrac{10^{22}}{N_A}$

$=\dfrac {10^{22}}{6.023 \times 10^{23}}$

$= 0.0166$ moles

Option

$D$ is correct.

Cations and anions present (if any) in

$NH_4NO_3$ are :

0%
Anions: $NO_{3}^{2-}$ Cations: $NH_{4}^{3+}$
0%
Cations: $NO_{3}^{-}$ Anions: $NH_{4}^{2+}$
0%
Cations: $NO_{3}^{-}$ Anions: $NH_{4}^{+}$
0%
Anions: $NO_{3}^{-}$ Cations: $NH_{4}^{+}$

Explanation

Ions present in

$NH_4NO_3$ are:

Cations

$\rightarrow NH_4^+$
Anions

$\rightarrow NO_3^-$

Calculate the molecular mass of the caustic potash :

0%
$K_2OH$ $= 95 g mol^{1}$
0%
$KOH = 56 g mol^{1}$
0%
$K(OH)_2$ $= 73 g mol^{1}$
0%
$KOH = 58 g mol^{1}$

Explanation

Potassium has valency

$+1$ and is represented as

$K^+$ , hydroxyl has valency

$-1$ and is represented as

$OH^-$ . Caustic potash is

$KOH.$ Molar mass -

$(39 +16+1) = 56 g mol^{-1}$

A sample of pure water, irrespective of source, contains 88.89% oxygen and 11.11% hydrogen
by mass. The data supports the:

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

Explanation

According to the law of constant composition in a given compound, the elements always combine in the same proportion as each other.

Water(

$H_{2}O$ ) molecule consists of two hydrogen atoms of relative mass 1 and one oxygen atom of relative mass 16.

Therefore, the ratio in which 2 atoms of hydrogen and one atom of oxygen are combined is

$1:8$ and will always be the same irrespective of the source of water.

Therefore, the correct option is

$B$

The molecular weight of calcium carbonate

$CaCO_{3}$ is:

0%
80
0%
90
0%
100
0%
110

Explanation

Molecular weight is the mass of whole molecule.

Steps:- (1) Chemical formula of calcium carbonate

$\longrightarrow CaCO_3$

(2) Mass of Calcium

$\longrightarrow 40$

Mass of Carbon

$\longrightarrow 12$

Mass of Oxygen

$\longrightarrow 16$

(3) Multiply mass of each element by number of atoms of that element.

(4) Add all the masses obtained after multiplication.

$\longrightarrow CaCO_3$

$=1\times 40+1\times 12+3\times 16$

$=40+12+48$

$=100$ .

One a.m.u. or one 'u' is equal to :

0%
$1.66053892 10^{-27} kg$
0%
$1.66053892 10^{-29} kg$
0%
$1.23457656 10^{-27} kg$
0%
$1.23457656 10^{-29} kg$

Explanation

One a.m.u.(atomic mass unit) or one 'u' is

$\dfrac{1}{12}$ of the mass of one carbon-

$12$ atom.
It is equal

$1.6605389210 \times 10^{-24} g$ or

$1.6605389210 \times 10^{-27} kg$ .

Combined atoms have more:

0%
unstability
0%
stability
0%
attraction
0%
name of these

Explanation

It has been observed that a system that has minimum energy is stable. The theory of chemical bonding shows that the formation of the chemical bonds decreases the potential energy of the system. Hence, two atoms combine to attain a state of lower potential energy and thus acquire more stability.

Example: Sodium electronic configuration

$Na\longrightarrow 1s^22s^22p^63s^1$ or

$2,8,1$

$(Z=11)$

Chlorine electronic configuration

$Cl\longrightarrow 1 s^2 2s^2 2p^6 3s^2 3p^5$ or

$2,8,7$

$(Z=17)$

$\underset {2,8,1}{Na}+\underset {2,8,7}{Cl}\longrightarrow \underset {2,8}{Na^+}+\underset {2,8,8}{Cl^-}$

Sodium is less stable with

$2,8,1$ electronic configuration and more stable with

$2,8$ electronic configuration. Similarly, chlorine is more stable with

$2,8,8$ configuration, because both have a complete octet.

