chemistry calculations. learning intentions 1)how can we work out the formula mass of a chemical?...
TRANSCRIPT
Chemistry Calculations
Learning Intentions
1) How can we work out the formula mass of a chemical?
2) What is a mole?
3) How can we use formula mass and moles to work out grams of a chemical?
Part 1: Formula Mass
Each element has a
Relative Atomic Mass Number
e.g. Na = 23, O = 16
Task:Use your data book to find the Atomic Mass for:Ca, Cl, S, H, N, C, Ar
Formula Mass
If we add up all the RAM nummbers present
in a chemical we get the
Formula Mass numberExample:H2O = = 2 X 1 + 1 X 16
2 X Hydrogen + 1 X Oxygen Mass Numbers
= A formula mass of 18
Task:
On your show me boards work out theformula mass of:1) NaOH2) HCl
3) O2
4) HNO3
5) H2SO4
6) (NH4)3PO4
(NH4)3PO4
Solution:
Split into 2 halves
2) PO4
P = 31 X 1O = 16 X 4PO4 = 95
54 + 95 = a formula mass of 149
1) (NH4)3 N = 14 X 1H = 1 X 4NH4 = 18(NH4)3 = 18 X 3 = 54
Learning Intentions
1) How can we work out the formula mass of a chemical?
2) What is a mole?
3) How can we use formula mass and moles to work out grams of a chemical?
Part 2: The Mole
Units of Measurement:
We use units of measurement in life to give us an
easier way to see large numbers.
meter = 100 cm, liter = 1000 ml, kilogram = 1000 g
The mole is a unit of measurement
In chemistry we use it to tell us how many atoms or molecules there are
The Mole
1 mole of a chemical is equal to the Formula Mass in grams
If I could weigh 6.02 X 1023 molecules of water
it would weigh 18g
Q) What is the formula mass of water?
18
Q) What is the relationship between the formula mass and 1 mole of a chemical?
Example
I have 40g of NaOH
The Formula Mass (FM) = 40
Therefore I have 1 mole NaOH
FM = 401 mole = 40g0.5 moles = 20g0.25 moles = 10getc
Learning Intentions
1) How can we work out the formula mass of a chemical?
2) What is a mole?
3) How can we use formula mass and moles to work out grams of a chemical?
Part 3: Mole Calculations
M = n X FM
(n)
n = M/FMFM = M/n
We can use moles and formula mass to work out mass of chemicals needed/used
ExampleIf I have 9g of water, how many moles do I have?
n = M/FMn = 9g/18n = 0.5
What is the mass of 0.25 moles N2?
M = n X FMM = 0.25 X 28M = 7g
(n)
Task:
1) If I have 9g water how many moles do I
have?
2) If I have 5g NaOH how many moles do I have?
3) If I have 0.5 moles O2 how many grams do I have?
Learning Intentions
1) How can we work out the formula mass of a chemical?
2) What is a mole?
3) How can we use formula mass and moles to work out grams of a chemical?