CBSE Class 11 Chemistry Basic Concepts Of Chemistry Important Questions

CBSE Class 11 Chemistry Basic Concepts Of Chemistry Important Questions

1 MARK QUESTIONS:

1. Round up the following upto three significant figures:
2. i) 35.296 ii) 12.2104
3. Why are the atomic masses of most of the elements fractional?
4. How many significant figures are present in the answer of following calculation: 5×1.35×1.1? (Ans: Two significant figures)

2 MARK QUESTIONS:

1. How many significant figures are present in the following: i) 0.0020 ii) 1.20x10⁴  
2. Calculate the mass percent of different elements present in nitric acid.  (Ans : H = 1.59%, N = 22.22%, O = 76.19% )
3. 4L of dinitrogen reacted with 22.7L of dioxygen and 45.4L of nitrous oxide was formed. The reaction is given below: 2N₂ (g) + O₂(g) à 2N₂O(g). Which law is obeyed in this statement? Write the statement of this law.
4. Which out of molality and molarity is preferred for expressing the concentration of solution and why?
5. Chlorine is prepared in the laboratory by treating MnO₂ with aqueous HCl solution according to the reaction: 4HCl (aq) + MnO₂(s) à 2H₂O (l) + MnCl₂(aq) + Cl₂(g) , how many grams of HCl react with 5.0g of MnO₂. (Atomic mass of Mn = 55u, Cl = 35.5u, O = 16u) (Ans: 8.40g)
6. Naphthalene ball contains 93.71% of carbon and 6.29% of hydrogen . If its molar mass is 128g/mol, calculate its molecular formula. (Ans: C₁₀H₈)

3 MARK QUESTIONS:

1. 3 molal NaOH solution has a density of 1.110g/mL. What is the molarity of the solution? (Ans: 2.973 M)
2. Calculate the concentration of nitric acid in moles per litre in a sample which has a density 1.41g/L and the mass percent of HNO₃ in it being 69%. (Ans: 15.44 M)
3. 50 Kg of N₂ (g) and 8.0 Kg of H₂ (g) are mixed to produce NH₃ (g). Calculate the amount of NH₃ (g) formed. Identify the limiting reagent in the production of NH₃ in the given situation. (At.mass in g/mol ,N=14, H=1) (Ans: H₂ is the limiting reagent, Mass of NH₃ formed = 56.217 kg)
4. Calculate the number of atoms in each of the following: i) 39 moles of He ii) 39 u of He iii) 39g of He (Ans i) 2.35 × 10²⁵ ii) 9.75 iii) 5.87×10²⁴)
5. A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38g CO₂ , 6.690g H₂O and no other products. A volume of 10.0L (at STP) of this welding gas is found to weigh 11.6g. Calculate i) Molar mass of the gas ii) Molecular formula of the gas.  (Ans: i) 26g/mol ii) C₂H₂) 
6. Two oxides of a metal contain 27.6% and 30.0% of oxygen respectively. If the formula of the first oxide is M₃O₄, find that of the second. (Ans: M₂O₃)
7. A crystalline salt when heated becomes anhydrous and loses 51.2% of its weight. The anhydrous salt on analysis gave the percentage composition as: Mg = 20.0%, S = 26.66% and O = 53.33%. Calculate the molecular formula of the anhydrous salt and crystalline salt. Molecular mass of the anhydrous salt is 120u. (Ans: MgSO₄.7H₂O)
8. An organic compound has carbon=40.687%, hydrogen=5.085%, oxygen=54.228%. Calculate molecular formula of the compound if its vapour density is 59. (Ans: C₄H₆O₄)
9. If the elemental composition of butyric acid is found to be 54.2% C, 9.2% H and 36.6% O. What will be its molecular formula if its molecular mass is 88 u? (Ans: C₄H₈O₂)
10. Calculate i) number of moles ii) no. of molecules iii) volume of gas at STP in 0.28g of nitrogen. (Ans: i) 0.01 mole ii) 6.022×10²¹ molecules iii) 0.227 L) 
11. In the reaction: 2A+4B à 3C+4D, when 5 moles of A react with 6 moles of B, then
    1. Which is the limiting reagent?
    2. Calculate the amount of C formed. (Ans: i) B ii) 4.5 moles)

HOTS:

1. Gastric juice contains about 3.0g of HCl per litre. If a person produces about 2.5 litres of gastric juice per day, how many antacid tablets each containing 400mg of Al(OH)₃ are needed to neutralize all the HCl produced in one day? (3 marks) (Ans: 14 tablets) 
2. What volume of 0.1M NaOH solution is required to neutralise 100 ml of concentrated aqueous sulphuric acid which contains 98% H₂SO₄ by mass. The density of concentrated sulphuric acid solution is 1.84g/ml. (Atomic mass of H=1u, S=32u, O=16u, Na=23u). (3 marks)(Ans: 36.76 L) 
3. Calcium carbonate reacts with aqueous HCl to give CaCl₂ and CO₂ according to the reaction: CaCO₃(s) + 2HCl(aq) à CaCl₂(aq) + CO₂(g) + H₂O(l). How many moles and how many grams of CaCl₂ will be formed when 250mL of 0.76 M HCl reacts with 1000g of CaCO₃ ? Name the limiting reagent also. ( Atomic Masses: Ca = 40u, Cl = 35.5u) (3 marks)

(Ans: HCl is the limiting reagent, CaCl₂ formed = 0.095 mol = 10.54g)

VALUE BASED QUESTION:

1. In 2015, some samples of maggi were found to contain compounds of lead so Govt. banned it for some time and also there is a check on the sale of junk food in school canteen. But still kids are very fond of Pizza, Pasta, and Burger etc. After reading news paper and other articles, Riya, a student of DPS decided not to eat junk food and to switch over to fresh fruits and homemade food only.
   1. What are the harmful effects of eating junk food? 
   2. What are the values associated with Riya?