In the previous chapter we had discussed matters. In this chapter we will explore more about pure substance and mixture. What are their properties, how different mixtures of substance can be separated what makes them together.
The substances which are formed by only one kind of particles and having a constant composition of chemicals and characteristic properties throughout the sample.
Mixtures are formed when two or more pure substances are mined together, for example : salt , solution ,air etc.
Types of mixture :
i). Homogenous mixture ii). Heterogenous mixture
i). Homogeneous mixture :
A homogenous mixture has a uniform composition throughout its mass.
The constituents of a homogeneous mixture cannot be seen easily.
Homogeneous mixture has no visible boundaries of separation between its constituents. E.g : salt solution.
ii). Heterogeneous mixture :
A heterogeneous, minture does not have a uniform composition throughout its mass.
The constituents of heterogeneous mixture can usually be seen easily.
Heterogeneous mixture has visible boundaries of respiration between the various constituents. e.g.: oil water mixture.
| Homogenous Mixture | Heterogeneous Mixture |
|
1. It has uniform composition properties. 2. The substances are completely mixed. 3. There is no bible boundary of separation. 4. All homogenous mixtures are called solution. 5. Its particle can not be seen with naked eye. |
1. It has non-uniform composition properties. 2. The substances remain separate. 3. There is a visible boundary of separation. 4. All the suspensions are colloids are heterogeneous. 5. Its particle can be seen with naked eye. |
Sol :
It is a heterogeneous mixture.
Its particle is too small to be seen by naked eye.
They scatter a beam of light.
Particles cannot be separated by filtration to and sedimentation.
Solution :
It is a homogeneous mixture.
Its particles are smaller than Inm, they are not visible to naked eye.
They do not scatter a beam of light.
Particles cannot be reported by filtration and sedimentation.
Suspension :
It is a heterogeneous mixture.
Its particles are visible to a naked eye.
They scatter a beam of light.
Particles can be separated.
Mass of solute ( NaCl ) = 36 gn
Mass of solvent (water) = 100 gm
Total mass of solution = mass of solute + mass of solvent
= 36 + 100
= 136 gm
Simple distillation separation technique We separate the two miscible liquids on the basis of their boiling point. Boiling point of petrol is lower than kerosene which will distill first in the form of vapours and will be collected in a separate beaker.
Kerosene having higher boiling point will distil later on and will be collected in another beaker.
(i). Separation of butter from curd can be done by. Centrifugation.
(ii). Separation of salt from sea water can be done by evaporating water, leaving salt behind that can be crystallized out.
(iii). Camphor undergoes sublimation and hence sublimation can be used to separate camphor k salt.
The process of crystallization is used to purity substances. Pure crystals can be formed from a mixture of impure solid by crystallisation, For example: separation of salt from sea water.
Physical change: There is no change in the chemical nature of substance. Only state change. for example: ice - water - water vapour.
Chemical change: A substance reacts with another substance and makes a new substance. It is an irreversible reaction.
• Physical change
• Physical change
• Chemical change (hydrated iron oxide)
• Physical change
• Chemical change
• Physical change
• Physical change
• Physical change (Co2, smoke, water vapour, ash)
Air (Mixture of gases)
Distilled water (Pure substance)
Milk (mixture)
Nacl (Pure substance)
Tap water (mixture)
Steel (mixture)
Ice-cream (mixture)
Alcohol (Pure, substance)
Baking soda (Pure substance)
a. Evaporation
b. Sublimation
c. Filtrations
d. Chromatography
e. Centrifugation
f. Separating funnel
g. Filtration
h. Magnetic separation
i. Winnowing
j. Centrifugation
Steps :
Take 100 ml of water in a pan on a solvent.
Boil it for few minutes
Add 1 teaspoon tea leaves, add 1 and half tea spoon sugar and 50 ml of milk in a pan. Here, sugar, tea leaves and milk behave like a solute.
Boil it for a few minutes until the sugar dissolves in water and tea leaves and milk also devolve in water. As sugar, tea leaves are soluble in water to form solutions.
