Victory for the ACT Student Text 15e

344 • S CIENCE

A chemistry student wishes to study weight relationships between compounds before and after reactions involving the compounds. Two experiments were conducted to investigate two different reactions. The reactions are shown below, together with the amount (grams) of each substance before and after each reaction has proceeded. Equations are balanced to show the ratio of each type of atom before and after the reactions. EXPERIMENT 1 & NaBr AgNO AgBr NaNO 3 3 Initial Mass (g) 103 170 0 0 Final Mass (g) 0 0 188 85 EXPERIMENT 2 & 2 Na CO HCl 2NaCl H O CO 2 3 2 2 Initial Mass (g) 106 73 0 0 (?) Final Mass (g) 0 0 117 18 (?) (The student has measured the quantities he could, but was unable to weigh the CO 2 because it is a gas. Since it is a gas, he assumes it has negligible mass.) Passage II 7. In Experiment 1, the data indicate that after the reaction has proceeded: A. all of the Na originally present has been converted to Ag. B. there are more molecules of NaNO 3 than there were molecules of AgNO 3 at the outset. C. no NaBr remains. D. no AgBr remains. 8. Which of the following is (are) conserved in the reaction in Experiment 1? I. mass II. number of atoms III. amount of AgNO 3 F. I only G. I and II only H. I and III only J. I, II, and III 9. In Experiment 2, the mass of the weighed products is: A. zero. B. less than the mass of reactants. C. equal to the mass of reactants. D. greater than the mass of reactants. 10. Experiment 2 differs from Experiment 1 in that: F. the number of atoms is not conserved. G. the reaction does not go to completion. H. there are no compounds involved. J. gas is produced. 11. The student’s assumption in neglecting the mass of one of the products in Experiment 2 would most likely lead him to draw which of the following conclusions? A. Mass is consumed as the reaction proceeds. B. Mass is produced as the reaction proceeds. C. Energy is consumed as the reaction proceeds. D. Mass is conserved as the reaction proceeds. 12. The student is advised of a means to weigh the CO 2 gas produced in the reaction and ϐ‹†• –Š‡ ƒ•• –‘ „‡ ͶͶ ‰”ƒ•Ǥ Š‡ •–—†‡– can now state that the two experiments: F. lead to similar conclusions: neither mass nor atoms are conserved. G. lead to similar conclusions: both mass and atoms are conserved. H. lead to different conclusions: the number of molecules is not the same for the reactants as for the products. J. lead to different conclusions: gases have negligible mass.