I currently have 4GB of corsair memory in my computer. I plan to buy another stick of 4GB soon of the same model to have 8GB but I am unsure whether it'll work. I have a b75 motherboard Mobo with an i3 3220
Well it is best to buy ram in sets But if you can find the same exact ram there should be no issues. Yes it is possible to mix match ram but this adds in the possibility that they wont work together properly.
Like I said trying to find the same exact ram is the safest solution besides buying a 2X4GB kit.