ACSBR 7E Chemical Calculations (Extensions) - Assignment ANS

Anglo-Chinese School (Barker Road) A Methodist Institution Founded in 1886 CHEMISTRY DEPARTMENT OF SCIENCE Name: ANSWERS ( ) Class: SEC 3 CHEMICAL CALCULATIONS (EXTENSIONS) – ASSIGNMENT ALEX LEE & SAMSON WOON/2010 PAGE 1 OF 4 PURE/COMBINED Multiple-Choice Questions [20 Marks] TOTAL SCORE / 30 Write in your selected answer for the multiple-choice questions in the boxes provided. 1 2 3 4 5 6 7 8 9 10 A A B C C A D D B B 11 12 13 14 15 16 17 18 19 20 D C D C D B D A A C 1. The ratio of the number of atoms in 2 moles of oxygen molecules to the number of atoms in 4 moles of helium is A 1 : 1 B 1 : 2 C 1 : 4 D 2 : 1 2. Which of the following contains the same number of atoms as 25.5 grams of ammonia? A 2.0 mol of CO2 B 3.0 mol of He C 4.0 mol of CH4 D 6.0 mol of O2 3. A 0.25 mol sample of an unknown metal Q is burnt in oxygen. The oxide formed was found to have a mass of 18 grams. Given that the relative atomic mass of Q is 64, what is the oxide formula? A QO B Q2O C QO2 D Q2O2 4. 0.1 mol MSO4 combines with 5.4 g of water to form the hydrate MSO4.nH2O. What is n? A 1 B 2 C 3 D 4 5. Which of the following contains the greatest mass of nitrogen for every 1 gram of substance? A (NH4)3PO4 B Mg(NO3)2 C NH3 D NH4NO3 6. Which of the following contains the greatest mass of nitrogen for every 1 mole of substance? A (NH4)3PO4 B Mg(NO3)2 C NH3 D NH4NO3

ALEX LEE & SAMSON WOON/2010 PAGE 2 OF 4 7. The empirical formula of an organic molecule was found to be CH2O. What other information is required in order to find its molecular formula? A melting and boiling points C products of combustion B percentage composition D relative molecular mass 8. Which of the following statements about empirical formula is false? A Ionic compounds are always represented by an empirical, and not molecular, formula. B Percentage composition by mass of a compound can be found from its empirical formula. C The empirical formula of a compound can be found from its percentage composition by mass. D Whether a substance has a simple or giant structure can be seen from its empirical formula. 9. An unknown chloride of phosphorus was found to contain 5.6 g of phosphorus and 32.0 g of chlorine. What is its empirical formula? A PCl3 B PCl5 C PCl6 D P2Cl5 10. An oxide of sulfur contains 1.5 times the mass of oxygen than sulfur. What is the empirical formula for this oxide? A SO2 B SO3 C S2O3 D S3O2 11. In an experiment to find the empirical formula of a metallic oxide, a strip of the unknown metal X is first weighed. Next, the strip of X is allowed to react completely in a covered crucible, and the residue allowed to cool. After cooling, the residue is then extracted and weighed. The results for the experiment are as shown. mass of metal X 3.0 grams mass of residue 5.0 grams Assuming that the relative atomic ma