Cliffs AP Chemistry, 3rd Edition

(c) (2) Restatement: Effect on the empirical formula if the silver strip had not been

dried thoroughly after being washed free of the silver chloride.

Because the strip has been washed free of the compound (silver chloride), you

assume that any silver missing from the strip went into the making of the silver

chloride. If the strip had been wet when you weighed it, you would have been

led to think that the strip was heavier than expected, and therefore that less sil-

ver had gone into the making of the silver chloride. Thinking that less silver had

been involved in the reaction, you would have calculated fewer moles of silver.

The calculatedratio of moles of silver to moles of chlorine would have been

less than expected.

2. Three compounds, D, E, and F, all contain element G. The percent (by weight) of ele-
   ment G in each of the compounds was determined by analysis. The experimental data are
   presented in the following chart.

Compound % by Weight of Element G Molecular Weight

D 53.9 131.7

E 64.2 165.9

F47.774.5

(a) Determine the mass of element G contained in 1.00 mole of each of compounds D,

E, and F.

(b) What is the most likely value for the atomic weight of element G?

(c) Compound F contains carbon, hydrogen, and element G. When 2.19 g of compound

F is completely burned in oxygen gas, 3.88 g of carbon dioxide gas and 0.80 g of

water are produced. What is the most likely formula for compound F?

Answer

2. Given: Compounds D, E, and F with % (by weight of element G) and their respective
   MW’s
   (a) Restatement: Calculate the mass of element G in 1.00 mole of compounds D, E, and F.
   0.539 ×131.7 g/mole = 71.0 g G/mole D
   0.642 ×165.9 g/mole = 107 g G/mole E
   0.477 ×74.5 g/mole = 35.5 g G/mole F
   (b) Restatement: Most likely atomic weight of G.
   According to the law of multiple proportions, the ratios of the mass of element G to the
   masses of compounds D, E, and F must be small, whole numbers. The largest common
   denominator of 71.0, 106.5, and 35.5 is 35.5, so our best estimate is that the atomic
   weight of G is 35.5(chlorine).

Part II: Specific Topics