Explore topic-wise InterviewSolutions in .

This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

5151.

(i) What is a catalyst ? Write the chemical equation to represent the hydrogenation of ethene. (ii) Which of the following compounds belong to the same homologous series ? C_(2)H_(6), C_(2)H_(6)O_(2), C_(2)H_(6)O, C_(4)H_(10).

Answer»

Solution :(i) Catalyst is a substance that cause a reaction to occur or PROCEED at a DIFFERENT rate without being affected itself.
`CH_(2)=CH_(2)overset"Nickel catalyst"underset(H_(2))rightarrowCH_(3)-CH_(3)`
`C_(2)H_(6)and C_(4)H_(10).`
Discussion
5152.

(i) What happens when silver nitrate solution is added to sodium chloride solution? Write the equation for the reaction which takes place. (ii) Name the type of reaction involved.

Answer»

SOLUTION :(i) When silver nitrate solution is ADDED to sodium CHLORIDE solution, a WHITE precipitate of silver chloride is formed along with sodium nitrate solution.
`AgNO_(3)(aq)+NaCl(aq)rarrunderset(("white ppt."))(AgCl(s))+NaNO_(3)(aq)`
(ii) This is double DISPLACEMENT reaction.
Discussion
5153.

(i) What is a functional group? (ii) State two properties of carbon which lead to huge number of carbon compounds we see around us.

Answer»

SOLUTION :(i) Functional group is an atom or a group of atoms in a carbon compound that GIVES the molecule its characteristic physical and CHEMICAL properties. It is the site of reactivity in an organic compound.
For example -
(i) Alcohol is - OH
(ii) Carboxylic acid is - COOH.
(ii) Two properties of carbon which lead to huge NUMBER of carbon compounds we see around us are -
(a) Catenation, (b) Tetravalency
Discussion
5154.

(i) What are metalloids? (ii) Name any four metalloids?

Answer»

Solution :(i) Borderline elements which are INTERMEDIATE in properties between metals and non-metals are CALLED METALLOIDS.
(II) Boron, silicon, germanium and arsenic.
Discussion
5155.

(i) Two solutions X and Y are tested with universal indicator. Solutions X turns orange whereas solution Y turns red. Which of the solutions is a stronger acid? (ii) State the meaning of strong acids and weak acids. Give one example of each.

Answer»

SOLUTION :(i) Solutions Y is a stronger ACID.
(ii) Strong acid: AN acid which dissociates completely in water and produces a LARGE amount of hydrogen ions are strong acids e.g HCL
Weak acid: An acid which dissociates PARTIALLY in water and produces small amount of hydrogen ions are weak acids e.g. `CH_3COOH`
Discussion
5156.

(i) State the law which is followed in balancing a chemical equation . (ii) Balance the following chemical equation: Fe+H_(2)Orarr Fe_(3)O_(4)+H_(2)

Answer»

Solution :(i) MASS can NEITHER be CREATED nor destroyed in a chemical reaction-Law of conservation of mass.
(II) `3Fe+4H_(2)Orarr Fe_(3)O_(4)+4H_(2)`
Discussion
5157.

(i) State the basis of classification of elements in the modern periodic table ? (ii) How does the metallic character of element vary as we go down the group.

Answer»

Solution :(i) Atomic number.
(II) Down the group, the EFFECTIVE nuclear charge experienced by the valence ELECTRON is decreasing because the outer most electrons are further away from the nucleus. Therefore, they can be lost EASILY. Hence metallic character increases down the group.
Discussion
5158.

(i) Solution of a substance 'X' is used for testing carbon dioxide . Write the equation of the reaction of 'X' with carbon dioxide. (ii) How is 'X' obtained? Write chemical equation.

Answer»

Solution :(i) SUBSTANCE X-Calcium HYDROXIDE.
`CA(OH)_(2)(aq)+CO_(2)(g)rarr UNDERSET (("White PPT."))(CaCO_(3)(S))+H_(2)O`
(ii) Calcium hydroxide is obatined by reaction ofcalcium oxide and water.
`CaO(s)+H_(2)O(l)rarr Ca(OH)_(2)(aq)+"Heat"`
Discussion
5159.

(i) Solid calcium oxide was taken in a container and water was added slowly to it : (a) Write the observation . (b) Write the chemical formula of the product formed (ii) What happens when carbon dioxide gas is bubbled through lime water : (a) In small amount , (b) In excess? (iii) Why do you apply paint on iron articles ?

