Textbook - IS MATTER AROUND US PURE? Questions in English

(N/A) pure substance is defined as a substance that consists of only one type of particles (atoms or molecules).
For example: $Hydrogen$,$Water$,$Gold$,etc.,are considered pure substances.
Note: All elements and compounds are classified as pure substances because they have a fixed chemical composition and uniform properties throughout.

(N/A) Homogeneous mixture:
$1$. Its constituent particles cannot be seen easily.
$2$. There are no visible boundaries of separation in a homogeneous mixture.
$3$. Its constituents cannot be easily separated.
$4$. Examples: Alloys,solution of salt in water,etc.
Heterogeneous mixture:
$1$. Its constituent particles can be seen easily.
$2$. It has visible boundaries of separation between the constituents.
$3$. Its constituents can be separated by simple physical methods.
$4$. Examples: Mixture of sand and common salt,mixture of sand and water,etc.

(N/A) Homogeneous mixture:
$1$. Its constituent particles cannot be seen easily.
$2$. There are no visible boundaries of separation in a homogeneous mixture.
$3$. Its constituents cannot be easily separated.
$4$. Examples: Alloys,solution of salt in water,etc.
Heterogeneous mixture:
$1$. Its constituent particles can be seen easily.
$2$. It has visible boundaries of separation between the constituents.
$3$. Its constituents can be separated by simple physical methods.
$4$. Examples: Mixture of sand and common salt,mixture of sand and water,etc.

(N/A) $Solution$ (true solution) is a homogeneous mixture. It does not show the $Tyndall$ effect. The solute particles are very small and cannot be filtered using filter paper. It is transparent. Examples: $Sea$ $water$,$alloys$,$lemon$ $juice$ in $water$.
$A$ $Sol$ (colloidal solution) is a heterogeneous mixture. It shows the $Tyndall$ effect. The particles cannot be separated by ordinary filter paper. It may be transparent or translucent. Examples: $Milk$ of $magnesia$,$cough$ $syrup$,$fog$,$smoke$.
$A$ $Suspension$ is a heterogeneous mixture. It shows the $Tyndall$ effect. The particles are large enough to be separated easily by filter paper. It is generally opaque. Examples: $Sand$ in $water$,$chalk$ in $water$.

(A) Mass of sodium chloride (solute) $= 36 \,g$
Mass of water (solvent) $= 100 \,g$
We know that,mass of solution $=$ mass of solute $+$ mass of solvent
$= 36 \,g + 100 \,g = 136 \,g$
Concentration (mass percentage) of the solution $= \frac{\text{Mass of Solute}}{\text{Mass of Solution}} \times 100$
$= \frac{36 \,g}{136 \,g} \times 100 = 26.47\,\%$

(B) Simple distillation is the method used to separate a mixture of two miscible liquids when the difference in their boiling points is greater than $25\,^{\circ}C$.
Method:
$1$. The mixture of kerosene and petrol is placed in a distillation flask.
$2$. The mixture is heated slowly,and the temperature is monitored using a thermometer.
$3$. Since petrol has a lower boiling point than kerosene,it vaporizes first.
$4$. The petrol vapours are passed through a condenser,where they cool down to form liquid petrol,which is then collected in a separate container.
$5$. The kerosene remains in the distillation flask as it has a higher boiling point.
$6$. Once the temperature begins to rise again,the heating is stopped,ensuring both components are separated.

(A) $(i)$ Butter can be separated from curd by using the centrifugation method. In this process,the mixture is rotated at high speed,causing the denser particles to settle at the bottom and lighter particles (butter) to rise to the top.
$(ii)$ Salt can be separated from sea-water by using the evaporation method. When the mixture is heated,water vaporizes,leaving behind the solid salt crystals.
$(iii)$ Camphor can be separated from salt by using the sublimation method. Camphor is a sublimable substance that turns directly into vapor upon heating,while salt remains as a solid residue.

(B) Crystallisation is a process that separates a pure solid in the form of its crystals from a solution.
It is primarily used for the purification of solids.
This technique is specifically used for mixtures containing soluble impurities that cannot be removed by simple filtration,as the impurities remain dissolved in the solvent while the pure substance forms crystals upon cooling or evaporation.

