## Saturday, 20 October 2012

### Calculating Percentage Solutions

For some reason percentage solution calculation cause students some problems. However, hopefully, once you have been through this blog post you should have a good understanding of percentage solutions, and how to do the calculations.

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What are percentage solutions?

A percentage solution is an amount or volume of something per 100 ml or 100 g of a solution. It is as simple as that. It is a percentage.

Why are they used?

Percentage solutions are just a convenient and easy way to record solution concentrations. One advantage of percentage solutions is that you don’t need to know anything about the compound in terms of molecular weight as all you need is the percentage of the required solution.

Why are their three types of percentage solutions?

This is slightly difficult to explain. However, there are three types of percentage solution:
• Percentage weight by volume (w/v)
• Percentage volume by volume (v/v)
• Percentage weight by weight (w/w)
The percentage weight by volume (w/v) is the number of grams of compound per 100 ml of solution. This type of percentage solution tends to be used when describing the amount of some powder made up in a solution. So, for example, 5 g of a powder made up to a final volume of 100 ml would be a 5% (w/v) solution. Likewise, 2.5 g of powder made up to 50 ml would also be a 5% (w/v) solution as you would have 5 g in 100 ml.

The percentage volume by volume (v/v) is the number of ml of some liquid per 100 ml of the solution. This type of percentage solution is usually used to describe a solution that is made by mixing two liquids. So, for example, 5 ml of a liquid made up to a final volume of 100 ml would be a 5% (v/v) solution. Likewise, 2.5 ml of a liquid made up to 50 ml would also be a 5% (v/v) solution as you would have 5 ml in 100 ml.