Some Basic Concepts of Chemistry Test

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Some Basic Concepts of Chemistry Test - 48

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Weekly Quiz Competition

Question 1
1 / -0

An organic compound made of $$C, H$$ and $$N$$ contains $$20$$% nitrogen. Its minimum molecular weight is:

A
$$70$$

B
$$140$$

C
$$100$$

D
$$65$$

Solution

Let the molecular weight be $$X$$. Then $$20$$% of $$X$$ is equal to molecular weight of Nitrogen ($$N$$).

$$20$$% of $$X$$ = $$14$$

$$X$$/$$5$$ = $$14$$

Therefore the minimun molecular weight is $$14×5$$ = $$70$$.
Question 2
1 / -0

At $$\displaystyle\, 80^{\circ}C$$ the vapour pressure of pure liquid A is 250 mm of Hg and that of pure liquid B is 1000 mm of Hg. If a solution of A and B boils at $$\displaystyle\, 80^{\circ}C$$ and 1 atm pressure, the amount of A in the mixture is (1 atm = 760 mm Hg)

A
50 mole percent

B
52 mole percent

C
34 mole percent

D
48 mole percent

Solution

$$P$$= $$P°_{a}$$*$$X_{a}$$+ $$P°_{b}$$*($$1$$ - $$X_{a}$$)
$$760$$ = $$250$$*$$X_{a}$$ + $$1000$$*($$1$$ - $$X_{a}$$)
$$X_{a}$$ = $$34$$ mole percent
Question 3
1 / -0

Which symbol is used to represent the unit of atomic mass, amu?

A
u

B
A

C
M

D
n

Solution

The symbol 'u' represents the unit of atomic mass, amu. For example, the atomic mass of carbon-12 is written as 12 u.
Hence, option A is correct.
Question 4
1 / -0

$$CH_3CH_2CH_2CH_{3(g)}\rightleftharpoons CH_3-\underset{iso-butane}{\underset{CH_3}{\underset{|}{C}H}}-CH_{3(g)}$$

A
$$75\%$$

B
$$90\%$$

C
$$30\%$$

D
$$60\%$$

Solution

$$K_c$$ for the above reaction is represented as
$$ K_c = \dfrac{isobutane}{butane}$$
$$ (isobutane) = 3(butane)$$
So the concentration of sobutane is thrice of butane in 100% solution of the isobutane and butane.
So isobutane $$= 75\%$$
Question 5
1 / -0

4.88 g of $$KClO_3$$ when heated produced 1.92 g of $$O_2$$ and 2.96 g of KCl. Which of the following statements regarding the experiment is correct?

A
The result illustrates the law of conservation of mass.

B
The result illustrates the law of multiple proportions.

C
The result illustrates the law of constant proportion.

D
None of the above laws is being illustrated here.

Solution

$$2KClO_3 \rightarrow 2KCl+3O_2$$
Mass of the reactant = total mass of the products ($$2.96 + 1.92=4.88\ g$$)
According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants. Therefore, this demonstrates the law of conservation of mass.
Option A is correct
Question 6
1 / -0

Which of the following statements best explains the law of conservation of mass, concerning a chemical change?

A
100 g of water is heated to give steam.

B
A sample of $$N_2$$ gas is heated at constant pressure without any change in mass.

C
36 g of carbon combines with 32 g of oxygen to form 68 g of $$CO_2$$.

D
10 g of carbon is heated in vacuum without any change in mass.

Solution

According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants.
Among the given option only option C involves a chemical change/reaction as:
$$C+O_2 \rightarrow CO_2$$
$$m_{reactants}=m_{products}$$
$$36+32=68\ g$$
option C is the best demonstration of the law of conservation of mass.
Question 7
1 / -0

The density of a gas is $$1.78 \ g \ L^{-1}$$ at STP. The weight of one mole of gas is:

A
$$39.9\ g$$

B
$$22.4\ g$$

C
$$3.56\ g$$

D
$$29\ g$$

Solution

Density $$=1.78 \ g L^{−1}$$ at STP

mass of $$1\ L$$ gas$$=1.78\ g$$

1 mol of gas at STP $$=22.4\ L$$

$$\therefore\ $$mass of $$22.4\ L$$ gas$$=22.4 \times 1.78=39.872\ g$$

Option $$A$$ is correct.
Question 8
1 / -0

At $$-50^0C$$, liquid $$NH_3$$ has ionic product is $$10^{-30}$$. How many amide $$(NH_2{^-})$$ ions are present per $$mm^3$$ in pure liquid $$NH_3$$ ? Take $$N_a \, = \, 6 \times \, 10^{23}$$

