Concentration of a Solution
A solution may have a small amount of solute dissolved in it while another solution may have a large amount of solute dissolved in it.The solution having small amount of solute is said to have low concentration.It is known as a dilute solution. The solution having a large amount of solute is said to be of high concentration. It is known as a concentrated solution (see Figure 36). We can now define the concentration of a solution as follows: The concentration of a solution is the amount of solute present in a given quantity of the solution. The concentration of a solution can be expressed in a number of different ways.The most common way of expressing the concentration of a solution is the 'percentage method'.The percentage method of expressing the concentration of a solution refers to the 'percentage of solute' present in the solution. The percentage of solute can be 'by mass' or 'by volume'. This point will become more clear from the following discussion.
If the solution is of a 'solid solute' dissolved in a liquid, then we consider the 'mass percentage of solute' in calculating the concentration of solution.So,in the case of a solid solute dissolved in a liquid solvent: The concentration of a solution is defined as the mass of solute in grams present in 100 grams of the solution.For example, a 10 per cent solution of common salt means that 10 grams of common salt are present in 100 grams of the solution. Please note that the 100 grams of solution also include 10 grams of the common salt.This means that the 100 grams of common salt solution contain 100 - 10 = 90 grams of water in it. Thus,we can prepare a 10 per cent solution of common salt by dissolving 10 grams of common salt in 90 grams of water (so that the total mass of the solution becomes 10 + 90 = 100 grams). Please note that the concentration of a solution refers to the mass of solute in 100 grams of the solution and not in 100 grams of the solvent. We can calculate the concentration of a solution in terms of mass percentage of solute by using the following formula :
Concentration of solution =X100
The mass of solution is equal to the mass of solute plus the mass of solvent.That is :
Mass of solution =Mass of+Mass of
solute solvent
So, we can obtain the mass of solution by adding the mass of solute and the mass of solvent.In the above given example :
Mass of solute (salt) = 10g
And, Mass of solvent (water) = 90g
So,Mass of solution = Mass of + Mass of
solute solvent
= 10 + 90
= 100g
Now,putting these values of 'mass of solute' and 'mass of solution' in the above formula,we get:Concentration of solution = x 100
= 10 percent (by mass)
Thus, the concentration of this salt solution is 10 per cent (or 10%) by mass. Please note that if the concentration is in terms of mass, then the words 'by mass' are usually not written with it.For example,in the above case we just say that it is a '10 per cent solution of common salt'.Since common salt is a solid,so it is understood that the percentage is by mass. This is because we do not consider the volume of solids in making solutions.We will now solve some problems based on the calculation of concentration of solutions.
Sample Problem 1.A solution contains 30 g of sugar dissolved in 370 g of water.Calculate the concentration of this solution.
Solution.This solution contains a solid solute (sugar) dissolved in a liquid solvent (water),so we have to calculate the concentration of this solution in terms of the mass percentage of solute (sugar).We know that
Concentration of solution= X100
Here,Mass of solute (sugar) = 30g
And,Mass of solvent (water) = 370g
So,Mass of solution = Mass of + Mass of
solute solvent
= 30 + 370
= 400 g
Now, putting the values of 'mass of solute'and 'mass of solution' in the above formula,we get:
Concentration of solution =x100
=
=7.5 percent (or 7.5%)
Thus, the concentration of this sugar solution is 7.5 per cent (or that it is a 7.5% sugar solution).
Sample Problem 2. If 110 g of copper sulphate is present in 550 g of solution, calculate the concentration of solution.
Solution. Here, Mass of solute (copper sulphate) = 110 g
and mass of solution = 550 g
now we know that:
Concentration of solution = X100
x100
Thus,the Concentration of this copper sulphate solution is 20 percent (or it is a 20% copper solution)
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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4. 11. Metals Usually Have a Silver or Grey Colour
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7. 7. Metals are Solids at the Room Temperature
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10. 7. Non-Metals may be Solid, Liquid or Gases at the Room Temperature.
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11. Separation Of Mixture Of a Solid And a Liquids
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12. 6. Non-Metals are Not Strong. They Have Low Tensile Strength.
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13. To Study the Properties of a Colloid
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16. To Study the Properties of a Compound of Iron and Sulphur
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18. 11. Non-Metals Have Many Different Colours.
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21. 1. Separation by a Suitable Solvent
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25. 6. Metals are Usually Strong. They Have High Tensile Strength.
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27. To Study the Properties of a Solution
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30. Separation of Mixture Of Two Solids
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36. To Distinguish a Colloid from a Solution
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38. 3. Metals are Good Conductors of Heat and Electricity.
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44. 1. Separation by Fractional Distillation
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47. Solutions, Suspensions And Colloids
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49. Chemical Formula for daily use material
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50. To Separate the Salt-Water Mixture (or Salt-Solution)
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