Empirical Formulas. When copper metal is heated in a crucible filled with sulfur

Question

Empirical Formulas. When copper metal is heated in a crucible filled with sulfur, a copper sulfide is formed. Identify the copper sulfide formed in this reaction. Use the expend justify your answer. Known copper sulfides are CuS, Cu_2S, and Cu_2S_2. Mass or crucible 39.3362 g Mass of crucible and copper wire 40.8193 g After first heating with sulfur 41.9989 g After second heating with sulfur 41.5678 g After third heating with sulfur 41.5677 g What is the number of moles of copper (atomic mast 63.546) used in the experiment? What is the number of moles of sulfur (atomic mass 32.066) incorporated into the product? What is the formula and systematic name of the copper sulfide product produced? What does the mass after each heating tell you about the reaction conditions at the end of each heating?

Explanation / Answer

3.(a): mass of copper used in the experiment = 40.8193 g - 39.3362 g = 1.4831 g

Hence moles of copper used in the experiment = mass / molar mass

= 1.4831 g / 63.546 g/mol = 0.02334 mol (answer)

(b): mass of sulfur incorporated into the product = 41.5677 g - 40.8193 g = 0.7484 g

Hence moles of S incorporated into the product = mass / molar mass

= 0.7484 g / 32.066 g/mol = 0.02334 mol (answer)

(c): moles of Copper : moles of S = 0.02334 mol : 0.02334 mol = 1:1

Hence 1 mole of Cu reacts with 1 mol of S to from 1 mol of CuS.

Hence the synthetic name is CuS.

(d) In the first heating CuS along with some sulfur atoms is deposited inside the crucible. On forther heating sulfur becomes volatile and evaporates to air resulting a slight decrease in the mass of the crucible. The volatile S reacts with O2 to form SO2 gas. Hence after repeated heating only nonvolatile CuS remain in the crucible.

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