Zn And HCl Reaction Calculating Moles Of ZnCl₂ And Limiting Reagent

Jul 13, 2025 by ADMIN 68 views

You have 195 grams of Zn and 195 grams of HCl. How many moles of ZnCl₂ can be produced? Which chemical is the limiting reagent?

Introduction

In this comprehensive article, we will delve into a classic stoichiometry problem involving the reaction between zinc (Zn) and hydrochloric acid (HCl). Our main objective is to determine the amount of zinc chloride (ZnCl₂) that can be produced from 195 grams of Zn and 195 grams of HCl. Additionally, we will identify the limiting reagent in this reaction, which is the reactant that dictates the maximum amount of product formed. To solve this problem, we will utilize the principles of stoichiometry, molar mass calculations, and the concept of limiting reactants.

The balanced chemical equation for the reaction is given as:

$Zn + 2HCl \rightarrow ZnCl_2 + H_2$

This equation tells us that one mole of zinc reacts with two moles of hydrochloric acid to produce one mole of zinc chloride and one mole of hydrogen gas. We are also provided with the molar masses of the elements involved: Zn = 65.38 g/mol, H = 1.008 g/mol, and Cl = 35.45 g/mol. These values are essential for converting grams to moles and vice versa.

This problem is a typical example of stoichiometry calculations, which are fundamental in chemistry. Stoichiometry allows us to quantitatively relate reactants and products in a chemical reaction. Understanding how to solve these problems is crucial for various applications, including industrial chemistry, pharmaceutical research, and environmental science. By mastering these concepts, one can predict the yield of a reaction, optimize reaction conditions, and ensure efficient use of resources.

In the following sections, we will break down the problem step by step, starting with the conversion of grams to moles, followed by the identification of the limiting reagent, and finally, the calculation of the moles of ZnCl₂ produced. Let's embark on this chemical journey together!

Step 1: Convert Grams to Moles

The first crucial step in solving this stoichiometry problem is to convert the given masses of the reactants, zinc (Zn) and hydrochloric acid (HCl), into moles. To accomplish this, we will use the molar masses of the substances. The molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). We are provided with the molar masses of Zn, H, and Cl, which will aid us in this conversion.

Moles of Zinc (Zn)

We are given 195 grams of Zn. To find the number of moles, we use the formula:

$Moles = \frac{Mass}{Molar \, Mass}$

The molar mass of Zn is 65.38 g/mol. Thus,

$Moles \, of \, Zn = \frac{195 \, g}{65.38 \, g/mol} \approx 2.98 \, moles$

Therefore, we have approximately 2.98 moles of zinc.

Moles of Hydrochloric Acid (HCl)

Similarly, we are given 195 grams of HCl. We need to calculate the molar mass of HCl first. HCl consists of one hydrogen atom (H) and one chlorine atom (Cl). The molar mass of H is 1.008 g/mol, and the molar mass of Cl is 35.45 g/mol. The molar mass of HCl is the sum of these:

$Molar \, Mass \, of \, HCl = 1.008 \, g/mol + 35.45 \, g/mol = 36.458 \, g/mol$

Now, we can calculate the moles of HCl:

$Moles \, of \, HCl = \frac{195 \, g}{36.458 \, g/mol} \approx 5.35 \, moles$

So, we have approximately 5.35 moles of hydrochloric acid.

Significance of Mole Conversion

Converting grams to moles is a fundamental step in stoichiometry because chemical reactions occur on a molar basis. The balanced chemical equation expresses the reaction in terms of moles, indicating the molar ratios of reactants and products. By converting the masses of reactants to moles, we can directly compare the amounts of reactants and determine which one will be completely consumed first, thus identifying the limiting reagent. This conversion is also essential for calculating the theoretical yield of the product.

In the next section, we will use these mole values to determine the limiting reagent in the reaction between zinc and hydrochloric acid. Understanding this concept is crucial for predicting the maximum amount of product that can be formed.

Step 2: Identify the Limiting Reagent

Identifying the limiting reagent is a critical step in stoichiometry, as it determines the maximum amount of product that can be formed in a chemical reaction. The limiting reagent is the reactant that is completely consumed first, thereby halting the reaction and limiting the amount of product. To identify the limiting reagent, we need to compare the mole ratios of the reactants to the stoichiometric ratios from the balanced chemical equation.

The balanced chemical equation for the reaction is:

$Zn + 2HCl \rightarrow ZnCl_2 + H_2$

This equation indicates that 1 mole of Zn reacts with 2 moles of HCl. We have already calculated that we have 2.98 moles of Zn and 5.35 moles of HCl.

Determining the Limiting Reagent

To determine the limiting reagent, we compare the mole ratio of the reactants to the stoichiometric ratio. We can do this by dividing the number of moles of each reactant by its coefficient in the balanced equation:

For Zn:

$\frac{Moles \, of \, Zn}{Coefficient \, of \, Zn} = \frac{2.98 \, moles}{1} = 2.98$

For HCl:

$\frac{Moles \, of \, HCl}{Coefficient \, of \, HCl} = \frac{5.35 \, moles}{2} = 2.675$

The reactant with the smallest value is the limiting reagent. In this case, HCl has a smaller value (2.675) compared to Zn (2.98). Therefore, HCl is the limiting reagent.

