The following data are obtained when dinitrogen and dioxygen react together to form different compounds Mass of dinitrogen Mass of dioxygen 14 g 16 g 14 g 32 g 28 g 32 g 28 g 80 g Which law of chemical combination is obeyed by the above experimental data? Give its statement .

If we fix the mass of dinitrogen is 28 g , then the masses of dioxygen that will combine with the fixed mass of dinitrogen are 32 , 64 , 32 , and 80 g . The masses of dioxygen bear a simple whole-number ratio 2 : 4 : 2 : 5 . Hence, given experimental data obeys the Law of multiple proportions. It states that "if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers".

Use the data given in the following table to calculate the molar mass of naturally occurring argon isotopes: Isotope Isotopic molar mass Abundance Ar 36 35 .96755 g mol - 1 0.337 % Ar 38 37 .96272 g mol - 1 0.063 % Ar 40 39 .9624 g mol - 1 99.600 %

Given : For Isotope Ar 36 , Isotopic molar mass is 35.96755 gmol - 1 Percentage abundance is 0 . 337 % . For Isotope Ar 38 , Isotopic molar mass = 37 . 96272 g mol - 1 Percentage Abundance 0 . 063 % For Isotope Ar 40 , Isotopic molar mass 39 . 9624 g mol - 1 . Percentage abundance 99 . 600 % . Average molar mass = molar mass of isotope 1 × % abundance of isotope 1 + molar mass of isotope 2 × % abundance of isotope 2 + molar mass of isotope 3 × % abundance of isotope 3 100 Average molar mass of argon = 35 .96755 × 0 .337 100 + 37 .96272 × 0 .063 100 + 39 .9624 × 90 .60 100 g mol - 1 = 0 .121 + 0 .024 + 39 .802 g mol - 1 = 39 .947 g mol - 1

Calcium carbonate reacts with aqueous HCl to give CaCl 2 and CO 2 according to the reaction, CaCO 3 s + 2 HCl aq → CaCl 2 aq + CO 2 g + H 2 O l . What mass of CaCO 3 is required to react completely with 25 mL of 0 .75 M HCl ?

Given, Volume of HCl solution = 25 mL Molarity of HCl solution = 0.75 M We know, molecular mass of CaCO 3 = 100 Now, moles = molarity × volume Moles of HCl = 0 .75 M × 25 mL 1000 = 0.01875 From the given chemical equation, CaCO 3 s + 2 HCl aq → CaCl 2 aq + CO 2 g + H 2 O l According to stoichiometry of reaction : ∴ 2 mol of HCl react with = 1 mol of CaCO 3 0.01875 mol HCl of react with = 1 2 × 0.01875 mol mol of CaCO 3 ( ∴ weight = moles × molecular weight ) Amount of CaCO 3 that will react = 1 2 × 0.01875 × 100 = 0.9375 g

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11th Jharkhand Board

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Chemistry (Vol 1)>Chapter 1 - Some Basic Concepts of Chemistry>EXERCISES>Q 1.17

A sample of drinking water was found to be severely contaminated with chloroform, ${CHCl}_{3}$ , supposed to be carcinogenic in nature. The level of contamination was $15 ppm$ (by mass).

Determine the molality of chloroform in the water sample. [Given Mass percent is $1.5 \times 10^{- 3}$ ]

MEDIUM

11th Jharkhand Board

IMPORTANT

Chemistry (Vol 1)>Chapter 1 - Some Basic Concepts of Chemistry>EXERCISES>Q 1.21

The following data are obtained when dinitrogen and dioxygen react together to form different compounds

Mass of dinitrogen	Mass of dioxygen
$14 g$	$16 g$
$14 g$	$32 g$
$28 g$	$32 g$
$28 g$	$80 g$

Which law of chemical combination is obeyed by the above experimental data? Give its statement .

HARD

11th Jharkhand Board

IMPORTANT

Chemistry (Vol 1)>Chapter 1 - Some Basic Concepts of Chemistry>EXERCISES>Q 1.29

Calculate the molarity of a solution of ethanol in water, in which the mole fraction of ethanol is $0.040$ .
(Assume the density of water to be one).
(Provide correct answer upto $2$ decimal places and no need to mention units.)

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11th Jharkhand Board

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Chemistry (Vol 1)>Chapter 1 - Some Basic Concepts of Chemistry>EXERCISES>Q 1.31

How many significant figures should be present in the answer of the following calculations?
$\frac{0.02856 \times 298.15 \times 0.112}{0.5785}$

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11th Jharkhand Board

IMPORTANT

Chemistry (Vol 1)>Chapter 1 - Some Basic Concepts of Chemistry>EXERCISES>Q 1.31

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

$5 \times 5.364$

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11th Jharkhand Board

IMPORTANT

Chemistry (Vol 1)>Chapter 1 - Some Basic Concepts of Chemistry>EXERCISES>Q 1.31

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

$0.0125 + 0.7864 + 0.0215$

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11th Jharkhand Board

IMPORTANT

Chemistry (Vol 1)>Chapter 1 - Some Basic Concepts of Chemistry>EXERCISES>Q 1.32

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

Isotope	Isotopic molar mass	Abundance
${}^{36}{Ar}$	$35 .96755 g {mol}^{- 1}$	$0.337 %$
${}^{38}{Ar}$	$37 .96272 g {mol}^{- 1}$	$0.063 %$
${}^{40}{Ar}$	$39 .9624 g {mol}^{- 1}$	$99.600 %$

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11th Jharkhand Board

IMPORTANT

Chemistry (Vol 1)>Chapter 1 - Some Basic Concepts of Chemistry>EXERCISES>Q 1.35

Calcium carbonate reacts with aqueous $HCl$ to give ${CaCl}_{2}$ and ${CO}_{2}$ according to the reaction,
${CaCO}_{3} (s) + 2 HCl (aq) \to {CaCl}_{2} (aq) + {CO}_{2} (g) + H_{2} O (l)$ .
What mass of ${CaCO}_{3}$ is required to react completely with $25 mL$ of $0 .75 M HCl$ ?

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