Question

You discover that the complex decomposes in water. You dissolve 0.1000 g of the complex in H2O and add excess CaHg(SCN)4, which precipitates Co(II) as CoHg(SCN)4(s). After the precipitate is washed and dried, its mass is 0.1102 g. How many grams of cobalt are contained in 0.100 g of the complex? Group of answer choices

Answer 1

Answer:

• 0.01320g

Explanation:

All the cobalt in the sample is in the precipitate, so you need to determine the amount of cobalt in the precipitate.

1. Calculate the molar mass of CoHg(SCN)₄

Atom  Number of atoms    Atomic mass      Product

                                                   g/mol             g/mol

Co                   1                         58.933             58.933

Hg                   1                         200.59            200.59

S                     4                         32.065             128.26

C                     4                         12.011              48.044

N                     4                          14.007            56.028

                                                                        =========

                                                 Molar mass:     491.855

2. Set a proportion

• 58.933g of Co / 491.855 g of compound = x / 0.1102 g of compound

Clear and compute:

• x = 0.1102 × 58.933 / 491.855 g of Co

• x = 0.01320393 g

Round to four significant figures: 0.01320g of cobalt ← answer