Chemical amounts (A2)
Read our general notes on Risk Assessment
I need to find out the % purity of iron in cast iron. I have found out how to do the calculations but it says that you have to work out the number of moles in potassium manganate. To do this I understand that you need the relative molecular mass of the potassium permanganate. Is that going to be KMnO4 or just MnO4-, and when adding up all the numbers because the oxygen is O4 does that mean that 4 is added onto the value of 16 because it has gained four electrons or does it stay at 16. Help would be appreciated. Thanks.
Igloo writes
The first thing to say is that in some cases you will be supplied with a solution of potassium permanganate with a concentration expressed in mol dm-3. If this is the case, then you will not need to know the relative molecular mass of this compound.
If, however, you are expected to make up your own solution and to weigh out some solid potassium permanganate to do this, then, yes, you will need to know its relative molecular mass in the subsequent calculations. I shall assume that this is the case.
You will be weighing out potassium permanganate, and not permanganate ions, MnO4-, so it is the relative molecular mass of potassium permanganate which you will need to know. Since its formula is KMnO4, this means that you will need to add together the relative atomic masses of potassium, manganese and four oxygen atoms (4x16).
Always carry out a risk assessment and check with your teacher before starting any practical work.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
Rate this page or react
Share your views on this page, 0 ratings so far
updated: 17 December 2006
