November 11/09

Today in chemistry 11 we learned how to calculate the mass of an elements in compounds.


Find the percentage of each of the following elements C2H2O

First you would have to get all the molar masses of the compound and add them together

2C - 24
2H - 2
1O - 16
total : 42

Then you choose 1 element lets say we go with carbon first so we would get the molar mass of carbon and divide it by the total mass of all the elements 24 / 42 and multiply it by 100 which gives you 57%. You would do the same for hydrogen 2 / 42 x 100 4% and do the same for oxygen 16 / 42 x 100 which gives you 38%.

Percent
C2 would be 57%
H2 would be 4%
O would be 38%


We also learned how to find a certain amount of an element in a certain amount of grams.

For example find the mass of magnessium contained in 50g sample of MgNa
First find the molar masses of all the elements

Magnessium = 24
Sodium = 22
Then add them both together which gives us 46

Second since were looking for the mass of magnessium we get the molar mass of magnessium 24 and divide it by the total mass of the two elements 24 / 46 which gives us .52

After we would get .52 and multiply it by the given grams in the samepl of MgNa which is 50 x .52 which gives us 26. This would tell us how many grams of magnessium are contained in a 50g sample of MgNa which is 26g.



Heres a video pretty much summing up todays lesson and giving us a head start on the next lesson empirical formulas and percentages.