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Copper (Cu) reacts with sulfur (S) to form copper sulfide as shown in the equation. A scientist adds 12.7 grams of Cu to 3.2 grams of S to start the reaction. In this reaction, all of the copper and all of the sulfur react. Before running the experiment, the scientist expected the products of the reaction will be a total of 15.9 grams of copper sulfide (Cu

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To determine whether the scientist’s expectation of a total of 15.9 grams of copper sulfide (CuS) is accurate, we need to begin with the balanced chemical equation for the reaction between copper (Cu) and sulfur (S):

\[ 2 \text{Cu} + \text{S} \rightarrow \text{Cu}_2\text{S} \]

This indicates that 2 moles of copper react with 1 mole of sulfur to produce 1 mole of copper sulfide.

Next, we'll calculate the number of moles of each reactant to determine the limiting reactant.

Step 1: Calculate moles of Cu and S

  1. Molar mass of Cu: Approximately 63.55 g/mol
  2. Molar mass of S: Approximately 32.07 g/mol

Now we calculate the number of moles:

  • Moles of Cu: \[ \text{Moles of Cu} = \frac{12.7 \text{ g}}{63.55 \text{ g/mol}} \approx 0.199 \text{ moles} \]

  • Moles of S: \[ \text{Moles of S} = \frac{3.2 \text{ g}}{32.07 \text{ g/mol}} \approx 0.100 \text{ moles} \]

Step 2: Determine the limiting reactant

According to the balanced equation, we require double the amount of copper for every mole of sulfur:

For 0.100 moles of sulfur, we need: \[ 0.100 \text{ moles S} \times 2 = 0.200 \text{ moles Cu} \]

We have approximately 0.199 moles of Cu available, which is slightly less than what is required. Therefore, copper (Cu) is the limiting reactant.

Step 3: Calculate the mass of copper sulfide produced

From the balanced equation, 2 moles of Cu produce 1 mole of CuS:

  • Moles of CuS produced: \[ \text{Moles of CuS} = \frac{0.199 \text{ moles Cu}}{2} \approx 0.0995 \text{ moles CuS} \]

Step 4: Calculate mass of CuS produced

  • Molar mass of CuS: \[ 63.55 \text{ g/mol (Cu)} + 32.07 \text{ g/mol (S)} \approx 95.62 \text{ g/mol} \]

Now, calculate the mass of CuS: \[ \text{Mass of CuS} = \text{Moles of CuS} \times \text{Molar mass of CuS} \] \[ = 0.0995 \text{ moles} \times 95.62 \text{ g/mol} \approx 9.52 \text{ g} \]

Step 5: Conclusion

The total mass of copper sulfide produced from this reaction is approximately 9.52 grams, which is significantly lower than the expected 15.9 grams. Therefore, the expectation of 15.9 grams of CuS is not accurate based on the given amounts of reactants.