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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: JChoiEx on November 19, 2009, 07:25:43 PM

Title: Molecular Mass Corrections..
Post by: JChoiEx on November 19, 2009, 07:25:43 PM
i've recently had some trouble with chemistry and as well as somethings that doesn't make sense to me. I've got a bad grade on this particular homework, and after using some calculators online, they all gave me the answer I got on my already graded assignment.

Example:
Calculate the mass for each of the particles shown below (Molecular and Formula Masses)

1.) K2C4H4O6
K 39 * 2 = 78
C 12 * 4 = 48
H 1 * 4 = 4
O 16 * 6 = 96
Total: 226 amu (This is the answer I had, and my teacher told me to round the tenth. I got it wrong, even though after checking through online calculators, it told me the same answer above.)
2.)
Dy(OH)3
Dy 162 * 1 = 162
O 16*3 = 48
H 1*3 = 3
Total: 213 amu

3.) NiSO4
Ni 58*1 = 58
S 32*1 = 32
O 16*4 = 64
Total: 154 amu (Again this is how I attempted the problems, exactly how my teacher said I should. Are they correct though?)

Main problem is, is that I don't understand why I got them wrong. Thanks!
Title: Re: Molecular Mass Corrections..
Post by: Borek on November 20, 2009, 02:41:43 AM
Quote from: JChoiEx on November 19, 2009, 07:25:43 PM
1.) K2C4H4O6
K 39 * 2 = 78
C 12 * 4 = 48
H 1 * 4 = 4
O 16 * 6 = 96
Total: 226 amu (This is the answer I had, and my teacher told me to round the tenth. I got it wrong, even though after checking through online calculators, it told me the same answer above.)

226.2676

Quote
2.)
Dy(OH)3
Dy 162 * 1 = 162
O 16*3 = 48
H 1*3 = 3
Total: 213 amu

213.522

Quote
3.) NiSO4
Ni 58*1 = 58
S 32*1 = 32
O 16*4 = 64
Total: 154 amu (Again this is how I attempted the problems, exactly how my teacher said I should. Are they correct though?)

154.756

No idea what your teacher means - perhaps s/he wanted higher accuracy. Your approach is correct. Just note that #2 and #3 should be rounded to 214 & 155, not 213 & 154 (that's the accuracy thing I have mentioned, although in most cases treating molar masses as integers gives results close enough to reality).
Title: Re: Molecular Mass Corrections..
Post by: JGK on November 20, 2009, 11:11:19 AM
If the teacher asked you to "round to the tenth", I suspect he/she wanted the answer rounded to 1 decimal place

K2C4H4O6 = 226.3

Dy(OH)3 = 213.5

NiSO4= 154.8
Title: Re: Molecular Mass Corrections..
Post by: sohailafzal on October 17, 2019, 03:30:10 PM
instead of calculating you can use calcurator.org (http://calcurator.org) to calculator molecular mass