Mix Example - IS MATTER AROUND US PURE? Questions in English

(A) pure substance consists of particles of only one kind,which have the same chemical nature. Therefore,statement $(i)$ is true.
Pure substances are either elements or compounds,not mixtures. Therefore,statement $(ii)$ is false.
Pure substances have a fixed composition and properties throughout,meaning they are homogeneous. Therefore,statement $(iii)$ is true.
Elements like nickel are pure substances. Statement $(iv)$ claims that all elements except nickel are pure substances,which is incorrect because nickel is also a pure substance. Therefore,statement $(iv)$ is false.
Thus,statements $(i)$ and $(iii)$ are correct.

(B) Rusting of iron is a process where iron reacts with oxygen and moisture to form hydrated iron$(III)$ oxide.
This process is known as corrosion.
Since a new substance is formed and the process is irreversible,it is classified as a chemical change.

(C) solution is a homogeneous mixture and does not show the Tyndall effect.
Colloids and suspensions are heterogeneous mixtures and exhibit the Tyndall effect.
The mixture of sulphur and carbon disulphide forms a true solution,as sulphur dissolves completely in carbon disulphide.

(D) Tincture of iodine is a well-known antiseptic solution.
It is prepared by dissolving a small amount of iodine $(I_2)$ in a mixture of alcohol and water.
Therefore,the correct composition is iodine dissolved in alcohol.

(A) homogeneous mixture is one that has a uniform composition throughout its mass.
$(i)$ Ice is a pure substance ($H_2O$ in solid state),which is homogeneous.
$(ii)$ Wood is a complex,heterogeneous mixture of cellulose,lignin,and other organic compounds.
$(iii)$ Soil is a heterogeneous mixture containing various particles,minerals,and organic matter.
$(iv)$ Air is a homogeneous mixture of various gases like nitrogen,oxygen,argon,and carbon dioxide.
Therefore,$(i)$ and $(iv)$ are homogeneous in nature.

(B) physical change is a change in which no new substance is formed and the chemical composition of the substance remains the same.
$(i)$ Melting of iron metal is a physical change because it only involves a change in the state of matter.
$(ii)$ Rusting of iron is a chemical change because iron reacts with oxygen and moisture to form iron oxide,which is a new substance.
$(iii)$ Bending of an iron rod is a physical change because it only involves a change in the shape of the metal.
$(iv)$ Drawing a wire of iron metal is a physical change because it involves a change in the shape/form of the metal without changing its chemical identity.
Therefore,$(i), (iii),$ and $(iv)$ are physical changes.

(C) chemical change is a process where one or more substances are altered into one or more new and different substances.
$(i)$ Decaying of wood: This is a chemical change because microorganisms break down the wood into new substances.
$(ii)$ Burning of wood: This is a chemical change because wood reacts with oxygen to form carbon dioxide,water vapor,and ash,which are new substances.
$(iii)$ Sawing of wood: This is a physical change because only the shape and size of the wood change,not its chemical composition.
$(iv)$ Hammering of a nail into a piece of wood: This is a physical change as it involves a mechanical action without altering the chemical identity of the wood or the nail.
Therefore,$(i)$ and $(ii)$ are chemical changes.

(B) The reaction $2A + B \to A_2B$ represents the formation of a chemical compound.
$(i)$ Incorrect: $A$ chemical compound $(A_2B)$ has properties entirely different from the constituent elements ($A$ and $B$).
$(ii)$ Correct: $A$ compound always has a fixed composition by mass.
$(iii)$ Incorrect: Since $A_2B$ is formed by the chemical combination of two substances in a fixed ratio,it is classified as a compound.
$(iv)$ Incorrect: $A_2B$ is a compound,not an element,as it consists of two different types of atoms chemically bonded together.
Therefore,statements $(i), (iii),$ and $(iv)$ are incorrect.

(A) $1$. According to the definition of elements,they are substances that cannot be broken down into simpler substances by simple chemical reactions. Since $X$ and $Y$ cannot be broken down,they are elements.
$2$. When two or more elements combine chemically in a fixed proportion,they form a compound. Here,$X$ and $Y$ combine to form $P$,so $P$ is a compound.
$3$. Compounds always have a fixed composition by mass.
$4$. Therefore,statements $(i)$,$(iii)$,and $(iv)$ are correct.

(N/A) Separation by using a separating funnel,as they are immiscible liquids with different densities.
$(b)$ Sublimation,as ammonium chloride sublimes upon heating while potassium chloride does not.
$(c)$ Filtration to remove sand,followed by evaporation to separate common salt from water.
$(d)$ Separation by using a separating funnel to remove kerosene oil,followed by evaporation or distillation to separate salt from water.

