Chemistry question!?

Question

Hi, got stuck on this for my revision:

A chemical company recieves an order to supply 100 tonnes of strontium. They need to calculate how much ore to process.
The ore typically contains 2% by mass of SrCO3.
Calculate the mass of ore that the company would need in order to produce 100 tonnes of Strontium.

1 tonnes = 10^6 g

Thanks!

Harry

Answer 1

Okay, you need to deliver 100 tonnes of Sr metal -- that's 10^8 grams (but you don't need to worry about that, because those units will cancel out in the end!))

MW of SrCO3 is 147.63 g/mole, of which 87.62g/mole is Sr. Thus, only 59.35% of your strontium carbonate is strontium.

2% is the same as a fraction of 2/100, or 0.02. 59.35%, likewise, is 0.5935.

So, you'd need to process 10^8 grams/(0.02 * 0.5935) = number of grams of ore you'd need to process.

A faster answer is to use the number of tonnes.

100 tonnes /(0.02 * 0.5935) = your answer

Now you can do the arithmetic.

Answer 2

Well here's how to do it.
You take your 100 tonnes, and convert that into grams. So, take 10^6 and multiply by 100. You should get 100,000,000 grams. (Large number to deal with, but don't worry). Now you want to multiply this number by the ratio of grams of SrCO3 to grams of Strontium.

If you use molecular weights, you find that SrCO3 is about 147.62 grams, and in that, 87.62 grams are of Strontium. Now, you can essentially use that as your ratio. So multiply 100,000,000 grams by (147.62/87.62), so you'll be left in units of "grams of SrCO3". Now you want to multiply this number by the ratio of grams ore to grams SrCO3. (You should have a number about 168,475,516.55 grams SrCO3)

Since you know that SrCO3 is 2% of the ore, you can use the ratio of 1/.02. So multiply 168,475,516.55 by (1 gram ore/ .02 grams SrCO3). Your answer should be about 8,423,875,827.4 grams or 8,423.88 tonnes.