Some Basic Concepts of Chemistry Test

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Some Basic Concepts of Chemistry Test - 43

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Question 1
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What is the percent $$X$$ by mass for compound $$XY_{2}$$ if compound $$XY$$ is $$74$$% $$X$$ by mass?

A
$$25$$%

B
$$40$$%

C
$$60$$%

D
$$75$$%

Solution

Given $$\%$$ of X in $$XY = 74\%$$
So, $$\%$$ Y in $$XY = 26\%$$
$$\Rightarrow \dfrac{\text{Mass of X}}{\text{Mass of X + Mass of Y}} = \dfrac{74}{100} $$

$$\Rightarrow 100 \text{ mass of X} = 74(\text{mass of X}) + 74(\text{mass of Y})$$
$$\Rightarrow 26 \text{ mass of X} = 74(\text{mass of Y})$$
$$\Rightarrow 13 \text{ mass of X} = 37(\text{mass of Y})$$
$$\%$$ of X in $$XY_2 = \dfrac{\text{Mass of X}}{\text{(Mass of X) + 2(Mass of Y)}} \times 100 = \dfrac{\dfrac{37}{13}(\text{Mass of Y})}{\dfrac{63}{13}(\text{Mass of Y} )} \times 100 = \dfrac{37}{63} \times 100 = 60\%$$
Question 2
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Who arranged elements his periodic table, based upon atomic weight:

A
Thomson

B
Mendeleev

C
Lavoisier

D
Sir Humphrey Davy

Solution

Mendeleev arranged the elements first in a regular table known as periodic table according to their molecular masses. The law that the properties of the elements are periodic functions of their atomic numbers.

Also called Mendeleev's law, (originally) the statement that the chemical and physical properties of the elements recur periodically when the elements are arranged in the order of their atomic weights

Hence, the correct option is $$B$$
Question 3
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Spectroscopy is :

A
the study of heat changes in a chemical reaction.

B
the use of the absorption, emission, or scattering of electromagnetic radiation by matter to study the matter or the chemical processes it undergoes.

C
the mathematical description of the motion and interaction of subatomic particles. It incorporates quantization of energy, wave-particle duality, the uncertainty principle, and their relationship to chemical processes.

D
none of the above

Solution

Spectroscopy is the study of interaction of electromagnetic radiation with matter. The phenomenon used in spectroscopy are absorption, emission, or scattering of electromagnetic radiation by matter.
Question 4
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A student carries out the following reaction in the laboratory:

Sodium carbonate + Copper sulphate $$\rightarrow $$ Copper carbonate + Sodium sulphate

How could you determine the reaction obeyed the law of conservation of mass?

A
Mass of the sample after the reaction is compared to the mass before the reaction begins

B
Mass of the sample as the reaction is run is measured

C
Filtering the reactants

D
Running the reaction in an open system

Solution

Law of conservation of mass states that mass of the reactants before the reaction should be same as the mass of the products after the reaction.

We will measure the mass of the product and see if it is the same as the mass of the reactants. Both will be same, thus showing the law of conservation of mass is obeyed.

$$\Rightarrow$$ Mass of the reactants = Mass of the products after the reaction
Question 5
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The reaction between dinitrogen monoxide, $$N_{2}O$$ and oxygen gas, $$O_{2}$$, carried out at high pressures, results in the formation of dinitrogen tetroxide, $$N_{2}O_{4}$$, as the only product. The unbalanced equation for the reaction is:

$$N_{2}O(g) +O_{2}(g)\rightarrow N_{2}O_{4}(g)$$

Given the legend and the $$N_{2}O/O_{2}$$ mixture shown below.
Which of the following represents the composition of the system after the reaction has gone to completion?

A

B

C

D

Solution

Balanced reaction:

$$N_{2}O(g) +1.5O_{2}(g)\rightarrow N_{2}O_{4}(g)$$

1 molecule of $$N_2O$$ reacts with 1.5 molecules of oxygen as per the balanced reaction.

