2. 1 Mole = 6.023 x 1023
One mole of atoms or a molecule of
any substance will have the same
mass in Grams as the Relative Mass
( Mr and Ar) for that substance
HEBA SAEY
4. Examples :
Substance Relative Mass One molar mass
Carbon ( C ) 12 12 g
Nitrogen ( π2) Mr = ( 14 x 2 )
28
28 g
Carbon Dioxide (πΆπ2) Mr = ( 12 x 2 )
44
44g
Water (π»2 π) Mr = (1 x 2) + 16
Mr = 18
18g
HEBA SAEY
5. Moles & Mass Formula
MASS
Moles x Mr
In GRAMS
Number of Moles given
Example 1) What is the mass in grams
of 3.5 moles of magnesium (mg)
Step 1) Mr of Mg = 24
Step 2) Identify which formula to use
Step 3) Mass = Moles x Mr
Step 4 ) Mass = 3.5 x 24
Step 5) Mass= 84 g
Example 2) How many moles are there
in 66g of Carbon dioxide?
Step 1) Mr of πΆπ2 = 12+ ( 16 x 2 ) = 44
Step 2) Identify which formula to use
Step 3) Moles = Mass Γ· Mr
Step 4 ) Moles = 66 Γ· 44 = 1.5
Step 5) Moles = 1.5 g
HEBA SAEY
7. Remember :
HEBA SAEY
Mass Concentration = π/π π π ππ π π πβπ
Volume = π π π ( if given in ππ π divide by 1000)
Mole concentration = πππ/π π π or πππ π πβπ
Mass = g ( grams)
8. How much has dissolved?
HEBA SAEY
You can find this out by evaporating the waterβ¦
If you have say, 500g of solution , you donβt need to use the whole lot,
you can just use for example 10gβ¦
1) Weigh a clean, dry evaporating basin
2) Weigh 10 g of the solution and put it in the basin
3) Gently heat the basin to evaporate the water from the solution
4) Check if the water seems to have evaporated
5) Weigh the dry basin and remaining solid
6) Reheat and reweigh until there's no further change in mass
STEP 6 IS TO ENSURE ALL WATER HAS EVAPORATED
Calculations on next page
9. Example:
HEBA SAEY
Mass of clean Basin = 54.6g
Mass of Basin with Solid = 56.9g
0.3 g difference..
We used 10g of 500g
0.3g is how much that has dissolved in 10 g
500 g = 10 x 50
0.3 x 50 = 15 g
15 g of substance has dissolved in 500g of
Water
11. EXAMPLE WORKING OUT MASS
CONCENTRATION
HEBA SAEY
3.75g of Sodium chloride are dissolved in 250 ππ3 of water. What is
the concentration in π/ππ3 of the final solution ?
1) Know which formula your using
2) Mass concentration = πππ π Γ· π£πππ’ππ
3) Mass = 3.27 and Volume = 250/1000= π. πππ π π π
4) 3.75 Γ· π. ππ = ππ
5) Mass concentration = ππ π/π π π
13. EXAMPLE 1 β converting Mass
concentration to Mole conc.
HEBA SAEY
Find the mole concentration of 196 π/ππ3 solution of π»2 ππ4
1) Know which formula your using
2) Mole concentration = πππ π πππππππ‘πππ‘πππ Γ· ππ
3) Mass conc. = 196 π/ππ3
4) Mr = ( 1 x 2) + 32 + ( 16 x 4) = 98
5) 196 Γ· 98
6) Mole concentration = π πππ/π π π
14. EXAMPLE 2 β converting Mole
concentration to Mass conc.
HEBA SAEY
Find the mass concentration of 2.5 πππ/ππ3 solution of HCL
1) Know which formula your using
2) Mass concentration = ππππ πππππππ‘πππ‘πππ Γ ππ
3) Mole conc. = 2.5 πππ/ππ3
4) Mr = 1 + 35.5 = 36.5
5) 36.5 x 2.5 = 91.25
6) Mass concentration = ππ. ππ π/π π π
16. Hard water makes SCUM ( a nasty ppt ). This is
because it doesnβt lather with soap.
HEBA SAEY
Hard water contains calcium ions ( πͺπ π+)
or / and
magnesium ions (π΄π π+)
In some areas water flows over rocks and through soils containing Magnesium/ Calcium ions.
Magnesium Sulfate, ππππ4 dissolves in water, and so does
Calcium Sulfate ,πΆπππ4
Calcium Carbonate usually exists as chalk, limestone or marble.
It can react with acid rain to create calcium hydrogencarbonate.
This is soluble and dissolves in water , releasing Calcium ions.
