bring your calculators to class. remember the mole? (not just a furry animal that digs holes in the...
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Bring your calculators to class
Remember the mole? (not just a furry animal that digs
holes in the yard.)
•unit used by chemist to measure things.•1 mole is 6.02 x 1023 particles (like a very
large dozen used for very small things)
•Defined as the number of carbon atoms in exactly 12 grams of carbon-12.
•Makes life very convenient
What sort of things are measured in moles?
Representative particles(The smallest pieces of a substance.)
For a molecular compound it is a molecule.
H2O
For an ionic compound it is a formula unit.
NaCl
For an element it is an atom.Au
+
- +
+
+---
Molar Mass generic term for the mass of one mole. Same as: Don’t WriteDon’t Write
1.gram atomic mass =The mass of 1 mole element in grams
2.gram formula mass =the mass of 1 mole of one formula unit is the sum of the atomic masses of all atoms of element
3.gram molecular mass =the mass of 1 mole of one molecule is the sum of all the atomic masses of all the atoms of elements in the molecule
1. Elements
The mass of 1 mole element in grams
1 mole of any element = atomic mass on periodic table
example: 1 mole of Na=23 g (22.989768 rounded to whole #)
1 mole of Cl = 35g
(35.4527 rounded to 35)
2. Ionic compounds
the mass of 1 mole of one formula unit is the sum of the atomic masses of all atoms of element
example: 1 mole of NaCl= 23 mass of Na
+ 35 mass of Cl
58 g
3. Molecular compounds
the mass of 1 mole of molecules is the sum of all the atomic masses of all the atoms of elements in a molecule
example: 1 mole of H2O2=
2 x 1g = 2g mass of H
2x16 + 32g mass of O
34g
Examples
Calculate the molar mass of the following and tell what type it is.
Na2S
N2O4
C
Ca(NO3)2
C6H12O6
Formula Mass = Molar Mass
Sum of the atomic masses of all the atoms in a chemical formula
H2O 2 H atoms each 1g= 2x1= 2
1 O atom 16 g +16
18 g 1mole of H2O = 18 g1 mole = 6.022 x 1023 particles
Using Molar Mass
Molar Mass =The number of grams of 1 mole of atoms, formula units, or molecules.
We can make conversion factors from these.
To change grams of a compound to moles or moles to grams of a compound use 1 mole= molar mass to make factor
Molar mass for NaOH
1mole Na = 23g
+1 mole O = 16g
+1 mole H = 1g
1 mole NaOH = 40g
5.69g NaOH 1mole NaOH
40 g NaOH
= 0.14 mole
For example: mass to moles
How many moles is 5.69 g of NaOH?
need to change grams to moles
Another Type: moles to massHow many grams are 2 moles H2O? Need to change from moles to grams
Molar mass of H2O
2 x 1g = 2 g of H
+16g of O
18g
2 moles H2O 18 g H2O
1 mole H2O
=36 g H2O
1 mole of H2O= 18g
Other Types of questions
How many molecules of CO2 are the in 4.56 moles of CO2 ?
1 mole = 6.02 x 1023 particles
4.5 moles 6.02 x 1023 molecules = 1 mole
2.79 x 1024 molecules
How many moles is 7.78 x 1024 formula units
of MgCl2?
7.78 x 1024 formula units 1 mole
6.02 x 1023 formula units
1.29 x 10 or 12.9 moles
Examples
How much would 2.34 moles of carbon weigh?
How many moles of magnesium in 24.31 g of Mg?
How many atoms of lithium in 1.00 g of Li?
How much would 3.45 x 1022 atoms of U weigh?
Hydrates- when some salts crystallize from a water solution and they bind water molecules in their crystal structure
Cu SO4•5H2O there are 5 water molecules for every copper(II) sulfate formula unit
copper(II) sulfate pentahydrate
Heating the crystal in a crucible drives off the water then the salt is called anhydrous
CuSO4•5H2O CuSO4 + 5H2O
CuCl2•2H2O CuCl2 + 2H2O
Example: Calculate the percent composition of Na in NaCl?
% Composition Like all percents part x 100 % = %
whole
1. Find the mass of each component
2. divide by the total mass x 100 %
mass Na x 100 % = 23 g x 100 % =39%mass NaCl 23 + 35
Empirical Formulas
-simplest whole number ratio of atoms
% to mass
mass to mole
divide by small
multiply ‘til whole
1. % to mass
assume 100 g so % = mass
53.73 g Fe & 46.27 g S
Example
What is the empirical formula of the compound that contains 53.73 % Fe and 46.27 % S?
2. Mass to mole
1 mole Fe = 55.85 g
53.73 g Fe 1mole = .96 mole Fe
55.85 g Fe
1 mole S = 32.06 g
46.2 g S 1 mole S = 1.44 mole S
32.06 g S
3. Divide by small
Fe .96/.96 = 1
S 1.44/.96 = 1.5
4. Multiply ‘til whole
Fe 1 x 2 = 2
S 1.5 x 2 = 3
Write empirical formula Fe2S3
Molecular formula = How the molecule actually existsIf the molar mass of the compound is known, then the molecular formula can be determined from the empirical formula. 1. Add the masses of all the atoms of each elements in the empirical formula.2.Divide the molar mass by the mass determined in step 1.3.Multiply each subscript in the empirical formula by the number calculated in step 2.
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