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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: ellis182 on March 16, 2005, 03:44:40 AM

Title: easy peasy lemon squeezy. apparently!
Post by: ellis182 on March 16, 2005, 03:44:40 AM

Guys just a really easy question i need clarification with..

How many moles of O-atoms in 25.7g of CaSO4?

I know moles = mass/molar mass

so..

25.7/(40.8 + 32.07 + 4x16) = .188

Is this the answer or do i multiply .188 by 4 because there is 4 oxygen atoms in CaSO4?

 

Also..

How many molecules in 13.72g oh hydrazine? N2H4? i dont even know where to start!

If anyone could help me at all it would be much appreciated!
 ;D

Title: Re:easy peasy lemon squeezy. apparently!
Post by: Borek on March 16, 2005, 05:10:01 AM

Quote from: ellis182 on March 16, 2005, 03:44:40 AM

25.7/(40.8 + 32.07 + 4x16) = .188

Is this the answer or do i multiply .188 by 4 because there is 4 oxygen atoms in CaSO4?

You have been asked about atoms - so multiply.

Quote

How many molecules in 13.72g oh hydrazine? N2H4? i dont even know where to start!

Hydrazine is like every other substance. Just calculate molar mass of N2H4, rest is obvious.

Title: Re:easy peasy lemon squeezy. apparently!
Post by: mPeppel on March 18, 2005, 12:00:12 PM

13.72g N2H2/ 30.04gN2H2  =  0.4567moles  
0.4567moles x 6.022 x10 23 molecules/ 1moles =2.750 x10  23 molecules