In a procedure developed to determine the percent zinc in post 1982 pennies, 50 ml of an HCl solution was used to react (dissolve) all of the zinc in the penny. To ensure complete reaction, the solution contains twice as many moles of HCl that is actually needed. What concentration of HCl should be used?

Introduction:

Determining the percent composition of different elements in a substance is an essential aspect of scientific research. In the field of analytical chemistry, various procedures and methods are employed to calculate the percentage of a particular element in a given sample. One such method involves the use of acid solutions to dissolve and react with the target element. This procedure is commonly used in determining the percentage of zinc in post-1982 pennies.

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What is the procedure for determining the percent zinc in post-1982 pennies?

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Description:

In the procedure developed to determine the percent zinc in post-1982 pennies, a 50 ml solution of hydrochloric acid (HCl) is used to react with and dissolve all of the zinc in the penny. The reaction between HCl and zinc produces zinc chloride and hydrogen gas. To ensure that the reaction is complete, a solution containing twice as many moles of HCl than are needed is used. This excess acid helps to dissolve all the zinc in the penny and ensures that no zinc is left undissolved. The concentration of HCl used in this procedure is critical, as it determines the extent of reaction and the accuracy of the zinc percentage calculation. Thus, careful consideration must be given to the selection of the appropriate HCl concentration to obtain reliable results.

Objectives:

1. To determine the percent content of zinc in post-1982 pennies.

2. To develop a procedure to react and dissolve all the zinc content in a penny.

3. To calculate the required concentration of HCl solution needed to ensure complete reaction.

Learning Outcomes:

1. Understand the process of determining the percent content of zinc in pennies.

2. Develop the skills to create a procedure for dissolving all the zinc in a penny.

3. Be able to calculate the concentration of HCl solution needed for the reaction to be complete.

4. Understand the importance of using twice as many moles of HCl solution as needed to avoid incomplete reaction.

Solution 1: Calculating the Required Concentration of HCl Solution

To calculate the required concentration of HCl solution, we need to use the balanced chemical equation of the reaction between HCl and zinc as follows:

Zn + 2HCl → ZnCl2 + H2

The equation shows that 2 moles of HCl react with 1 mole of zinc. Therefore, to ensure complete reaction, the HCl solution should contain twice as many moles of HCl as there are moles of zinc in the penny. Since the weight of zinc in the penny is approximately 2.5 grams, we can calculate the number of moles of zinc as follows:

2.5 g Zn × 1 mol Zn/65.39 g Zn = 0.0382 moles Zn

Therefore, the HCl solution should contain:

2 × 0.0382 = 0.0764 moles HCl

To calculate the required concentration of HCl solution, we can use the formula:

Moles of solute/volume of solution = Molarity

Rearranging the formula, we get:

Molarity = Moles of solute/volume of solution

Substituting the values, we get:

0.0764 moles HCl/0.050 L = 1.53 M

Therefore, the concentration of HCl solution required to dissolve all of the zinc in the penny is 1.53 M.

Solution 2: Preparing the Required HCl Solution

To prepare the required HCl solution, we need to measure out the appropriate amount of concentrated hydrochloric acid and dilute it with water to the required concentration. Since the required concentration is 1.53 M, we can use the formula:

M1V1 = M2V2

where M1 is the initial concentration of the concentrated HCl solution, V1 is the volume of the concentrated HCl solution used, M2 is the final concentration of the diluted HCl solution, and V2 is the volume of the diluted HCl solution.

Assuming we have concentrated HCl solution of 12 M, we can calculate the volume of HCl solution required as follows:

M1V1 = M2V2

(12 M)(V1) = (1.53 M)(0.050 L)

V1 = 0.006375 L

Therefore, we need to measure out 6.375 ml of 12 M HCl solution and dilute it with enough water to make 50 ml of solution. This will give us a 1.53 M HCl solution that contains twice as many moles of HCl as the number of moles of zinc in the penny, ensuring complete reaction.

Suggested Resources/Books:

1. Principles of Chemical Analysis by Robert L. Pecsok

2. Quantitative Chemical Analysis by Daniel C. Harris

3. Analytical Chemistry: An Introduction by John Kenkel

Similar Asked Questions:

1. How can you determine the percent composition of a mixture using titration?

2. How is a pH meter used to determine the concentration of a solution?

3. What factors affect the precision and accuracy of a chemical analysis?

4. How does the choice of indicator affect the results of an acid-base titration?

5. What is the difference between a primary and a secondary standard in chemical analysis?In a procedure developed to determine the percent zinc in post 1982 pennies, 50 ml of an HCl solution was used to react (dissolve) all of the zinc in the penny. To ensure complete reaction, the solution contains twice as many moles of HCl that is actually needed. What concentration of HCl should be used?

