Chapter 1 Some Basic Concepts Of Chemistry

Question 1. Two students performed the same experiment separately and each one of them recorded two readings of mass which are given below. Correct reading of mass is 3.0 g. On the basis of given data, mark the correct option out of the following statements.

(i) Results of both the students are neither accurate nor precise.

(ii) Results of student A are both precise and accurate.

(iii) Results of student B are neither precise nor accurate.

(iv) Results of student B are both precise and accurate.

Question 2. A measured temperature on Fahrenheit scale is 200 °F. What will this reading be on Celsius scale?

(i) 40 °C

(ii) 94 °C

(iii) 93.3 °C

(iv) 30 °C

Question 3. What will be the molarity of a solution, which contains 5.85 g of NaCl(s) per 500 mL?

(i) 4 mol L^–1

(ii) 20 mol L^–1

(iii) 0.2 mol L^–1

(iv) 2 mol L^–1

Question 4. If 500 mL of a 5M solution is diluted to 1500 mL, what will be the molarity of the solution obtained?

(i) 1.5 M

(ii) 1.66 M

(iii) 0.017 M

(iv) 1.59 M

Question 5. The number of atoms present in one mole of an element is equal to Avogadro number. Which of the following element contains the greatest number of atoms?

(i) 4g He

(ii) 46g Na

(iii) 0.40g Ca

(iv) 12g He

Question 6. If the concentration of glucose ($C_6H_{12}O_6$) in blood is 0.9 g L^–1, what will be the molarity of glucose in blood?

(i) 5 M

(ii) 50 M

(iii) 0.005 M

(iv) 0.5 M

Question 7. What will be the molality of the solution containing 18.25 g of HCl gas in 500 g of water?

(i) 0.1 m

(ii) 1 M

(iii) 0.5 m

(iv) 1 m

Question 8. One mole of any substance contains $6.022 \times 10^{23}$ atoms/molecules. Number of molecules of $H_2SO_4$ present in 100 mL of 0.02M $H_2SO_4$ solution is ______.

(i) $12.044 \times 10^{20}$ molecules

(ii) $6.022 \times 10^{23}$ molecules

(iii) $1 \times 10^{23}$ molecules

(iv) $12.044 \times 10^{23}$ molecules

Question 9. What is the mass percent of carbon in carbon dioxide?

(i) 0.034%

(ii) 27.27%

(iii) 3.4%

(iv) 28.7%

Question 10. The empirical formula and molecular mass of a compound are $CH_2O$ and 180 g respectively. What will be the molecular formula of the compound?

(i) $C_9H_{18}O_9$

(ii) $CH_2O$

(iii) $C_6H_{12}O_6$

(iv) $C_2H_4O_2$

Question 11. If the density of a solution is 3.12 g mL^–1, the mass of 1.5 mL solution in significant figures is _______.

(i) 4.7g

(ii) $4680 \times 10^{-3}g$

(iii) 4.680g

(iv) 46.80g

Question 12. Which of the following statements about a compound is incorrect?

(i) A molecule of a compound has atoms of different elements.

(ii) A compound cannot be separated into its constituent elements by physical methods of separation.

(iii) A compound retains the physical properties of its constituent elements.

(iv) The ratio of atoms of different elements in a compound is fixed.

Question 13. Which of the following statements is correct about the reaction given below:

$4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(g)$

(i) Total mass of iron and oxygen in reactants = total mass of iron and oxygen in product therefore it follows law of conservation of mass.

(ii) Total mass of reactants = total mass of product; therefore, law of multiple proportions is followed.

(iii) Amount of $Fe_2O_3$ can be increased by taking any one of the reactants (iron or oxygen) in excess.

(iv) Amount of $Fe_2O_3$ produced will decrease if the amount of any one of the reactants (iron or oxygen) is taken in excess.

Question 14. Which of the following reactions is not correct according to the law of conservation of mass.