Answer»

Solution :(i) (a) Calcium OXIDE a LARGE reacts vigorously with water and releases a large amount of heat .
(b) Calcium hydrooxide (Slaked lime ) i.e., `Ca(OH)_(2)` is formed .
(iii) (a) In small amount, solution becomes milky due to the formation of calcium carbonate .
`Ca(OH)_(2)+CO_(2)rarrCACO_(3)+H_(2)O`.

(b) In excess,milkiness disappears because calcium carbonate changes to calcium hydrogencarbonate which is colourless in nature.
`CaCO_(3)+H_(2)O+CO_(2)rarrunderset("Colourless") (Ca(HCO_(3))_(2))`
(iii) Paint forms a projective COATING on the surface of iron , so thatoxygen and moisture present in theair cannot have a direct contact with iron .
Discussion
5160.

(i) "Sodium is a highly reactive metal and it cannot be obtained from its oxide by heating with carbon". Give reason. (ii) How can sodium be obtained from sodium chloride ?

Answer»

Solution :(i) Metallic compounds like sodium cannot be reduced by carbon or any other REDUCING agent due to their high AFFINITY with OXYGEN.
(ii) Sodium is obtained from sodium chloride by ELECTROLYTIC reduction. Sodium chloride in molten form is electrolysed
Sodium is deposited at cathode and chlorine is liberated at anode
At cathode : `Na^(+) + e^(-) rarr Na`
At anode : `2Cl^(-) rarr Cl_(2) + 2e`
Discussion
5161.

{:("i. "NH_(3)","CH_(4),"(a) Polyatomic molecule"),("ii. "O_(2)","N_(2),"(b) Monoatomic molecule"),("iii. He, Ne","(c) Heteroatomic molecule"),("iv. Sulphur","(d) Diatomic molecule"):}

Answer»

SOLUTION :`i-c,ii-d,iii-b,iv-a`
Discussion
5162.

i) Name the property of ethanol which makes it useful in medicines, ii) Name the organic compound which is used in pickles. Mention its composition. iii) Mention any two uses of alcohol in medicine.

Answer»

Solution :i] Ethanol is USED as a very good SOLVENT in making medicines.
ii] Vinegar is WIDELY used as a preservative in pickles. It is 5.8% solution of ethanoic acid in water.
III) Alcohol is used in TINCTURE of iodine and in cough syrups.
Discussion
5163.

(i) Name the products formed when sodium hydrogencarbonate is heated. (ii) Write the chemical equation for the reaction involved in it.

Answer»

Solution :(i) On heating sodium hydrogencarbonate `(NaHCO_3)` , it decomposes to form sodium CARBONATE `(NaHCO_3)`, WATER `(H_(2)O)` and carbon dioxide `(CO_2)` .
(ii) `2NaHCO_(3)(s)overset("Heat")rarrunderset("SODA ash")underset("Sodium carbonate")(Na_(2)CO_(3)(s))+CO_(2)(G)+H_(2)O(l)`
Discussion
5164.

(i) Name the method used to extract metals of high reactivity. (ii) Name the main ore of mercury. How is mercury obtained from its ore ? Give balanced chemical equations. (iii) Explain what is thermite reactions with the help of balanced equation. How is it used join railway tracks or cracked machine parts ?

Answer»

Solution :(a) Electrolytic reduction.
(B) Cinnabar (HGS)
By roasting and then self reduction
`2HgS + 3O_(2) overset("Heat")rarr 2HgO + 2SO_(2)`
`2HgO overset("Heat")rarr2Hg + O_(2)`
(c ) Reaction of `Fe_(2)O_(3)` with Al is used to join railway tracks and machine PARTS as it is exotermic.
This reaction is known as thermite reaction.
`Fe_(2)O_(3) + 2Al rarr 2Fe + Al_(2)O_(3) + "Heat"`
The amount of heat evolved is so large that the metal (Fe) is produced in the molten STATE.
Discussion
5165.

Name the major constituent of biogas. Write the properties of biogas which make it a good fuel. ii. Name the two devices that work using heat energy of the sun.

Answer»

Solution :(i) Methane/`CH_(4)`
Leaves no residue LIKE ash.
It burns without SMOKE.
Its heating capacity is high.
Bio-gas is ALSO used for lighting.
(ii) Solar WATER heater.
Solar cooker.
Discussion
5166.

(i) Name the gas which is liberated when an acid reacts with a metal. How will you test the presence of the gas. (ii) Write the chemical equations for the reaction for zinc metal with : (a) Hydrogen acid and (b) Sodium hydroxide Write the chemical name of salt obtained in each case.

