Ch01 Laboratory Safe Use

CHEMISTRY 1ST PAPER CHAPTER 1 Laboratory Safe Use Question 1 Eleven class students Palash and Shimul prepared two solutions of Na2CO3 in two measuring flasks of 500 mL after weighing in a Paul Bunge balance. The initial weight of weighing bottle and Na2CO3 was 26.6550 g. On the right pan of the balance, Shimul placed weights like one 5.0 g, one 500 mg, one 100 mg, one 20 mg and one 5 mg rider on the beam at 20th division. On the other hand, Palash placed, on the same balance, the weights like one 5.0 g, two 200 mg, one 100 mg, two 20 mg and placed the rider on the beam at 25th division. (a) Write full name of MSDS. (b) What do you understand by primary standard substance? (c) As per stem, calculate the rider constant of the Paul Bunge balance. (d) Show mathematically, whose solution of the two students will have higher concentration. Solution (a) The full name of MSDS is Material Safety Data Sheet. (b) A primary standard substance is a pure solid that remains unchanged in air. It does not absorb moisture, oxygen or carbon dioxide from the air. Its mass can be measured exactly in a chemical balance. A standard solution is prepared directly by dissolving a weighed mass. The concentra

Rider constant = 0.0001 g (d) The weights on the right pan balance the Na2CO3 taken by each student. The rider adds 0.0001 g for each division. Mass of Na2CO3 taken by Shimul, 𝑤1 = 5.0 + 0.500 + 0.100 + 0.020 + (20 × 0.0001) g = 5.6220 g Mass of Na2CO3 taken by Palash, 𝑤2 = 5.0 + (2 × 0.200) + 0.100 + (2 × 0.020) + (25 × 0.0001) g = 5.5425 g Molar mass of Na2CO3 is 𝑀= (2 × 23) + 12 + (3 × 16) = 106 g mol−1. The volume of each solution is 𝑉= 500 mL. The molarity of a solution is 𝑆= 𝑤× 1000 𝑀× 𝑉 𝑆1 = 5.6220 × 1000 106 × 500 M = 0.1061 M 𝑆2 = 5.5425 × 1000 106 × 500 M = 0.1046 M Student Mass of Na2CO3 (g) Concentration (M) Shimul 5.6220 0.1061 Palash 5.5425 0.1046 Both flasks have the same volume. Shimul dissolved a larger mass of Na2CO3. 𝑆1 > 𝑆2 Hence the solution of Shimul has the higher concentration. ahbab.dev 2

Question 2 Observe the different glass apparatus given below and answer the related questions. 1 M 250 mL H2SO4 A 500 mL B 10 20 30 40 50 C D (a) What is first aid box? (b) Explain the benefit of using rider in Paul Bunge balance. (c) Calculate the mass of H2SO4 present in solution of container A. (d) Explain, which apparatus are essential in volumetric analysis. Solution (a) A first aid box is a box of medicines and materials for the primary treatment. (b) The smallest weight in the weight box is 10 mg. A mass below 10 mg cannot be balanced with these weights. The rider is a thin bent wire of fixed mass. It is moved along the divisions of the beam. Each division adds 0.0001 g to the right pan. Hence a mass is measured up to the fourth decimal place of a gram. (c) Here, Concentration of the solution 𝑆= 1 M Volume of the solution 𝑉= 250 mL Molar mass of H2SO4 𝑀= (2 × 1) + 32 + (4 × 16) = 98 g mol−1 𝑤= 𝑆𝑀𝑉 1000 = 1 × 98 × 250 1000 g = 24.5 g 𝑤= 24.5 g The solution of container A contains 24.5 g of H2SO4. (d) Volumetric analysis finds the amount of a substance from exact volumes of solutions. Each apparatus is judged by the accuracy of its volume. ahbab.dev 3