Post on 16-Dec-2015
transcript
Entry task: Feb 13th-14th Block #2
NOT AN ENTRY TASK!Agenda:Sign off on Post Lab question- DiscussNotes on Molecular Formulas and HydratesHW: Molecular formula and hydrates #1
Fast Flash of Molecular formulaEmpirical formula is CHBut it was experimentally determined to have a
molecular mass of 26 grams
How many CH masses are there in 26 g?
What is the Empirical mass of CH?
C= 12.01 + H = 1.0079= 13g is the empirical mass
The Set up:
Experimental molar mass (given in problem)Empirical mass
26g13g
Divide the two!
2 is the amount that the empirical formula is off by
The Fix:
2(CH)
Multiply 2 through the empirical formula
The molecular formula is
(C2H2)
Empirical to Molecular Formula
49.98 g carbon 1 mole of C
12.01 of C---------= 4.16 Moles of Carbon
-------------
10.47 g hydrogen 1 mole of H
1.007g of H---------= 10.39 Moles of Hydrogen
-------------
A compound was found to contain 49.98g carbon and 10.47g hydrogen. The molar mass is found to be 58.12 g/mol. Determine the molecular formula.
Start with empirical formula
Empirical to Molecular FormulaDivide by the smallest ratio.
4.16 Moles of Carbon= 1 Moles of Carbon
4.16 Moles of Carbon
10.39 Moles of Hydrogen= 2.5 Moles of hydrogen
4.16 Moles of Carbon
C2H5
CAN’T HAVE ½ a mole
X 2
Empirical to Molecular Formula
2 Moles of Carbon
C2H5 empirical formula- get its mass
1 mole of C
12.01 of C
---------= 24.02 g of Carbon
-------------
5 Moles of hydrogen
1 mole of H
1.007 of H
---------= 5.04 g of Hydrogen
-------------------
Empirical mass is 29.055g
Empirical mass to the fix
58.12 g/mole29.055 g/mole
A compound was found to contain 49.98g carbon and 10.47g hydrogen. The molar mass is found to be 58.12 g/mol. Determine the molecular formula.
2.00 Multiply the empirical formula by 2.
Experimental molar mass (given in problem)Mass of empirical mass
2.00(C2H5)
C4H10 is the molecular formula
You Try!
46.68 g nitrogen 1 mole of N
14.006 of N---------= 3.33 Moles of Nitrogen
-------------
53.32 g oxygen 1 mole of O
15.999 g of O---------= 3.33 Moles of Oxygen
-------------
A colorless liquid composed of 46.68% nitrogen and 53.32% oxygen has a molar mass of 60.01 g/mol. What is the molecular formula?
Empirical FormulaDivide by the smallest ratio.
3.33 Moles of nitrogen= 1 Moles of nitrogen
3.33Moles of nitrogen
3.33 Moles of oxygen= 1 Moles of oxygen
3.33 Moles of oxygen
NO
Empirical mass
1 Moles of nitrogen
NO empirical formula
1 mole of N
14.00 of N
---------= 14.00 g of Nitrogen
-------------
1 Moles of oxygen
1 mole of O
15.999 of O
---------= 15.999 g of Oxygen
-------------------
Empirical mass is 30.00 g
Empirical mass to the fix
60.01 g/mole30.00 g/mole
2.00 Multiply the empirical formula by 2.
Experimental molar mass (given in problem)Empirical mass
2.00(NO)
N2O2 is the molecular formula
A colorless liquid composed of 46.68% nitrogen and 53.32% oxygen has a molar mass of 60.01 g/mol. What is the molecular formula?
What are hydrates?
• Have you heard of something being hydrated?• Something to do with water?• Yes! You are right.
Hydrates• Hydrates are compounds that has a specific number of
water molecules bound to its atoms.
• This is methane surrounded by water molecules.
• Opals are hydrates, the trapped water molecules give its unusual color
Hydrates
It’s a RATIO of the compound and its water companion.
Naming HydratesNa2CO3 10H2OSodium carbonate decahydrate
FePO4 4H2OIron III phosphate tetrahydrate
Analyzing a HydratesYou can drive off the water by heating it.When this is done the substance is called anhydrous.
Hydrated Cobalt II chloride
AnhydrousCobalt II chloride
How much water?Suppose you have 5.0 grams of hydrated Barium chloride.
BaCl2 XH2OBefore heating = 5.0g After heating = 4.26g
0.74 g of H2O
But how many moles is this?
0.74 g of H2O------ 1 mole of H2O
18.0 g of H2O---------= 0.041 moles of H2O
How much water was driven off?
What is the relationship to its compound?BaCl2 XH2O
Use the mass of the anhydrous BaCl2 = 4.26 g
4.26 g of BaCl2------ 1 mole of BaCl2
208.23 of BaCl2---------= 0.0205 moles of BaCl2
How many moles are in this mass?
What is the relationship to its compound?
0.0205 moles of BaCl2
= 2 mole of H2O
= 0.0205 moles of BaCl2 = 0.041 moles of H2O
Get the ratios divide smallest mole into others
0.041 moles of H2O
BaCl2 2H2O
You try!Suppose you have 2.50 grams of hydrated Copper II sulfate.
CuSO4 XH2OBefore heating = 2.50g After heating = 1.59g
0.91 g of H2O
But how many moles is this?
0.91g of H2O------ 1 mole of H2O
18.0 g of H2O---------= 0.050 moles of H2O
How much water was driven off?
What is the relationship to its compound?CuSO4 XH2O
Use the mass of the anhydrous CuSO4 = 1.59 g
1.59 g of CuSO4------ 1 mole of CuSO4
159.6 of CuSO4---------= 0.00996 moles of CuSO4
How many moles are in this mass?
What is the relationship to its compound?
0.00996 moles of CuSO4
= 5 mole of H2O
= 0.00996 moles of CuSO4 = 0.050 moles of H2O
Get the ratios divide smallest mole into others
0.050 moles of H2O
CuSO4 5H2O
Copper II sulfate pentahydrate