Introduction:

Determining the percent composition of different elements in a substance is an essential aspect of scientific research. In the field of analytical chemistry, various procedures and methods are employed to calculate the percentage of a particular element in a given sample. One such method involves the use of acid solutions to dissolve and react with the target element. This procedure is commonly used in determining the percentage of zinc in post-1982 pennies.

Description:

In the procedure developed to determine the percent zinc in post-1982 pennies, a 50 ml solution of hydrochloric acid (HCl) is used to react with and dissolve all of the zinc in the penny. The reaction between HCl and zinc produces zinc chloride and hydrogen gas. To ensure that the reaction is complete, a solution containing twice as many moles of HCl than are needed is used. This excess acid helps to dissolve all the zinc in the penny and ensures that no zinc is left undissolved. The concentration of HCl used in this procedure is critical, as it determines the extent of reaction and the accuracy of the zinc percentage calculation. Thus, careful consideration must be given to the selection of the appropriate HCl concentration to obtain reliable results.

Objectives:

1. To determine the percent content of zinc in post-1982 pennies.

2. To develop a procedure to react and dissolve all the zinc content in a penny.

3. To calculate the required concentration of HCl solution needed to ensure complete reaction.

Learning Outcomes:

1. Understand the process of determining the percent content of zinc in pennies.

2. Develop the skills to create a procedure for dissolving all the zinc in a penny.

3. Be able to calculate the concentration of HCl solution needed for the reaction to be complete.

4. Understand the importance of using twice as many moles of HCl solution as needed to avoid incomplete reaction.

Solution 1: Calculating the Required Concentration of HCl Solution

To calculate the required concentration of HCl solution, we need to use the balanced chemical equation of the reaction between HCl and zinc as follows:

Zn + 2HCl → ZnCl2 + H2

The equation shows that 2 moles of HCl react with 1 mole of zinc. Therefore, to ensure complete reaction, the HCl solution should contain twice as many moles of HCl as there are moles of zinc in the penny. Since the weight of zinc in the penny is approximately 2.5 grams, we can calculate the number of moles of zinc as follows:

2.5 g Zn × 1 mol Zn/65.39 g Zn = 0.0382 moles Zn

Therefore, the HCl solution should contain:

2 × 0.0382 = 0.0764 moles HCl

To calculate the required concentration of HCl solution, we can use the formula:

Moles of solute/volume of solution = Molarity

Rearranging the formula, we get:

Molarity = Moles of solute/volume of solution

Substituting the values, we get:

0.0764 moles HCl/0.050 L = 1.53 M

Therefore, the concentration of HCl solution required to dissolve all of the zinc in the penny is 1.53 M.

Solution 2: Preparing the Required HCl Solution

To prepare the required HCl solution, we need to measure out the appropriate amount of concentrated hydrochloric acid and dilute it with water to the required concentration. Since the required concentration is 1.53 M, we can use the formula:

M1V1 = M2V2

where M1 is the initial concentration of the concentrated HCl solution, V1 is the volume of the concentrated HCl solution used, M2 is the final concentration of the diluted HCl solution, and V2 is the volume of the diluted HCl solution.

Assuming we have concentrated HCl solution of 12 M, we can calculate the volume of HCl solution required as follows:

M1V1 = M2V2

(12 M)(V1) = (1.53 M)(0.050 L)

V1 = 0.006375 L

Therefore, we need to measure out 6.375 ml of 12 M HCl solution and dilute it with enough water to make 50 ml of solution. This will give us a 1.53 M HCl solution that contains twice as many moles of HCl as the number of moles of zinc in the penny, ensuring complete reaction.

Suggested Resources/Books:

1. Principles of Chemical Analysis by Robert L. Pecsok

2. Quantitative Chemical Analysis by Daniel C. Harris

3. Analytical Chemistry: An Introduction by John Kenkel

Similar Asked Questions:

1. How can you determine the percent composition of a mixture using titration?

2. How is a pH meter used to determine the concentration of a solution?

3. What factors affect the precision and accuracy of a chemical analysis?

4. How does the choice of indicator affect the results of an acid-base titration?

5. What is the difference between a primary and a secondary standard in chemical analysis?

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