Answer»

SOLUTION :(i) Hydrogen gas: When a burning matchstick is brought near the hydrogen gas , it burns with a pop sound.
(ii) (a) `Zn(s)+2HCl to ZnCl_2(AQ)+H_2(G)`
Zinc chloride
(b) `Zn(s)+NAOH to Na_2ZnO_2+H_2(g)`
Sodium zincate
Discussion
5167.

{:("i. Monoatomic molecule","(a) Ozone"),("ii. Diatomic molecule","(b) Phosphorous"),("iii. Triatomic molecule","(c) Helium"),("iv. Polyatomic molecule","(d) Oxygen"):}

Answer»

SOLUTION :`i-c,ii-d,iii-a,iv-b`
Discussion
5168.

(i) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements? (ii) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer»

Solution :(i) All these METALS have one electron in their respective OUTERMOST shells.Also, all these elements of group 1 form basic oxides.(II) The outermost shells of the ATOMS of helium and neon are completely filled with electrons.
Discussion
5169.

(i) List any two changes which take place when oilyfood gets oxidized. (ii) Mention a measure which prevents or slows down its oxidation.

Answer»

Solution :(i) (a) Food BECOMES RANCID .
(b) Its taste and SMELL changes.
(ii) Keeping food in air tight containers/flushing the container with an inert gas like NITROGEN `(N_(2))`.
Discussion
5170.

{:("i. Isotopes","(a) "S_(8)","P_(4)),("ii. Isobars","(b) "_(6)C^(13)","_(7)N^(14)),("iii. Isotones","(c) "_(1)H^(1)","_(1)H^(2)","_(1)H^(3)),("iv. Polyatomic molecule","(d) "_(18)Ar^(40)","_(20)Ca^(40)):}

Answer»

SOLUTION :`i-c,ii-d,iii-b,iv-a`
Discussion
5171.

(i) In the following schematic diagram for the preparation of hydrogen gas as shown in figure , what would happen if following changes are made ? (a) In place of zinc granules , same amount of zinc dust is taken in the test tube . (b) Instead of dilute sulphuric acid , dilute hydrochloric acid is taken . (c) Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated . (ii) How do metal carbonates and metal hydrogencarbonates react with acids ?

Answer»

SOLUTION :(i) (a) Hydrogen gas will evolve with greater SPEED.
(b) Almost same amount of gas is evolved.
(c) If SODIUM hydroxide is TAKEN, hydrogen gas will be evolved .
`Zn +2NaOH rarrunderset("Sodium zincate")(Na_2ZnO_2)+H_2`
(ii) All metal carbonates and hydrogencarbonates react with acids to form a corresponding salt, carbon dioxide and water .
Metal carbonate + Acid `rarr` Salt + Carbon dioxide + Water
Metal hydrogencarbonate + Acid `rarr` Salt + Carbon dioxide + Water
Forexample , sodium carbonate reacts with dilute hydrochloric acid as FOLLOWS :
`Na_(2)CO_(3)(s)+2HCl(aq) rarr2NaCl(aq)+H_(2)O(l)+CO_2(g)`
Sodium hydrogencarbonate reacts with dilute hydrochloric acid as follows :
`NaHCO_(3) (s) + HCl(aq) rarr NaCl(aq)+H_(2)O(l)+CO_(2)(g)`
Discussion
5172.

(i) In Mendeleev's Periodic Table, the elements were arranged in the increasing order of atomic masses. However, cobalt with atomic mass of 58.93 a.m.u. was placed before nickel having an atomic mass of 58.71 a.m.u. Give reason for the same. (ii) Write the formula of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.

Answer»

SOLUTION :(i) It was because elements with similar properties were GROUPED together and increasing order of atomic MASS COULD not be followed.
(ii) Germanium is Eka-silicon. The FORMULA is `GeCl_(4)`. Gallium is Eka-aluminium. The formula is `GaCl_(3)`.
Discussion
5173.

(i) Identify the compound of calcium which is yellowish powder and is used for disinfecting drinking water. Wtite its chemical name and formule. How is it manufactured ? Write the chemical equation for the reaction incolved. Also list two other used of the compound. (ii) Write the balanced chemical equation of chlor-alkali process.

