So for our final example question on this page, we're going to deal with a dilution. Now, it's one thing to use the dilution equation to solve within a classroom, but it's another thing when you're in the lab and asked to do a dilution yourself. Dilutions can be a bit tricky. The approach we want to take is to create a 100-fold dilution. Just remember, in a dilution, that means that our solvent has to be larger than our solution. So knowing this, we know that option a won't work because in a, the solvent is less than the solution. And when it comes to a dilution, they want us to achieve a 100-fold dilution. That means it's going to be a ratio of 100 to 1. But what exactly is the 100 referring to, and what exactly is the 1 referring to? In a dilution, we're going to say here it is the total of solvent and solution. That's what 100:1 is referring to. A 100-fold dilution is 100:1, meaning we have 100 parts total of solvent and solution together compared to 1 part of the solution. So here we know that a is out.

If we take a look at the other options, for b, we have 90 parts solvent + 10 parts solution. That’d be 90+10, which totals up to 100, and then 10 for the solution alone. If you divide both by 10, this would represent a 10:1 dilution, or a 10-fold dilution, which is not what we want. Next, for c, we have 99 parts solvent + 1 part solution. That'd be 99+1, summing to 100, and then 1 for the solution alone. This would represent our 100-fold dilution.

Looking at the last options, here we have 100 parts solvent to 1 part solution, summing to 101. This would be a 101:1 ratio, not quite what we want. This would be a 101-fold dilution, which is not what we seek. Lastly, we have an option with 10 parts solvent + 1 part solution, totaling 11. That'd be 11 to 1, representing an 11-fold dilution. So, just remember, in a 100-fold dilution, we have 100 parts of the combined solvent and solution compared to just the amount of the solution alone.