Chapter-2 Is Matter Around Us Pure?

Explanation:

A substance is a form of matter that has a constant or specific composition and distinct

chemical and physical properties. It can be an element, a compound, or a mixture of compounds.

An element is considered a pure substance which consists of only one type of atom. Examples include gold, carbon, and oxygen.

A compound is a substance made up of two or more different elements chemically bonded together in a fixed proportion. Water (H2O) and carbon dioxide (CO2) are some examples.

Using a physical method a substance can never be separated.

Explanation:

These are some of the differences between homogenous and heterogenous mixtures:

Explanation:

Given below are some differences between homogeneous and heterogeneous mixtures:

Explanation:

The following are the differences between sol, solution and suspension:

Explanation:

The concentration of 36g of sodium chloride(NaCl) in 100g of water at 293 K can be calculated as

The mass of the solute and solvent which is already given

Mass of solute sodium chloride(NaCl): 36g

Mass of solvent water(H2O) : 100g

Then we have

Mass of solution(NaCl + H2O) : 136g

And, Concentration can be calculated as

Concentration=Mass of soluteMass of solution100

putting all the values in the above equation, we get

Concentration=36136100=26.47%

The concentration of the solution is 26.47%.

Explanation:

                               Diagram of a simple distillation apparatus 

 Petrol and kerosene are miscible, and the difference in their boiling points is more than 25 degrees celsius, 25 degrees celsius is a significant difference. So, the two can be separated using a process known as distillation.

Distillation is the process of separating mixtures based on the difference of their boiling points.

The petrol and kerosene mixture will be poured into a distillation flask which will be heated. As petrol has a lower boiling point, it will start evaporating first and create vapours as the temperature of the mixture rises. A condenser then condenses the vapours of the petrol and collects them through a condenser into another container. The kerosene will be left behind in the distillation flask as it has higher boiling point.

Hence, effectively separating the two mixtures. 

Explanation:

a) Butter from curd

Centrifugation, also known as churning specifically for butter, is the process that is used to separate butter from curd.

Centrifugal force is applied to the mixture by spinning it rapidly resulting in the separation of   the substances based on their density.

b) Salt from seawater

The process of evaporation is simply used to separate salt from seawater.

On applying heat the water evaporates leaving only the salt behind.

This process can be done both naturally and artificially.

c) Camphor from salt

A process known as sublimation is used to separate camphor from salt.

Sublimation is an odd phenomenon in which a solid substance directly transitions into gaseous   phase without going through the liquid phase.

So, in this case camphor sublimates leaving only the salt behind.

Explanation:

Crystallisation technique can be used to separate solid particles from a liquid mixture. It works on the basis of precipitation.

The particles dissolved in a mixture start settling down and clumping together to form solid crystals of very high purity.

This process of crystallisation can also be used to separate and purify impure substances. Crystallisation has a wide range of industrial applications like in chemical and pharmaceutical industries.

Explanation:

a) Cutting of trees

Cutting of trees is a physical change as there is no change happening in the chemical composition of the tree.

b) Melting of butter in pan

It is a physical change as the butter just changes from solid to liquid the internal composition remains the same.

c) Rusting of almirah

Rusting is a chemical change as the metal surface of almirah chemically reacts with the oxygen in air and oxidises.

d) Boiling of water to form steam

This is a physical change as water turned into steam simply changes its state; nothing changes chemically.

e) Passing of electric current through water and water breaking into hydrogen and oxygen gases.

This process is a chemical reaction known as electrolysis of water, in this reaction the electricity passing through the water decomposes it into hydrogen and oxygen. 

                                                       2H2O2H2+O2

f) Dissolving common salt in water

It is a physical change as the salt simply gets dissolved in water, both their chemical composition remains the same.

g) Making a fruit salad with raw fruits

Physical change as understandably nothing chemically changes about the fruits.

h) Burning of paper and wood

This is a chemical change as burning is a reaction between fuel and oxygen giving off heat and light.

                                                       Fuel + O2 CO2+H2O

Explanation:

Below are some of the things around us that are either pure substances or mixtures

Explanation:

a) Sodium chloride from its solution in water

Sodium chloride or salt can be separated from water through the process of evaporation.

b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride

Ammonium chloride can be separated using sublimation.

c) Small pieces of metal in the engine oil of a car

They can be separated using simple filtration apparatus like a sieve.

d) Different pigments from an extract of flower petals

A technique called chromatography is used to separate out different pigments from an extract.

e) Butter from curd

Centrifugation, also known as churning specifically for butter, is the process that is used to separate butter from curd.

f) Oil from water

Let the denser liquid(oil) settle down then using a funnel can be used to separate out the two immiscible liquids.

g) Tea leaves from tea

They can easily be separated using any filtrator, e.g. sieve.

h) Iron pins from sand

Magnets can be used to separate iron pins from sand.

i) Wheat grains from husk

Winnowing is the process used to separate wheat from husk.

