Some Basic Concepts of Chemistry Test

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Some Basic Concepts of Chemistry Test - 59

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Question 1
1 / -0

Which of the following weights the most?

A
$$10^{23}$$ molecules of $$H_{2}$$

B
$$1$$ mole of $$H_{2}O$$

C
$$1$$ mole of $$N_{2}$$

D
$$10^{22}$$ atoms of oxygen

Solution
Question 2
1 / -0

$$AB_2$$ and $$A_2B_2$$ are two compounds of the elements A and B. 0.25 mole of each of these compounds weights 9 g and 16 g respectively. Find the atomic masses of A and B.

A
28,4

B
28,8

C
13, 19

D
52,36

Solution
Question 3
1 / -0

Hemoglobin contains 0.334 % of iron by weight. The molecular weight of hemoglobin is approximately 67200.The number of iron atoms (Atomic weight of Fe is 56) present in one molecule of hemoglobin is

A
4

B
6

C
3

D
2

Solution
Question 4
1 / -0

The critical density of the gas $$CO_2$$ is 0.44 $$g\ cm^{–3}$$ at a certain temperature. If $$r$$ is the radius of the molecule, $$r^3$$ in $$cm^3$$ is approximate:

[N is Avogadro number]

A
$$\cfrac {25} {\pi N}$$

B
$$\cfrac {100} {\pi N}$$

C
$$\cfrac {6} {\pi N}$$

D
$$\cfrac {25} {4N\pi}$$

Solution

Critical density of a gas $$= 0.44 gcm^{-3}$$
Molar mass of $$CO_2$$ = 44 g/mole

$$Density = mass /volume $$
Mass of N molecules = 44 g of $$CO_2$$ $$N =6.022\times 10^{23}$$

Mass of 1 molecule $$= \dfrac{44}{N}$$
The volume of 1 molecule $$=\cfrac {4}{3}\pi r^3$$
Putting the values,
$$ 0.44 = \dfrac{\dfrac{44}{N}}{\cfrac {4}{3}\pi r^3}$$

$$ r^3 = \dfrac{100}{\pi N}$$
Question 5
1 / -0

The solubility of potassium chloride in water at $$20^oC$$ is $$34.7g$$ in $$100g$$ of water. The density of solution is $$1.3g/ml$$. Calculate the % of mass/volume concentration of potassium chloride.

A
$$25.76\%$$

B
$$33.49\%$$

C
$$24.7\%$$

D
$$1.3\%$$

Solution
Question 6
1 / -0

In $$\overset { 14 }{ \underset { 7 }{ N } } $$ if mass attributed to electron were doubled & the mass attributed to protons were halved, the atomic mass would become approximately:-

A
Halved

B
Doubled

C
Reduced by 25%

D
Remain same

Solution
Question 7
1 / -0

The weight of 1 mole of a gas of density is $${\text{0}}{\text{.1784}}{\kern 1pt} {\kern 1pt} {\text{g}}{\kern 1pt} {{\text{L}}^{ - 1}}{\text{at}}{\kern 1pt} {\text{NTP}}{\kern 1pt} {\text{is}}{\kern 1pt} - $$

A
0.1784 g

B
1 g

C
4 g

D
4 amu

Solution
Question 8
1 / -0

Find the concentration of glucose in blood which have osmotic pressure $$\pi = 7.7 \ atm$$ at $$T = 25^oC$$

A
$$0.31M$$

B
$$0.45M$$

C
$$0.56M$$

D
$$0.89M$$

Solution

$$\pi = CRT$$
$$7.7 = C \times 0.082 \times 298$$
$$C = \dfrac{7.7}{24.44} \times 100 = 0.31$$
Question 9
1 / -0

$$12$$ gm of an alkaline earth metal gives $$14.8$$g of its nitride. The atomic mass of metal is:

A
$$12$$

B
$$24$$

C
$$20$$

D
$$40$$

Solution

Let the alkaline earth metal be $$A$$.

$$\therefore 3A+N_{2}\rightarrow A_{3}N_{2}$$

$$\Rightarrow \dfrac{Molecular\ mass\ of\ compound}{Atomic\ mass\ of\ metal}$$

$$=\dfrac{Wt.\ of\ compound}{Wt.\ of\ metal}$$

Let the atomic mass of metal be $$x$$.

$$\rightarrow$$ Molecular mass of compound$$=3x+28$$

$$\Rightarrow \dfrac{3x+28}{3x}=\dfrac{14.8}{12}$$

$$\Rightarrow x=40$$
Question 10
1 / -0

A gas mixture contains $$50\%$$ helium and $$50\%$$ methane by volume. What is the percent by weight of methane in the mixture?

A
$$19.97\%$$

B
$$20.05\%$$

C
$$50\%$$

D
$$80.03\%$$

Solution

Solution contain $$He+CH_4$$

$$\%$$ by volume is same as $$\%$$ by moles.

Molecular wt. of $$He=4\ g/mol$$

Molecular wt. of $$CH_4=16\ g/mol$$

Assuming 1 mole of $$He$$ and 1 mole $$CH_4$$

$$\%\ wt$$ of $$CH_4=\dfrac{wt\ of\ CH_4}{Total\ wt}\times 100=\dfrac{16}{4+16}\times 100=80.0\%$$