Calcium hydrogencarbonate = πΆπ(π»πΆπ3)2
17. Removing Temporary Hardness β
BOILING.
HEBA SAEY
Temporary hardness is caused by Calcium Hydrogencarbonate
πͺπ(π―πͺπΆ π) π
πΆπ(π»πΆπ3)2 aq β πΆππΆπ3 π + π»2 π π + πΆπ2 π
Calcium hydrogencarbonate β ππππππ’π ππππππππ‘π + π€ππ‘ππ + ππππππ ππππ₯πππ
.
Calcium hydrogencarbonate decomposes.
The lime scale in your kettle is Calcium Carbonate β its insoluble
18. Removing Permanent and Temporary
Hardness β ion exchange resin
HEBA SAEY
Permanent hardness is caused by ππππ4 and
πΆπππ4
EXAMPLE: ππ2 π ππ ππ π + πΆπ2+ β πΆππ ππ ππ π + 2ππ+(aq).
Resin is an insoluble solid polymer. Water is supplied trough an ion
exchange resin. The resin contains a lot of Sodium ions ( or hydrogen)
and exchanges them for the Cπ2+ and Mπ2+ ions when the water runs
through them .
20. Basicβs about Titrations
HEBA SAEY
Acid-base titration is a neutralisation reaction
π»+ ππππ ππππ πππ π΄πΆπΌπ· πππππ‘ π€ππ‘β ππ»β ππππ π π πππ’πππ π΅π΄ππΈ
IONIC equation:
π»+
(aq) + ππ»β
β π»2 π
REMEMBER : ACID + ALKALI β ππ΄πΏπ + ππ΄ππΈπ
Titrations help find out exactly how much of acid is
required to neutralise a quantity of alkali ( or vice versa)
21. How to do a titration - Step 1
HEBA SAEY
Using a pipette and pipette filler, add some
alkali ( About 25ππ2
) to a conical flask ,
along with two or three drops of indicator.
( use of indicator depends on strength)
Type of Indicator Strength of Acid Strength of Alkali
Phenolphthalein Weak Strong
Methyl orange Strong Weak
Any Strong Strong
22. How to do a titration - Step 2
HEBA SAEY
-Fill a burette with acid.
-Using the burette add the acid to the
alkali at a time giving it a swirl
23. HEBA SAEY
How to do a titration - Step 3
The indicator changes colour when
all the alkali has been neutralised.
( stop adding in alkali). Repeat this
whole experiment 2/3 times
E.G Phenolphthalein turns colourless in acids and
pink in Alkalis
24. HEBA SAEY
Moles
VolumeConc.
Calculations β Working out number of moles to find Conc.
ππ0π» π»2 π04
Moles in Balanced Eq. 2 1
Moles in Experiment 0.025 x 0.1 = 0.0025 0.0025/2 = 0.00125
Volume 25 /1000 = 0.025 30/1000 = 0.03
Concentration 0.1 0.00125/0.03= 0.0416
πΈπ₯πππππ: 25ππ3 ππ πππππ’π βπ¦ππππ₯πππ βππ π πππππππ‘πππ‘πππ ππ 0.1 πππ/ππ3 it
π‘ππππ 30ππ3 ππ ππ’πππ’πππ ππππ π‘π πππ’π‘πππππ π ππ‘ .
πβππ‘ ππ π‘βπ πππππππ‘πππ‘πππ ππ π‘βπ ππππ?
Start off by writing the balanced equation then adding in the information given to you.
2ππ0π» + π»2 π04 β ππ2Sπ4 + 2π»2 π
ANSWER : 0.0416 πππ/ππ3
25. HEBA SAEY
Moles
VolumeConc.
Calculations β Working out number of moles to find Conc.
πΆπ(ππ»)2 2π»πΆπ
Moles in Balanced Eq. 1 2
Moles in Experiment 0.025 x 0.5 = 0.0125 0.0025/2 = 0.00125
Volume 25/1000 = 0.025 32.5/1000 = 0.0325
Concentration 0.5 0.00125 / 0.0325 = 0.77
πΈπ₯πππππ: 32.5 ππ3
ππ π»π¦ππππβπππππ ππππ ππ ππππ’ππππ π‘π πππ’π‘πππππ π 25ππ3
ππ
0.5πππ/ππ3 ππ πΆπππππ’π βπ¦ππππ₯πππ. πΉπππ π‘βπ πππππππ‘πππ‘πππ ππ π‘βπ ππππ.
Start off by writing the balanced equation then adding in the information given to you.
πΆπ(ππ»)2 + 2π»πΆπ β πΆππΆπ2 + 2π»2 π
ANSWER : 0.77 πππ/ππ3