(A) The tube $(a)$ will be more effective as a condenser.
The presence of marbles increases the surface area available for cooling.
This allows more time for the vapours to condense,and hence it would be more effective than the column without marbles.

(B) Crystallization is a process that separates a pure solid in the form of its crystals from a saturated solution. It is a better technique than evaporation because evaporation can cause decomposition of some solids or contamination due to impurities,whereas crystallization provides a purer form of the substance.

(N/A) Homogeneous mixture: When we consider sea-water as a solution of various salts dissolved in water,it appears uniform throughout,making it a homogeneous mixture.
Heterogeneous mixture: In its natural state,sea-water contains not only dissolved salts but also suspended particles like mud,sand,decayed plant matter,and microorganisms. Because these components are not uniformly distributed and can be physically separated,it is classified as a heterogeneous mixture.

(DISTILLATION) Acetone can be separated from the mixture using the technique of distillation.
Distillation is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.
Since the boiling point of acetone $(56\,^oC)$ is significantly lower than that of water $(100\,^oC)$,acetone will vaporize first upon heating.
The vapors can then be passed through a condenser to be collected as a liquid,effectively separating it from the salt-water solution.

(N/A) As the solubility of potassium chloride decreases with a decrease in temperature,solid potassium chloride crystals will separate out from the solution.
$(b)$ Initially,the water will evaporate,leaving behind sugar. Upon further heating,the sugar will undergo thermal decomposition and get charred (turn black).
$(c)$ Iron and sulphur react chemically to form a new compound,iron$(II)$ sulphide $(FeS)$,which is a black solid.

(N/A) The particles in a colloidal solution are very small (ranging from $1 \ nm$ to $1000 \ nm$) and remain in a state of continuous random motion known as Brownian motion. This motion,along with the electrostatic repulsion between charged colloidal particles,prevents them from settling down due to gravity. In contrast,particles in a suspension are much larger (greater than $1000 \ nm$). Because of their larger size,gravity acts more effectively on them,and the intermolecular forces are not sufficient to keep them suspended,causing them to settle down when left undisturbed.

(B) Both fog and smoke are types of aerosols where the dispersion medium is a gas.
In fog,the dispersed phase is liquid (tiny water droplets suspended in air).
In smoke,the dispersed phase is solid (fine carbon or soot particles suspended in air).

(N/A) Physical properties: $(a)$ and $(c)$. These describe the inherent characteristics or composition of the substance without changing its chemical identity.
Chemical properties: $(b)$ and $(d)$. These describe the ability of a substance to undergo a specific chemical change or reaction,resulting in the formation of new substances.

(C) Student $C$ has made the desired solution.
The formula for mass by volume percentage is:
$\text{Mass by volume } \% = \frac{\text{Mass of solute (g)}}{\text{Volume of solution (mL)}} \times 100$
For student $C$:
$\text{Mass by volume } \% = \frac{50\,g}{100\,mL} \times 100 = 50\%$
Students $A$ and $B$ did not make the correct solution because they added $50\,g$ of $NaOH$ to $100\,mL$ or $100\,g$ of solvent,which results in a total solution volume greater than $100\,mL$.

(N/A) Sublimation: Dry ice ($CO_2$ in solid state) directly converts into gas at room temperature.
$(b)$ Diffusion: The intermixing of particles of ink with water particles.
$(c)$ Dissolution/Diffusion: The solute (potassium permanganate) dissolves and spreads throughout the solvent.
$(d)$ Evaporation: Acetone has a low boiling point and turns into vapor at room temperature.
$(e)$ Centrifugation: The process of separating denser particles from lighter particles by spinning.
$(f)$ Sedimentation: The process where heavier insoluble particles settle down at the bottom due to gravity.
$(g)$ Scattering of light (Tyndall effect): The phenomenon where light is scattered by colloidal particles.

(B) Sample $B$ will not freeze at $0\,^{\circ}C$ because it is not pure water.
At $1 \text{ atm}$ pressure,the boiling point of pure water is $100\,^{\circ}C$ and its freezing point is $0\,^{\circ}C$.
Since sample $B$ boils at $102\,^{\circ}C$,it indicates the presence of impurities (solutes) dissolved in the water.
The presence of impurities leads to the phenomenon of freezing point depression,meaning the freezing point of the solution will be lower than $0\,^{\circ}C$.

(B) Pure gold ($24$ carat) is extremely soft and ductile,making it unsuitable for making jewelry as it would easily deform. By alloying gold with small amounts of copper or silver,the metal gains significant hardness and structural strength. This allows the ornaments to maintain their shape and durability over time.