(i) $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$

(ii) $C_3H_8(g) + O_2(g) \rightarrow CO_2(g) + H_2O(g)$

(iii) $P_4(s) + 5O_2(g) \rightarrow P_4O_{10}(s)$

(iv) $CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O (g)$

Question 15. Which of the following statements indicates that law of multiple proportion is being followed.

(i) Sample of carbon dioxide taken from any source will always have carbon and oxygen in the ratio 1:2.

(ii) Carbon forms two oxides namely $CO_2$ and CO, where masses of oxygen which combine with fixed mass of carbon are in the simple ratio 2:1.

(iii) When magnesium burns in oxygen, the amount of magnesium taken for the reaction is equal to the amount of magnesium in magnesium oxide formed.

(iv) At constant temperature and pressure 200 mL of hydrogen will combine with 100 mL oxygen to produce 200 mL of water vapour.

Question 16. One mole of oxygen gas at STP is equal to _______.

(i) $6.022 \times 10^{23}$ molecules of oxygen

(ii) $6.022 \times 10^{23}$ atoms of oxygen

(iii) 16 g of oxygen

(iv) 32 g of oxygen

Question 17. Sulphuric acid reacts with sodium hydroxide as follows :

$H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O$

When 1L of 0.1M sulphuric acid solution is allowed to react with 1L of 0.1M sodium hydroxide solution, the amount of sodium sulphate formed and its molarity in the solution obtained is

(i) 0.1 mol L^–1

(ii) 7.10 g

(iii) 0.025 mol L^–1

(iv) 3.55 g

Question 18. Which of the following pairs have the same number of atoms?

(i) 16 g of $O_2(g)$ and 4 g of $H_2(g)$

(ii) 16 g of $O_2$ and 44 g of $CO_2$

(iii) 28 g of $N_2$ and 32 g of $O_2$

(iv) 12 g of C(s) and 23 g of Na(s)

Question 19. Which of the following solutions have the same concentration?

(i) 20 g of NaOH in 200 mL of solution

(ii) 0.5 mol of KCl in 200 mL of solution

(iii) 40 g of NaOH in 100 mL of solution

(iv) 20 g of KOH in 200 mL of solution

Question 20. 16 g of oxygen has same number of molecules as in

(i) 16 g of CO

(ii) 28 g of $N_2$

(iii) 14 g of $N_2$

(iv) 1.0 g of $H_2$

Question 21. Which of the following terms are unitless?

(i) Molality

(ii) Molarity

(iii) Mole fraction

(iv) Mass percent

Question 22. One of the statements of Dalton’s atomic theory is given below:

“Compounds are formed when atoms of different elements combine in a fixed ratio”

Which of the following laws is not related to this statement?

(i) Law of conservation of mass

(ii) Law of definite proportions

(iii) Law of multiple proportions

(iv) Avogadro law

Question 23. What will be the mass of one atom of C-12 in grams?

Question 24. How many significant figures should be present in the answer of the following calculations?

$\frac{2.5 \times 1.25 \times 3.5}{2.01}$

Question 25. What is the symbol for SI unit of mole? How is the mole defined?

Question 26. What is the difference between molality and molarity?

Question 27. Calculate the mass percent of calcium, phosphorus and oxygen in calcium phosphate $Ca_3(PO_4)_2$.

Question 28. 45.4 L of dinitrogen reacted with 22.7 L of dioxygen and 45.4 L of nitrous oxide was formed. The reaction is given below:

$2N_2(g) + O_2(g) \rightarrow 2N_2O(g)$

Which law is being obeyed in this experiment? Write the statement of the law?

Question 29. 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 whole number ratio.

(a) Is this statement true?

(b) If yes, according to which law?

(c) Give one example related to this law.

Question 30. Calculate the average atomic mass of hydrogen using the following data :

Question 31. Hydrogen gas is prepared in the laboratory by reacting dilute HCl with granulated zinc. Following reaction takes place.

