# Video: EC17-18-S2-Q28A

EC17-18-S2-Q28A

02:56

### Video Transcript

What is the name for the process of determining the concentration of a substance of known volume using another substance of known concentration and volume?

If you read the question carefully, you should be able to figure out that what we’re dealing with are two solutions. Here, I’m going to call one a solution of A and the other a solution of B. For the solution of A, we know the volume but not the concentration. And for the solution of B, we know the volume and the concentration. What we’re being asked to recall is the name for the process whereby we can determine the concentration of the solution of A using the solution of B.

What we can infer from this is there must be some kind of a reaction between A and B that we can measure. In this process, we add this solution of B, where we know both the volume and the concentration, until the reaction stops. We can then work out the number of moles of B used by multiplying the concentration of B by its volume. Work out the number of moles of A used based on whatever equation it is that they react by. And then work out the concentration of the solution of A by dividing the number of moles of A by the volume. Hopefully, all of this would’ve triggered a recollection of the type of procedure we’re dealing with here.

Picture a conical flask containing our solution of A. We know the volume, but we don’t know the concentration. Now picture a burette containing a solution of B where we know its volume. And we know its concentration. Where we have a solution like this, we often call it a standard solution. Because it is the standard against which other solutions are measured. Or, because it has a standardized concentration, for instance 0.1 molar. The standard solution of B is added into the unknown concentration solution of A until the reaction is over. In many cases, a chemical indicator is added to the solution of A. And it will change color at the endpoint.

Some examples of this process, there will be a color change, naturally, because of the reaction. Hopefully, all of this will remind you of the name for this process, which is titration. Common types of titration are acid base or redox. So we’ve just recalled the name for the process where one solution of known concentration and volume is used to determine the concentration of another solution of known volume.