(N/A) The element is classified as a $Metal$.
Metals are elements that typically exhibit properties such as being sonorous (producing a ringing sound when struck) and ductile (can be drawn into thin wires).
Other characteristics expected to be possessed by this element include:
$1$. Lustre: They have a shiny appearance.
$2$. Malleability: They can be beaten into thin sheets.
$3$. Conductivity: They are good conductors of heat and electricity.
$4$. High melting and boiling points.

(A-D) Example: Salt and water. Method: Evaporation or distillation.
$(b)$ Example: Acetone and water. Method: Distillation.
$(c)$ Example: Oil and water. Method: Separation by using a separating funnel.
$(d)$ Example: Ammonium chloride and salt. Method: Sublimation.
$(e)$ Example: Components of ink. Method: Chromatography.

(N/A) colloid is a heterogeneous mixture and its components can be separated by the technique known as centrifugation.
$(b)$ Ice,water,and water vapour look different and display different physical properties but they are chemically the same.
$(c)$ The upper layer in the separating funnel will be of water and the lower layer will be that of chloroform (hint: density of water is less than that of chloroform).
$(d)$ $A$ mixture of two or more miscible liquids,for which the difference in the boiling points is less than $25 \, K$,can be separated by the process called fractional distillation.
$(e)$ When light is passed through water containing a few drops of milk,it shows a bluish tinge. This is due to the scattering of light by milk and the phenomenon is called Tyndall effect. This indicates that milk is a colloidal solution.

(A) It is a pure substance.
Even though the sucrose crystals are obtained from different sources (sugarcane and beetroot),their chemical composition is identical.
$A$ pure substance consists of particles of only one type of substance.
Since the chemical formula for sucrose is $C_{12}H_{22}O_{11}$ regardless of its origin,the mixture of these crystals remains a pure substance.

(D) The Tyndall effect is the scattering of light by particles in a colloid or a very fine suspension.
$(a)$ When a beam of light enters a dark room through a small hole,the dust particles present in the air scatter the light,making the path of the beam visible.
$(b)$ In a dense forest,the canopy of trees allows small beams of sunlight to pass through,which get scattered by tiny water droplets or mist particles in the air,creating a visible light path.
$(c)$ Similarly,light passing through fog or mist is scattered by water droplets,demonstrating the Tyndall effect.

(N/A) No,we cannot separate alcohol dissolved in water using a separating funnel.
This is because alcohol and water are miscible liquids,meaning they mix completely to form a single homogeneous phase.
$A$ separating funnel is only used to separate immiscible liquids (liquids that do not mix and form distinct layers,such as oil and water).
Since alcohol and water form a homogeneous mixture,they must be separated using other methods like fractional distillation,which relies on the difference in their boiling points.

(N/A) This is a chemical change because a new substance is formed and the process is irreversible under normal conditions.
$(b)$ Yes,acidic and basic solutions can be prepared by dissolving the products in water:
$1.$ Basic solution: Calcium oxide $(CaO)$ reacts with water to form calcium hydroxide $(Ca(OH)_2)$,which is basic in nature.
$CaO + H_2O \rightarrow Ca(OH)_2$
$2.$ Acidic solution: Carbon dioxide $(CO_2)$ reacts with water to form carbonic acid $(H_2CO_3)$,which is acidic in nature.
$CO_2 + H_2O \rightarrow H_2CO_3$

(N/A) Iodine is a lustrous non-metal.
$(b)$ Bromine is the only non-metal that exists as a liquid at room temperature.
$(c)$ Graphite is an allotrope of carbon and is a good conductor of electricity due to the presence of free electrons.
$(d)$ Carbon is known to form the largest number of compounds due to its unique property of catenation.
$(e)$ Sulphur and phosphorus are non-metals other than carbon that exhibit allotropy.
$(f)$ Oxygen is a non-metal essential for the process of combustion.

(N/A) Based on the chemical composition,the substances are classified as follows:
Elements: These are pure substances consisting of only one type of atom. From the figure,the elements are: $Cu$ (Copper),$Zn$ (Zinc),$O_2$ (Oxygen),$F_2$ (Fluorine),$Hg$ (Mercury),and Diamond (an allotrope of Carbon).
Compounds: These are substances formed by the chemical combination of two or more elements in a fixed proportion. From the figure,the compounds are: $H_2O$ (Water) and $CaCO_3$ (Calcium carbonate).
Note: Substances like Sand,$NaCl(aq)$,and Wood are mixtures,not pure elements or compounds.