$Zn + 2HCl \rightarrow ZnCl_2 + H_2$

Calculate the volume of hydrogen gas liberated at STP when 32.65 g of zinc reacts with HCl. 1 mol of a gas occupies 22.7 L volume at STP; atomic mass of Zn = 65.3 u.

Question 32. The density of 3 molal solution of NaOH is 1.110 g mL^–1. Calculate the molarity of the solution.

Question 33. Volume of a solution changes with change in temperature, then, will the molality of the solution be affected by temperature? Give reason for your answer.

Question 34. If 4 g of NaOH dissolves in 36 g of $H_2O$, calculate the mole fraction of each component in the solution. Also, determine the molarity of solution (specific gravity of solution is 1g mL^–1).

Question 35. The reactant which is entirely consumed in reaction is known as limiting reagent. In the reaction $2A + 4B \rightarrow 3C + 4D$, when 5 moles of A react with 6 moles of B, then

(i) which is the limiting reagent?

(ii) calculate the amount of C formed?

Question 36. Match the following:

(i) 88 g of $CO_2$

(ii) $6.022 \times 10^{23}$ molecules of $H_2O$

(iii) 5.6 litres of $O_2$ at STP

(iv) 96 g of $O_2$

(v) 1 mol of any gas

(a) 0.25 mol

(b) 2 mol

(c) 1 mol

(d) $6.022 \times 10^{23}$ molecules

(e) 3 mol

Question 37. Match the following physical quantities with units

Question 38. Assertion (A) : The empirical mass of ethene is half of its molecular mass.

Reason (R) : The empirical formula represents the simplest whole number ratio of various atoms present in a compound.

(i) Both A and R are true and R is the correct explanation of A.

(ii) A is true but R is false.

(iii) A is false but R is true.

(iv) Both A and R are false.

Question 39. Assertion (A) : One atomic mass unit is defined as one twelfth of the mass of one carbon-12 atom.

Reason (R) : Carbon-12 isotope is the most abundunt isotope of carbon and has been chosen as standard.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) Both A and R are false.

Question 40. Assertion (A) : Significant figures for 0.200 is 3 where as for 200 it is 1.

Reason (R) : Zero at the end or right of a number are significant provided they are not on the right side of the decimal point.

(i) Both A and R are true and R is correct explanation of A.

(ii) Both A and R are true but R is not a correct explanation of A.

(iii) A is true but R is false.

(iv) Both A and R are false.

Question 41. Assertion (A) : Combustion of 16 g of methane gives 18 g of water.

Reason (R) : In the combustion of methane, water is one of the products.

(i) Both A and R are true but R is not the correct explanation of A.

(ii) A is true but R is false.

(iii) A is false but R is true.

(iv) Both A and R are false.

Question 42. A vessel contains 1.6 g of dioxygen at STP (273.15K, 1 atm pressure). The gas is now transferred to another vessel at constant temperature, where pressure becomes half of the original pressure. Calculate

(i) volume of the new vessel.

(ii) number of molecules of dioxygen.

Question 43. Calcium carbonate reacts with aqueous HCl to give $CaCl_2$ and $CO_2$ according to the reaction given below:

$CaCO_3(s) + 2HCl(aq) \rightarrow CaCl_2(aq) + CO_2(g) + H_2O(l)$

What mass of $CaCl_2$ will be formed when 250 mL of 0.76 M HCl reacts with 1000 g of $CaCO_3$? Name the limiting reagent. Calculate the number of moles of $CaCl_2$ formed in the reaction.

Question 44. Define the law of multiple proportions. Explain it with two examples. How does this law point to the existance of atoms?

Question 45. A box contains some identical red coloured balls, labelled as A, each weighing 2 grams. Another box contains identical blue coloured balls, labelled as B, each weighing 5 grams. Consider the combinations AB, $AB_2$, $A_2B$ and $A_2B_3$ and show that law of multiple proportions is applicable.