The Case of a Liquid Solute Dissolved in a Liquid Solvent
If the solution is of a 'liquid solute dissolved in a liquid solvent,then we usually consider the 'volume percentage of solute' in determining the concentration of solution. So,in the case of a liquid solute dissolved in a liquid solvent : The concentration of a solution is defined as the volume of solute in millilitres present in 100 millilitres of the solution. For example, a 20 per cent solution of alcohol means that 20 millilitres of alcohol are present in 100 millilitres of solution. Please note that the 100 millilitres volume of solution also includes 20 millilitres volume of alcohol. This means that the 100 millilitres of alcohol solution contain 100 - 20 = 80 millilitres of water in it. Thus, we can prepare a 20 per cent solution of alcohol by mixing 20 mL of alcohol in 80 mL of water (so that the total volume of the solution becomes 20 + 80 = 100 mL). Please note that in this case the concentration of solution refers to the volume of liquid solute in 100 mL of solution and not in 100 mL of solvent. In general, we can calculate the concentration of a solution in terms of volume percentage of solute by using the formula :Concentration of solution = x100
In the above example :
Volume of solute (alcohol) = 20 mL
And, Volume of solvent (water) = 80 mL
So,Volume of solution = Volume of + Volume of
solute solvent
= 20 + 80
= 100 mL
Now, putting these values of Volume of solute' and Volume of solution' in the above formula, we get: Concentration of solution = x100
= 20 per cent (by volume)
Thus, the concentration of this alcohol solution is 20 per cent or that it is a 20% alcohol solution (by volume). We will now solve some problems based on the calculation of concentration of solutions containing liquid solutes.
Sample Problem 1. A solution contains 50 mL of alcohol mixed with 150 mL of water. Calculate the concentration of this solution.
Solution. This solution contains a liquid solute (alcohol) mixed with a liquid solvent (water), so we have to calculate the concentration of this solution in terms of volume percentage of solute (alcohol). Now,we know that:Concentration of solution = x100
Here, Volume of solute (alcohol) = 50 mL
And, Volume of solvent (water) = 150 mL
So,Volume of solution = Volume of + Volume of
solute solvent
= 50 + 150
= 200 mL Now, putting these values of Volume of solute' and 'volume of solution' in the above formula we get:
Concentration of solution = x100= 25 per cent (by volume)
Thus, the concentration of this alcohol solution is 25 per cent or that it is a 25% alcohol solution (by volume).
Sample Problem 2. If 2 mL of acetone is present in 45 mL of its aqueous solution, calculate the concentration of this solution.
Solution. This solution also contains a liquid solute (acetone) mixed with a liquid solvent water (because it is an aqueous solution), so we have to calculate the concentration of this solution in terms of volume percentage of solute (acetone).
Here, Volume of solute (acetone) = 2 mL
And, Volume of solution = 45 mL
Now we know that:
Concentration of solution = x100
x100
= 4.4 per cent (by volume)
Thus, the concentration of this acetone solution is 4.4 per cent or that it is a 4.4% acetone solution (by volume).
In industry, when the concentration of a solution is expressed as 'per cent by mass' or 'per cent by weight', it is denoted by the symbol w/w (which means 'weight by weight'). Please note that here the terms 'mass' and 'weight' are being used in the same sense. And when the concentration of a solution is expressed as 'per cent by volume', then it is denoted by the symbol v/v (which means 'volume by volume').We can see the symbols w/w or v/v on the labels of bottles of many liquid medicines. For example, a particular bottle of the digestion mixture 'Milk of Magnesia' has these words written on the label of its bottle "contains approximately 8.0 % w/w of hydrated magnesium oxide".(Please note that'hydrated magnesium oxide' means 'magnesium hydroxide').
Notes
Matter in Our Surroundings - Notes
1. 3. Non-Metals are Bad Conductors of Heat and Electricity.
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3. The Case of a Liquid Solute Dissolved in a Liquid Solvent
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5. 7. Metals are Solids at the Room Temperature
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6. 11. Metals Usually Have a Silver or Grey Colour
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8. 7. Non-Metals may be Solid, Liquid or Gases at the Room Temperature.
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11. 6. Non-Metals are Not Strong. They Have Low Tensile Strength.
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12. Separation Of Mixture Of a Solid And a Liquids
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14. To Study the Properties of a Compound of Iron and Sulphur
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16. To Study the Properties of a Colloid
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19. 11. Non-Metals Have Many Different Colours.
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21. 1. Separation by a Suitable Solvent
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24. To Distinguish a Colloid from a Solution
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27. 6. Metals are Usually Strong. They Have High Tensile Strength.
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28. To Study the Properties of a Solution
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32. 2. Separation by a Separating Funnel
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34. 3. Metals are Good Conductors of Heat and Electricity.
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35. Separation of Mixture Of Two Solids
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37. 1. Non-Metals are Not Malleable. Non-Metals are Brittle.
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41. 1. Separation by Fractional Distillation
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