NOVEMBER 10

In the beginning of class Mr. Doktor gave us the answers to the 10-2 worksheet # 1-30
But ofcourse right after that we got some notes on the board !

PERCENTAGE MASS OF ELEMENTS IN COMPOUNDS
Molar Mass: g/mol
Molar Volume: 1/mol

example: 0.0263 mol of gas occupies a volume of 482.0 mL
calculate the molar volume. Is this at STP?
Molar Volume=0.482L/0.0263 mol = 18.33 L/mol
--> Find the % carbon by mass in ethane (C2H6)
C2H6
2(12)+6(1)=30g/mol
%C 24g/mol /(over) 30g/mol x100= 80%
%H 6g/mol / (over) 30g/mol

--> Find the % mass of each element in K2Cr2O7
2K= 78.2g/mol
2Cr= 104g/mol
70= 112g/mol/(over) 294.2g/mol
%K= 78.2g/mol /(over) 294.2g/mol =26.6% %Cr=104g/mol /(over)294.2g/mol =35.4%
%O= 112g/mol /(over)294.2g/mol =38.1%

FINDING MASS OF AN ELEMENT IN A GIVEN SAMPLE

example: Find the mass of carbon contained in a 25.0g sample of CO2

1C= 12g/mol %carbon= 12g/mol /(over) 44g/mol =27.3%
2O=32g/mol /(over) 44g/mol (o.273)(25.0g)=6.82g

32/44= (0.727)(25g)=18.12g
25g-6.82g=18.12g

Find the mass of Potassium, carbon and oxygen contained in 450.0 of K2CO3--138.2g/mol
K=254.7g K=56.6%
C=39.2g C=8.7%
O=156.2g O=34.7%

After taking notes Mr. Doktor gave us time to do our homework while checking around if we had completed the worksheet 10-2

Homework: worksheet # 20 & 21