Answer»

Solution :(i) The YELLOWISH white SOLID is known as BLEACHING powder. Chemically, it is known as calcium oxychloride or calcium hypochlorite. Its chemical formula is `CaCOCl_(2).` For its manufacture and uses, consult section `2.15.`
(ii) Chemical equation for chlor-alkali process.
`2NaCl+2H_(2)Ounderset("Current")overset("ELECTRIC")to2NaOH+H_(2)+Cl_(2)`
Discussion
5174.

(i) Identify the acid and the base whose combination forms the common salt that you use in your food. Write its formula and chemical name of this salt. Name the source from where it is obtained. (ii) What is rock salt? Mention its colour and the reason due to which it has this colour. (iii) What happens when electricity is passed through brine? Write the chemical equation for it.

Answer»

SOLUTION :(i) Hydrochloric acid and sodium hydroxide
`NaOH+HCl to NaCl+H_2O`
NaCl, Sodium Chloride, Ocean water.
(ii) DEPOSITS of solid SALT are found in several PARTS of the world. These large crystals are CALLED rock salt.
Colour of rock salts is brown, due to impurities.
(iii) `2NaCl+2 H_2O to^(El ectricity) 2NaOH+Cl_2+H_2`
Discussion
5175.

(i) Identify from the following the hydrocarbons that can undergo addition reactions: C_(3)H_(4),CH_(4), C_(2)H_(6), C_(2)H_(4). Justify your answer. (ii) Write the name of the homologous series to which they belong to.

Answer»

SOLUTION :(i) `C_(3)H_(4),C_(2)H_(4)` will undergo addition REACTIONS because they are UNSATURATED compounds.
`C_(3)H_(4)` : Alkyne
`C_(2)H_(4)` : Alkene
Discussion
5176.

(i) How will you bring about following conversion? Write the concerned chemical equations: (a) Ethanol to Ethene (b) Ethanol to Ethanoic acid. (ii) Give one example with chemical equation for following reactions: (a) Substitution reaction (b) saponification (c) combustion reaction.

Answer»

Solution :(i) (a) `underset("Ethanol")(CH_(3)CH_(2)OH)underset(4443K)overset(H_(2)SO_(4)(conc.))tounderset("Ethene")(CH_(2)=CH_(2))+H_(2)O`
(B) `underset("Ethanol")(CH_(3)CH_(2)OH)underset(("OXIDATION"))overset(K_(2)Cr_(2)O_(7)//H_(2)SO_(4))tounderset("Ethanoic acid")(CH_(3)COOH)`
(ii) (a) `underset("Methane")(CH_(4))+Cl_(2)underset("sun light")overset("DIFFUSED")toCH_(3)CL+HCl`
(b) `underset("Ethylethanoate")(CH_(3)COOC_(2)H_(5))+NaOHtounderset("Sod. Ethanoate")(CH_(3)COONa)+underset("Ethanol")(C_(2)H_(5)OH)`
(c) `underset("Ethene")(2C_(2)H_(4))+5O_(2)overset(heat)to4CO_(2)+2H_(2)O`.
Discussion
5177.

(i) How does the tendency to gain electrons change as we go down the group ? Give reason. (ii) Given below is a part of the periodic table. How does the valency vary, as we move vertically downward from Li to Fr. Give reason.

Answer»

SOLUTION :(i) Tendency to gain electrons decreases on moving down the group because with increase in SIZE, effective .+ve. nuclear charge decreases.
(II) Valency remains constant as we move DOWNWARDS. Elements of the same group have the same number of VALENCE electrons.
Discussion
5178.

(i) How chloride of lime chemically differs from calcium chloride? (ii) What happens when chloride of lime reacts with sulphuric acid. Write chemical equation involved. (iii) Mention two uses of chloride of lime.

Answer»

Solution :(i) Chloride of lime is calcium HYPOCHLORITE `CaOCl_2` which is alkaline while calcium chloride is `CaCl_2` which is neutral.
(ii) `2CaOCl_2 (s)+H_2SO_4(AQ) to CaSO_4(aq)+CaCL_2(aq)+2HClO(aq)`
(iii) (a) Bleaching powder is USED for bleaching purposes in textile and paper industry and in laundry.
(B) It is also used as a DISINFECTANT for water
Discussion
5179.

{:("i. "H_(2)O,"(a) 180 g"),("ii. "NH_(3),"(b) 44g"),("iii. "CO_(2),"(c) 17g"),("iv. "C_(6)H_(12)O_(6),"(d) 18g"):}

Answer»

SOLUTION :`i-d,ii-c,iii-b,iv-a`
Discussion
5180.

