Determining the Percent Yield in the Zinc-Sulfur Reaction: A Step-by-Step Guide

Introduction

In chemistry, the yield of a reaction is a critical measure of its efficiency. This article explores the process of determining the percent yield in the reaction between zinc (Zn) and sulfur (S) to form zinc sulfide (ZnS), a key step in understanding chemical reactions. We will also discuss the factors influencing the yield and how to calculate the percent yield.

Background

The reaction between zinc and sulfur is a well-known example of a synthesis reaction, where elemental zinc reacts with elemental sulfur to produce zinc sulfide. When these two elements are combined, a vigorous exothermic reaction occurs, producing heat and resulting in the formation of zinc sulfide (ZnS).

Reaction Details

The balanced equation for the reaction is:

Zn(s) S(s) → ZnS(s)

In this reaction, the mole ratio of zinc to sulfur to zinc sulfide is 1:1:1. This means that one mole of zinc reacts with one mole of sulfur to produce one mole of zinc sulfide.

Calculating Molar Masses and Moles

First, let's calculate the molar masses of the reactants and product:

Molar mass of Zn: 65.38 g/mol Molar mass of S: 32.06 g/mol Molar mass of ZnS: 97.44 g/mol (as calculated: 65.38 32.06)

Next, we determine the initial moles of each reactant:

Initial moles of Zn: 25.0,g,text{Zn} div 65.38,g/mol 0.3824,mol,Zn Initial moles of S: 30.0,g,text{S} div 32.06,g/mol 0.9357,mol,S

Given the balanced equation and the mole ratio of Zn: S: ZnS (1:1:1), the limiting reactant plays a crucial role in determining the yield of ZnS.

Identifying the Limiting Reactant

To identify the limiting reactant, we calculate the theoretical yield of ZnS from each reactant:

Theoretical yield from Zn: 0.3824,mol,Zn times 97.44,g/mol 37.3,g,ZnS Theoretical yield from S: 0.9357,mol,S times 97.44,g/mol 91.6,g,ZnS

Since the actual yield is 35.0 grams of ZnS, the limiting reactant is zinc (Zn) as it produces the smaller amount of ZnS.

Calculating the Percent Yield

Finally, we calculate the percent yield using the formula:

Percent Yield (Actual Yield / Theoretical Yield) times 100

In this case:

text{Percent Yield} frac{35.0,g,ZnS}{37.3,g,ZnS} times 100 93.8%

This indicates that the reaction has an efficient yield of 93.8%, suggesting a well-controlled reaction condition.

Conclusion

The process of determining the percent yield in a chemical reaction, such as the synthesis of zinc sulfide, is essential for evaluating the efficiency of the reaction. By identifying the limiting reactant and calculating the theoretical and actual yields, we can accurately determine the percent yield and ensure optimal reaction conditions.