Atoms and Molecules Test

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Atoms and Molecules Test - 65

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Weekly Quiz Competition

Question 1
1 / -0

The minimum mass of water needed to slake $$1\ kg$$ of quicklime, assuming no loss by evaporation, is:

A
$$243.2\ g$$

B
$$642.8\ g$$

C
$$160.7\ g$$

D
$$321.4\ g$$

Solution

$$CaO+H_2O\longrightarrow Ca(OH)_2$$

moles of $$CaO=\dfrac {1000}{56}=17.85$$ moles

$$1$$ mole $$CaO\equiv 1$$ mole $$H_2O$$

mass of $$H_2O\equiv 17.85\times 18$$

$$=321.42$$ gram

So, the correct option is $$D$$
Question 2
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What is the definition of relative atomic mass, $$A_{r}$$?

A
$$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C}\right )\times 12$$

B
$$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C \times 12}\right )$$

C
$$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C}\right )$$

D
$$\left (\dfrac {\text {mass of one atom of}^{12}C}{\text {average mass of naturally occurring atoms of an element}}\right )$$

Solution

It is the ratio of the average mass per atom of an element from a given sample to $$\cfrac{1}{12}$$ the mass of a carbon-$$12$$ atom.

Relative atomic mass, $${A}_{r} = \left( \cfrac{\text{average mass of naturally occurring atoms of an element}}{\text{mass of one atom of } {^{12}{C}}} \right) \times 12$$

Hence, option A is correct.
Question 3
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Molecular mass of dry air is ________________.

A
less than moist air

B
greater than moist air

C
equal to moist air

D
may be greater or less than moist air

Solution

The molecular mass of dry ice is greater than moist air.
As dry air consists of nitrogen and oxygen while moist air contains water vapour which less mass than that of oxygen and nitrogen making the mass of moist air lower.

$$M.M $$ of dry air $$\simeq 28.9\ gm$$

$$M.M $$ of moist air $$< 28.9\ gm$$
Question 4
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Cortisone is a molecular substance containing $$21$$ atoms of carbon per molecule. The mass percentage of carbon in cortisone is $$69.98$$%. What is the molecular mass of cortisone?

A
$$180.05$$

B
$$360.1$$

C
$$312.8$$

D
$$205.8$$

Solution

Here $$69.98$$% of carbon.
i.e $$100$$ gram of cortisone $$\equiv 69.98\ gram\ $$Carbon
As $$21$$ atoms of carbon per molecules
$$\therefore 21\times 12=252\ gram $$ Carbon
$$100\ gram$$ Cortisone $$\equiv 69.98\ gram$$ Carbon
$$x\ gram$$ cortisone $$\equiv 252\ gram $$ Carbon
$$\therefore x=\dfrac{100\times 252}{69.98}$$
$$=360.1\ gram/mole$$
$$\therefore$$ Option $$B$$ correct
Question 5
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The percentage of copper and oxygen in samples of $$CuO$$ obtained by different methods were found to be the same. This illustrates the law of

A
Constant proportions

B
Conservation of mass

C
Multiple proportions

D
Reciprocal proportions

Solution

In chemistry, the law of constant proportions, or the law of definite composition, states that a chemical compound always contains exactly the same proportion of elements by mass and this law further says that, in any particular chemical compound, all samples of that compound will be made up of the same elements in the same proportion or ratio. For example, any water molecule is always made up of two hydrogen atoms and one oxygen atom in a ratio.
Here the percentage of copper and oxygen obtained by the different methods are the same in $$CuO$$ which indicates that it illustrates the law of constant proportion.
Option $$A$$ is correct.
Question 6
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Which phrase would be incorrect to use:

A
A molecule of a compound

B
An atom of an element

C
An atom of a molecule

D
None of these
Solution
- Compounds are made of molecules. A molecule is the smallest defining particle of a compound. So the phrase 'a molecule of a compound' is correct.
- Elements are made of the same atoms, but can be monoatomic, diatomic, etc. An atom is the smallest defining particle of an element. So, the phrase, 'an atom of an element' is correct.
- 'An atom of a molecule' is also a correct phrase because molecules are made of atoms.
Question 7
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Which of the following statement (s) is/are correct about the Avogadro's number ?

A
It is the number of atoms contained in one mole of any element.

B
It is the number of electrons required to deposit one mole of atoms of any metallic element from a solution of its salt.

C
It is the number of grams of any element that contains its $$6.022\times 10^{23}$$ atoms.

