Question

A 20.0g sample of mercury(II) oxide (HgO, M = 216.6) is heated strongly, causing it to decompose to metallic Hg and O2 gas. What volume of O2 gas is produced( measured at STP)
(A) 1.03L (B) 2.07L (C) 4.14L (D) 14.0L
When 30.0 ml of 0.10 M AgNO3 is added to 30.0 mL of 0.10 M NaCl, aqueous NaNO3 and solid AgCl are formed. How much solid AgCl is produced?
(A) 0.003 mol (B) 0.0060 (C) 0.030 mol (D) 0.060

Answer 1

For the first reaction, we use it stoichiometric coefficients and the molar mass of zinc. Also, we use the conditions at STP that 1 mol of a substance is equal to 22.4 L. Calculation is as follows:20.0 g (1 mol / 216.6 g)(1 mol O2 / 2 mol Hg)(22.4 L O2 / 1 mol O2) = 1.03 L
Thus, the answer is A.

For the second reaction, we use also the stiochiometric coefficients to find the amount of AgCl produced from the given conditions.(0.10 mol AgNO3 / 1L soln) (30.0 mL soln) (1L / 1000 mL) ( 1 mol AgCl / 1 mol AgNO3) =0.003 mol AgCl
Thus, the answer is A.