A
602

B
567

C
450

D
892

Solution

$$\displaystyle 2NH_3 \to NH_4^++NH_2^- $$
The ionic product $$\displaystyle [NH_2^-][NH_4^+]=10^{-30} $$
$$\displaystyle [NH_2^-]=[NH_4^+]$$
$$\displaystyle [NH_2^-]^2=10^{-30} $$
$$\displaystyle [NH_2^-]=10^{-15} \ mol/dm^3 $$
$$\displaystyle 1 \ dm^3 =10^6 \ mm^3$$
$$\displaystyle [NH_2^-]=10^{-15} \ mol/dm^3 \times \dfrac {1 \ dm^3}{10^6 \ mm^3}$$
$$\displaystyle [NH_2^-]=10^{-21} \ mol/mm^3 $$
$$\displaystyle N_a=6 \times 10^{23} \ ions/mol$$
$$\displaystyle [NH_2^-]=10^{-21} \ mol/mm^3 \times \dfrac { 6 \times 10^{23} \ ions} { 1 \ mol }$$
$$\displaystyle [NH_2^-]= 600 \ ions/mm^3 $$
Hence, $$\displaystyle [NH_2^-]= 602 \ ions/mm^3 $$ is correct answer.
Question 9
1 / -0

Which of the following gases will have least volume if 10 g of each gas is taken at same temperature and pressure?

A
$$CO_2$$

B
$$N_2$$

C
$$CH_4$$

D
$$HCl$$

Solution

Avogadro’s Law states that under same conditions of temperature and pressure, volume of gases (V) is proportional to the amount of gases in moles(n).

$$V \propto n$$

$$n=\dfrac{mass}{molar\ mass}$$

Mass of gases are same = 10 g

$$V \propto \dfrac{1}{Molar\ mass}$$

Molar mass of $$CO_2=12+2\times 16=44\ g$$
Molar mass of $$N_2=2\times 14=28\ g$$
Molar mass of $$CH_4=12+4\times 1=16\ g$$
Molar mass of $$HCl=1+35.5=36.5\ g$$

Order of volume of 10 g of given gases is:
$$CH_4>N_2>HCl>CO_2$$
Question 10
1 / -0

What will be the mass of 100 atoms of hydrogen?

A
$$100\ g$$

B
$$1.66 \times 10^{-22}$$ g

C
$$6.023 \times 10^{23}$$ g

D
$$100 \times 6.023 \times 10^{23}$$ g

Solution

Mass of 1 mol or ($$6.022 \times 10^{23}$$ atoms) of $$H=1\ g$$
Mass of 100 atoms = $$\dfrac{1}{6.022 \times 10^{23}} \times 100$$ g
$$=0.166 \times 10^{-23}=1.66 \times 10^{-22}$$ g

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Some Basic Concepts of Chemistry Test - 48

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Some Basic Concepts of Chemistry Test - 48

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SHARING IS CARING

Question 1

$$70$$

$$140$$

$$100$$

$$65$$

Solution

Question 2

50 mole percent

52 mole percent

34 mole percent

48 mole percent

Solution

Question 3

u

A

M

n

Solution

Question 4

$$75\%$$

$$90\%$$

$$30\%$$

$$60\%$$

Solution

Question 5

The result illustrates the law of conservation of mass.

The result illustrates the law of multiple proportions.

The result illustrates the law of constant proportion.

None of the above laws is being illustrated here.

Solution

Question 6

100 g of water is heated to give steam.

A sample of $$N_2$$ gas is heated at constant pressure without any change in mass.

36 g of carbon combines with 32 g of oxygen to form 68 g of $$CO_2$$.

10 g of carbon is heated in vacuum without any change in mass.

Solution

Question 7

$$39.9\ g$$

$$22.4\ g$$

$$3.56\ g$$

$$29\ g$$

Solution

Question 8

602

567

450

892

Solution

Question 9

$$CO_2$$

$$N_2$$

$$CH_4$$

$$HCl$$

Solution

Question 10

$$100\ g$$

$$1.66 \times 10^{-22}$$ g

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

$$100 \times 6.023 \times 10^{23}$$ g

Solution

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