$Na^++Cl^-\longrightarrow Na^+Cl^-$ Atoms combined by an ionic bond. Both are more stable in a combined state.

Which of the following obeys the law of constant proportions in their formation?

0%
Mixtures
0%
Compounds
0%
Elements
0%
Colloids

Explanation

The Law of constant proportion is the rule where elements combine in a fixed proportion by mass.

Thus compounds are the kind that is formed from a fixed proportion of elements.

For example, Water

$\rightarrow H_2O$ is obtained from any source of water like a river, lake, pond. Here the ratio of

$H$ and

$O$ will be always

$2:1$ .

Hence, option B is correct.

The number of atoms in one mole of a substance is equal to ................ ?

0%
Avagadro number
0%
Mass number
0%
Both (a) and (b) above
0%
Density

Explanation

Avagadro's number is the number of units in one mole of any substance, equal to

$6.023\times10^{23}$ . The units may be electrons, ions or molecules depending on nature of the substance & character of the relation.

$\Rightarrow$ If one mole

$=[6.023\times10^{23}]$ , then number of atoms is Avagadro's number.

Rahul dropped 150 g of marble chips into 1 kg of HCl solution containing 0.1 of its weight of pure acid. The mass of marble chips that remained undissolved will approximately be:

0%
6.50 g
0%
13 g.
0%
26 g.
0%
15 g.

Identify the correct statement(s) from the following.

0%
The ion having a positive charge on it, is known as electro-positive ion.
0%
The ion having a negative charge on it, is known as electro-negative ion.
0%
Simple ion is an ion which contains one or more atoms of the same element.
0%
Compound ion is an ion which contains two or more atoms of different elements.

Explanation

The ion carrying a positive charge is known as an electropositive ion (cation).

Cations may be either ion of atoms or of molecules.

Ex.

$Ag^{+}, Na^{+}, NH_{4}^{+} etc$

The one carrying a negative charge is called an electronegative ion (anion).

Ex.

$Cl^-, O^{2-},PO_4^{3-} etc.$

A simple ion contains one or more ions of the same element. It may be cation or anion.

(Example:

$Na^{+}, Ca^{2+}, Cl^- etc$ ).

Compound ion contains two or more atoms of different elements forming a single unit

(Example:

$NH_4^{+}, PO_4^{3-},SO_4^{2-} etc.$ )

Hence, all the given options are correct.

The weight of

$100$ molecules of each of the following substances is:
(a) Chlorine gas
(b) Calcium oxide

0%
(a) $6.022\times 10^{-23}$ g (b) $9.29\times 10^{-21}$ g
0%
(a) $11.78\times 10^{-23}$ g (b) $9.29\times 10^{-23}$ g
0%
(a) $23.96\times 10^{-21}$ g (b) $9.29\times 10^{-23}$ g
0%
(a) $11.78\times 10^{-21}$ g (b) $9.29\times 10^{-21}$ g

Explanation

Number of molecules

$=N_m$

$=100$

Weight of 100 molecules

$=m$

We know,

$N_m=\dfrac{m}{MW}\times 6.023\times 10^{23}$

$\Rightarrow {m}=\dfrac{N_m\times MW}{6.023\times 10^{23}}$ .....(1)

Let us apply the equation (1) to each of the given cases -

(a) Chlorine gas (MW=

$71$ g/mol)

$m \ = \dfrac{100\times 71}{6.023\times 10^{23}}$

$=11.78\times 10^{-21}$ g

(b) Calcium oxide (MW=

$56$ g/mol)

$m=\dfrac{100\times 56}{6.023\times 10^{23}}$

$=9.29\times 10^{-21}$ g
Option

$D$ is correct.

Total number of atoms in 20 g of calcium carbonate is ________.

0%
none of the above
0%
$N_A$
0%
$5N_A$
0%
$\dfrac {1}{5}N_A$

Explanation

number of moles in

$20$ g of

$CaCO_3$

$1$ molecule has

$5$ atoms.

