**When buying chemical products online, you will notice that the concentrations are either marked as v/v, w/w or w/v. These are common expressions, so what do they mean exactly?**

**% V/V **

Volume concentration of a solution is expressed as % v/v, which stands for volume per volume. This is used when both chemicals in a solution are liquid.

For example, when 50ml of sulphuric acid is diluted with 50ml of water, there will be 50ml of sulphuric acid in a total volume of 100ml. Therefore, we would express the concentration of this solution as sulphuric acid 50% v/v.

**% W/W**

Weight concentration of a solution is expressed as % w/w. Like before, this stands for weight per weight. In this case, the volume of each chemical is disregarded and only the weight is used.

So, if the total mass of a 100g solution is made up of 30g hydrochloric acid in 70g of water, then we would express this as hydrochloric acid 30% w/w.

**% W/V**

Mass concentration of solution is expressed as % w/v for weight per volume. It can alternatively be abbreviated to m/v for mass per volume. This is used when a solid chemical is dissolved in a liquid.

If 1g of potassium iodide is used to make up a total volume of 100ml, then a 1% w/v solution of potassium iodide has been made.

**Calculating Percentages**

Each percentage type can be calculated by making small changes to the same method. For example, to find the % w/v of a solution the calculation is:

**(Mass of Solute (g) / Volume of Solution (ml)) x 100**

Therefore, to figure out the % w/v of a 100ml solution that is made up of 65g nitric acid, we would divide 65g by 100ml and then multiply the answer by 100. This tells us that there is a nitric acid solution of 65% w/v.

When working out the % v/v of a solution, the same method is used except it is the volume of the solute (ml) that is divided by the volume of the solution (ml). For example, a 1000ml solution that contains 450ml methanol has a methanol concentration of 45% v/v (450 / 1000 x 100).

Again, the method for calculating % w/w uses the same steps instead it is weight divided by weight.

**It is important to understand exactly what you’re purchasing. That’s why, at ReAgent, we have a skilled and dedicated team who you can speak with about any product enquiry you may have. Get in touch today to see how we can help.**