Atoms and Molecules Test

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Atoms and Molecules Test - 14

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following ions is mono-atomic?

A
Nitrate

B
Sulphite

C
Sulphide

D
Hydroxide

Solution

Sulphide (S²⁻) ion is mono-atomic since it consists of only one single charged atom.

The correct answer is C.
Question 2
1 / -0

Which of the following compounds has a molecular mass equal to 95 u?

A
Sodium nitrate

B
Carbon disulphide

C
Calcium hydroxide

D
Magnesium chloride

Solution

The molecular mass of any substance is the sum of the atomic masses of all atoms in a molecule of that substance.

Molecular mass of magnesium chloride (MgCl₂)

= 1 × Atomic mass of Mg + 2 × Atomic mass of Cl

= 1 × 24 + 2 × 35.5

= 24 + 71

= 95 u

The correct answer is D.
Question 3
1 / -0

The molecular mass of calcium hydroxide is

A
57 u

B
58 u

C
74 u

D
97 u

Solution

The chemical formula of calcium hydroxide is Ca(OH)₂.

We know that,

Atomic mass of calcium (Ca) = 40 u

Atomic mass of oxygen (O) = 16 u

Atomic mass of hydrogen (H) = 1 u

Molecular mass of any substance is the sum of the atomic masses of all atoms in a molecule of that substance.

Thus, the molecular mass of Ca(OH)₂

= 1× atomic mass of Ca + 2× atomic mass of O + 2× atomic mass of hydrogen

= 1 × 40 + 2 × 16 + 2 × 1

= 40 + 32 + 2

= 74 u

Hence, the molecular mass of calcium hydroxide is 74 u.

The correct answer is C.
Question 4
1 / -0

Formula unit mass cannot be used in case of

A
CH₄

B
NaCl

C
K₂O

D
CaCl₂

Solution

Formula unit mass is used in case of a compound whose constituent particles are ions. Methane (CH₄) is a covalent compound. The constituent particles of CH₄ are not ions; they are carbon and hydrogen atoms. Thus, formula unit mass is not used in case of CH₄.

Hence, the correct answer is option A.
Question 5
1 / -0

The formula unit mass of potassium chloride is

A
74.5 u

B
59.0 u

C
113.5 u

D
110.0 u

Solution

Calculation of the formula unit mass is done in the same manner as that of the calculation of molecular mass. The formula unit mass of a substance is the sum of atomic masses of all atoms in a formula unit of that compound.

The chemical formula of potassium chloride is KCl.

Atomic mass of potassium (K) = 39 u

Atomic mass of chlorine (Cl) = 35.5 u

Thus, formula unit mass of potassium chloride (KCl)

= 1 × atomic mass of K + 1 × atomic mass of Cl

= 1 × 39 u + 1 × 35.5 u

= (39 + 35.5) u

= 74.5 u

The correct answer is A.
Question 6
1 / -0

What is the atomic mass nitrogen atom?

A
1 u

B
28 g

C
14 u

D
14 g

Solution

Atomic mass of nitrogen = 14 u (atomic mass unit)

Hence, the correct answer is option C.
Question 7
1 / -0

The number of nitrogen atoms present in 1.5 moles of nitrogen atoms is

A
6.022 × 10²³

B
9.033 × 10²³

C
12.044 × 10²³

D
18.066 × 10²³

Solution

We know that 1mole of any substance contains 6.022 × 10²³ particles (atoms, molecules, or ions).

Thus, the number of nitrogen atoms present in 1 mole of atoms of nitrogen is 6.022 × 10^23.

Therefore, the number of atoms present in 1.5 moles of atoms of nitrogen

= 1.5 × 6.022 × 10²³

= 9.033 × 10²³

The correct answer is B.
Question 8
1 / -0

Which of the following statements represents the law of conservation of mass?

A
Atoms of a given element are identical in mass.

B
Atoms of different elements have different masses.

C
Mass can neither be created nor destroyed in a chemical reaction.

D
In a chemical substance, elements are always present in definite proportions by mass.

Solution

The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. Thus, the total mass before a reaction is equal to the total mass after the reaction.

The correct answer is C.
Question 9
1 / -0

Which of the following statements is not one of the postulates of Dalton’s atomic theory?

