Atoms and Molecules Test

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Atoms and Molecules Test - 66

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Weekly Quiz Competition

Question 1
1 / -0

The modern atomic weight scale is based on

A
$$C^{12}$$

B
$$O^{16}$$

C
$$H^1$$

D
$$C^{13}$$

Solution

Modern atomic weight scale is based on $$C^{12}$$. The standard unit for expressing the mass of atom is amu (atomic mass unit). It is equal to 1/12 of the mass of an atom of carbon-12.
Question 2
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If the atomic weight of carbon were set at 24 amu, the value of the Avogadro constant would be:

A
$$ 6.022 \times 10^{23} $$

B
$$ 12.044 \times 10^{23} $$

C
$$ 3.011 \times 10^{23} $$

D
None of these

Solution

1 amu $$ \times N_A = 1g $$ [ from general definition ]

Wt of 1 mole of $$ C^{12} = 12 g $$

If mass of one atom of $$ C^{12} $$ is set to be 24 amu then ( mass of one atom $$ \times $$ avogadro's no = mass of 1 mole of $$ C^{12} $$)

$$ 24 amu \times N_A = 12 g $$

$$ N_A =\dfrac {12 g}{24 amu}= \dfrac {12g}{ 224 \times \dfrac {1}{6.023 \times 10^{23} g } } $$

$$ = \dfrac {6.023}{2} \times 10^{23} = 3.011 \times 10^{23} $$

Hence, Option "C" is the
Question 3
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1 amu is equal to

A
$$\dfrac{1}{12}$$ of C-12

B
$$\dfrac{1}{14}$$ of O-16

C
$$1\,g$$ of hydrogen

D
$$1.66 \times 10^{-23} kg$$

Solution

One atomic mass unit or amu is a mass unit equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12.
Question 4
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A molecule can be defined as the:

A
A group of two or more atoms that are chemically bonded together

B
The smallest particle of an element or a compound that is capable of independent existence and shows all the properties of that substance

C
The substance which is formed by the combination of atoms of the same element or of different elements

D
All these are correct.

Solution

A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound. A molecule is formed by the combination of atoms of the same element or of different elements.
So, all the statements are correct.

Thus option $$D$$ is correct.
Question 5
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In water, the proportion of oxygen and hydrogen by mass is:

A
$$ 1: 4 $$

B
$$ 1 : 8 $$

C
$$ 4 : 1 $$

D
$$ 8 : 1 $$

Solution

The chemical formula of water is $$H_2O$$. The molar mass of oxygen and hydrogen is $$16$$ and $$1 \ g/mol$$ respectively. Water has $$2H$$ and one oxygen atom.
In water, the ratio of oxygen to hydrogen is $$8:1$$ by mass.
Hence, option D is correct.
Question 6
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Which of the following represents amu?

A
Mass of 1 hydrogen atom

B
Mass of C-12 atom

C
mass of O-16 atom

D
1/12th of mass of C-12 atom

Solution

An atomic mass unit (symbolized amu) is defined as precisely $$\frac{1}{12}th$$ the mass of an atom of carbon-12. The carbon-12 (C-12) atom has six protons and six neutrons in its nucleus.

Hence, option $$D$$ is correct.
Question 7
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Which of the following is not an element?

A
Oxygen gas

B
Carbon dioxide gas

C
Sulphur dioxide gas

D
Nitrogen dioxide gas

E
All of the above

Solution

Elements are pure substances that cannot be further broken down into simpler substances.
Oxygen gas, Carbon dioxide gas, sulphur dioxide gas, nitrogen dioxide gas are examples of compounds and they can be further broken down into elements by chemical reactions. There is no element in the given options.
Hence, option $$E$$ i.e. All of the above is the correct answer.
Question 8
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Fill in the blanks:-

The formula unit mass of $$Ca_3(PO_4)_2$$ is_______.

A
310

B
270

C
330

D
410

Solution

Formula unit mass of $$Ca_3{(PO_4)}_2$$

$$ = (3 \times atomic \ mass \ of \ Ca) + (2 \times atomic \ mass \ of \ P) + (8 \times atomic \ mass \ of \ oxygen)$$

$$=(3 \times 40) + (2 \times 31) + (8 \times 16)$$

$$=310$$

$$\therefore$$ The formula unit mass of $$Ca_3{(PO_4)}_2$$ is $$310$$

Hence, option A is correct.
Question 9
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Which of the following reactions is not according to the law of conservation of mass?

A
$$2Mg(s)+O_2(g)\to 2MgO(s)$$

B
$$C_3H_3(g)+O_2(g)\to CO_2(g)+H_2O(g)$$

C
$$P_4(s)+5O_2(g)\to P_4O_{10}(s)$$

D
$$CH_4(g)+2O_2(g)\to CO_2(g)+2H_2O(g)$$

Solution

Number of atoms in the reactant side is not equal to the number of atoms in the product side for the reaction given in option B.
Question 10
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The outermost shell of an atom is known as

A
valency

B
valence electrons

C
nucleus

D
valence shell

Solution

The outermost shell of an atom is called a valence shell as the electrons present in the outermost shell contribute towards the valency of the atom.

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Re-Attempt Weekly Quiz Competition

Atoms and Molecules Test - 66

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Atoms and Molecules Test - 66

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Question 1

$$C^{12}$$

$$O^{16}$$

$$H^1$$

$$C^{13}$$

Solution

Question 2

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

$$ 12.044 \times 10^{23} $$

$$ 3.011 \times 10^{23} $$

None of these

Solution

Question 3

$$\dfrac{1}{12}$$ of C-12

$$\dfrac{1}{14}$$ of O-16

$$1\,g$$ of hydrogen

$$1.66 \times 10^{-23} kg$$

Solution

Question 4

A group of two or more atoms that are chemically bonded together

The smallest particle of an element or a compound that is capable of independent existence and shows all the properties of that substance

The substance which is formed by the combination of atoms of the same element or of different elements

All these are correct.

Solution

Question 5

$$ 1: 4 $$

$$ 1 : 8 $$

$$ 4 : 1 $$

$$ 8 : 1 $$

Solution

Question 6

Mass of 1 hydrogen atom

Mass of C-12 atom

mass of O-16 atom

1/12th of mass of C-12 atom

Solution

Question 7

Oxygen gas

Carbon dioxide gas

Sulphur dioxide gas

Nitrogen dioxide gas

All of the above

Solution

Question 8

310

270

330

410

Solution

Question 9

$$2Mg(s)+O_2(g)\to 2MgO(s)$$

$$C_3H_3(g)+O_2(g)\to CO_2(g)+H_2O(g)$$

$$P_4(s)+5O_2(g)\to P_4O_{10}(s)$$

$$CH_4(g)+2O_2(g)\to CO_2(g)+2H_2O(g)$$

Solution

Question 10

valency

valence electrons

nucleus

valence shell

Solution

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