(N/A) Physical Change: These are changes where no new substance is formed and the chemical composition remains the same.
- Cutting of trees
- Melting of butter in a pan
- Boiling of water to form steam
- Dissolving common salt in water
- Making a fruit salad with raw fruits
Chemical Change: These are changes where new substances with different chemical properties are formed.
- Rusting of almirah (Iron reacts with oxygen and moisture to form iron oxide)
- Passing of electric current through water and the water breaking down into hydrogen and oxygen gases (Electrolysis)
- Burning of paper and wood (Combustion reaction)

(N/A) pure substance consists of only one type of particles,whereas a mixture consists of two or more different types of particles.
$(a)$ Wood: Mixture (It contains cellulose,lignin,water,and other organic compounds).
$(b)$ Coal: Mixture (It is a complex mixture of carbon,hydrogen,nitrogen,oxygen,and sulfur).
$(c)$ Milk: Mixture (It is a colloid containing water,fats,proteins,lactose,and minerals).
$(d)$ Sugar: Pure substance (It consists only of sucrose molecules,$C_{12}H_{22}O_{11}$).

(N/A) pure substance consists of only one type of particles,whereas a mixture contains two or more substances mixed in any proportion.
$(a)$ Common salt $(NaCl)$: Pure substance (it is a compound with a fixed chemical composition).
$(b)$ Soap: Mixture (it is a complex mixture of sodium or potassium salts of fatty acids,water,and additives).
$(c)$ Soil: Mixture (it contains sand,clay,organic matter,water,and air in varying proportions).
$(d)$ Rubber: Pure substance (natural rubber is a polymer of isoprene,$C_5H_8$,which is a single chemical compound).

(N/A) Evaporation: The solution is heated until the water evaporates,leaving behind solid sodium chloride.
$(b)$ Sublimation: Ammonium chloride sublimes on heating,while sodium chloride does not,allowing for separation.
$(c)$ Filtration: Metal pieces are solid particles that can be separated from the liquid oil using a filter.
$(d)$ Chromatography: This technique is used to separate different pigments based on their differential solubility in a solvent.
$(e)$ Centrifugation: Butter is separated from curd by spinning it at high speeds,which forces the denser components to the bottom and lighter butter to the top.

(N/A) Decantation using a separating funnel.
$(b)$ Filtration.
$(c)$ Magnetic separation.
$(d)$ Winnowing.
$(e)$ Coagulation (using alum) followed by decantation or filtration.

(N/A) Method of preparation of tea:
$(i)$ Take some water $(solvent)$ in a pan and heat it.
$(ii)$ Add some sugar $(solute)$ and boil to $dissolve$ the sugar completely; the obtained homogeneous mixture is called a $solution$.
$(iii)$ Add tea leaves (which are $insoluble$) to the $solution$ and boil the mixture.
$(iv)$ Add milk and boil again.
$(v)$ Filter the mixture through a tea strainer. The liquid collected in the cup is the $filtrate$ (containing $soluble$ substances),and the tea leaves left behind in the strainer are the $residue$.

(N/A) According to the table,the solubility of potassium nitrate at $313 \,K$ is $62 \,g$ per $100 \,g$ of water.
To find the mass needed for $50 \,g$ of water:
Mass $= (62 \,g / 100 \,g) \times 50 \,g = 31 \,g$.
Thus,$31 \,g$ of potassium nitrate is required.
$(b)$ As the solution cools,Pragya will observe the formation of crystals of potassium chloride. This occurs because the solubility of most solid solutes in water decreases as the temperature decreases. When the solution cools,it becomes supersaturated,and the excess solute crystallizes out of the solution.

(D) Solubility of each salt at $293 \,K$:
- Potassium nitrate: $32 \,g$ per $100 \,g$ of water.
- Sodium chloride: $36 \,g$ per $100 \,g$ of water.
- Potassium chloride: $35 \,g$ per $100 \,g$ of water.
- Ammonium chloride: $37 \,g$ per $100 \,g$ of water.
Ammonium chloride has the highest solubility ($37 \,g$ per $100 \,g$ of water) at $293 \,K$.
$(b)$ The solubility of most solid salts increases with an increase in temperature and decreases with a decrease in temperature.

(N/A) Saturated solution: $A$ solution in which no more amount of solute can be dissolved at a particular temperature is called a saturated solution.
Example: When sugar is dissolved repeatedly in a given amount of water,a condition is reached at which further dissolution of sugar is not possible in that amount of water at room temperature.
$(b)$ Pure substance: $A$ substance made up of a single type of particles (atoms and/or molecules) is called a pure substance.
All elements and compounds are considered pure substances.
Example: Water $(H_2O)$,Gold $(Au)$,etc.