A
All matter is made of very tiny particles called atoms

B
Atoms can neither be created nor destroyed in a chemical reaction

C
Atoms combine in small whole numbers to form compounds

D
The relative number and kinds of atoms vary in a given compound

Solution

According to Dalton’s atomic theory, the relative number and kinds of atoms are constant in a given compound.

The correct answer is D
Question 10
1 / -0

Use the following information to answer the next question.

The ratio by mass of carbon and oxygen in carbon dioxide is 3:8.

The respective masses of carbon and oxygen required to react completely to form 33 g of carbon dioxide are

A
9 g and 24 g

B
12 g and 21 g

C
21 g and 12 g

D
24 g and 9 g

Solution

It is given that the ratio by mass of carbon and oxygen in carbon dioxide is 3:8.

Let the required mass of carbon and oxygen be 3x g and 8x g respectively.

Now, 3x + 8x = 33

⇒ 11x = 33

⇒ x = 3

Therefore, the required mass of carbon = 3 × 3 g

= 9 g

And, the required mass of oxygen = 8 × 3 g

= 24 g

The correct answer is A.
Question 11
1 / -0

Which of the following elements has atomicity 2?

A
Helium

B
Nitrogen

C
Aluminium

D
Phosphorus

Solution

The number of atoms constituting a molecule is known as its atomicity. A molecule of nitrogen molecule consists of two atoms of nitrogen. Hence, it is a diatomic molecule and its atomicity is 2.

Hence, the correct answer is option B.
Question 12
1 / -0

Which of the following symbols is approved by the IUPAC for copper?

A
Ca

B
Co

C
Cu

D
Cl

Solution

The IUPAC approves the symbol Cu for copper.

The correct answer is C.
Question 13
1 / -0

The ratio by the number of atoms for aluminium oxide is

A
Al:O = 1:2

B
Al:O = 1:3

C
Al:O = 2:3

D
Al:O = 3:2

Solution

A molecule of aluminium oxide (Al₂O₃) consists of two aluminium atoms and three oxygen atoms. Therefore, the ratio by the number of atoms for Al₂O₃ is

Al:O = 2:3.

The correct answer is C.
Question 14
1 / -0

The mass of 1 mole of chlorine molecule is

A
17.0 g

B
28.5 g

C
35.5 g

D
71.0 g

Solution

Atomic mass of chlorine= 35.5 u

1 mole of chlorine molecules = Gram molecular mass of chlorine

= 71 g

The correct answer is D.
Question 15
1 / -0

The ratio by mass of atoms for sodium oxide is

A
Na:O = 8:23

B
Na:O = 16:23

C
O:Na = 16:23

D
O:Na = 8:23

Solution

A molecule of sodium oxide (Na₂O) consists of one oxygen (O) and two sodium (Na) atoms.

Atomic mass of Na = 23 u

Atomic mass of O = 16 u

Thus, the ratio by mass of atoms for Na₂O can be calculated as:

Na:O = 2 × 23 : 1 × 16

= 46:16

= 23:8

The correct answer is A.

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Atoms and Molecules Test - 14

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Question 1

Nitrate

Sulphite

Sulphide

Hydroxide

Solution

Question 2

Sodium nitrate

Carbon disulphide

Calcium hydroxide

Magnesium chloride

Solution

Question 3

57 u

58 u

74 u

97 u

Solution

Question 4

CH4

NaCl

K2O

CaCl2

Solution

Question 5

74.5 u

59.0 u

113.5 u

110.0 u

Solution

Question 6

1 u

28 g

14 u

14 g

Solution

Question 7

6.022 × 1023

9.033 × 1023

12.044 × 1023

18.066 × 1023

Solution

Question 8

Atoms of a given element are identical in mass.

Atoms of different elements have different masses.

Mass can neither be created nor destroyed in a chemical reaction.

In a chemical substance, elements are always present in definite proportions by mass.

Solution

Question 9

All matter is made of very tiny particles called atoms

Atoms can neither be created nor destroyed in a chemical reaction

Atoms combine in small whole numbers to form compounds

The relative number and kinds of atoms vary in a given compound

Solution

Question 10

9 g and 24 g

12 g and 21 g

21 g and 12 g

24 g and 9 g

Solution

Question 11

Helium

Nitrogen

Aluminium

Phosphorus

Solution

Question 12

Ca

Co

Cu

Cl

Solution

CH₄

K₂O

CaCl₂

6.022 × 10²³

9.033 × 10²³

12.044 × 10²³

18.066 × 10²³