Calculating the Number of Moles of HCl in Each Solution

Oct 13, 2025 by wbrum.org 72 views

Understanding the Problem

To solve this problem, we need to understand the concept of molarity and how it changes when two solutions of different concentrations are mixed. Molarity is defined as the number of moles of a substance per liter of solution. In this case, we have two solutions of hydrochloric acid (HCl) with different concentrations: 0.20 mol dm³ and 0.30 mol dm³.

Calculating the Number of Moles of HCl in Each Solution

First, we need to calculate the number of moles of HCl in each solution. We can do this by multiplying the concentration of each solution by its volume in liters.

For the first solution (0.20 mol dm³):

volume = 150 cm³ = 0.15 dm³ (converting cm³ to dm³)
moles_HCl_1 = concentration_1 * volume_1 = 0.20 mol dm³ * 0.15 dm³ = 0.03 mol

For the second solution (0.30 mol dm³):

volume = 250 cm³ = 0.25 dm³ (converting cm³ to dm³)
moles_HCl_2 = concentration_2 * volume_2 = 0.30 mol dm³ * 0.25 dm³ = 0.075 mol

Calculating the Total Number of Moles of HCl

Now, we need to calculate the total number of moles of HCl in the resulting solution. We can do this by adding the number of moles of HCl from each solution.

total_moles_HCl = moles_HCl_1 + moles_HCl_2 = 0.03 mol + 0.075 mol = 0.105 mol

Calculating the Total Volume of the Resulting Solution

Next, we need to calculate the total volume of the resulting solution. We can do this by adding the volumes of the two solutions.

total_volume = volume_1 + volume_2 = 0.15 dm³ + 0.25 dm³ = 0.40 dm³

Calculating the Concentration of HCl in the Resulting Solution

Finally, we can calculate the concentration of HCl in the resulting solution by dividing the total number of moles of HCl by the total volume of the solution.

concentration_HCl_result = total_moles_HCl / total_volume = 0.105 mol / 0.40 dm³ = 0.2625 mol dm³

Rounding the Answer

Since the answer choices are given in one decimal place, we can round our answer to one decimal place.

concentration_HCl_result_rounded = round(concentration_HCl_result, 1) = 0.26 mol dm³

The final answer is 0.26.

Conclusion

In this problem, we calculated the concentration of hydrochloric acid in the solution formed by adding 150 cm³ of 0.20 mol dm³ HCl(aq) to 250 cm³ of 0.30 mol dm³ HCl(aq). We used the concept of molarity and calculated the number of moles of HCl in each solution, the total number of moles of HCl, the total volume of the resulting solution, and finally, the concentration of HCl in the resulting solution. Our answer was 0.26 mol dm³.

Frequently Asked Questions

What is molarity? Molarity is defined as the number of moles of a substance per liter of solution.
How do I calculate the concentration of a solution? To calculate the concentration of a solution, you need to know the number of moles of the substance and the volume of the solution in liters.
What is the difference between molarity and molality? Molarity is defined as the number of moles of a substance per liter of solution, while molality is defined as the number of moles of a substance per kilogram of solvent.

References

Chemistry textbook by [Author]
Online resources on chemistry and molarity

Frequently Asked Questions

Q: What is molarity?

A: Molarity is defined as the number of moles of a substance per liter of solution. It is a measure of the concentration of a solution, expressed in units of moles per liter (mol/L).

Q: How do I calculate the concentration of a solution?

A: To calculate the concentration of a solution, you need to know the number of moles of the substance and the volume of the solution in liters. You can use the formula: concentration = number of moles / volume.

Q: What is the difference between molarity and molality?

A: Molarity is defined as the number of moles of a substance per liter of solution, while molality is defined as the number of moles of a substance per kilogram of solvent. Molality is a measure of the concentration of a solution, expressed in units of moles per kilogram (mol/kg).

Q: How do I calculate the number of moles of a substance?

A: To calculate the number of moles of a substance, you need to know the mass of the substance and its molar mass. You can use the formula: number of moles = mass / molar mass.

Q: What is the significance of molarity in chemistry?

A: Molarity is a crucial concept in chemistry, as it helps us understand the concentration of solutions and how they behave in different chemical reactions. It is used to calculate the amount of substance required for a reaction, as well as the amount of product formed.

Q: How do I convert between different units of concentration?

A: To convert between different units of concentration, you can use the following conversion factors:

1 mol/L = 1 M
1 mol/kg = 1 m
1 g/L = 1 mg/mL

Q: What are some common mistakes to avoid when calculating molarity?

A: Some common mistakes to avoid when calculating molarity include:

Using the wrong units for the volume of the solution
Failing to account for the density of the solution
Not using the correct molar mass of the substance

Q: How do I calculate the concentration of a solution using the formula: concentration = number of moles / volume?

A: To calculate the concentration of a solution using the formula: concentration = number of moles / volume, you need to know the number of moles of the substance and the volume of the solution in liters. You can use the following steps:

Calculate the number of moles of the substance using the formula: number of moles = mass / molar mass.
Calculate the volume of the solution in liters.
Divide the number of moles by the volume to get the concentration.

Q: What is the difference between a strong acid and a weak acid?

A: A strong acid is an acid that completely dissociates in water, producing a high concentration of hydrogen ions. A weak acid is an acid that only partially dissociates in water, producing a low concentration of hydrogen ions.

Q: How do I calculate the pH of a solution?

A: To calculate the pH of a solution, you need to know the concentration of hydrogen ions in the solution. You can use the formula: pH = -log[H+], where [H+] is the concentration of hydrogen ions in moles per liter.

Conclusion

In this article, we have answered some of the most frequently asked questions about molarity and concentration of solutions. We have covered topics such as calculating the concentration of a solution, converting between different units of concentration, and calculating the pH of a solution. We hope that this article has been helpful in clarifying some of the concepts and formulas involved in understanding molarity and concentration of solutions.

References

Chemistry textbook by [Author]
Online resources on chemistry and molarity
Scientific articles on molarity and concentration of solutions