chemistry - some basic concepts of chemistry

Class 11 - Chemistry

Some Basic Concepts of Chemistry

MCQ
Q&A
Question:

Express the following in scientific notation:
(i) 0.0048 (v) 6.0012 (ii) 234,000 (iii) 8008 (iv) 500.0

Answer:

ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-18



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Questions and Answers


Some Basic Concepts of Chemistry - Questions
1.

Calculate the mass percent of different elements present in sodium sulphate (Na2 SO4).


Answer
2.

Determine the empirical formula of an oxide of Iron which has 69.9 % iron and 30.1 % dioxygen by mass.


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3.

Calculate the concentration of nitric acid in moles per litre in a sample which has a density 1.41 g  mL-1  and the mass percent of nitric acid in it is being 69%.


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4.

How much copper can be obtained from 100 g of copper sulphate (CuSO4  )? (Atomic mass of Cu= 63.5 amu)


Answer
5.

Determine the molecular formula of an oxide of iron in which the mass percent of iron and oxygen are 69.9 and 30.1 respectively. Given that the molar mass of the oxide is 159.8 g  mol-1(Atomic mass: Fe = 55.85, O = 16.00 amu)Calculation of Empirical Formula.


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6.

Calculate the atomic mass (average) of chlorine using the following data:
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-9


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7.

In three moles of ethane (C2H6), calculate the following:
(i) Number of moles of carbon atoms (ii) Number of moles of hydrogen atoms
(iii) Number of molecules of ethane


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8.

If the density of methanol is 0.793 kg  L -1, what is its volume needed for making 2.5 L of its 0.25 M solution?


Answer
9.

Pressure is determined as force per unit area of the surface. The S.I. unit of pressure, pascal, is as shown below:1 Pa = 1  Nm-2.If mass of air at sea level is 1034 g  cm-2,calculate the pressure in pascal.


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10.

What is the S.I. unit of mass?


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11.

Match the following prefixes with their multiples:
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-15


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12.

What do you mean by significant figures?


Answer
13.

A sample of drinking water was found to be severely contaminated with chloroform, CHCly supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
(i) Express this in percent by mass
(ii) Determine the molality of chloroform in the water sample.


Answer
14.

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


Answer
15.

Round up the following upto three significant figures:
(i) 34.216 (ii) 10.4107 (iii) 0.04597 (iv) 2808


Answer
16.

The following data were obtained when dinitrogen and dioxygen react together to form compounds:
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-19


Answer
18.

In the reaction, A + B2——> AB2, identify the limiting reagent, if any, in the following  mixtures
(i) 300 atoms of A + 200 molecules ofB
(ii) 2 mol A + 3 mol B
(iii) 100 atoms of A + 100 molecules ofB
(iv) 5 mol A + 2.5 mol B
(v) 2.5 mol A + 5 mol B


Answer
19.

Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation:(i)  N2 (g) + 3H2(g) —–> 2NH3 (g)
(ii) Will any of the two reactants remain unreacted?
(iii) If yes, which one and what would be its mass?


Answer
20.

How are 0.50 mol  Na2C03  and 0.50 M  Na2C03  different?


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21.

If ten volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour could be produced?


Answer
22.

Convert the following into basic units:
(i) 28.7 pm (ii) 15.15 µs (iii) 25365 mg


Answer
23.

Which one of the following will have largest number of atoms?
(i) 1 g Au (s) (ii) 1 g Na (s) (iii) 1 g Li (s) (iv) 1 g of  Cl2(g)  (Atomic masses: Au = 197, Na = 23, Li = 7, Cl = 35.5 amu)


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24.

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040.


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26.

How many significant figures should be present in the answer of the following?
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-29


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27.

Use the data given in the following table to calculate the molar mass of naturally occurring argon.
ncert-solutions-for-class-11-chemistry-chapter-1-some-basic-concepts-of-chemistry-30


Answer
28.

Calculate the number of atoms in each of the following:
(i) 52 moles of He (ii) 52 u of He (iii) 52 g of He


Answer
29.

Calcium carbonate reacts with aqueous HCl according to the reaction

CaC03 (s) + 2HCl (aq) ———->CaCl2  (aq) +C02(g) +H2O(l).

What mass of CaC03 is required to react completely with 25 mL of 0.75 M HCl?


Answer
30.

Chlorine is prepared in the laboratory by treating manganese dioxide (Mn02) with aqueous hydrochloric acid according to the reaction.
4 HCl (aq) + Mn02 (s) ———–> 2 H2O (l) + MnCl2(aq) +Cl2(g)

How many grams of HCl react with 5.0 g of manganese dioxide? (Atomic mass of Mn = 55 u)


Answer
31.

What is the SI unit of molarity?


Answer
32.

What do you understand by stoichiometric coefficients in a chemical equation?


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33.

Give an example of a molecule in which the ratio of the molecular formula is six times the empirical formula.


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34.

What is an atom according to Dalton’s atomic theory?


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35.

Why air is not always regarded as homogeneous mixture?


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36.

Define the term ‘unit’ of measurement.


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37.

Define law of conservation of mass.


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38.

How is empirical formula of a compound related to its molecular formula?


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39.

How many oxygen atoms are there in 18 g of water?


Answer
40.

Name two factors that introduce uncertainty into measured figures.


Answer
41.

State Avogadro’s law.


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42.

How are 0.5 ml of NaOH differents from 0.5 M of NaOH?


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43.

What is one a.m.u. or one ‘u’?


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44.

What is the number of significant figures in 1.050 x 104?


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45.

Define molality. How does molality depend on temperature?


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46.

Convert 2.6 minutes in seconds.


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47.

Calculate the number of moles in each of the following.


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48.

A compound on analysis was found to contain C = 34.6%, H = 3.85% and O = 61.55%. Calculate the empirical formula.


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49.

Calculate:
(a) Mass of 2.5 gram atoms of magnesium,
(b) Gram atom in 1.4 grams of nitrogen (Atomic mass Mg = 24, N = 14)


Answer
50.

What is the molecular mass of a substance each molecule of which contains 9 atoms of carbon, 13 atoms of hydrogen and 2.33 x  10-23  g other component?


Answer
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