[MarySunshine]

Hydrogen fluoride is produced industrially by the action of sulphuric acid on CaF2. Suppose 400 kg of CaF2 is treated with an excess of sulphuric acid and 140 kg of HF is produced.

What is the percent yield of HF?
   
What of CaF2 remains?

I have attempted this question by finding how many kg HF would be produced if we used 400kg of CaF2 then divided it by 140kg then multiplied it by 100%.  I got the wrong answer and have two more attempts of answering the question before I get it marked wrong. How would I go about answering this question?

[Dan]

I have attempted this question by finding how many kg HF would be produced if we used 400kg of CaF2 then divided it by 140kg then multiplied it by 100%.

Your method is incorrect - it will give an answer >100% yield (which is impossible). Also, show your calculation for the theoretical maximum amount of HF that could be produced.

Strip the problem down to the basics.

Answer this question, then apply the same method:

An orange contains 250 mL of orange juice. The orange is squeezed, and 200 mL of juice is collected. Express the amount of orange juice obtained as a percent yield.

[MarySunshine]

400 000g CaF2 * (1 molCaF2/78.08gCaF2) * (2molHF/1molCaF2) * (20.01gHF/1molHF) = 205 020.49gHF

This is how I found the theoretical amount of HF.

Is this how I would find the percent yield?

(140 000g/205 020.49g) * 100 = 68.286%

[Dan]

Yes, good job.