Solutions
Solutions
• A solution is made up of a solute dissolved
in a solvent.
• Example: seawater is a solution.
• It is made up of salt (the solute) dissolved
in water (the solvent).
• Solutions can be described as concentrated or
dilute.
• A concentrated solution has a large amount of
solute per solvent
• A dilute solution has a small amount of solute
per solvent.
Concentration of solutions
• The concentration of a solution is the
amount of solute dissolved in a certain
amount of solvent.
1. Moles per litre
Concentration can be measured in :
• moles of litre (mol L-1 ).
• This is also known as molarity.
• 1M solution =
• 1 mole in 1 litre =
• 1 mole in 1000cm3
2. Grams per litre
Concentration can be measured in :
Grams per litre of litre (g l-1 ).
• 1g l-1 solution =
• 1g in 1 litre =
• 1g in 1000cm3
Example 1
A solution contains 10g of Sodium Hydroxide in I litre of solution.
What is the concentration expressed in moles per litre.
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
How many moles in 1 litre of solution?
10g / RMM = moles
10g / 40 = 0.25
There are 0.25 moles of NaOH in one litre.
Answer = 0.25 mol L-1
Example 2
A solution contains 28g of Potassium Hydroxide (KOH) in I litre of
solution.
What is the concentration in moles per litre.
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
28g / RMM = moles
28 / 56 = 0.5
There are 0.5 moles of KOH in one litre.
Answer = 0.5 mol L-1
Example 3:
A solution contains 48g of MgSO4 in 3 litres of water.
What is the concentration in moles per litre.
Given Grams per 3 litres
GRAMS PER LITRE
How many grams in 1L ?
48/ 3
= 16
There are 16g of MgSO4 in one litre.
Find MOLES PER LITRE
Given Grams per 3 litres
GRAMS PER LITRE
Find MOLES PER LITRE
How many moles in 1 litre of solution?
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
16 / RMM = moles
16
120
= 0.1333
There are 0.1333 moles of MgSO4 in one litre.
Answer = 0.1333 mol L-1
Q219
• Calculate the molarity of a solution which
contains 65g of HCl in a litre
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
65 / rmm = moles
65 / 36.5 = 1.7808 moles in a litre
Answer : 1.7808M
Q219b
• Calculate the molarity of a solution which
contains 65g of HCl in a litre
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
25 / rmm = moles
25 / 56 = 1.7857 moles in 250cm3
1.7857 x 4 = 7.1428 moles in a litre
Answer : 7.1428 M
Q219c
• Calculate the molarity of a solution which
contains 22g of H2SO4 per 100cm3 of a
solution
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
22 / rmm = moles
22 / 98 = 0.2245 moles in 100cm3
0.2245 x 10 = 2.2448 moles in a litre
Answer : 2.2448 M
Q219d
• Calculate the molarity of a solution which
contains 10g of NaOH per 2L solution
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
10 / rmm = moles
10 / 40 = 0.25 moles in 2L
0.25 /2 = 0.125 moles in a litre
Answer : 0.125 M
Q219e
• Calculate the molarity of a solution which
contains 12.5g of Na2CO3 per 200cm3
solution
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
12.5 / rmm = moles
12.5 / 106 = 0.1179 moles in 200cm3
0.1179 x 5 = 0.5896 moles in a litre
Answer : 0. 5896 M
221
• A chemist dissolves 98.4 g of FeSO4 in
enough water to make up 2L of solution.
• What is the molarity of the solution?
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
98.4 / rmm = moles
98.4 / 152 = 0.6474 moles in 2L
0.6474 / 2 = 0.3237 moles in a litre
Answer : 0. 3237 M
Q220
• 0.080g of ethanol in 100cm3 of blood
• 0.080 x 10 = 0.8g of ethanol in 1L of blood
• 0.8/ RMM= Moles of ethanol
• 0.8/ 46 = 0.0174 moles in 1L
• Answer = 0.0174M
Q223
• Calculate the mass of NaOH in 20cm3 of
0.1M NaOH
X Relative Molecular Mass
Mass of X in
g
Moles of X
÷ Relative Molecular Mass
Moles x rmm = mass
0.1 x 40 = 4.0g in 1L
4.0g /1000 = .004g in 1cm3
0.004 x 20 = 0.08 g in 20cm3
Answer :0.08g
q223
•
•
•
•
B) 1.53g
C)0.0158g
D) 146g
E)0.196g
Q224
•
•
•
•
•
A) 40gl-1
B)112gl-1
C)12.25gL-1
D)1.06gl-1
E)0.49gl-1
Example 4
What is the concentration in grams per litre of a 0.025M solution
of Ca(OH)2?
