Cocoa powder

I have a can of cocoa powder, which i use for protein shakes, to add some taste to them (i use about 1 tsp. of it for 1 shake). I got it a few months ago. But today i was looking at the ingredients list on the back, and it said "Ingredients: cocoa, sodium carbonate". What is sodium carbonate? Is it safe? Should i look for another brand that contains only cocoa, or can i keep using this. Is cocoa powder safe to use a few times a week?