Matter Around Us (IX-NCERT)

Is matter around us pure solved question answer[NCERT SOLUTION]

Q.1: Which separation techniques will apply for the separation of the following?

(a) Sodium chloride from its solution in water.

(b) Ammonium Chloride from a mixture containing Sodium Chloride and Ammonium Chloride.

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

(d) Different pigments from an extract of flower petals.

(e) Butter from curd.

(f) Oil from water.

(g) Tea leaves from tea.

(h) Iron pins from sand.

(i) Wheat grains from husk.

(j) Fine mud particles suspended in water.

Ans: (a) Crystallization or Evaporation. 

(b) Sublimation. 
(c) Centrifugation or Sedimentation. 
(d) Chromatography. 
(e) Centrifugation. 
(f) Separating funnel. 
(g) Hand-picking. 
(h) Magnetic separation. 
(i) Winnowing. 
(j) Centrifugation.

Q.2: Write the steps you would use for making tea. Use the words - solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Ans: Take the solvent, water, in a kettle. Heat it. When the solvent boils, add the solute, milk. Milk and water forms a solution. Then pour some tea leaves over a sieve. Pour slowly hot solution of milk over tea leaves. Colour of tea leaves goes into solution as filtrate. The remaining tea leaves being insoluble remains as residue. Add requisite sugar which dissolves and the tea is ready.

Q.3: Explain the following giving examples:

(a) Saturated solution, (b) Pure substance, (c) Colloid, (e) Suspension.

Ans: (a) Saturated Solution - a solution in which no more of the solid (solute) can be dissolved at a given temperature is called a saturated solution. Suppose 50 gm of a solute is the maximum amount that can be dissolved in 100 gm water at 298 K. Then 150 gm of solution so obtained is the saturated solution at 298 K.

(b) Pure Substance - A pure substance consists of a single of matter or particles and can not be separated into other kind of matter by any physical process. Pure substances always have the same colour, taste and texture at a given temperature and pressure. For example, pure water is always colourless, odorless and tasteless and boils at 373 K at normal atmospheric pressure.

(c) Colloid - Colloids are heterogeneous mixtures the particle size is too small to be seen with a naked eye, but it is big enough to scatter light. The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium. Colloids are useful in industry and daily life.

A colloid has the following characteristics:

(1) It is a heterogeneous mixture.

(2) The size of particles of a colloid lies between 1 - 100 nm and can not be seen by naked eyes.

(3) The particles of colloid can scatter a beam of light passing through it and make the path visible.

(4) The particles of colloid can not be separated from the mixture by filtration. The process of separation of colloidal particles is known as ‘centrifugation’.

(5) They do not settle down when left undisturbed. In other words colloids are quite stable e.g. smoke, milk, fog, cloud etc.

(d) Suspension – A ‘suspension’ is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.

A suspension has the following characteristics:

(1) It is a heterogeneous mixture.

(2) The size of particles of a suspension is greater than 100 nm and is visible to naked eyes.

(3) The particles of suspension can scatter a beam of light passing through it.

(4) The particles of a suspension settle down when left undisturbed.

(5) The particles of a suspension can be separated from its mixture by filtration.  

Q.4: Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air, soil, vinegar, filtrated tea.  

Ans: Homogeneous mixture - soda water, air, vinegar, filtered tea.

         Heterogeneous mixture - wood, soil.

Q.5: How would you confirm that a colourless liquid given to you is pure water?

Ans: Every liquid has a characteristic boiling point at 1 atmospheric pressure. If the given colourless liquid boils exactly at 373 K at 1 atmospheric pressure, then it is pure water. If the boiling point is different then the water is contaminated.

Q.6: Which of the following materials fall in the category of a ‘pure substance’?

(a) Ice (b) Milk (c) Iron (d) Hydrochloric acid (e) Calcium oxide (f) Mercury (g) Brick (h) Wood (i) Air.  

Ans: (a), (c), (d), (e) and (f) are pure substances.

Q.7: Which of the following will show “Tyndall effect”?

(a) salt solution (b) milk (c) copper sulphate solution (d) starch solution.  

Ans: (b) and (d) are colloids and will show Tyndall Effect.

Q.8: Classify the following into elements, compounds and mixtures.

(a) sodium (b) soil (c) sugar solution (d) silver (e) calcium carbonate (f) tin (g) silicon (h) coal (i) air (j) soap (k) methane (l) carbon dioxide (m) blood

Ans:  Elements - sodium, silver, tin, silicon.

        Compounds - calcium carbonate, methane, carbon dioxide.

        Mixtures - soil, sugar solution, coal, air, soap, blood.

Q. 9. In the formation of sodium chloride from its constituent elements, do the properties of its elements change. Explain.

 Ans:  Sodium is a very reactive metal that reacts exothermically with water. If we were to ingest a pinch of sodium, it would burn our intestines. Chlorine is a greenish yellow gas with a characteristic irritating odour and pungent taste. When sodium and chlorine combine to form sodium chloride, the properties of the elements are totally changed. Sodium chloride is a white substance totally safe to be ingested and is used to add flavour to our food.