$20$ of calcium carbonate has

$\Rightarrow \dfrac{20}{100}\times 5 \times N_A$

$N_A$

Hence, option

$A$ is the answer.

The ratio by mass of sulphur and oxygen in

$SO_2$ is:

0%
1 : 2
0%
2 : 1
0%
1 : 1
0%
1 : 4

Explanation

$SO_{2}$ , molar mass of S =

$32\ g\ mole^{-1}$ & molar mass of

$O_{2}$ =

$32\ g\ mol^{-1}$ .

Therefore the ratio of their masses = 32:32 = 1:1.

A substance formed by the reaction of hydrogen and oxygen is called a/an:

0%
element
0%
compound
0%
solution
0%
mixture

Explanation

When hydrogen and oxygen are reacted, water is formed.

$2H_2+O_2 \rightarrow 2H_2O$

Water is a compound and its properties are different from the properties of both hydrogen and oxygen.

Hence, option B is the correct answer.

Atoms have a tendency to form molecules to attain stability.

0%
True
0%
False

Explanation

Atoms combine to form molecules to attain stability because atoms in combined form possess less energy and it has been observed that a system that has minimum energy is stable.

Chemical combination is also because of the tendency of an atom to acquire noble gas configuration i.e.

$ns^2np^6$ .

Noble gases have completely filled valence shell and are stable. Atoms also combine to attain noble gas configuration and acquire maximum stability.

Smallest particles of matter which cannot be further divided are called:

0%
molecules
0%
objects
0%
atoms
0%
none of these

Hydrogen, oxygen and carbon dioxide are taken in containers of

$2\:l$ volume each. Compare the number of molecules of the three gases under same conditions of temperature and pressure.

0%
Hydrogen > oxygen > carbon dioxide
0%
Hydrogen = oxygen > carbon dioxide
0%
Hydrogen > oxygen = carbon dioxide
0%
All have equal

The modern atomic mass unit is based on the mass of :

0%
C-12 isotope
0%
hydrogen
0%
oxygen
0%
nitrogen

Explanation

One a.m.u. or one 'u' is equal to

$1.66053892 10^{-24}\ g$ or

$1.66053892 10^{-27}\ kg$ . It is equal to

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

It is used as a standard. The masses of all other atoms are determined relative to the mass of an atom of carbon-12.

$1 \,amu$ is equal to

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

0%
True
0%
False

Explanation

$1amu=\cfrac {1}{12}^{th}$ mass of one

$C-12$ atom

$N_o$ (Avogadro number) =

$6.023\times 10^{23}$

Mass of

$6.023\times 10^{23}$ atoms of carbon =

$12g$

Mass of

$1$ atom of

$^{12}_{6}C=\cfrac {12g}{6.023\times 10^{23}}$

$\therefore 1amu=\cfrac {1}{12}\times \cfrac {12g}{6.023\times 10^{23}}=1.66\times 10^{-24}g$

A magnesium ion has a net positive charge while the magnesium atom has no charge.

0%
True
0%
False

Explanation

Ion is defined as an atom or molecule having positive or negative charge by the loss or gain of electrons.

(i) Negatively charged ions are called anions. Example:

$F^-,OH^-$

(ii) Positively charged ions are called cations. Example:

$Pb^{+4},Pb^{+2},Fe^{+2},Mg^{+2}$

Electronic configuration of

$Mg$ is

$2,8,2$ . It loses

$2$ electrons to attain octet and become stable. Hence, gets a net positive charge of

$2$ .

Magnesium atom with no loss of electron has no charge.

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

0%
the total mass of reactants, barium chloride, and sodium sulphate taken is greater than the total mass of products, barium sulphate, sodium chloride formed
0%
the total mass of reactants, barium chloride, and sodium sulphate is less than the total mass of products, barium sulphate, and sodium chloride
0%
the total mass of the reactants is equal to the total mass of products
0%
none of the above

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

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

Explanation

Law of conservation of mass states that in a chemical reaction, the total mass of the product is equal to the total mass of the reactants.

