Some Basic Concepts of Chemistry Test

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Some Basic Concepts of Chemistry Test - 60

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Weekly Quiz Competition

Question 1
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300 gm of 25% w/w solution of solute A is mixed with 400 gm of 40 (w/w) solution of another solute B. What is the w/w percentage of new mixture.

A
10.71% in A

B
35% in B

C
25% in A

D
40% in B

Solution

A : 300 g of 25% w/w
B : 400 g of 40% w/w
$$w/w \, \% \, of \, A= \dfrac{25\% \, of \, 300}{300 + 400} = \dfrac{75}{700} \times 100 = 10.71\%$$
$$w/w \, \% \, of \, B = \dfrac{40\% \, of \, 400}{300 + 400} \times 100 = 22.85\%$$
Question 2
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48 g of Mg contain the same number of atoms as 160 g another mono-atomic element.The atomic mass the element is:

A
24

B
320

C
80

D
40

Solution
Question 3
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Number of $$g$$ of oxygen in $$32.2\ g\ Na_{2}SO_{4}\ 10H_{2}O$$ is:[$$Mol. w t=322$$ ]

A
$$16.0$$

B
$$2.24$$

C
$$18.0$$

D
$$22.4$$

Solution

Number of gm of oxygen in 32.2 g $$Na_2SO_4.10H_2O$$ is No. of oxygen atoms in one molecule =4+10=14

Thus moles of oxygen in n moles of compound=14n

Molar mass of $$Na_2SO_4.10H_2O$$=46+32+64+180=322g/mol

Thus
$$32.2g= \dfrac{32.2}{322}=0.1\ mols$$

Thus moles of $$O=0.1\times14=1.4 $$
So weight is

$$16\times 1.4=22.4g$$

Hence, the correct option is $$D$$
Question 4
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A $$5\%$$ solution of sucrose is isotonic with $$3\%$$ solution of a solute find molecular weight of that solute?

A
$$54 g$$

B
$$108 g$$

C
$$216 g$$

D
$$65 g$$

Solution

$$5\%$$ Glucose solution is isotonic with $$3\%$$ of unknown solute

$$\therefore$$ conc. of glucose $$=$$ conc. of solute

$$\dfrac{5}{180} = \dfrac{3}{M}$$

$$M = \dfrac{3 \times 180 }{5}= 108 g$$

Therefore, the option is B.
Question 5
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3 g of a solute was dissolved in 9 g of water. Find the percentage mass of solute

A
25%

B
33.33%

C
18.7%

D
20%

Solution
Question 6
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The crystalline salt $$Na_{2}SO_{4}.xH_{2}O$$ on heating loses 55.9% of its weight. The formula of the crystalline salt is :

A
$$Na_{2}SO_{4}. 5 H_{2}O$$

B
$$Na_{2}SO_{4}. 7H_{2}O$$

C
$$Na_{2}SO_{4}. 2H_{2}O$$

D
$$Na_{2}SO_{4}. 10H_{2}O$$

Solution
Question 7
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There are two common oxides of Sulphur, one of which contains $$50$$% $${O}_{2}$$ by weight, the other almost exactly $$60$$%. The weights of sulphur which combine with $$1g$$ of $${O}_{2}$$ (Fixed) are in the ratio of:

A
$$1:1$$

B
$$2:1$$

C
$$2:3$$

D
$$3:2$$

Solution

There are two common oxides of sulphur,one of which contains 50% $$O_2$$ by weight the other almost exactly 60%.

% of sulphur % of oxygen

First oxide 50% 50%

Second oxide 40% 60%

In first oxide 1 part of oxygen combines with sulphur = $$\dfrac{50}{50} = 1$$

Im second oxide 1 part of oxygen will combine with sulphur = $$\dfrac {40}{60} = 0.67$$

Therefore weight of sulphur which combines with 1 g of $$O_2$$ are in the ratio : $$\dfrac{1}{0.67}= 1:0.67 = 3:2$$

Hence option D is correct answer.
Question 8
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A sample of oxygen contain $$_{ 8 }^{ 16 }{ O },_{ 8 }^{ 17 }{ O }$$ and $$_{ 8 }^{ 18 }{ O }$$ atoms has average atomic mass $$16.12$$. If mole $$\%$$ of $$_{ 8 }^{ 16 }{ O }$$ is $$90$$, then weight $$\%$$ of $$_{ 8 }^{ 18 }{ O }$$ is

A
$$2$$

B
$$2.33$$

C
$$1.79$$

D
$$8$$
Question 9
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Iron forms two oxides, in first oxide $$56$$ grams of Iron is found to be combined with $$16$$ gram oxygen and in second oxide $$112$$ gram of Iron is found to be combined with $$48$$ gram oxygen. This data satisfy the law of

A
Conservation of mass

B
Reciprocal proportion

C
Multiple proportions

D
Combining volume

Solution
Question 10
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Calculate the concentration in $$m/v \%$$ (in (mg/mL) of KCl solution which contains 0.0245 gm of KCl in 35 mL of solution.

A
40

B
60

C
70

D
30

Solution