[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to calculate the concentration of a solution in grams per desm cubed higher tier students should also be able to explain how the mass of the solute and the volume of the solution affect the concentration so let's start by looking at what's meant by concentration the concentration tells us the mass of a solute in a given volume of solution now I should point out that if you're a higher tier student you learn another definition of concentration as well as this one in a later video but if you're doing Foundation then you only need to learn this definition so what's meant by a solute well a solute is a chemical which is dissolved in a solvent and in chemistry water is often used as a solvent the unit of concentration for this definition is G per decim cubed a cubed is what used to be called a liter but scientists don't use that word anymore now we calculate the concentration using this equation this equation is not in the spec but I do think it's worth learning the concentration in grams per decimeter cubed is the mass in grams divided by the volume in decimet cubed and here's a triangle to help you learn this so let's look at a typical question 200 g of a chemical is dissolved in water to a final volume of 1 DM cu cubed calculate the concentration of the solution here's the equation to find the concentration we divide the mass and grams by the volume in decimet cubed this gives us a final concentration of 200 g per decim cubed now that was quite an easy one so let's look at something a bit more challenging 150 g of a chemical is dissolved in water to a final volume of 0.5 DM cubed calculate the concentration of the solution pause the video and try this yourself okay dividing 150 G by 0.5 DM cubed gives us a final concentration of 300 G per decim cubed okay now in the exam you could be asked to rearrange this equation and calculate the mass of a solute or the volume of a solution so here's another question for you to try calculate the mass of a chemical needed to dissolve in a final volume of 0.4 DM cubed to give a concentration of 600 G per per decim cubed now to answer this question it's worth using the triangle pause the video and try this yourself we're calculating Mass so we multiply the concentration by the volume multiplying 600 by .4 gives us a final mass of 240 G here's one more question for you to try calculate the final volume of a solution containing 200 g of a chemical with a concentration of 800 G per decim cubed here's a triangle pause the video and try this yourself okay we're calculating the volume so we need to divide the mass by the concentration 200 g ID 800 G per decim cubed gives us a final volume of .25 decim cubed now if you're a higher student you need to be able to explain how the mass of the solute and the volume of the solution affect the concentration here are the two facts that you need to know if we increase the mass of solute and keep the volume the same then we increase the concentration if we increase the volume of the solution and keep the mass of the solute the same then we decrease the concentration remember that you'll find plenty more questions on concentration in my revision workbook which you can get by clicking on the link above okay so hopefully now you should be able to calculate the concentration of a solution and grams per decimeter cubed and if you're a higher tier student you should be able to explain how the mass of the solute and the volume of the solution affect the [Music] concentration