(A, C, E, F, G, I) compound is a substance formed when two or more chemical elements are chemically bonded together. Elements are pure substances consisting of only one type of atom.
$1$. Chlorine gas $(Cl_2)$ is an element.
$2$. Potassium chloride $(KCl)$ is a compound.
$3$. Iron $(Fe)$ is an element.
$4$. Iron sulphide $(FeS)$ is a compound.
$5$. Aluminium $(Al)$ is an element.
$6$. Iodine $(I_2)$ is an element.
$7$. Carbon $(C)$ is an element.
$8$. Carbon monoxide $(CO)$ is a compound.
$9$. Sulphur powder $(S)$ is an element.
Therefore,the substances that are not compounds are: Chlorine gas,Iron,Aluminium,Iodine,Carbon,and Sulphur powder.

(N/A) The key component that makes fractional distillation efficient is the fractionating column. This column is typically packed with glass beads or other inert materials.
$1$. The glass beads provide a large surface area for the vapours to collide,lose energy,and undergo repeated condensation and evaporation cycles as they rise through the column.
$2$. This process ensures that the component with the higher boiling point condenses more easily and returns to the flask,while the component with the lower boiling point reaches the top of the column as a vapour.
$3$. The length of the column further increases the efficiency of this separation process,allowing for the effective separation of liquids with small boiling point differences.
(Refer to the provided diagram for the setup of the fractional distillation apparatus.)

(N/A) Alloys are classified as homogeneous mixtures because they have a uniform composition throughout their entire mass.
$(b)$ No,this statement is incorrect. Solutions can exist in different states of matter,including solid solutions (e.g.,brass,which is an alloy of copper and zinc) and gaseous solutions (e.g.,air,which is a mixture of various gases).
$(c)$ No,by definition,a solution is a homogeneous mixture of two or more substances. If a mixture is heterogeneous,it is not classified as a solution.

(N/A) When part $A$ is heated,iron and sulphur react to form iron sulphide $(FeS)$:
$Fe + S \rightarrow FeS$
When dilute hydrochloric acid $(HCl)$ is added to the iron sulphide $(FeS)$,hydrogen sulphide $(H_2S)$ gas is evolved:
$FeS + 2HCl \rightarrow FeCl_2 + H_2S$
Hydrogen sulphide gas has a characteristic foul smell,similar to that of rotten eggs.
When dilute hydrochloric acid is added to the unheated mixture of iron and sulphur (part $B$),iron reacts with the acid to release hydrogen $(H_2)$ gas,while sulphur remains unreacted:
$Fe + S + 2HCl \rightarrow FeCl_2 + H_2 + S$
Hydrogen gas is identified by bringing a burning matchstick near it,which causes the gas to burn with a characteristic 'pop' sound.

(N/A) $(i)$ If the ink contains three different coloured components,we would expect to see three different coloured bands on the filter paper at different heights,as each component travels at a different speed depending on its solubility in the solvent.
$(ii)$ The technique used is Chromatography.
$(iii)$ One more application of this technique is to separate pigments present in natural colours (e.g.,chlorophyll) or to separate drugs from blood.

(N/A) Milk is a colloid. Colloidal particles are large enough to scatter a beam of light passing through them,which makes the path of light visible. This phenomenon is known as the Tyndall effect.
$(b)$ $A$ salt solution is a true solution. The particles in a true solution are extremely small (less than $1 \ nm$ in diameter) and are unable to scatter the beam of light passing through them. Therefore,the path of light is not visible in a salt solution.
$(c)$ Two other examples of colloidal solutions that show the Tyndall effect are starch solution and soap solution.

(A) Physical changes: $(a), (b), (e)$. These are physical changes because no new substance is formed,and the chemical composition remains the same.
Chemical changes: $(c), (d)$. These are chemical changes because new substances are formed with different chemical properties. Burning of kerosene involves a combustion reaction,and adding lemon juice to tea causes a chemical reaction between the acid in the lemon and the pigments in the tea.

$(a)$ No, the two solutions do not have the same concentration.
$(b)$ The formula for mass percentage is:
$\text{Mass } \% = \frac{\text{Mass of solute}}{\text{Mass of solute} + \text{Mass of solvent}} \times 100$
For Ramesh's solution:
$\text{Mass of solute} = 10\,g$, $\text{Mass of solvent} = 100\,g$
$\text{Mass } \% = \left( \frac{10}{10 + 100} \right) \times 100 = \frac{10}{110} \times 100 \approx 9.09\%$
For Sarika's solution:
$\text{Mass of solute} = 10\,g$, $\text{Total mass of solution} = 100\,g$
$\text{Mass } \% = \left( \frac{10}{100} \right) \times 100 = 10\%$
Conclusion: The solution prepared by Sarika $(10\%)$ has a higher mass percentage than the solution prepared by Ramesh $(\approx 9.09\%)$.