Given Moles PER LITRE
Find Grams PER LITRE
(0.025)(74)
There are 1.85g of Ca(OH)2 in one litre.
Answer = 1.85gL-1
Example:
What is the mass of CuSO4 in 250cm3 of a 3M solution?
Given Moles PER LITRE
Find Grams PER LITRE
How many grams in 1 litre of solution?
There are 478.5g of CuSO4 in one litre.
Answer =478.5 gL-1
Grams per 250cm3
Given Moles PER LITRE
Find Grams PER LITRE
Grams per 250cm3
How many grams in 250cm3 litre of solution?
(478.5)/ 4 =
Answer = 119.625grams in 1 litre
= 119.625gl-1
3. Mass per volume
• Concentration is also measured in
% mass of solute(g) per volume of solvent(cm3)
• This is written as % (w/v)
• 1% (w/v) means 1g of solute in 100cm3 of solvent
• 20% (w/v) means 20g of solute in 100cm3 of solvent
The solution of KOH has 70g in 500cm3 of water.
Express the concentration in w/v%
Answer:
w/v means how many grams of KOH are in 100cm3 of water
Given mass in 500cm3
70g of KOH in 500cm3 of water
You need to divide by 5!
70/5 = 14
14g of KOH in 100cm3 of solution
Answer = 14w/v%
Want mass in 100cm3
Q225 .A solution of sodium chloride consists of 75 grams in a
250cm3 volume of water.
Express the concentration in w/v%
Answer:
w/v means how many grams of NaCl are in 100cm3 of water
Given mass in 250cm3
75g of NaCl in 250cm3
75 / 250 x 100 = 30
30g of NaCl in 100cm3 of solution
Answer = 30 w/v%
Want mass in 100cm3
4. Volume per volume
• Concentration is also sometimes
measured in % volume of solute (cm3) per
solvent (cm3)
• This is written as % (v/v)
• 5% (v/v) means 1cm3 of solute in 100cm3 of
solvent
USE: This is used for expressing
the alcohol content in wine
• 11% written on a bottle of wine means
11cm3 of alcohol in 100cm3 of wine!
The label on a bottle of whiskey says that the ethanol content is
40% (v/v).
How many cm3 of ethanol are there is 30cm3 of the whiskey?
Answer:
40%v/v means 40cm3 of ethanol in 100cm3 of whiskey
Given volume in 100cm3
• x cm3 of ethanol = 30cm3 of whiskey
40cm3 of ethanol = 100cm3 of whiskey
(30)(40) = (100)(x)
1200 = x
100
12 = x
12cm3 of ethanol in 30cm3 of whiskey
Want volume in 30cm3
Q226.The label on a bottle of beer says that the ethanol content
is 4.8% (v/v). How many cm3 of ethanol are there in one pint
568cm3 of the beer?
Answer:
4.8%v/v means 4.8cm3 of ethanol in 100cm3 of beer
Given volume in 100cm3
(568)(4.8) / (100) = 27.264
27.264 cm3 of ethanol in 30cm3 of beer
Want volume in 568cm3
5. Mass per mass
• Concentration is also sometimes
measured in % mass of solute(g) per
mass of solvent(g)
• This is written as % (w/w)
• 36% (w/w) means 36g of solute in 100g of
solvent
A solution has a w/w% concentration of 35%. What mass of
solute would be present in 450g of solvent?
Answer:
35% w/w means 35g of solute in 100g of solvent
Given mass in 100g
Want mass in 450g
(35)/100 x 450 = ?
(35)/100 x 450 = 157.5
157.5g of solute in 450g of solvent
Answer: 157.5g
Q227. Concentrated hydrochloric acid is a 37.9 (w/w)%
solution of HCl in water. What mass of this solution would
have to be taken so that it contains 5g of HCl?
