1. Solutions

2. 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).

3. 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.

4. Concentration of solutions
The concentration of a solution is the amount of solute dissolved in a certain amount of solvent.

5. 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

6. 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

7. How many moles in 1 litre of solution? 10g / RMM = moles
Example 1 A solution contains 10g of Sodium Hydroxide in I litre of solution. What is the concentration expressed in moles per litre.
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ 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

8. There are 0.5 moles of KOH in one litre. Answer = 0.5 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.
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ 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

9. There are 16g of MgSO4 in one litre.
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 Find MOLES PER LITRE
How many grams in 1L ?
48/ = 16
There are 16g of MgSO4 in one litre.

10. How many moles in 1 litre of solution?
Given Grams per 3 litres GRAMS PER LITRE Find MOLES PER LITRE
How many moles in 1 litre of solution?
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ Relative Molecular Mass
16 / RMM = moles =
120
There are moles of MgSO4 in one litre.
Answer = mol L-1

11. Q219
Calculate the molarity of a solution which contains 65g of HCl in a litre
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ Relative Molecular Mass
65 / rmm = moles
65 / 36.5 = moles in a litre
Answer : M

12. Q219b
Calculate the molarity of a solution which contains 65g of HCl in a litre
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ Relative Molecular Mass
25 / rmm = moles
25 / 56 = moles in 250cm3
x 4 = moles in a litre
Answer : M

13. Q219c
Calculate the molarity of a solution which contains 22g of H2SO4 per 100cm3 of a solution
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ Relative Molecular Mass
22 / rmm = moles
22 / 98 = moles in 100cm3
x 10 = moles in a litre
Answer : M

14. Q219d
Calculate the molarity of a solution which contains 10g of NaOH per 2L solution
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ Relative Molecular Mass
10 / rmm = moles
10 / 40 = 0.25 moles in 2L
0.25 /2 = moles in a litre
Answer : M

15. Q219e
Calculate the molarity of a solution which contains 12.5g of Na2CO3 per 200cm3 solution
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ Relative Molecular Mass
12.5 / rmm = moles
12.5 / 106 = moles in 200cm3
x 5 = moles in a litre
Answer : M

16. 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?
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ Relative Molecular Mass
98.4 / rmm = moles
98.4 / 152 = moles in 2L
/ 2 = moles in a litre
Answer : M

17. 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 = moles in 1L
Answer = M

18. Q223 Calculate the mass of NaOH in 20cm3 of 0.1M NaOH
Moles of X
Mass of X in g
X Relative Molecular Mass
÷ 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

19. q223
B) 1.53g
C)0.0158g
D) 146g
E)0.196g

20. Q224
A) 40gl-1
B)112gl-1
C)12.25gL-1
D)1.06gl-1
E)0.49gl-1

21. There are 1.85g of Ca(OH)2 in one litre. Answer = 1.85gL-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

22. Example: What is the mass of CuSO4 in 250cm3 of a 3M solution?
Given Moles PER LITRE Find Grams PER LITRE Grams per 250cm3
How many grams in 1 litre of solution?
There are 478.5g of CuSO4 in one litre.
Answer =478.5 gL-1

23. How many grams in 250cm3 litre of solution?
Given Moles PER LITRE Find Grams PER LITRE Grams per 250cm3
How many grams in 250cm3 litre of solution?
(478.5)/ 4 =
Answer = grams in 1 litre
= gl-1

24. 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

25. 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 Want mass in 100cm3
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%

26. Express the concentration in w/v%
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 Want mass in 100cm3
75g of NaCl in 250cm3
75 / 250 x 100 = 30
30g of NaCl in 100cm3 of solution
Answer = 30 w/v%

27. 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

28. 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!

29. How many cm3 of ethanol are there is 30cm3 of the whiskey?
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 Want volume in 30cm3
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

30. Q226. The label on a bottle of beer says that the ethanol content is 4
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 Want volume in 568cm3
(568)(4.8) / (100) =
cm3 of ethanol in 30cm3 of beer

31. 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

32. A solution has a w/w% concentration of 35%
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

33. Q227. Concentrated hydrochloric acid is a 37
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 =
There would need to be g of solution
Answer: g

34. Standard solutions
A standard solution is a solution whose concentration is accurately known

35. 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.

36. Examples of Primary Standards
Sodium Chloride
Examples of Primary Standards
Potassium Dichromate
Anhydrous Sodium Carbonate

37. 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.

38. 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??

39. How to make a standard solution
A special technique is used so that the concentration of the solution can be accurately known!
Find the mass of the solute accurately using a mass balance, and a clock glass.

40. 2. The solute is transferred to a clean beaker (filled with some deionised water) using a stirring rod

41. 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.

42. 5. The solution from the beaker is poured into a volumetric flask

43. 6. Any solution remaining in the beaker is washed into the volumetric flask, using a wash bottle

44. 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.

45. 8. The flask is stoppered, and inverted 20 times to sure the solution is mixed properly!

46. 6. Expressing concentration in parts per million (ppm)
ppm (parts per million) = milligrams in a litre

47. Convert the following to ppm 0.62g / 500cm3
Given grams per 500cm Grams per 1000cm Need: mg per 1000cm3
0.62g in 500cm3
(0.62) / 500 x 1000 = 1.24g
1.24g in 1000cm3
To convert grams to milligrams
1.24 x 1000 = 1240
1240 mg in 1000cm3
Answer = 1240ppm

48. 228(a)Convert the following to ppm 0.54g / 1L
Grams per 1000cm Need: mg per 1000cm3
To convert grams to milligrams multiply by 1000
0.54g x 1000 = 540
540 mg in 1000cm3
Answer = 540ppm

49. 228(b)Convert the following to ppm 0.18g / 1L
Grams per 1000cm Need: mg per 1000cm3
To convert grams to milligrams
0.18g x 1000 = 180
180 mg in 1000cm3
Answer = 180ppm

50. 228c)Convert the following to ppm 0.077g / 100cm3
Given grams per 100cm Grams per 1000cm Need: mg per 1000cm3
(0.077) x 10 = 0.77
0.77g in 1000cm3
To convert grams to milligrams
(1000)(0.77) = 770
770 mg in 1000cm3
Answer = 770ppm

51. 228d)Convert the following to ppm 0.0009g / 100cm3
Given grams per 100cm Grams per 1000cm Need: mg per 1000cm3
(0.0009) x 10 = 0.009
0.009g in 1000cm3
To convert grams to milligrams
0. 009g x 1000 = 9
9 mg in 1000cm3
Answer = 9ppm

52. 228e)Convert the following to ppm 0.0017g / 100cm3
Given grams per 100cm Grams per 1000cm Need: mg per 1000cm3
(0.0017) x 10 = 0.017
0.017g in 1000cm3
To convert grams to milligrams
0. 017g x 1000 = 17
17 mg in 1000cm3
Answer = 17ppm

53. 228f)Convert the following to ppm 0.0003g / 100cm3
Given grams per 100cm Grams per 1000cm Need: mg per 1000cm3
(0.0003) x 10 = 0.003
0.003g in 1000cm3
To convert grams to milligrams
0. 003g x 1000 = 3
3 mg in 1000cm3
Answer = 3ppm

54. colour of a solution
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

55. Effect of Dilution on Concentration
When a solution is diluted, more solvent is added.
The quantity of solute remains unchanged.