Search for word then add value in a cell nearby

I'm sure there isn't too hard of a way to do this but I can't think of it atm. I have a list of different chemicals that all have a value or amount. They info is sent to me randomly and so organizing proves difficult. Is there a way I can set up a function that, when it sees a certain chemical in the column (methanol for example) it will take the value near it and add that to a total?

If I need to give more detail I can for now I will attach an example.Chemical Adding.xlsx

Yeah for some reason I'm finding it hard to explain. I'll go into more detail. So each of these chemicals has multiple ingredients. After I create a full list of these chemicals there will be multiple chemicals with the same ingredients each ingredient will have a certain weight based on its composition in the chemical. I want to set up a table of those ingredients that when it finds an ingredient with the same name it will take the value in the weight cell and add it to a total. So at the end if say 50 chemicals have ethanol as an ingredient, i have a cell that searches for ethanol and adds the weight to the total at the end. Hope that is more clear!

Thanks for the help, I'll look into VLOOKUP some more.

Thanks guys for the replies! I will drop outta the merged cells to prevent that. Thanks for the tips!