(N/A) The components of the given mixture can be separated by the following methods:
$(i)$ $Using$ $a$ $magnet$: Hovering a magnet over the mixture will result in iron filings getting stuck to the magnet. Thus, iron will be separated.
$(ii)$ $Sublimation$: The remaining mixture is heated in a china dish. Ammonium chloride is a sublime substance and hence it will evaporate without undergoing the liquid phase. The crust of ammonium chloride can be collected by placing an inverted funnel on top of the china dish.
$(iii)$ $Sedimentation,$ $decantation,$ $and$ $filtration$: The remaining mixture is dissolved in water. The mixture is allowed to settle for some time. Sand, being insoluble in water, settles at the bottom. The liquid is decanted into another beaker. Then, the liquid is filtered to remove any trace of sand in it.
$(iv)$ $Evaporation$: The liquid is now a solution of sodium chloride in water. This is heated in a beaker so that the water evaporates. Once all the water evaporates, we get sodium chloride in the beaker.

(A) The mass percentage of a solution is calculated using the formula:
$\text{Mass } \% = \frac{\text{mass of solute}}{\text{mass of solute} + \text{mass of solvent}} \times 100$
Given that the concentration is $0.01\%$ by mass,we test option $(a)$:
$\text{Mass } \% = \frac{0.01 \, g}{0.01 \, g + 99.99 \, g} \times 100$
$= \frac{0.01}{100} \times 100 = 0.01\%$
Thus,option $(a)$ correctly represents the composition of the solution.

(B) Let the mass of sodium sulphate required be $x\,g$.
The mass of the solution is the sum of the mass of the solute and the mass of the solvent (water).
Mass of solution $= (x + 100)\,g$.
The formula for mass percentage is: $\text{Mass percentage} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100$.
Given that the mass percentage is $20\%$,we have:
$20 = \frac{x}{x + 100} \times 100$.
Dividing both sides by $20$:
$1 = \frac{x}{x + 100} \times 5$.
$x + 100 = 5x$.
$4x = 100$.
$x = 25\,g$.
Therefore,the mass of sodium sulphate required is $25\,g$.

(B) In a true solution,the size of the solute particles is extremely small (less than $1 \ nm$ in diameter).
Because of their tiny size,these particles are unable to scatter the beam of light passing through the solution.
Therefore,the path of the light beam remains invisible,and the Tyndall effect is not observed.

(N/A) The principle involved in separating a mixture of kerosene and water is based on the difference in the densities of the two liquids. Kerosene and water are immiscible liquids,meaning they do not mix with each other. When left undisturbed,they form separate layers. Since water is denser than kerosene,it settles at the bottom,while kerosene,being lighter,forms the upper layer. This mixture can be separated using a separating funnel.

(CENTRIFUGATION) The components of a colloidal solution cannot be separated by ordinary filtration. However,they can be separated by a process known as $Centrifugation$. In this process,the colloidal solution is spun at a very high speed,causing the dispersed phase particles to settle down at the bottom due to their density,allowing the separation of the components.

(N/A) solution is a homogeneous mixture of two or more substances. The two main components of a solution are:
$(i)$ Solute: The component that is present in a smaller quantity and is dissolved in the solvent.
$(ii)$ Solvent: The component that is present in a larger quantity and in which the solute is dissolved.

(N/A) The concentration of a solution is defined as the amount of solute present in a given amount (mass or volume) of the solution or solvent.
It represents the relative proportion of solute and solvent in the mixture.
Mathematically, it can be expressed as: $\text{Concentration} = \frac{\text{Amount of solute}}{\text{Amount of solution}}$.

(B) solution is classified as dilute,concentrated,or saturated based on the amount of solute dissolved in a given amount of solvent or solution.
$1$. $A$ dilute solution contains a relatively small amount of solute.
$2$. $A$ concentrated solution contains a relatively large amount of solute.
$3$. $A$ saturated solution is one in which no more solute can be dissolved at a given temperature.

(N/A) pure substance consists of only one type of particles (atoms or molecules) with uniform chemical properties. In contrast,an impure substance,also known as a mixture,consists of two or more different types of particles or molecules mixed together in any proportion.

(N/A) The Tyndall effect is the scattering of light by particles in a colloid or a very fine suspension. In a dense forest, the air contains mist, which consists of tiny water droplets suspended in the air. These water droplets act as colloidal particles. When sunlight enters the forest through the canopy, these tiny droplets scatter the light, making the path of the light beam visible. This phenomenon is known as the Tyndall effect.