D
It is the number of particles (atoms, molecules or ions) required to make one gram of the substance under consideration
Question 8
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Pressure of $$1$$g of an ideal gas A at $$27^o$$C is found to be $$2$$ bar. When $$2$$ g of another ideal gas B is introduced in the same flask at same temperature the pressure becomes $$3$$ bar. What is the relationship between their molecular masses?

A
$$2M_B=M_A$$

B
$$M_B=M_A$$

C
$$M_B=4M_A$$

D
$$M_B=2M_A$$

Solution

Let, the molecular masses of $$A$$ and $$B$$ be $$M_A$$ and $$M_B$$

$$(2)\times(V)=\left(\dfrac{1}{M_A}\right)\times(R)\times(300)$$

$$(3)\times(V)=\left(\dfrac{1}{M_A}+\dfrac{2}{M_B}\right)\times(R)\times(300)$$

$$\therefore \dfrac{2}{3}=\dfrac{\dfrac{1}{M_A}}{\dfrac{1}{M_A}+\dfrac{2}{M_B}}$$

$$\therefore \dfrac{2}{M_A}+\dfrac{4}{M_B}=\dfrac{3}{M_A}$$

$$\therefore \dfrac{4}{M_B}=\dfrac{1}{M_A}$$

$$\therefore \dfrac{M_A}{M_B}=\dfrac{1}{4}$$

$$\therefore M_B=4M_A$$

So, the correct option is $$C.$$
Question 9
1 / -0

Equivalent mass of a bivalent metal is $$32.7$$ Molecular mass of its chloride is _____________.

A
$$68.2$$

B
$$103.7$$

C
$$136.4$$

D
$$4166.3$$

Solution

Given that,

Equivalent weight of metal $$= 32.7$$

As the given metal is bivalent, so charge on metal $$= 2$$

Molar mass of metal $$= 2 \times 32.7 $$ $$ =65.4 $$

The chloride of given metals $$= MCl_{2}$$

$$ = 65.4 +( 2 \times 35.5 $$ )

$$ = 65.4 + 71 $$

$$ = 136.4 \, gm^{-1}$$

So, the correct option is $$C$$
Question 10
1 / -0

A sample of ozone gas is found to be $$40\%$$ dissociated into oxygen. The average mass of sample should be

A
$$41.60$$

B
$$40$$

C
$$42.35$$

D
$$38.40$$

Solution

Given that,
$$\alpha = 40\% = 0.4$$
$$2O_{3} \longrightarrow 3O_{2}$$
$$O_{3} \longrightarrow \dfrac {3}{2} O_{2}$$
We know that,
$$\alpha = \dfrac {D-d}{(n-1)d}$$
$$D=\dfrac {48}{2} =24,\ d = ?,\ n = \dfrac {3}{2} = 1.5$$
$$0.4 = \dfrac {24-d}{(1.5-1)d} = \dfrac {24-d}{0.5d}$$
$$0.2d=24$$
$$d= \dfrac {24}{12} = 20 $$
Molar mass $$= 2 \times 20 = 40$$

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Atoms and Molecules Test - 65

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Atoms and Molecules Test - 65

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Question 1

$$243.2\ g$$

$$642.8\ g$$

$$160.7\ g$$

$$321.4\ g$$

Solution

Question 2

$$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C}\right )\times 12$$

$$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C \times 12}\right )$$

$$\left (\dfrac {\text {average mass of naturally occurring atoms of an element}}{\text {mass of one atom of}^{12}C}\right )$$

$$\left (\dfrac {\text {mass of one atom of}^{12}C}{\text {average mass of naturally occurring atoms of an element}}\right )$$

Solution

Question 3

less than moist air

greater than moist air

equal to moist air

may be greater or less than moist air

Solution

Question 4

$$180.05$$

$$360.1$$

$$312.8$$

$$205.8$$

Solution

Question 5

Constant proportions

Conservation of mass

Multiple proportions

Reciprocal proportions

Solution

Question 6

A molecule of a compound

An atom of an element

An atom of a molecule

None of these

Solution

Question 7

It is the number of atoms contained in one mole of any element.

It is the number of electrons required to deposit one mole of atoms of any metallic element from a solution of its salt.

It is the number of grams of any element that contains its $$6.022\times 10^{23}$$ atoms.

It is the number of particles (atoms, molecules or ions) required to make one gram of the substance under consideration

Question 8

$$2M_B=M_A$$

$$M_B=M_A$$

$$M_B=4M_A$$

$$M_B=2M_A$$

Solution

Question 9

$$68.2$$

$$103.7$$

$$136.4$$

$$4166.3$$

Solution

Question 10

$$41.60$$

$$40$$

$$42.35$$

$$38.40$$

Solution

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