## How many neutrons and protons are there inthe following nuclei?

[question] Question. How many neutrons and protons are there inthe following nuclei? ${ }_{6}^{13} \mathrm{C}$ ${ }_{8}^{16} \mathrm{O}$ ${ }_{12}^{24} \mathrm{Mg}$ ${ }_{26}^{56} \mathrm{Fe}$ ${ }_{38}^{88} \mathrm{Sr}$ [/question] [solution] Solution: ${ }^{13}{ }_{6} \mathrm{C}:$ Atomic mass $=13$ Atomic number $=$ Number of protons $=6$ Number of neutrons $=$ (Atomic mass) $-$ (Atomic number) $=13-6=7$ ${ }_{8}^{16} \bigcirc$ Atomic mass $=16$ Atomic number $=8$ Number of protons $=8$ Number...

## Use the data given in the following table to calculate the molar mass of naturally occurring argon isotopes

[question] Question. Use the data given in the following table to calculate the molar mass of naturally occurring argon isotopes [/question] [solution] Solution: Molar mass of argon $=39.947 \mathrm{gmol}^{-1}$ [/solution]...

## How many significant figures should be present in the answer of the following calculations

[question] Question. How many significant figures should be present in the answer of the following calculations? (i) $\frac{0.02856 \times 298.15 \times 0.112}{0.5785}$ (ii) $5 \times 5.364$ (iii) $0.0125+0.7864+0.0215$ [/question] [solution] Solution: (i) $\frac{0.02856 \times 298.15 \times 0.112}{0.5785}$ Least precise number of calculation = 0.112 Number of significant figures in the answer = Number of significant figures in the least precise number = 3 (ii) $5 \times 5.364$ Least precise num...

## What will be the mass of one ${ }^{12} \mathrm{C}$ atom in $\mathrm{g}$ ?

[question] Question. What will be the mass of one ${ }^{12} \mathrm{C}$ atom in $\mathrm{g}$ ? [/question] [solution] Solution: 1 mole of carbon atoms $=6.023 \times 10^{23}$ atoms of carbon $=12 \mathrm{~g}$ of carbon $\therefore$ Mass of one ${ }^{12} \mathrm{C}$ atom $=\frac{12 \mathrm{~g}}{6.022 \times 10^{23}}$ $=1.993 \times 10^{-23} \mathrm{~g}$ [/solution]...

## Dinitrogen and dihydrogen react with each other

[question] Question. Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation $\mathrm{N}_{2}(g)+\mathrm{H}_{2}(g) \rightarrow 2 \mathrm{NH}_{3}(g)$ (i) Calculate the mass of ammonia produced if $2.00 \times 10^{3} \mathrm{~g}$ dinitrogen reacts with $1.00$ $\times 10^{3} \mathrm{~g}$ of dihydrogen. (ii) Will any of the two reactants remain unreacted? (iii) If yes, which one and what would be its mass? [/question] [solution] Solution: (i)Bal...

## In a reaction

[question] Question. In a reaction $A+B_{2} \rightarrow A B_{2}$ Identify the limiting reagent, if any, in the following reaction mixtures (i) 300 atoms of $A+200$ molecules of $B$ (ii) $2 \mathrm{~mol} A+3 \mathrm{~mol} B$ (iii) 100 atoms of $A+100$ molecules of $B$ (iv) $5 \mathrm{~mol} \mathrm{~A}+2.5 \mathrm{~mol} \mathrm{~B}$ (v) $2.5 \mathrm{~mol} \mathrm{~A}+5 \mathrm{~mol} \mathrm{~B}$ [/question] [solution] Solution: A limiting reagent determines the extent of a reaction. It is the reac...

## Round up the following upto three significant figures

[question] Question. Round up the following upto three significant figures (i)34.216 (ii)10.4107 (iii)0.04597 (iv)2808 [/question] [solution] Solution: (i)34.2 (ii)10.4 (iii)0.0460 (iv)2810 [/solution]...

## How many significant figures are present in the following

[question] Question. How many significant figures are present in the following (i) $0.0025$ (ii) 208 (iii) 5005 (iv) 126,000 (v) $500.0$ (vi) $2.0034$ [/question] [solution] Solution: (i)0.0025 There are 2 significant figures. (ii)208 There are 3 significant figures. (iii)5005 There are 4 significant figures. (iv)126,000 There are 3 significant figures. (v)500.0 There are 4 significant figures. (vi)2.0034 There are 5 significant figure [/solution]...