{:("i. "H_(2),"(a) Hetero diatomic molecule"),("ii. "HCl,"(b) Monoatomic molecule"),("iii. "H_(2)O,"(c) Homo diatomic molecule"),("iv. "Ne,"(d) Hetero triatomic molecule"):}

Answer»

SOLUTION :`i-c,ii-a,iii-d,iv-b`
Discussion
5181.

{:("i. Group 18",,"(a) Main group elements"),("ii. Group 3-12",,"(b) Noble gases"),("iii. Group 13-18",,"(c) Halogens"),("iv. Group 17",,"(d) Transition elements"):}

Answer»

SOLUTION :i-b, ii-d, iii-a, iv-c
Discussion
5182.

(i) Giving reason for each. State which of the following will conduct electricity and which will not? (a) A solution of glucose (b) Dil. Hydrochloric acid (iii)If acetic acid and hydrochloric acid of same concentration are taken, which of the two is a stronger acid and why? (iii) How is the strength of an acid affected when some water is added to it?

Answer»

Solution :(i) (a) Solution of glucose will not conduct electricity because it does not have IONS.
(B)Dil. HCl will conduct electricity because it produces `H^+` ions in WATER.
(II) HCl is stronger because it GIVES more `H^+` ions than acetic acid.
(iii) The strength of the acid decreases.
Discussion
5183.

(i) Give the constituents of baking powder. (ii) Why cake or bread swells on adding baking powder. Write chemical equation.

Answer»

Solution :(i) BAKING powder contains SODIUM hydrogen carbonate and tartaric ACID.
(ii) It is due to carbondioxide
`2NaHCO_(3)(s)overset("HEAT")toNa_(2)CO_(3)(s)+CO_(2)(g)=H_(2)O(L)`
Discussion
5184.

(i) Give an examplefor an a combination reactionwhich is exothermic . (ii) Identify the oxidising agen, reducing agent in the following reaction : H_(2)S+Clrarr2HCl+S (iii) Name the phenomenon due to which the taste and smell of oily food changes when kept for a long time in open. Suggest one method to prevent it.

Answer»

SOLUTION :(i) `CaO+H_(2)OrarrCa(OH)_(2)+"heat"`
(ii) OXIDISING agent __`Cl_(2)`
Reducing agent ___`H_(2)S`
(iii) Rancidity , keep food inn airtight containers.
Discussion
5185.

(i) Give a chemical test to distinguish between saturated and unsaturated hydrocarbons. (ii) Name the products formed when ethane burns in air. Write the balanced chemical equation for the reaction showing the types of energies liberated. (iii) Why is reaction between methane and chlorine in the presence of sunlight considered a substitution reaction?

Answer»

Solution :(i) `Br_(2)` - water test: `Br_(2)` - water is a brown coloured liquid.
Unsaturated hydrocarbons give addition reaction with `Br_(2)`, so the colour of `Br_(2)` - water gets decolourised.
Saturated hydrocarbons do not react with `Br_(2)` - water, so the colour of `Br_(2)` - water does not get decolourised.
(ii) On burning ethane in air, the products obtained are carbon dioxide and water, along with heat and light.
`2C_(2)H_(6)(g)+7O_(2)(g) to 4CO_(2)(g) +6H_(2)O(l)+"Heat"+"Light" `
(III) Methane REACTS with chlorine in the presence of sunlight to FORM chloromethane and hydrogen chloride.
`underset("Methane")(CH_(4))+underset("Chlorine")(Cl_(2)) overset("Sunlight")to underset("Chloromethane")(CH_(3)Cl)+underset("Hydrogen chloride")(HCl)`
With the excess of chlorine, all the four hydrogen atoms of methane are replaced by chlorine atoms to form carbon tetrachloride `(C Cl_(4))`. This reaction is considered as substitution reaction because hydrogen of methane is substituted by chlorine.
Discussion
5186.

i] Give a chemical test to distinguish between saturated and unsaturated hydrocarbon. ii] Name the product formed when ethane burns is air. Write the balanced chemical equation for the reaction showing the types of energies liberated. iii] Why is the reaction between methane and chlorine in the presence of sunlight considered a substitution reaction?

