Warm Up
Write the electron configuration for Br1. Using the noble gas configuration
2. The non condensed configuration
3. Show the energy levels with arrows
(hund’s rule)
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this
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Part 3: Mole Calculations
We can use moles and formula mass to work
out mass of chemicals needed/used
M = n X FM
n
= M/FM
FM = M/n
(n)
Example
If I have 9g of water, how many
moles do I have?
n = M/FM
n = 9g/18
n = 0.5
(n)
What is the mass of
0.25 moles N2?
M = n X FM
M = 0.25 X 28
M = 7g
Working out the formula
• 1.4 g of Nitrogen reacts with 0.3 g of hydrogen
to form a compound. What is the formula of
the compound?
Working out the formula
• 1.4 g of Nitrogen reacts with 0.3 g of hydrogen
to form a compound. What is the formula of
the compound?
• First work out the number of moles
• 1.4g Nitrogen = mass/AM = 1.4/14 = 0.1
• 0.3g hydrogen = mass/AM = 0.3/1 = 0.3
Working out the formula
• 1.4 g of Nitrogen reacts with 0.3 g of hydrogen
to form a compound. What is the formula of
the compound?
• Work out the ratio of the number of moles of
each element to the lowest whole numbers
N
:
H
0.1 :
0.3
1
:
3
Working out the formula
• 1.4 g of Nitrogen reacts with 0.3 g of hydrogen
to form a compound. What is the formula of
the compound?
• Therefore there are 3 times as many hydrogen
atoms as N atoms in the compound. The
formula must be NH3 (ammonia)
Do You Understand Molecular Mass?
How many moles of H are in 72.5 g of C3H8O ?
Mass and Moles of a Substance
• Mole calculations
– Suppose we have 3.25 moles of glucose,
C6H12O6. What is its mass?
Using equations
2NaOH + Cl2  NaOCl + NaCl + H20
If we have a solution containing 100g of
NaOH, how much chlorine gas should we
pass through the solution to make
bleach (NaOCl)?
2NaOH + Cl2  NaOCl + NaCl +
H20
Hydrates
% H2O in a Hydrate
Certain substances have water molecules associated with their structure. Many salts
fall into this category and we refer to them as hydrated salts. Different salts have
different numbers of water molecules - BaCl2•2H2O; CuSO4•5H2O.
PROBLEM: Calculate the % by mass of
water in one mole of BaCl2•2H2O
%H2O = (mass of H2O in one Mol/mass of BaCl2•2H2O) x 100
%H2O = (36 grams/243 grams) x 100 = 14.8% H2O
Review
Naming monatomic cations –
alkali and alkaline-earth metals.
•
• A. Naming ions for alkali and
alkaline-earth metals is easy. Just
use the element’s name plus the word
ion (or cation if you prefer).
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•
•
Atom
Ion formed
Ion name
•
Li
________
____________________________
•
Na
________
____________________________
•
Mg
________
____________________________
•
Ca
________
____________________________
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Molecular Formula
Molecular Formula = Actual Formula
Example:
C2H6
molecular
MF = (EF)x
CH3
empirical
where X = Molecular mass
Empirical mass
Example:
The empirical formula of a compound was found to be P2O5. Experimentation shows that the molar
mass of this compound is 283.89 g/mol. What is the compound’s molecular formula?