Title 1-Stoichiometry (Revision Test) - Engeecon Academy 2.0.pdf ✅

Pick up the pair of isoelectronic species: A. K & Mg B. Ca & Al C. Ne & Mg D. Ar & O 1. A. 2. B. 3. C. 4. D. Incorrect Explanation: C Both neon & Mg contain 10 electrons. + +2 +2 +3 +2 -2 +2 2. Question 1 points 49g of H SO contains how many oxygen atoms: A. 3.01 × 1023 B. 6.02 × 1023 C. 1.2 × 1024 D. 2.4 × 1024 1. A. 2. B. 3. C. 4. D. Incorrect Explanation: C 49g H SO = 0.5 moles No of oxygen atoms in 0.5 moles of H SO = 4 × 0.5 × 6.02×1023 → 1.2×1024 2 4 2 4 2 4 3. Question 1 points 50g of a substance containing Mg metal was burnt & it yielded 20g of MgO. What is the %age of Mg in the sample? 1. A. 40% 2. B. 24% 3. C. 12% 
4. D. 48% Incorrect Explanation: B Molar mass of MgO = 40g 40g of MgO contains = 24g Mg & 16g O 20g of MgO contains = 12g Mg & 16g O So total 12g Mg was present in initial sample that all got converted to MgO %age = 12g/50g × 100% = 24% 4. Question 1 points 24g of O contains as many oxygen atoms as: A. No of oxygen atoms in 0.5 moles of CO B. Number of molecules in 24g of CH C. Number of sigma bonds in 78g of benzene. D. Total number of ions in 65g of H SO 1. A. 2. B. 3. C. 4. D. Incorrect Explanation: B No of Oxygen atoms in 24g of O = 24g/48g × 3 × 6.02×1023 → 1.5 × 6.02 × 1023 No of molecules in 24g of CH = 24g/16g × 6.02 × 1023 → 1.5 × 6.02×1023 3 2 4 2 4 3 4 5. Question 1 points A compound contains 60% carbon, 32% oxygen & 8% hydrogen by mass. If the molar mass of compound is equal to mass of 2 moles of product obtained by reacting quick lime with CO . What is the molecular formula of compound? A. C O H B. C H O C. C H O D. C H O 1. A. 2. B. 3. C. 4. D. 2 5 2 8 10 16 4 6 8 2 8 16 4 
Incorrect Explanation: B Empirical formula = C O H molar mass of compound = 2×100g (mass of 1 mole of CaCO ) = 200g Empirical formula mass = 5×12g + 2×16g + 8g = 100g n = molar mass / empirical mass = 200/100 = 2 molecular formula = n × empirical formula = 2 × C O H = C O H 5 2 8 3 5 2 8 10 4 16 6. Question 1 points If two moles of H react with 2 moles of O to give water, how many moles of water would be produced? 1. A. 2 2. B. 4 3. C. 1 4. D. 1⁄2 Incorrect Explanation: A According to equation: 2H + O → 2H O 2 moles of H give 2 moles of water since H is limiting reactant. 2 2 2 2 2 2 2 7. Question 1 points 56g of N is reacted with excess of H to give: A. 17g NH B. 34g NH C. 68g NH D. 136g NH 1. A. 2. B. 3. C. 4. D. 2 2 3 3 3 3 
Incorrect Explanation: C Moles of N in 56g = 56g/28g = 2 According to equation: N + 3H → 2NH 2 moles of N give = 4 moles of NH Mass of 4 moles of NH = 4 × 17g = 68g 2 2 2 3 2 3 3 8. Question 1 points Efficiency of a chemical reaction is measured by: 1. A. Actual yield 2. B. Theoretical yield 3. C. Limiting reactant 4. D. %age yield Incorrect Explanation: D Percentage yield is a measure of efficiency of a chemical reaction & is given by % = actual yield/theoretical yield × 100% 9. Question 1 points 40g of C is reacted with 48g of oxygen to give CO . What mass of CO is produced & how much excess reagent is left? 1. A. 66g, 4g 2. B. 132g, 4g 3. C. 66g, 22g 4. D. 88g, 22g Incorrect Explanation: C C + O → CO Moles in 40g of C = 40/12 = 3.33 Moles in 48g of O = 48/32 = 1.5 1.5 moles of O react with 1.5 moles of C to give 1.5 moles of CO = 1.5×44g = 66g CO Excess reagent is carbon, carbon left = 40g – 1.5×12g = 22g 2 2 2 2 2 2 2 2 10. Question 1 points 