Is Matter Around Us Pure? Blog 6

May 18, 2020

Chapter Is Matter Around Us Pure?

Lesson 6

Hello Learners,

At the end of this topic, learner will be able to

(i) solve numerical based on mass by mass percentage of a solution.

(ii) solve numerical based on mass by volume percentage of a solution.

(iii) solve numerical based on volume percentage of a solution.

(iv) define suspension.
(v) tell the properties and examples of suspension.
(vi) define colloids.
(vii) tell the properties and examples of colloids

IMPORTANT INSTRUCTIONS:

1. Reading of NCERT Text Book is very important, so refer your book while studying through BLOGS.

2. Complete your Note Books. Write-ups that is in red colour need to be copied in your notebooks rest need to be read carefully for better understanding.

3. Complete blue box questions and back exercise of your text book in your respective note book.

4. Complete the notes/home assignment given in the last of every blog in your Chemistry copy.

So, let us start the topic for today.................

In the previous blog, we have discussed about unsaturated, saturated and super saturated solution. Click on the link to revise it.

https://www.youtube.com/watch?v=-mnk_89BXmM

Now, let us continue further....

We always discuss a solution being diluted or concentrated; this is a qualitative way of expressing the concentration of the solution. A dilute solution means the quantity of solute is relatively very small, and a concentrated solution implies that the solution has a large amount of solute. But these are relative terms and do not give us the quantitative concentration of the solution.

Click on the link to get the better understanding of term concentration and dilution

https://www.youtube.com/watch?v=V6-mlh9xRjg

So, to quantitatively describe the concentrations of various solutions around us, we commonly express levels in the following way:
Refer your text book for formulae (i) Mass by mass percentage of a solution = mass of solute X 100
mass of solvent

(ii) Mass by volume percentage of a solution = mass of solute X 100
Volume of solution

(iii) Volume by volume percentage of a solution = volume of solute X 100
volume of solution

Let us practice numerical

Numerical 1 A solution contains 40 g of common salt in 320 g of water. Calculate the concentration in terms of mass by mass percentage of the solution.

Solution: Mass of solute (salt) = 40 g
Mass of solvent (water) = 320 g

therefore, mass of solution = 40 + 320 = 360 g

Mass percentage of solution = mass of solute X 100
mass of solution

= 40 X 100
360

= 11.1%

Numerical 2. Calculate the mass of glucose and mass of water required to make 250 g of 25% solution of glucose.

Solution: Mass by mass percentage = 25 %
Mass of solution = 250 g
Mass of solute = x

Formula used
mass by mass percentage of solution = mass of solute X 100
mass of the solution

On putting the values
25 = x X 100
250

therefore, 25 X 250 = x
100

62.5 g = x

therefore, mass of water = mass of solution - mass of solute
= 250 - 62.5
= 187.5 g

Numerical 3 A solution contains 5mL of alcohol in 70 mL of water. Calculate the volume by volume percentage of the solution.

What is a Suspension?

Try to recall the activity 2.2 in which we added insoluble substance such as chalk powder or wheat flour in a test tube. We saw that there was a layer of separation when the solution was left unattended for sometime.

So, when an insoluble substance such as chalk powder, wheat flour or mud is added to water we get suspension in which the solids are dispersed in liquids.

A suspension is a hetrogeneous mixture in which the solute particles do not dissolved but remain suspended throughout the bulk of the medium and the particles of suspension are visible to the naked eyes.

Suspension https://www.youtube.com/watch?v=UktHPe4oQLc

Properties of Solution

1. Suspension is a heterogeneous mixture.
2. The particles of a suspension can be seen by the naked eyes. The particle of suspension is between 10^-5 to 10^-7 m

3. The particles of a suspension scatter a beam of light passing through it and make its path visible.

4. The solute particles settle down when a suspension is left undisturbed.
5. A suspension is unstable.
6. The solute particles of suspension can be separated from the mixture by the process of filtration.

7. Suspension is either opaque to translucent.

Examples of Suspension

1. Paints are suspension of coloured substance in water or some other liquid.

2. Lime water used for white wash is suspension of calcium hydroxide in water.

3. Milk of magnesia is a suspension of magnesium hydroxide in water.

4. Bleaching powder in water is a suspension of bleaching powder insoluble in water.

What is a Colloidal Soution?

We have discussed earlier that there are certain substance like common salt, sugar, copper sulphate etc, which dissolve in water to from a true solutions. The solute particles of a true solution are very small and hence are invisible to our naked eye. On the other side there are certain substances like chalk powder, calcium oxide, bleaching powder etc. are insoluble in water. The solute particles of a suspension are quite large and are clearly visible to the naked eye.

In between these two categories of substance, there is third category of substance which dissolve in water or any other liquid to form a mixture in which the size of the particles lies between 1-100 nm are called Colloidal Solutions.

Solutions in which the size of the particles lies in between those of true solutions and suspensions are called colloidal solution.

NOTE: Due to relatively smaller size of particles, these mixtures appears to be homogeneous in nature but are actually heterogeneous in nature.

Tyndall Effect: The Tyndall effect was first discovered by (and is named after) the Irish physicist John Tyndall.

The Tyndall effect is the phenomenon in which the particles in a colloid scatter the beams of light that are directed at them. This effect is exhibited by all colloidal solutions and some very fine suspensions. Therefore, it can be used to verify if a given solution is a colloid. The intensity of scattered light depends on the density of the colloidal particles as well as the frequency of the incident light.

When a beam of light passes through a colloid, the colloidal particles present in the solution do not allow the beam to completely pass through. The light collides with the colloidal particles and is scattered (it deviates from its normal trajectory, which is a straight line). This scattering makes the path of the light beam visible, as illustrated below.

Tyndall Effect https://www.youtube.com/watch?v=Z-1pQPhbP5A

Dispersed Phase and Dispersion Medium

We have stated that colloidal solution are heterogeneous mixtures. This means that the constituents or components of a colloidal solution are not present in one single phase but are actually present in two separate phases. They are called dispersed phase and the dispersion medium.The solute-like component which has been dispersed or distributed throughout in a solvent-like medium is called the dispersed phase while the solvent like medium in which the dispersed has been distributed is called dispersion medium.

Colloids https://www.youtube.com/watch?v=QAH-cCK1bS8

Common Examples of Colloids

(Make this table in your chemistry note book)

Properties of Colloids

1. A colloidal solution is heterogeneous in nature consisting of two phases called the dispersed phase and the dispersion medium.

2. The size of the colloidal particles lies in the range 1 – 100nm in between those of true solution and suspensions.

3. Colloidal particles pass through ordinary filter paper, hence they cannot be separated from the dispersion medium by filtration.

4. Colloidal particles do not settle when left undisturbed.

5. Colloidal particles are not visible to naked eye.

6. Colloidal particles are continuously moving in a zig-zag movement (Brownian movement).

7. Colloidal particles are big enough to scatter light passing through it.

Home Assignment
1. Complete the notes in your chemistry note book.
2. Try to make the comparison of characteristic of true solution, colloidal solution and suspension on the bases on (i) Particle size (ii) Appearance (iii) Nature Homogeneous/Heterogeneous (iv) Filtrability (v) Settling of particles (vi) Visibility of particles (vii) Tyndall Effect.