Explore topic-wise InterviewSolutions in Current Affairs.

(a) Four - The zeros are significant figures.

(b) Four - The exponential term does not add to the number of significant figures.

(i) 1 pound per inch² = 6894.76 Nm^–2

^{\(\therefore\)} 14 pound per inch² = 6894.76 × 14

= 96526.64 N/m²

(ii) 1 mile/hr = \(\frac{1.6\times10^3m}{3600\,s}\)

= 0.444 m/sec

\(\therefore\) 200 mile/hr = 200 × 0.444

= 88.8 m/sec

(iii) 1 m = 39.37 inch 

1 feet = 12 inch 

5 feet 2 inch = 5 × 12 + 2 inch

= 60 + 2 = 62 inch

\(\therefore\) 5 feet 2 inch = \(\frac{62}{39.37}\) = 1.5748 m

Avogadro's hypothesis: Under similar conditions of pressure and temperature, equal volumes of gases contain equal number of molecules.

H₂         +       Cl₂         →          2HCl

1 vol              1 vol                      2 vol

n molecules   n molecules        2n molecules

                                          (By Avogadro's law)

1/2 molecules 1/2 molecules   1 molecules

                          (By dividing throughout by 2n)

It implies that one molecule of hydrogen chloride gas is made up of 1/2 molecule of hydrogen and 1/2 molecule of chlorine. Since a molecule is made up of two or more atoms, so 1/2 molecule is possible and may contain one or two atoms. Thus, this result does not contradict Dalton's atomic theory.

\(\because\) 1 pm = 10^–12 m

\(\therefore\) 450 pm = 450 × 10^–12 m

= 4.5 × 10^–10 m

(i) 0.0125 + 0.8250 + 0.025

= 0.8625 = 0.863

\(\because\) 0.025 has three digits including zero after the decimal point so the result should be reported only upto three digits after the decimal point.

There are three significant figures in the answer.

(ii) \(\frac{0.025\times298.15\times0.1155}{0.5785}\)

= \(\frac{0.860908125}{0.8785}\)

= 1.48817

= 1.49

\(\because\) 298.15 has two digits after the decimal point so the result should be reported only upto two digits after the decimal point. There are three significant figures.

Prop-2-yn-1-ol

(I) 7nm= 7nm/nm× 10 ^-9 m=7×10^-9 m. 

(II) 40Em= 40×10¹⁸m=4×10¹⁹m. (Note E= Exa, 1E= 10¹⁸) 

(III) 1.4Gm= 1.4×10⁹ m.

The significant figures in any number are all certain digits plus one doubtful digit.

Inorganic compound is made up of two or more elements containing rare percentage of carbon eg: NaCl, KCl, ZnS, etc.

Mass of organic compound = 0.157 g

Mass of BaSO₄ = 0.4813 g

Percentage of sulphur = \(\frac{32}{233}\) x \(\frac{Mass\,of\,BaSO_4}{Mass\,of\,organic\,compound}\) x 100

= \(\frac{32}{233}\) x \(\frac{0.4813}{0.157}\) x 100

= 42.10 %

15 ppm means 5 parts in million(10⁶) parts. 

∴ % by mass = 15/10⁶ × 100 = 15×10^-4 = 1.5×10^-3 % 

(ii) Molar mass of chloroform(CHCl₃) = 12+1+(3×35.5) = 118.5 g mol^-1 

100g of the sample contain chloroform = 1.5×10^-3g 

∴ 1000 g(1 kg) of the sample will contain chloroform = 1.5×10^-2 g 

= 1.5×10^-2/118.65 mole = 1.266×10^-4 mole 

Hence: Molality = 1.266×10^-4 m.

Organic compound contains essentially carbon, hydrogen along certain elements like N, P, S, O, halogen, etc., eg: urea, sugar.

(i) Two, because the zeros in the left of the first nonzero digit are not significant.

