Homework Help Forum: chemistry

Posted by Jamie Marie on Thursday, October 29, 2009 at 2:59pm.

How would you find the empirical formula for this... a substance was found by analysis to contain 20% by mass calcium and 80% by mass bromine. Would it be CaBr2? This is what I did... 50g Ca * 20 mol Ca/801.56g Ca = .499 mol Ca 80g Br * 80 mol Br/6392.32g Br = 1.001 mol Br 1.001/.499 = 2 so CaBr2

• chemistry - DrBob222, Thursday, October 29, 2009 at 3:09pm

  Yes, the answer is CaBr2 but I don't buy the way you obtained that formula. Did you just pull 50 g Ca and 80 g Br out of thin air? The proper way to work it is the way I showed you in your first post.

  
  

• chemistry - Manas, Thursday, October 29, 2009 at 4:06pm

  First we find the moles of each assuming that mixture is having total mass of 100 grams. So mass of Ca = 20 g and Br =80 Moles of Ca = 20 g/40.08 (g/mole)= 0.499 Mole Moles of Br = 80 g/ 1.001 moles So now we can find the molar ratio = 0.499/1.001 =1/2 That means Ca1Br2 so the empirical formula would be CaBr2. This is absolutely right.

  
  

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