Q. 10. Briefly describe how to separate, i) Sulphur from a mixture of sulphur and sand. ii) Black CuO from a mixture of CuO and ZnO.
 Answer:  i) Add a solvent to the mixture of sulphur and sand. Sulphur dissolves in carbon disulphide while sand does not. When filtered, the residue is sand. The filtrate is kept open, carbon disulphide evaporates and the sulphur crystals form. 

ii) Add a solvent to the mixture of CuO and ZnO that dissolves only one component e.g. sodium hydroxide. When sodium hydroxide is added to the mixture, ZnO dissolves. Filter to obtain the residue of CuO.


NOTESDefinitions

Humidity:

The term Humidity is usually taken in daily language to refer to relative humidity. Relative humidity is defined as the amount of water vapor in a sample of air compared to the maximum amount of water vapor the air can hold at any specific temperature. Humidity may also be expressed as Absolute humidity and specific humidity. Relative humidity is an important metric used in forecasting weather. Humidity indicates the likelihood of precipitation, dew, or fog. High humidity makes people feel hotter outside in the summer because it reduces the effectiveness of sweating to cool the body by preventing the evaporation of perspiration from the skin. This effect is calculated in a heat index table. Warm water vapor has more thermal energy than cool water vapor and therefore more of it evaporates into warm air than into cold air.

 Mixture:

A mixture is a substance made by combining two or more different materials with no chemical reaction occurring. The objects do not bond together in a mixture. A mixture can usually be separated back into its original components. Some examples of mixtures are: fruit salad, ocean water and soil. Mixtures are the product of a mechanical blending or mixing of chemical substances like elements and compounds, without chemical bonding or other chemical change, so that each ingredient substance retains its own chemical properties and makeup. 

Solution:

a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. A common example is a solid, such as salt or sugar, dissolved in water, a liquid. Gases may dissolve in liquids, for example, carbon dioxide or oxygen in water. Liquids may dissolve in other liquids. Gases can combine with other gases to form mixtures, rather than solutions.

Solvent:

solvent is a liquid that dissolves a solid, liquid, or gaseous solute, resulting in a solution. The most common solvent in everyday life is water. Most other commonly-used solvents are organic (carbon-containing) chemicals. These are called organic solvents. Solvents usually have a low boiling point and evaporate easily or can be removed by distillation, leaving the dissolved substance behind. Solvents should therefore not react chemically with the dissolved compounds — they must be inert. Solvents can also be used to extract soluble compounds from a mixture, the most common example is the brewing of coffee or tea with hot water. Solvents are usually clear and colorless liquids and many have a characteristic odor. The concentration of a solution is the amount of compound that is dissolved in a certain volume of solvent. The solubility is the maximal amount of compound that is soluble in a certain volume of solvent at a specified temperature.

Homogeneous mixture:

Homogeneous mixtures are mixtures that have definite, consistent composition and properties. Particles are uniformly spread. For example, any amount of a given mixture has the same composition and properties. Examples are solutions and some alloys (but not all). A homogeneous mixture is a uniform mixture consisting of only one phase. Examples are gasoline and margarine.

 Heterogeneous mixture:

Heterogeneous mixtures are mixtures with inconsistent, non-uniform composition. The parts of a heterogeneous composition can be mechanically separated from each other. Examples include salad, trail mix and granite.

Colloid:

A colloid or colloidal dispersion is a type of homogenous mixture. A colloid consists of two separate phases: a dispersed phase and a continuous phase. In a colloid, the dispersed phase is made of tiny particles or droplets that are distributed evenly throughout the continuous phase. The size of the dispersed-phase particles are between 1 nm and 100 nm in at least one dimension. Homogeneous mixtures with a dispersed phase in this size range may be called colloidal aerosols, colloidal emulsions, colloidal foams, colloidal dispersions, or hydrosols. The dispersed-phase particles or droplets are largely affected by the surface chemistry present in the colloid.

Filtration:

Filtration is a mechanical/physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a medium to fluid flow through which the fluid can pass, but the solids (or at least part of the solids) in the fluid are retained. It has to be emphasized that the separation is NOT complete, and it will depend on the pore size and the thickness of the medium as well as the mechanisms that occur during filtration.

Concentration:

concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in a substance.

 Saturated solution:

in physical chemistry, saturation is the point at which a solution of a substance can dissolve no more of that substance and additional amounts of that substance will appear as a precipitate. This point of maximum concentration, the saturation point, depends on the temperature of the liquid as well as the chemical nature of the substances involved. This can be used in the process of recrystallisation to purify a chemical: it is dissolved to the point of saturation in hot solvent, then as the solvent cools and the solubility decreases, excess solute precipitates. Impurities, being present in much lower concentration, do not saturate the solvent and so remain dissolved in the liquid. If a change in conditions (e.g. cooling) means that the concentration is actually higher than the saturation point, the solution has become supersaturated.

