Solved Numerical of 9th Class Chemistry Chapter 1
Question no: 1 Sulphuric acid is the king of chemicals if you need 5 moles of Sulphuric acid for a reaction. How many grams of it will you weigh? Solution: Molar mass of H 2 SO 4 = 2 + 32 + 64 Moles of H 2 SO 4 = 5 Mass/Weight=? Formula: Unknown mass = moles * molar mass = 5 * 98g We will weigh 490 g of sulphuric acid to get 5 moles ( Answer) Question no: 2 Calcium Carbonate is insoluble in water. If you have 40g of it how many Ca +2 and Co 3 -2 ions are present in it? Solution: CaCo 3 ———–> Ca +2 + Co 3 -2 1 Molecule of CaCo 3 Gives 1 Ca +2 and 1 Co 3 -2 ions Given Mass = 40g Moles =? Molar mass of CaCo vertical-align: baseline;">3 = 100g Formula Moles = Given Mass/Molar Mass Moles = 40/100 = 0.4 Number of Ca +2 ions = 1 (moles × N A ) = 1 (0.4 × 6.02 × 10 23 ) = 2.4 × 10 23 Number of Co 3 -2 ions = 1 (moles × N A ) = 1 (0.4 × 6.02 × 10 23 ) = 204 × 10 23 40g of calcium carbonate has 2.4 × 10 23 Ca +2 ions and 2.4 × 10 23 Co 3 -2 ions. (