Implications of the Limiting Reagent

The limiting reagent, HCl, will be completely consumed in the reaction, and the amount of ZnCl₂ produced will be determined by the initial amount of HCl. The other reactant, Zn, is present in excess, meaning there will be some Zn left over after the reaction is complete. The concept of the limiting reagent is vital in chemical reactions because it helps predict the theoretical yield of the product. The theoretical yield is the maximum amount of product that can be formed based on the amount of the limiting reagent.

Understanding the limiting reagent also has practical implications in industrial chemistry and research. By controlling the amount of the limiting reagent, chemists can optimize the reaction to produce the desired amount of product efficiently and minimize waste.

In the next section, we will use the amount of the limiting reagent (HCl) to calculate the moles of ZnCl₂ produced in the reaction.

Step 3: Calculate Moles of ZnCl₂ Produced

Now that we have identified hydrochloric acid (HCl) as the limiting reagent, we can calculate the moles of zinc chloride (ZnCl₂) that can be produced in the reaction. The amount of product formed is directly related to the amount of the limiting reagent, as the reaction will stop once all of the limiting reagent is consumed.

The balanced chemical equation is:

$Zn + 2HCl \rightarrow ZnCl_2 + H_2$

From the equation, we see that 2 moles of HCl produce 1 mole of ZnCl₂. This stoichiometric relationship is the key to calculating the moles of ZnCl₂ produced.

Calculation of Moles of ZnCl₂

We have 5.35 moles of HCl (the limiting reagent). Using the stoichiometric ratio from the balanced equation, we can set up a proportion to find the moles of ZnCl₂ produced:

$\frac{Moles \, of \, ZnCl_2}{Moles \, of \, HCl} = \frac{1 \, mole \, ZnCl_2}{2 \, moles \, HCl}$

Plugging in the moles of HCl we have:

$\frac{Moles \, of \, ZnCl_2}{5.35 \, moles} = \frac{1 \, mole \, ZnCl_2}{2 \, moles \, HCl}$

Solving for moles of ZnCl₂:

$Moles \, of \, ZnCl_2 = \frac{5.35 \, moles \, HCl}{2} \approx 2.675 \, moles$

Therefore, approximately 2.675 moles of ZnCl₂ can be produced from the reaction of 195 grams of Zn and 195 grams of HCl.

Significance of Product Calculation

Calculating the amount of product formed is crucial in chemistry for several reasons. It allows chemists to predict the yield of a reaction, which is essential for planning experiments and industrial processes. The theoretical yield, which we have just calculated, is the maximum amount of product that can be obtained under ideal conditions. In reality, the actual yield may be less than the theoretical yield due to various factors such as incomplete reactions, side reactions, and loss of product during purification.

Knowing the theoretical yield is also important for determining the efficiency of a reaction. The percent yield, which is the ratio of the actual yield to the theoretical yield, is a measure of how effectively the reaction converted reactants into products. A high percent yield indicates that the reaction was efficient, while a low percent yield suggests that there were significant losses or side reactions.

In conclusion, we have successfully calculated the moles of ZnCl₂ produced in the reaction by using the amount of the limiting reagent (HCl) and the stoichiometric relationship from the balanced chemical equation. This calculation is a fundamental aspect of stoichiometry and is essential for understanding and predicting the outcomes of chemical reactions.

Conclusion

In this detailed exploration, we addressed the problem of determining the amount of zinc chloride (ZnCl₂) produced from 195 grams of zinc (Zn) and 195 grams of hydrochloric acid (HCl), and identifying the limiting reagent. Through a step-by-step approach, we converted grams to moles, identified the limiting reagent, and calculated the moles of ZnCl₂ produced.

Summary of Key Findings

Conversion of Grams to Moles: We converted the given masses of Zn and HCl to moles using their respective molar masses. We found that 195 grams of Zn is approximately 2.98 moles, and 195 grams of HCl is approximately 5.35 moles.
Identification of the Limiting Reagent: By comparing the mole ratios of the reactants to the stoichiometric ratios from the balanced chemical equation, we determined that HCl is the limiting reagent. This means that HCl will be completely consumed in the reaction, and the amount of ZnCl₂ produced is limited by the amount of HCl available.
Calculation of Moles of ZnCl₂ Produced: Using the stoichiometric relationship from the balanced equation, we calculated that approximately 2.675 moles of ZnCl₂ can be produced from the reaction.

Significance of Stoichiometry

This problem highlights the importance of stoichiometry in chemistry. Stoichiometry is the foundation for quantitative analysis of chemical reactions, allowing us to predict the amounts of reactants and products involved in a reaction. Understanding stoichiometry is crucial for various applications, including:

Industrial Chemistry: Stoichiometry is essential for optimizing chemical processes in industries, ensuring efficient use of resources, and maximizing product yield.
Pharmaceutical Research: In drug development, stoichiometry helps in synthesizing compounds and determining the correct dosages of medications.
Environmental Science: Stoichiometry is used to analyze pollutants, understand chemical reactions in the environment, and develop strategies for remediation.
Research and Development: In chemical research, stoichiometry is indispensable for designing experiments, interpreting results, and developing new materials and technologies.

Final Thoughts

The ability to solve stoichiometry problems is a fundamental skill for any chemist or student of chemistry. By mastering these concepts, one can confidently predict the outcomes of chemical reactions, optimize reaction conditions, and contribute to advancements in various fields. This problem involving the reaction between Zn and HCl serves as a classic example of how stoichiometry principles can be applied to solve real-world chemical problems. We hope this comprehensive guide has provided you with a clear understanding of the steps involved in solving stoichiometry problems and has enhanced your appreciation for the quantitative aspects of chemistry.