Solubility:

Solubility is a physical property referring to the ability for a given substance, the solute, to dissolve in a solvent. It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium. The resulting solution is called a saturated solution. Certain liquids are soluble in all proportions with a given solvent, such as ethanol in water. This property is known as miscibility. Also, the equilibrium solubility can be exceeded under various conditions to give a so-called supersaturated solution, which is metastable.

Tyndall effect:

The Tyndall effect is the effect of light scattering on particles in colloid systems, such as suspensions or emulsions. It is named after the 19th century UK scientist John Tyndall. The Tyndall effect is used to tell the difference between the different types of mixtures, namely solution, colloid, and suspension. For example, the Tyndall effect is noticeable when car headlamps are used in fog. The light with shorter wavelengths scatters better, thus the color of scattered light has a bluish tint. This is also the reason why the sky looks blue when viewed away from the sun: the blue light from the sun is scattered to a greater degree and is therefore visible far from its source.

Emulsion:

An emulsion is a mixture of two immiscible (unblendable) substances. One substance (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include butter and margarine, milk and cream, espresso, mayonnaise, the photo-sensitive side of photographic film, and cutting fluid for metal working. In butter and margarine, a continuous liquid phase surrounds droplets of water (a water-in-oil emulsion). In milk and cream, oil is dispersed within a continuous water phase (an oil-in-water emulsion). Emulsification is the process by which emulsions are prepared.

Centrifugation:

Centrifugation is a process that involves the use of the centripetal force for the separation of mixtures, used in industry and in laboratory settings. In chemistry and biology, increasing the effective gravitational force on a test tube so as to more rapidly and completely cause the precipitate ("pellet") to gather on the bottom of the tube. The remaining solution is properly called the "supernate" or "supernatant liquid". Since "supernatant" is an adjective, its usage alone is technically incorrect, although many examples can be found in scientific literature. The supernatant liquid is then either quickly decanted from the tube without disturbing the precipitate, or withdrawn with a Pasteur pipette. The rate of centrifugation is specified by the acceleration applied to the sample, typically measured in revolutions per minute (RPM) or g. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity.

Miscible liquid:

Miscibility is a term in chemistry that refers to the property of liquids to mix in all proportions, forming a homogeneous solution. In principle, the term applies also to other phases (solids and gases), but the main focus is on the solubility of one liquid in another. For example, water and ethanol are miscible in all proportions.

Sublimation:

Sublimation of an element or compound is a transition from the solid to gas phase with no intermediate liquid stage. Sublimation is a phase transition that occurs at temperatures and pressures below the triple point

Chromatography:

chromatography is the collective term for a family of laboratory techniques for the separation of mixtures. It involves passing a mixture dissolved in a "mobile phase" through a stationary phase, which separates the analyte to be measured from other molecules in the mixture and allows it to be isolated.

Distillation:

Distillation is a method of separating chemical substances based on differences in their volatilities in a boiling liquid mixture. Distillation usually forms part of a larger chemical process, and is thus referred to as a unit operation.

Decomposition:

Decomposition, biological process through which organic material is reduced
Boiling point:

the boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid. A liquid in a vacuum environment has a lower boiling point than when the liquid is at atmospheric pressure. And a liquid in a high pressure environment has a higher boiling point than when the liquid is at atmospheric pressure. In other words, all liquids have an infinite number of boiling points.

Condensation:

Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid. Condensation commonly occurs when a vapor is cooled to a liquid, but can also occur if a vapor is compressed (i.e., pressure on it increased) into a liquid, or undergoes a combination of cooling and compression. Liquid which has been condensed from a vapor is called condensate. A device or unit used to condense vapors into liquid is called a condenser. Condensers are used in heat exchanges which have various designs, and come in many sizes ranging from rather small (hand-held) to very large.

Fractional distillation:

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation. Generally the component parts boil at less than 25°C from each other under a pressure of one atmosphere (ATM). If the difference in boiling points is greater than 25°C, a simple distillation is used.

Crystallisation:

Crystallization is the (natural or artificial) process of formation of solid crystals from a uniform solution. Crystallization is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.

Inflammability:

Inflammation is the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. It is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue. Inflammation is not a synonym for infection. Even in cases where inflammation is caused by infection it is incorrect to use the terms as synonyms: infection is caused by an exogenous pathogen, while inflammation is the response of the organism to the pathogen.

Compound:
Compound (chemistry), a combination of two or more elements
Ductile:

Ductility is a mechanical property which describes how much plastic deformation a material can sustain before fracture occurs. Examples of highly ductile metals are gold, copper, and aluminum. The ductility of steels varies depending on the alloying constituents. Increasing levels of carbon decreases ductility, i.e., the steel becomes more brittle.

Combustion:
Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames.
Residue: In general chemistry, a residue is what is left behind by a reaction