## Express the following in the scientific notation

[question] Question. Express the following in the scientific notation (i) $0.0048$ (ii) 234,000 (iii) 8008 (iv) $500.0$ (v) $6.0012$ [/question] [solution] Solution: (i) $0.0048=4.8 \times 10^{-3}$ (ii) $234,000=2.34 \times 10^{5}$ (iii) $8008=8.008 \times 10^{3}$ (iv) $500.0=5.000 \times 10^{2}$ (v) $6.0012=6.0012$ [/solution]...

## Calculate the concentration of nitric acid in moles

[question] Question. Calculate the concentration of nitric acid in moles per litre in a sample which has a density, $1.41 \mathrm{~g} \mathrm{~mL}^{-1}$ and the mass per cent of nitric acid in it being $69 \%$. [/question] [solution] Solution: Mass percent of nitric acid in the sample = 69 % [Given] Thus, 100 g of nitric acid contains 69 g of nitric acid by mass. Molar mass of nitric acid (HNO3) $=\{1+14+3(16)\} \mathrm{g} \mathrm{mol}^{-1}$ = 1 + 14 + 48 $=63 \mathrm{~g} \mathrm{~mol}^{-1}$ Num...

## Calculate the mass of sodium acetate $\left(\mathrm{CH}_{3} \mathrm{COONa}\right)$ required to make

[question] Question. Calculate the mass of sodium acetate $\left(\mathrm{CH}_{3} \mathrm{COONa}\right)$ required to make $500 \mathrm{~mL}$ of $0.375$ molar aqueous solution. Molar mass of sodium acetate is $82.0245 \mathrm{~g} \mathrm{~mol}^{-1}$ [/question] [solution] Solution: 0.375 M aqueous solution of sodium acetate ≡ 1000 mL of solution containing 0.375 moles of sodium acetate Number of moles of sodium acetate in 500 mL Molar mass of sodium acetate $=82.0245 \mathrm{~g}$ mole $^{-1}$ (Giv...

## Calculate the amount of carbon dioxide that could be produced when

[question] Question. Calculate the amount of carbon dioxide that could be produced when (i)1 mole of carbon is burnt in air. (ii)1 mole of carbon is burnt in 16 g of dioxygen. (iii)2 moles of carbon are burnt in 16 g of dioxygen [/question] [solution] Solution: The balanced reaction of combustion of carbon can be written as: (i) As per the balanced equation, 1 mole of carbon burns in1 mole of dioxygen (air) to produce1 mole of carbon dioxide. (ii) According to the question, only 16 g of dioxygen...

## Determine the empirical formula of an oxide of iron which has 69.9%

[question] Question. Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1% dioxygen by mass [/question] [solution] Solution: % of iron by mass = 69.9 % [Given] % of oxygen by mass = 30.1 % [Given] Relative moles of iron in iron oxide Relative moles of oxygen in iron oxide Simplest molar ratio of iron to oxygen = 1.25: 1.88 = 1: 1.5 = 2: 3 $\therefore$ The empirical formula of the iron oxide is $\mathrm{Fe}_{2} \mathrm{O}_{3}$. [/solution]...

## Calculate the mass percent of different elements

[question] Question. Calculate the mass percent of different elements present in sodium sulphate $\left(\mathrm{Na}_{2} \mathrm{SO}_{4}\right)$. [/question] [solution] Solution: The molecular formula of sodium sulphate is $\mathrm{Na}_{2} \mathrm{SO}_{4}$. Molar mass of $\mathrm{Na}_{2} \mathrm{SO}_{4}=[(2 \times 23.0)+(32.066)+4(16.00)]$ $=142.066 \mathrm{~g}$ Mass percent of an element $=\frac{\text { Mass of that element in the compound }}{\text { Molar mass of the compound }} \times 100$ Mas...

## Calculate the molecular mass of the following

[question] Question. Calculate the molecular mass of the following (i) $\mathrm{H}_{2} \mathrm{O}$ (ii) $\mathrm{CO}_{2}$ (iii) $\mathrm{CH}_{4}$ [/question] [solution] Solution: (i) $\mathrm{H}_{2} \mathrm{O}:$ The molecular mass of water, $\mathrm{H}_{2} \mathrm{O}$ = (2 × Atomic mass of hydrogen) + (1 × Atomic mass of oxygen) = [2(1.0084) + 1(16.00 u)] = 2.016 u + 16.00 u = 18.016 = 18.02 u (ii) $\mathrm{CO}_{2}$ : The molecular mass of carbon dioxide, $\mathrm{CO}_{2}$ = (1 × Atomic mass of ...

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