6 molecules of $$N_2O$$ reacts with 9 molecules of oxygen as per the balanced reaction.

Since the reactant is present in stoichiometric ratio so all the reactants will be converted to product i.e. 6 $$N_2O_4$$ molecules.
Question 6
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Consider the four decompositions shown here:
Reaction I: $$Ca(NO_{3})_{2}(s)\xrightarrow {\Delta} CaO(s) + N_{2}O_{5}(g)$$
Reaction II: $$CaSO_{3}(s) \xrightarrow {\Delta} CaO(s) + SO_{2}(g)$$
Reaction III: $$Ca(ClO_{3})_{2}(s) \xrightarrow {\Delta} CaCl_{2}(s) + 3O_{2}(g)$$
Reaction IV: $$CaCO_{3}(s) \xrightarrow {\Delta} CaO(s) + CO_{2}(g)$$
In each case, a solid compound of calcium undergoes thermal decomposition, producing a gaseous product and a calcium containing residual solid.
Assuming equal masses of the four compounds, $$Ca(NO_{3})_{2}, CaSO_{3}, Ca(ClO_{3})_{2}$$, and $$CaCO_{3}$$, are heated in open containers to constant mass, in which case will the mass of solid in the container change by the smallest percentage?

A
Reaction I

B
Reaction II

C
Reaction III

D
Reaction IV

Solution

Reaction I: $$ Ca_(NO_3)_2$$(s)−→ΔCaO(s)+$$N_2O_5$$(g)Ca(NO3)2(s)→ΔCaO(s)+N2O5(g)
Reaction II: $$ CaSO_3$$(s)−→ΔCaO(s)+$$SO_)2$$(g)CaSO3(s)→ΔCaO(s)+SO2(g)
Reaction III: $$ Ca(ClO_3)_2$$(s)−→$$ΔCaCl_2$$(s)+$$3O_2$$(g)Ca(ClO3)2(s)→ΔCaCl2(s)+3O2(g)
Reaction IV: $$ CaCO_3$$(s)−→ΔCaO(s)+$$CO_2($$g)
The reaction which has less atomic mass at the reatant side and
produced less residual when all reactant has same mass
MASS OF REACTED
$$ Ca_(NO_3)_2$$ = 164
$$ CaSO_3$$ = 120
$$ Ca(ClO_3)_2$$ = 208
$$ CaCO_3$$ = 100
answer is D
Question 7
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Atom is the word derived from the Greek word atomio, which means:

A
uncutable

B
cutable

C
in between

D
combined

Solution

Atom is the word derived from the Greek word atomio, which means uncutable or indivisible.
Question 8
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A 5% by mass of an aqueous solution of $$A$$ of molar mass 342 g mol$$^{-1}$$ is isotonic with 0.878% by mass of an aqueous solution of another substance B. The molar mass of $$B$$ in g mol$$^{-1}$$ is:

A
120

B
180

C
60

D
90

Solution

Isotonic solution has same concentration.
$$C_1 = C_2$$
$$\dfrac {5}{342} = \dfrac{0.878}{\text{Molar mass of B}}$$
So $$5 \times M=0.878\times 342$$
So $$M=60.052$$
Hence, option C is correct.
Question 9
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Who proposed that equal volumes of gases at the same temperature and pressure have same number of molecules.

A
Heisenberg

B
Avogadro

C
Dalton

D
Boyle

Solution

Avogadro's law is: Avogadro's law states that "equal volumes of all gases, at the same temperature and pressure, have the same number of molecules"
Hence, the correct option is $$B$$
Question 10
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Which one of the following statements is false?

A
Photochemical smog causes irritation in eyes

B
London smog is a mixture of smoke and fog

C
Photochemical smog results in the formation of PAN

D
London smog is oxidising in nature

Solution

Reducing smog is known as the London smog. Smog is a mixture of smoke and fog and they cause irritation in eyes