(N/A) Colloid: $A$ heterogeneous mixture in which the solute particle size is too small to be seen with the naked eye,but is large enough to scatter light is known as a colloid. There are two phases in a colloidal solution:
$1.$ Dispersed phase: The solute-like particles are said to be the dispersed phase.
$2.$ Dispersion medium: The medium in which the solute particles are spread is called the dispersion medium.
Example: Milk,clouds,etc.,are examples of colloids.
$(b)$ Suspension: $A$ suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension are visible to the naked eye.
Example: $A$ mixture of sand and water,muddy water,etc.

(A) homogeneous mixture is a mixture in which the composition is uniform throughout the mixture. Examples: Air (gaseous solution),soda water (gas in liquid),vinegar (acetic acid in water),and filtered tea (solutes dissolved in water).
$A$ heterogeneous mixture is a mixture in which the composition is not uniform throughout the mixture. Examples: Wood (contains fibers,resins,and minerals) and soil (contains sand,clay,organic matter,and pebbles).

(B) To confirm if a colorless liquid is pure water,we can determine its boiling point.
Pure water has a fixed boiling point of $100\,^{\circ}\text{C}$ at standard atmospheric pressure.
If the liquid boils exactly at $100\,^{\circ}\text{C}$,it is pure water.
If the boiling point is different,it indicates the presence of impurities.

(A) pure substance consists of particles of only one type of chemical nature. Its composition remains the same throughout.
$(a)$ Ice is solid water $(H_2O)$,which is a pure compound.
$(b)$ Milk is a mixture (colloid) of water,fats,and proteins.
$(c)$ Iron $(Fe)$ is an element,which is a pure substance.
$(d)$ Hydrochloric acid is typically an aqueous solution of hydrogen chloride gas $(HCl)$ in water,making it a mixture.
$(e)$ Calcium oxide $(CaO)$ is a pure compound.
$(f)$ Mercury $(Hg)$ is an element,which is a pure substance.
$(g)$ Brick is a mixture of various minerals and soil components.
$(h)$ Wood is a complex mixture of cellulose,lignin,and other organic compounds.
$(i)$ Air is a mixture of various gases like nitrogen,oxygen,argon,and carbon dioxide.
Therefore,the pure substances are $(a), (c), (e),$ and $(f)$.

(A) solution is a homogeneous mixture of two or more substances.
$(1)$ Sea water is a homogeneous mixture of water and various dissolved salts.
$(2)$ Air is a homogeneous mixture of various gases like nitrogen,oxygen,argon,carbon dioxide,etc.
$(3)$ Soda water is a homogeneous mixture of carbon dioxide gas dissolved in water.
Soil and coal are heterogeneous mixtures because their composition is not uniform throughout.
Therefore,the solutions are $(b)$ Sea water,$(c)$ Air,and $(e)$ Soda water.

(B, D) The 'Tyndall effect' is the scattering of light by particles in a colloid or a very fine suspension.
Among the given options,both milk and starch solution are colloids.
Therefore,they scatter a beam of light passing through them,exhibiting the 'Tyndall effect'.
Salt solution and copper sulphate solution are true solutions,which do not show the 'Tyndall effect'.

(N/A) Elements: These are pure substances consisting of only one type of atom. Examples: Sodium,silver,tin,and silicon.
Compounds: These are pure substances formed by the chemical combination of two or more elements in a fixed proportion. Examples: Calcium carbonate,methane,and carbon dioxide.
Mixtures: These are substances formed by the physical mixing of two or more components in any proportion. Examples: Soil,sugar solution,coal,air,soap,and blood.

(A, B, D, E, G) Chemical changes involve a change in the chemical composition of a substance,resulting in the formation of new substances.
$(a)$ Growth of a plant: Involves complex biochemical reactions.
$(b)$ Rusting of iron: Iron reacts with oxygen and moisture to form iron oxide.
$(d)$ Cooking of food: Involves chemical breakdown of nutrients.
$(e)$ Digestion of food: Enzymes break down complex molecules into simpler ones.
$(g)$ Burning of a candle: Combustion is a chemical reaction.
Mixing of iron filings and sand $(c)$ and freezing of water $(f)$ are physical changes because no new chemical substances are formed.