(ii) Three significant figures

(iii) Four significant figures

(iv) Three significant figures

(v) Four significant figures

(vi) Five

We know that, ppm = {Mass of chloroform}/{Mass of solution} x 10⁶

Given ppm of chloroform = 15

If the mass of solution is 1 kg (1000 gm) the mass of chloroform

= {15 x 1000}/{10⁶} = 0.015 g

It means 1000 g of solution contains 0.015 g of chloroform

Thus the % of the solution = {0.015 x 100}/{1000} = 0.0015%

Because the solution is very dilute and the density of water is 1.0 g mL^-1, therefore the mass of the solution will be nearly same to volume of the solution, thus

Molarity = {Mass of chloroform}/{Molar mass of chloroform} x {1000}/{Volume of solution}

= {0.015}/{119.5} x {1000}/{1000} = 12.6 x 10^-5 m

= 1.25 x 10^-4 m

(I) 4.8 × 10^-3 (II) 2.34 × 10⁵ (III) 8.008 × 10³ (Iv) 5.000 × 10²

(i), (iv). Statements (i) and (iv) involve masses and volume, respectively. Therefore, these are not related to the statements.

(I) 2 

(II) 3 

(III) 4 

(IV) 3

(I) 4.8 x 10^-3 

(II) 2.34 x 10⁵ 

(III) 8.008 x 10³ 

(Iv) 5.000 x 10²

Correct option is  : (d)

Strategy : using the mole concept equate the moles of Mg₃ (PO₄ )₂ to the number of atoms of oxygen in the formula of the compound.

Solution : 1 mole of Mg₃ (PO₄ )₂ contains 8 moles of oxygen atoms. 

Therefore 0.25 moles of oxygen atoms are present in 1/8 x 0.25 moles of Mg₃ (PO₄ )₂   = 3.125 x 10^-2 moles of Mg₃ (PO₄ )₂ 

 Hit and trial method, Oxidation number method.

SI unit would be N m^-2 (m³ ) ² (K)² / mol 

N m⁴ K² mol^-1

(i) 4

(ii) 2

(C) 2.5x100^-3

One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g (or 0.012 kg) of the ¹²C isotope.

A limiting reagent is a reactant which is present in lesser amount in a reaction. When it gets consumed, the reaction will not proceed irrespective of the amount of other reactant present in the reaction. It limits the amount of product formed. In other words, it determines the extent of reaction. Consider the reaction between hydrogen and oxygen to form water. It can be represented as:
2H₂ + O₂ = 2H₂O
From the above reaction, it is clear that 2 moles of hydrogen react with 1 mole of oxygen.
Molar mass of H₂ = 2 g
Molar mass of O₂ = 32 g
This means that
4 g of H₂ reacts with 32 g of O₂
3 g of H₂ reacts with = (32/4) x 3 g of O2 gas = 24 g
As the given amount of O₂ is more than required.
Therefore, O₂ is in excess and H₂ is limiting reagent here.

Dalton’s Atomic Theory: Main postulates of
Dalton’s atomic theory are as follow :

(i) Matter is composed of very tiny or microscopic particles called “Atom”.

(ii) Atom is an indivisible particle.

(iii) Atom can neither be created nor be destroyed.

(iv) Atoms of an element are identical in size, shape, mass and in other properties.

(v) Atoms of different elements are different in their properties.

(vi) Atoms combine with each other in small whole numbers.

(vii) All chemical reactions are due to combination or separation of atoms.

Percentage of oxygen = 100 - (40 + 6.66) = 100 - 46.6 = 53.4%

Hence, empirical formula = CH₂O
Now, empirical formula mass
= 12 + (2 × 1) + 16 = 12 + 2 + 16 = 30″
Molecular mass = 2 x Vapour density = 2 × 30 = 60
n = Molecular mass / Empirical formula mass
= \(\frac{60}{30}\) = 2
Thus, Molecular formula = (Empirical formula) × n = (CH₂O) × 2 = C₂H₄O₂

Avogadro’s law states that “equal volumes of all gases, at the same temperature and pressure, have the same number of molecules”.

