Monday, December 13, 2010

Lesson 17: Multistep Conversions

MULTISTEP CONVERSIONS

EXAMPLES:
1.       10.5g of N2 gas are placed in a balloon at STP. Determine the volume of the balloon.

                    10.5g x 1 mol x 22.4 L = 8.40 L
                                  28.0g    1 mol

2.       How many Formula Units are there in 5.2 g of Manganese (II) Sulphide?
MnS
                   5.2g x 1 mol x 6.02x10^23 F.U. =3.5981 F.U.
                               87.0g             1 mol           = 3.6 F.U.

3.       A container of oxygen holds 40.1 L of methane gas at STP. How many molecules of methane is this?
                    40.1 L x 1 mol x 6.02x10^23 molecules = 1.0776 molecules
                                  22.4 L                   1 mol                = 1.08 molecules

4.       2.6x10^22 chlorine atoms are present in a sample of chlorine gas. How many litres of gas at STP is this?
Cl2
                    2.6x10^22 atoms x 1 molecule x               1 mol                x 22.4 L = 0.4837 L
                                                      2 atoms       6.02x10^23 molecules     1 mol = 0.48 L

5.       A sample of CaCl2 occupies 8.50 L. How many Chlorine atoms are present in this sample?

                    8.50 L x 1 mol x 6.02x10^23 molecules x         2 atoms            = 4.56875 x 10^23 atoms of Chlorine                   22.4 L                 1 mol                    1 CaCl2 molecules    = 4.57 x 10^23 atoms of Chlorine

~Kelly~

posted by chemistry11 @ 10:34 PM 0 Comments

Lesson 16: STP

STP: Standard Temperature & Pressure 

  • At a specific pressure and temperature, one mole of any gas occupies the same volume. 
  • At 0 degrees Celsius and 101.3 kPa   ->  1 mol = 22.41 
  • This temperature and pressure is called STP
  • 22.4 L/mol is the molar volume at STP
How many litres will 2.3 mol of O2 occupy at STP? 
(2.3 mol) (22.4 L/1 mol) = 51.52 = 52 L 

Loureal's Awesome Gas Company is found to occupy 12.1 L at STP.
How many moles of gas are there? 
(12.1 L) (1 mol/22.4 L) =  0.54 mol 


22.4 L/mol   such a magical number <3 

~ knipp 

posted by chemistry11 @ 10:33 PM 0 Comments

Lesson 15: Molar Mass

  • The mass (in grams) of 1 mole of a substance is called the molar mass 
  • Determined from the atomic mass on the periodic table 
  • Measured in g/mol 
Molar Mass of Compounds 
  • To determine the molar mass of a compound, add the mass of all the atoms together 
Element                   Molar Mass
FeO                         55.8 + 16.0 = 46.0 g/mol 
H2O                        2(1.0) + 16.0 + 18.0 g/mol 
NaNO3                   23.0 + 14.0 + 3(16.0) = 85.0 g/mol 

Converting between MOLES & MASS
  • To convert, we use molar mass as the conversion factor 
  • Be sure to cancel the appropriate units                 
How many grams is there in 2.2 mol of N2?
(2.2mol) (28g/1mol) = 62 g  

How many moles are there in 131 g of NaO? 
(131g) (1mol/39g) = 3.36 mol 

How many moles are present in a 1.2 g sample of Ammonium Phosphate? 
(NH4)3PO4  ->  3(14.0) + 12(1.0) + 31.0 + 4 (16.0) = 149 

(1.2g) (1mol/149g) = 0.008 = 8.0 x 10^-3 mol


~ knipp 

posted by chemistry11 @ 10:32 PM 0 Comments