NOVEMBER 17 2009

(Heidi)

NOVEMBER 13 2009

EMPIRACAL FORMULAS

Find the total mass of Carbon in a 3.0kg sample of ethanol.
(C2H5OH)
^ ^ ^ ^
2(12) 5(1) 1(16) 1(1)=46.0g/mol

C2H6O<--Empiracal Formula Empiracal Formulas are simplest formulas Molecular Empiracal
P4H10 ------> P2H5
C1oH22 ------> C5H11
C6H18O3 ------> C2H6O
N2O4 ------> NO2
(*Think lowest common denomenator*)

Empiracal Formulas the simplest whole number ratios in a compound
Molecular formulas show the actual atoms/ and ...(guys finish the sentence.. i can't read my writing)

FINDING EMPIRACAL FORMULAS:
A sample of an unknown compound is analyzed and found to contain 8.4g of 'C', 21g of 'H', and 5.1g of 'O'
Find the empiracal formula


Example: 0.888 grams of a compound made up of C2H7O
C, H, and O are found to contain 0.576g of C and 0.120g of H
a) Find the mass of oxygen
b) Find the empiracal formula

0.120g

+ 0.57g

-----------

.696

*.696

-.888

----------

.192-->oxygen

C=.192 x mol=0.48-->4

H=.120xmol=.12--->10

O= .192xmol=.012-->1

Homework: Worksheet questions # 22, 23, 24

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

November 6, 2oo9

This class we did a review on moles by using the new chart that Mr. Doktor drew for us!



Here is the chart we used:

Here are a few questions that Mr. Doktor reviewed with us:

1. Liquid Mercury has a density of 13.55 g/mL. Find the volume of Mercury occupied by 1.806 x 10^27 atoms of Hg.
   molecules -> moles -> mass
   
   1.806 x 10^27 moles x 1mol/6.02 x 10^23 moles x 200.6 g/1mol = 601800 g
   
   V = m/d = 601800/13.55 g/mL = 44413 mL = 44.41 L
2. A 5.00 mL sample of lead is known to contain 0.274 mol of Pb. Calculate the density of lead.
   
   0.274 mol x 207.2 g/1mol = 56.773 g
   
   D = m/v = 56.773 g/ 5.00mL = 11.4 g/mL
3. 250 mL of a gas which is known to contain only fluoride and sulfur has a mass of 1.63 g at STP.
   a. Find the molar mass:
   250mL/1 x 1L/1000mL x 1mol/22.4L = 0.0116 mol
   
   1.63g/0.0116 = 146 g/mol
   
   b. Find the chemical formula
   S(x)F(y) = 146 g/mol
   
   x=1 & y=6

November 4, 2oo9

November 2, 2oo9

This class we worked on the

Molar Volume Lab

.

The problem of the lab was to experimentally determine the molar volume of a gas

For homework we had to do the prelab questions. What we found was that the chemical formula for butane is C4H10 and also that the molar mass of butane is 58.124 g/mol.

Also for homework we had to write out a procedure for the lab before doing it, and this is what we wrote:

1. Weigh the lighter on the weigh scale and record it
2. Fill your sink with water, about three inches from the top
3. Place the 100 mL graduated cylinder under water until there are no more bubbles
4. Put the lighter under water at the opening of the graduated cylinder and carefully release butane from the lighter (about 10 mL)
5. Record the volume to the nearest mL
6. Dry the water from the light and then measure the mass of the lighter again on the weigh scale

What we observed during the lab was that after adding the butane gas, the amount of water in the beaker decreased.

Homework: Do analysis and conclusion questions from the lab! =)

November. 4,2009

In the beginning of class, Mr. doktor handed back our mole ration lab. After, we marked the unit 2 homework sheet numbers 11-15.
Mr. Doktor taught a new topic about DENSITY & MOLES:
To find either the density, volume or even mass we can use this triangle.
To use this triangle, you cover the one that you are trying to find.

Let us say that you need to find the mass. You cover the mass and your left with density times volume. Just remember to cover the one that you are trying to find and the triangle will tell you how.

DENSITY OF GASES @STP
To find the density of gases @ STP you can use this formula:

DensitySTP = mass of 1 mole/volume of 1 mole = molar mass/ 22.4 L = gram per mole/liter per mole = gram/litre

DENSITY OF GASES @ STP