Percentage of iron = \(\frac{3.438}{10}\) × 100 = 34.38%
Percentage of Chlorine = \(\frac{6.65}{10}\) × 100 = 66.5%

Thus, the empirical formula of iron chloride is FeCl₃

Atomic mass: The atomic mass of an element is defined as the number of times an atom of that element is heavier than an atom of carbon-12. It is expressed in a.m.u. or atomic mass unit. In place of a.m.u., symbol u is used which is known as unified mass.
Atomic mass = Mass of an atom × 1 /12 mass of carbon atom

Molecular mass: Molecular mass of any substance is defined as the average relative mass of its molecules as compared to mass of an atom of carbon-12. Molecular mass is expressed as a.m.u. It is given by,
Molecular mass = Mass of one molecule of substance /(1/12) x mass of carbon -12. ,

Equivalent mass: Quantity of a substance in which is numerically equal to its equivalent mass is called its gram equivalent mass.
Calculation of Molarity:
Molar mass of K₂CO₃= 138 g/mol
Volume of solution = 500 mL or 0.5 L
Mass of  K₂CO₃ = 20.7
Number of moles = 20.7/138 = 0.149
Now,
Molarity = Number of moles/Volume of solution
= \(\frac{0.149}{0.5}\) = 0.299 M
Thus, molarity of solution is 0.299 M.

Molar mass of CO₂ = (1 x atomic mass of C + 2 × atomic mass of O)
= 1(1 × 12) + (2 × 16)
= 12 + 32 = 44 g/mol.

Gram atomic mass of oxygen is 16 g
So, 16 g oxygen contains 6.023 × 10²³ atoms
Hence 32 g oxygen will contain 6.023 × 10²³ × 2 atoms
=12.046 x 10²³
Now, gram atomic mass of Nitrogen = 14 g
So, 14 g nitrogen contains 6.023 × 10²³ atoms

Number of moles = mass of substance/mass of one mole
= \(\frac{1.68}{56}\) = 0.03 moles
1 mole of iron contains 6.023 × 10²³ atoms
0.03 moles of iron will contain 0.03 x 6.023 × 10²³  atoms
= 1.8 ×10²²  atoms

Number of moles of carbon in 1 mol of C₆H₁₂O₆ = 6
Number of carbon atoms in 1 mole of C₆H₁₂O₆
= 6 × 6.023× 10²³ atoms
Number of carbon atoms is 0.1 mol of C₆H₁₂O₆
= 0.1 × 6 × 6.023 × 10²³ atoms
= 3.6138 × 10²³ atoms

The main principles of Islam: 

1. There is only one God and Muhammad is his Prophet, (z’z) Muslims must turn towards Mecca and say their prayers five times a day. 

2. They must fast from dawn to dusk during the holy month of Ramzan. 

3. They must help the poor and needy by giving away a portion of their wealth in charity. 

4. They must make a pilgrimage to Mecca at least once in their lifetime.

Law of conservation of mass is the fundamental principle for balancing a chemical equation. 

Law of Conservation of Mass: Mass cannot be created and cannot be destroyed.

When a reaction takes place in both directions, it is called reversible reaction. In a reversible reaction, the moment a product is formed it starts changing into reactant.

(i) Exothermic

(ii) Endothermic

Correct answer is (a) Catalyst

(d) Bio-catalyst

Catalyst alters the speed of a chemical reaction.

Name the catalyst Nickel facilitates change of vegetable oil to vegetable ghee.

Displacement reaction.

Slow reaction and fast reaction.

Quick lime is CaO. On adding water to it large amount of heat is released, with the formation of Ca (OH)₂. 

CaO + H₂O → Ca(OH)₂

A change after which a new substance is formed is called a chemical change.