Chemistry Centre
The Mole
The Mole
Let start off with Math Review
Rounding (off to the 100's)
-If the number being rounded, is beside a number greater than (5) round up
1.049 ---- 1.05
- If the number being rounded, is besides a number less than (5) the number stay the same
1.042 ---- 1.04
What is the number is (5)
- If the number being rounded is beside the number (5) look to the next number.
1.0459 ----- 1.05
1.0451 ----- 1.05
1.0450 ----- 1.04
-If the number being rounded is:
-(5) with other non 0 digits, round up
- (5) followed by zeros keep the number the same
- (Odd): Round up
3.275 ----- 3.28
Significant Figures
- When adding/subtracting, and dividing/multiplying, your answer should be rounded to the same/lowest number of SIG FIGS
1.267(4 sig figs) *4.353178(7 sig figs) = 5.515
Key formulas to be aware of
n = Number of moles (mol) (amount)
m = Mass of substance (g)
M = Molar mass of substance (g/mol)
How do we isolate for m and n?
n=m/M
- To isolate for (m) we must multiply M by each side.
n(M)=m/M(M)
The (M(M)) will cross each other out leaving the isolated version for (m)
m= n(M)
Significant figures
What is a significant figure?
- It is any digit in a number that increases its accuracy.
Example:
0.256 -- is more accurate than -- 0.26
(3 sig figs) (2 sig figs)
Rules to consider
- Non-zero numbers are significant
(2.38 --- 3 sig figs)
- Any zer place holder does not affect accuracy
(2500 --- 2 sig figs)
- Zeros between 2 non-zeros count!
(2.034 --- 4 sig figs)
- Zeros infront of the decimal are NOT a sig fig
(00.256 --- 3 sig figs)
Avogadros Number
Named after an italian physicts Avogadro who was able to empirically determine this number for practice use. NA - 6.02 x 10^23 is defined as the number of atoms in exactly 12-g of carbon.
The mole
What is a mole?
-Symbol = n
-A unit of amount
-1 mole contains 6.02x 10^23 entities
-Entities include subatomic particles, molecules, ions, and atoms
1 doz = 12 of something (12 doghnuts, 12 oranges ect)