As husk is lighter than wheat they are separated using blows of wind.

j) Fine mud  particles suspended in water

Letting mud particles settle down at the bottom and then separating the two out is used, this process is called sedimentation.

Explanation:

1. Pour milk which acts as the solvent into a vessel or an utensil and put it on the stove.

2. Add sugar into the milk, sugar is a solute here and is soluble in the hot milk.

4. Add tea leaves into the solution, tea leaves are another solute but they are insoluble in the mix.

5. Continue boiling the mixture.

6. Despite being insoluble, tea leaves give taste and colour to the tea.

6. Continue heating until the sugar completely dissolves.

7. Once the solution is boiled enough, turn off the heat and filter out the tea leaves which are the       residue from the solution into a cup.

Explanation:

a) From the table we know that 62g of potassium nitrate(KNO3) is required in 100g of water to form a saturated solution at 313K.

So, the mass of potassium nitrate required to form a saturated solution in 50g of water at 313K is given as

    Mass=6250100=31

The required mass of potassium nitrate is 31g.

b) As the solution of potassium chloride in water starts to cool down, Pragya would observe the formation of crystals of potassium chloride. Because the stability and solubility of potassium chloride in water decrease with decrease in temperature.

c) From the data given in the table at 293K, we gather the following values of solubility of the four salts

1. Solubility of ammonium chloride(NH4Cl)=37g

2. Solubility of potassium chloride(KCl)=35g

3. Solubility of potassium nitrate(KNO3)=32g

4. Solubility of sodium chloride(NaCl)=36g

Clearly, from this data we observe ammonium chloride has the highest solubility at 293K.

d) As observed from the data, on increasing the temperature the solubility of the salts also increases; this is due to the fact that on increasing the temperature the saturation point of a solute in a solvent also increases.

Explanation:

a) Saturated solution

The state of a solution in which no more solute can be dissolved without increasing the temperature of the solution is called saturation.

Solution which achieves saturation is called a saturated solution.

E.g. Excess salt remains as residue in cold water.

b) Pure Substance

A type of substance which is made up of only one kind of atom, molecule or compound.

E.g. Gold, water

c) Colloid

Substances which consist of particle size between 1nm to 1000nm i.e. consisting of particles sized between solution and suspension.

There are various types of colloids, some of them are heterogeneous in nature and are visible under a microscope.

They also show the Tyndall effect.

d) Suspension

A heterogenous mixture which consists of solute particles that are insoluble in the solvent, they are only suspended in the solution, hence the name suspension.

The particles are big enough to be visible to the naked eye.

Explanation:

It is a fact that water boils at 100°C (at standard atmospheric pressure), so we can use this property of water to determine the purity of it. If there is a change in the boiling point then there are some impurities present in the water.

In industrial and commercial applications a TDS meter is used to check the purity of water.

Explanation:

These are the only pure substances from the list mentioned above:

a) Iron

Iron is an element entirely made up of only iron atoms(Fe).

b) Ice

Ice comprises only water but in solid form.

c) Hydrochloric acid

Hydrochloric acid is made up of hydrogen and chlorine atoms(HCl) dissolved in water.

d) Calcium oxide

Calcium oxide comprise of calcium and oxygen(CaO), it is also known as quicklime.

e) Mercury

Mercury is a chemical element with symbol (Hg ).

Explanation:

The following are the only solutions from the list of mixtures given in the question:

a) Sea water is a solution as it is a mixture of salts and pure water.

b) Air is also a solution as it comprises various gases and particles.

c) Soda water is a mixture of carbon dioxide dissolved in water.

Soil and coal are not considered solutions as they are not in the form of liquid or gas.

Explanation:

The Scattering of light by a medium is called the Tyndall effect.

This phenomenon of scattering of light is usually observed in colloidal solutions and also in suspensions.

From the list above only Milk and Starch solutions exhibit the tyndall effect as both milk and starch solution are colloids.

Salt solution and copper sulphate do not exhibit tyndall effect because they are true solutions with particle size less than a nanometer.

Explanation:

Here are the chemical changes from the list mentioned above:

a) Growth of a plant

It is a chemical change because the plants change their form, bearing fruits and flowers as they grow older.

b) Rusting of iron

Rusting is a chemical change as the metal surface of iron chemically reacts with the oxygen in air and oxidises.

c) Cooking of food

It is a chemical change as cooked food is entirely different from uncooked food in its chemical composition and other properties too.

d) Digestion of food

Our stomach breaks down food using acids and enzymes and that process is a chemical process.

e) Burning of candle

It is a chemical change as the wax burns and gets converted to heat, light and carbon dioxide.