Lesson 14 - Calculating Molar Concentration
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Overview of this Lesson
In this lesson, we continue to work problems that involve calculating molar concentration of a solution. Specifically, the molar concentration is used to solve more complex chemistry problems that involve more than one step to solve.
For example, lets say that you would like to calculate how many moles of NaOH are required to prepare 1.5 L of solution with molar concentration of 0.1 M NaCl? How do you solve this problem? How does calculating molar concentration fit into the process?
The key here is that you want to know how many moles of NaCl are needed. We learned in the last lesson that the molar concentration of any solution is:
Molar Concentration = (Moles of Solute) / (Volume of Solution)
In this problem, we wish to calculate how many moles of solute (in this case NaCl) are required to make the specified solution that has these characteristics:
- 1.5 L of solution
- Final molar concentration of 0.1 M NaCl
Putting this info into the equation above we arrive at the following:
0.1 M NaCl = (moles of NaCl) / (1.5 L of solution)
Multipy both sides of this relation by 1.5 to clear this number from the right hand side and we arrive at the answer:
Moles of NaCl = 0.15 moles of NaCl required to make this solution.
In other words, if we use 0.15 moles of NaCl and add water to make the final solution volume of 1.5 liters, we know that the molar concentration of the final solution will be 0.1 M NaCl as specificied in the problem statement.
This is a very simple problem to illustrate how the concepts of calculating molar concentration can be used to solve problems in chemistry. In this lesson, we will solve additional problems with greater complexity to give the student additional practice with these methods an concepts.