The prepared solution is passed to the tea retainer.
The insoluble tea leaves remain in the tea retainer as residue.
The tea (solution) is collected in the cup as filtrate.
Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).
| Substance Dissolved | Tem | per | atu | re | in K |
| 283 | 293 | 313 | 333 | 353 | |
| Potassium nitrate | 21 | 32 | 62 | 106 | 167 |
| Sodium chloride | 36 | 36 | 36 | 37 | 37 |
| Potassium chloride | 35 | 35 | 40 | 46 | 54 |
| Ammonium chloride | 24 | 37 | 41 | 55 | 66 |
(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt?
(a). 62 gm Potassium nitrate dissolved in 100 gm of water
62 / 2 = 31 gm
Potassium nitrate dissolved in 50 gm of water.
(b). In the given table, we see Potassium chloride solubility at different temperature then solubility was increased as the temperature was increased. An temperature decrease the solubility of Potassium chloride was decreased and the remains potassium chloride at higher lower temperature precipitate out.
(c). Ammonium chloride
(d). Solubility was increased as the temperature was increased.
(a) A solution in which no more solute can be dissolved at a particular temperature. i.e. it contains the maximum amount of salute. Example: an aqueous sugŠ°r solution in which more sugar cannot be added.
(b) The substance which is formed by only one kind of particle and having a constant. Composition of chemicals and characteristics. Properties throughout the sample. Example :- sugar and salt contains only one kind of particle and have the name composition throughout.
(c) It is a heterogeneous mixture having salute size greater than Ihm and smaller than 100 mm. They can scatter beams of light passing through. Example :- in milk, rubber, clouds etc.
(d) These are heterogenous mixtures of solids dispersed in liquids. The solute particles are insoluble and remain suspended throughout the bulk of medium. the solute size is greater than 100 mm. Example - dust article in air, muddy water etc
Homogenous mixture: Uniform composition of constituents.
Heterogenous mixture: Non-uniform composition of constituents.
Homogenous Heterogenous
- Soda water - wood (C,O,H,N)
- Vinegar - air (O2, N2, H2,Co2, etc)
- Filtered tea - soil
Take a sample of colourless liquid, put it on the stove and if it starts boiling at exactly 100* c, then it confirms that it is a pure water. Any other colourless liquid such as vinegar will always have a different boiling point.
Which shows constant composition throughout i.e it is made of one type of atom, element or compound is known as pure substance.
(a) Ice
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
Solution: In which the solute is evenly distributed in the solute. e.g.:- salt water
(b) Sea water
(c) Air
(e) Soda water is the solution among the following mixtures.
Air in a gaseous solution and soda water is a liquid solution.
Tyndall effect: It is the property of colloidal solutions. The particle of colloidal solution can scatter light.
(b) Milk and (d) Starch solution shows tyndall effect.
But (a) Salt solution and (c) Copper sulphate solution is a true solution.
Elements: Elements cannot break in similar particles because it is also a similar particle. e.g. fe, H etc. Sodium, Silver, Tin, Silicon
Compound: When two or more than two elements are chemically combined known as compound. eg.: H2O. Calcium carbonate, Methane, Carbon Dioxide.
Mixture: It is a physical combination of two or more substances because there is no chemical reactions occur between them. Soil, Sugar Solution, Coal, Air, Soap, Blood.
(a). Growth of a plant is a chemical change because at the time of photosynthesis, plants convert sunlight into chemical energy and this is an irreversible process.
(b). Rusting of iron is a chemical change because there is formation of new substance i.e.- Fe2O3, xH2O (Rust).
(c). Mixing of iron filings and sand is a physical change process.
(d). Cooking of food in a chemical change because there is change in chemical composition by supplying heat in addition to some food additives, oil, butter etc.
(e). Digestion of food is à chemical change because the enzyme present in stomach are break large macromolecules into simple molecules.
(f). Freezing of water is a physical change. because there is change in physical state of water notinitis composition.
(g). Burning of a candle is a chemical change because there is emission of CO2 and water vapours during the burning of candles.