Answer:
37.9% w/w means 39.7g of solute in 100g of solvent
Given mass in 100g
Want mass of solvent with 5g of
solute
37.9/ 100 = 0.379g in 1cm3 of solvent
5/0.379 = 13.1926
There would need to be 13.1926g of solution
Answer: 13.1936g
Standard solutions
• A standard solution is a solution whose
concentration is accurately known
Primary Standard solution
• A primary standard is a water soluble
substance that is stable and available in
pure form.
• They are used to make standard solutions.
Sodium Chloride
Examples of Primary
Standards
Potassium Dichromate
Anhydrous
Sodium
Carbonate
Common substances that are not primary
standards include:
– Sulfuric acid – absorbs water vapour from the
air.
– Sodium hydroxide – absorbs water vapour
from the air.
– Iodine – sublimes.
Preparation of a standard solution
of sodium carbonate.
We want to make up 250cm3 of a 0.1M
solution of Na2CO3
What mass of sodium carbonate is
needed??
How to make a standard solution
• A special technique is used so that the
concentration of the solution can be
accurately known!
1. Find the mass of the solute accurately using
a mass balance, and a clock glass.
2. The solute is transferred to a
clean beaker (filled with some deionised
water) using a stirring rod
3. A wash bottle (filled with deionised water) is
used to rinse the clock glass and stirring rod into
the beaker.
The solution is stirred to dissolve the solute
completely.
5. The solution from the beaker is poured
into a volumetric flask
6. Any solution remaining in the beaker
is washed into the volumetric flask,
using a wash bottle
• 7. The flask is filled up to close to the
calibration mark with a wash bottle, and
then drop wise until the bottom of the
meniscus is at the calibration mark.
• 8. The flask is stoppered, and inverted 20
times to sure the solution is mixed
properly!
6. Expressing concentration in
parts per million (ppm)
• ppm (parts per million) = milligrams in a
litre
Convert the following to ppm
3
0.62g / 500cm
Given grams per 500cm3
Grams per 1000cm3
Need: mg per 1000cm3
To convert grams to milligrams
0.62g in 500cm3
1.24 x 1000 = 1240
(0.62) / 500 x 1000 = 1.24g
1.24g in 1000cm3
1240 mg in 1000cm3
Answer = 1240ppm
228(a)Convert the following to ppm
0.54g / 1L
Grams per 1000cm3
Need: mg per 1000cm3
To convert grams to milligrams multiply by 1000
0.54g x 1000 = 540
540 mg in 1000cm3
Answer = 540ppm
228(b)Convert the following to ppm
0.18g / 1L
Grams per 1000cm3
Need: mg per 1000cm3
To convert grams to milligrams
0.18g x 1000 = 180
180 mg in 1000cm3
Answer = 180ppm
228c)Convert the following to ppm
0.077g / 100cm3
Given grams per 100cm3
Grams per 1000cm3
Need: mg per 1000cm3
To convert grams to milligrams
(0.077) x 10 = 0.77
0.77g in
1000cm3
(1000)(0.77) = 770
770 mg in 1000cm3
Answer = 770ppm
228d)Convert the following to ppm
0.0009g / 100cm3
Given grams per 100cm3
Grams per 1000cm3
Need: mg per 1000cm3
To convert grams to milligrams
(0.0009) x 10 = 0.009
0. 009g x 1000 = 9
9 mg in 1000cm3
0.009g in 1000cm3
Answer = 9ppm
228e)Convert the following to ppm
0.0017g / 100cm3
Given grams per 100cm3
Grams per 1000cm3
Need: mg per 1000cm3
To convert grams to milligrams
(0.0017) x 10 = 0.017
0.017g in
1000cm3
0. 017g x 1000 = 17
17 mg in 1000cm3
Answer = 17ppm
228f)Convert the following to ppm
0.0003g / 100cm3
Given grams per 100cm3
Grams per 1000cm3
Need: mg per 1000cm3
To convert grams to milligrams
(0.0003) x 10 = 0.003
0.003g in
1000cm3
0. 003g x 1000 = 3
3 mg in 1000cm3
Answer = 3ppm
• If the solution is coloured
then the more concentrated
a solution the more intense
the colour will be!!
Colorimetry is when colour is used to measure
the concentration of solutions
Effect of Dilution on Concentration
• When a solution is diluted, more solvent is
added.
• The quantity of solute remains unchanged.