By pure protein do you mean isolate?
Also there are tiny amounts of carbs/fats in it yeah. Even in isolate, but it's usually very little. And 100g of the powder won't get you 100g protein. Thinking off the top of my head you're probably going to need about 120g-130g of the powder to hit 100g protein. This is going from what whey I've seen, rice could be different (most likely you're going to need more).
But as said above check the package. If it's not on the package it will be on their website if you bought online (I buy online, my package has no values!)
Also as posted above, GNC is a good place to check. I haven't actually been inside their shops since I get all my stuff online, but they're likely to have some scoops you can use to weigh your stuff. If you need recommendations on what brands to buy just send me a PM or ask here, I'll be watching!