For example

$CaCO_3\rightarrow CaO+CO_2$

The total mass of reactant

$CaCO_3$

$=40+12+(16\times 3)=100$

The mass of

$CaO=40+16=56$

Mass of

$CO_2=12+(16\times 2)=44$

The total mass of products

$CaO+CO_2=56+44=100$ .

Hence the above example illustrates that the total mass of reactants

$=$ total mass of products.

Assertion : Formula mass (in grams) of magnesium chloride has

$12.044\times 10^{23}$ magnesium ions. Reason : One formula mass of an ionic compound has

$6.022\times 10^{23}$ ions of each type.

0%
Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
0%
Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
0%
Assertion is correct but Reason is incorrect
0%
Assertion is incorrect but Reason is correct
0%
Both assertion and reason are incorrect.

Explanation

Formula mass of magnesium chloride

$(MgCl_2)$ is 1 mole of

$MgCl_2$ which has avogadro number of magnesium ions i.e.,

$6.022\times 10^{23}$ magnesium ions. One formula mass of an ionic compound has ions equal to product number of atoms and avogadro number of each type of atoms.

What is the mass (in grams) of

$3$ moles of

$N$ atom?

0%
$28$ g
0%
$42$ g
0%
$84$ g
0%
$14$ g

Explanation

Atomic mass of

$N$ is

$14$ u. We know that the molar mass is numerically equal to the atomic mass but expressed in g.

Mass of one mole of

$N$ = Molar mass =

$14$ g

Mass of

$3$ moles of

$N$

$= 14\times 3 = 42$ g

$1$ g of

$^{12}C$ contains

$6.022\times 10^{23}$ atoms of Carbon.

0%
True
0%
False

Explanation

No. of moles in $1$ gm of carbon $(12)$ $= \dfrac{1}{12}$

No. of atoms $= \dfrac{1}{12}$ $\times { 6.022} \times {10}^{23}$

$Na$ represent 2 molecules of sodium.

0%
True
0%
False

Explanation

$2Na$ represent

$2$ atoms of sodium not

$2$ molecules of sodium.

Molecules are made up of atoms of same element or different element and held together by chemical bond.

Example:-

(i)

$Cl_2,O_2$ [molecule of same atom]

(ii)

$H_2O,NaCl$ [molecules of different element]

$2Na$ is not written as

$Na_2$ because it is very unstable.

Plumbous ion is represented as

$Pb^{+4}$ .

0%
True
0%
False

Explanation

Plumbous ion is represented as

$Pb^{+2}$ .

Ion is defined as an atom or molecule having a positive or negative charge.

(i) Negatively charged ions are called anions.

Example:-

$\underset {Chloride\ Ion}{Cl^-}$ ,

$\underset {Sulphate\ Ion}{SO_4^{2-}}$

(ii) Positively charged ions are called cations.

Example:-

$\underset {Cuprous\ Ion}{Cu^+}$ ,

$\underset {Ferric\ Ion}{Fe^{3+}}$

Chemical compounds are formed to have constant composition irrespective of their

0%
Method of formation (or) Source
0%
Conditions for formation
0%
Substances taken for formation
0%
Time of formation

What is the mass of one atom of

$C-12$ in grams?

0%
1.992 $\displaystyle \times 10^{-23}$ gm
0%
1.989 $\displaystyle \times 10^{-23}$ gm
0%
1.892 $\displaystyle \times 10^{-23}$ gm
0%
1.965 $\displaystyle \times 10^{-23}$ gm

Explanation

Mass of

$1$ mole =

$12\,gm$

Mass of

$6.022 \times 10^{23}\,atom = 12\,gm$

mass of

$1$ atom =

$\dfrac{12}{6.023 \times 10^{23}} = 1.993 \times 10^{-23}\,gm$

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 3 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

CBSE Questions for Class 9 Chemistry Atoms And Molecules Quiz 3 - MCQExams.com

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Practice Class 9 Chemistry Quiz Questions and Answers

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