Atoms and Molecules Test

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Atoms and Molecules Test - 36

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Weekly Quiz Competition

Question 1
1 / -0

In a chemical reaction, when 14 g of sodium carbonate reacted with 10g of acetic acid (ethanoic acid), then it was observed that, 16.67 g of sodium acetate solution in water and 7.33 g of carbon dioxide were produced. Which law does this depicts?

A
Law of definite proportions

B
Law of conservation of mass

C
Law of constant proportions

D
Avogadro's law

Solution

In the given reaction,
$$\underset {(14g)}{\text {Sodium carbonate}}+\underset {(10g)}{\text {Ethanoic acid}}\Rightarrow \underset {(16.67)}{(Sodium ethanoate+water)}+\underset {(7.33 g)}{Carbon dioxide gas}$$
Total mass of all reactants combined
$$=14 g+10 g=24 g$$
Total mass of all the products formed
$$= 16.67 g + 7.33 g =24 g$$.
It is observed that Total mass of all reactants combined $$= 24 g =$$ Total mass of all the products formed. Therefore, the given observations are in agreement with the law of conservation of mass.
Question 2
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Smallest particle of an element or a compound which is capable of independent existence is called:

A
atom

B
molecule

C
element

D
compound

Solution

Smallest particle of an element or a compound which is capable of independent existence is called molecule.A molecule is formed when two or more atoms join together chemically.Molecules of elements like noble gases such as helium,neon etc are made up of one atom only(molecules are capable of independent existence while atoms are not capable of independent existence).Only in these case atoms are capable of independent existence.Noble gases are monoatomic.
Question 3
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720 g of water contains ______ moles of water.

A
20

B
40

C
60

D
80

Solution

Given, mass of $$H_2O = 720\ g$$
We know that, molar mass of water = $$18 g/mol$$

Moles of water $$= \displaystyle \frac{\text{Mass of water}}{\text{Molar mass of water}}$$

$$= \displaystyle \frac{720}{18} = 40\ moles$$
Question 4
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Any sample of pure water, irrespective of its source, contains 88.89% oxygen and 11.11 % hydrogen by mass. The data supports the:

A
Law of conservation of mass

B
Law of constant composition

C
Law of multiple proportion

D
Law of reciprocal proportion

Solution

The ratio of the mass of hydrogen to the mass of oxygen is
always 1:8, whatever the source of water.
$$\cfrac {\text { mass of hydrogen}}{\text {mass of oxygen}}=\cfrac {11.11}{88.89}=1:8$$

Hence the given data supports law of Constant proportion.
Question 5
1 / -0

Which law stated that 'matter is neither created nor destroyed'?

A
Law of multiple proportion

B
Law of conservation of energy

C
Law of constant composition

D
Law of conservation of mass

Solution

The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations.

According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants.
Question 6
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Which of these is not a molecule?

A
$$H_2$$

B
$$Cl$$

C
$$O_3$$

D
$$NaCl$$

Solution

Hint: Molecules are made up of atoms that are held together by chemical bonds.

Correct Answer: Option $$B$$

Explanation of Correct Option:
A molecule is combination of two or more than two atoms.
The symbol $$Cl$$ represents an atom of chlorine. The molecule of chlorine is represented by the symbol $$Cl_2$$.

Explanation of Incorrect Option:
$$H_2$$ is a symbol of a molecule of hydrogen.
$$O_3$$ is a symbol of a molecule of ozone.
$$NaCl$$ is a symbol of Sodium Chloride, it is a compound.
Question 7
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Since Avogadro number is $$6.023\times {10}^{23}$$ and atomic mass of nitrogen is $$14$$ amu, one mole of $$N_2$$ gas will have:

A
$$0.5\times 6.023\times {10}^{23}$$ atoms

B
$$2\times 6.023\times {10}^{23}$$ atoms

C
$$14\times 6.023\times {10}^{23}$$ atoms

D
$$28\times 6.023\times {10}^{23}$$ atoms

Solution

1 molecule of $$N_2$$ = 2 atoms of $$N$$
1 mole of $$N_2 = 2 \times N_A$$ atoms of $$N$$ (since, one mole$$ = 6.023 \times 10^{23}$$ number of entities)
1 mole of $$N_2$$ gas $$= 2\times 6.023 \times 10^{23}$$ atoms of $$N$$.
Question 8
1 / -0

The mass of $$Na$$ present in 11.7 g of $$NaCl$$ is:

A
2.3 g

B
4.6 g

C
6.9 g

D
7.1 g

Solution

Molar mass of NaCl is 58 g

58 g of NaCl has $$Na=23 \ g$$

11.7g of NaCl has Na=$$\dfrac{23}{58}\times{11.7}=4.63g$$

Option B is correct.
Question 9
1 / -0

Smallest possible unit of a compound which has independent existence is :

A
molecule

B
atom

C
ion

D
electron

Solution

Smallest possible unit of a compound which has independent existence is a molecule.
A molecule is the smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecule are made up of atoms that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electrons among atoms.
Question 10
1 / -0

Which of the following elements has the same molecular mass as its atomic mass?

A
Nitrogen

B
Neon

C
Oxygen

D
Chlorine

Solution

Neon is the element having same molecular mass as its atomic mass.
Actually Neon would be listed as having an atomic mass of about 20.18, because of a mixture of isotopes, Z = Atomic number, the number of protons in the nucleus which defines the element.

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Atoms and Molecules Test - 36

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Atoms and Molecules Test - 36

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Question 1

Law of definite proportions

Law of conservation of mass

Law of constant proportions

Avogadro's law

Solution

Question 2

atom

molecule

element

compound

Solution

Question 3

20

40

60

80

Solution

Question 4

Law of conservation of mass

Law of constant composition

Law of multiple proportion

Law of reciprocal proportion

Solution

Question 5

Law of multiple proportion

Law of conservation of energy

Law of constant composition

Law of conservation of mass

Solution

Question 6

$$H_2$$

$$Cl$$

$$O_3$$

$$NaCl$$

Solution

Question 7

$$0.5\times 6.023\times {10}^{23}$$ atoms

$$2\times 6.023\times {10}^{23}$$ atoms

$$14\times 6.023\times {10}^{23}$$ atoms

$$28\times 6.023\times {10}^{23}$$ atoms

Solution

Question 8

2.3 g

4.6 g

6.9 g

7.1 g

Solution

Question 9

molecule

atom

ion

electron

Solution

Question 10

Nitrogen

Neon

Oxygen

Chlorine

Solution

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