Answer»

Solution :i]a) Saturated HYDROCARBON burns with blue and non smoke flame, due to their complete combustion, Unsaturated hydrocarbons GENERALLY burns with sooty flame due to their INCOMPLETE combustion.
b) Unsaturated hydrocarbons decolourise bromine water.
Eg: `CH_2 = CH_2 + Br_2 (aq) to underset(Br)underset(|)(CH_2)-underset(Br)underset(|)(CH_2)`
c] Saturated hydrocarbon does not decolourises bromine water.
ii) When ethane burns in air Carbon dioxide and water are formed
`CH_3 -CH_2 +7//2O_2 to 2CO_2 + 3H_2O`
OR
`2(CH_3 - CH_3) + 7O_2 to 4CO_2 + 6H_2O`
iii) The reaction in which a reagent substitutes or replaces atom or a group of atoms from the reactant are called substitution reaction.
Generally saturated hydrocarbons undergo substitution reaction. When methane reacts with chlorine in sunlight the hydrogen atoms in methane are successively replaced lay chlorine atoms and forms four substitution products.
`CH_4 + Cl_2 overset("Sunlight")(rarr) underset("CHLOROMETHANE")(CH_3Cl + HCl)`
`CH ""_(3)Cl + Cl_(2) overset("Sunlight")(rarr)underset("Dichlorimethane")(CH_3Cl + HCl)`
`CH ""_(3)Cl_(2) + Cl_(2) overset("Sunlight")(rarr)underset("CHLOROFORM"("Trichloroo methane"))(CHCl_3 + HCl)`
`CHCl_(3) + Cl_(2) overset("Sunlight")(rarr) underset("Carbon tetrachloride" ("Tetrachloromethane"))(C Cl_4 + HCl)`
Discussion
5187.

You have four solutions A, B, C and D. The pH of solution A is 6, B is 9, C is 12 and D is 7. (i) identify the most acidic and the most basic of the solutions. (ii) Arrange the above four solutions in the increasing order of the H+ ion concentration. (iii) State the change in colour of pH paper on dipping in solution C and D.

Answer»

Solution :(i) HCl will give rise to more `H^+` ions and `CH_3COOH` produces less `H^+` ions on dissociations. The colour of pH paper DEPENDS on the concentration of `H^+` ion. Colour BECOMES red for HIGH `H^+` concentration.
(ii) (a) Most ACIDIC- A most basic- C
(B) C,B,D,A/C `lt` B `lt` D `lt` A
(c ) In C blue in D green.
Discussion
5188.

{:("i. "F_(2),"(a) Polyatomic molecule"),("ii. "O_(3),"(b) Monoatomic molecule"),("iii. "P_(4),"(c) Diatomic molecule"),("iv. He","(d) Triatomic molecule"):}

Answer»

SOLUTION :`i-c,ii-d,iii-a,iv-b`
Discussion
5189.

(i) Element 'Y' with atomic number 3 combines with element 'A' with atomic number 17. What would be the formula of the compound ? (ii) What is the electronic configuration of an element with atomic number 10 ? What will be its valency?

Answer»

Solution :(i) Electronic CONFIGURATION of ELEMENT .Y. with ATOMIC number 3 = 2, 1
Element .A. with atomic number 17 = 2, 8, 7
Formula of the compound : YA.
(ii) Electronic configuration of element configuration of the element with atomic number 10 = 2, 8
Valency : Zero.
Discussion
5190.

(i) Electropositive nature of the element(s) increases down the group and decreases across the period(ii) Electronegativity of the element decreases down the group and increases across the period (iii) Atomic size increases down the group and decreases across a period (left to right)(iv) Metallic character increases down the group and decreases across a period.On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9. (a) Name the most electropositive element among them. (b) Name the most electronegative element. (c) Name the element with smallest atomic size. (d) Name the element which is a metalloid. (e) Name the element which shows maximum valency.

Answer»

Solution :(a) LITHIUM(b) FLUORINE(C ) Fluorine (d) Boron (E) Carbon
Discussion
5191.

(i) Differentiate between alkanes and alkenes. Name and draw the structure of one member of each. (ii) Alkanes generally burn with clean flame. Why?

Answer»

Solution :

(ii) ALKANES are saturated hydrocarbons which always burn with a CLEAN BLUE flame because complete combustion TAKES place in sufficient oxygen to `CO_(2)` and `H_(2)O` with the liberation of large amount of heat and light.
Discussion
5192.

(i) Describe the mechanism of cleansing action of soaps. (ii) Why do soaps not work in hard water?

Answer»

Solution :(i) Soap MOLECULES form micelles where ionic end of soap dissolves in water while carbon chain dissolves in oil. The emulsion in water THUS formed HELPS in dissolving the dirt in water and we can wash our clothes.
(ii) Soaps react with calcium or magnesium IONS to form an insoluble substance which RESULTS in wastage of soap
Discussion
5193.

(i) Define universal indicator. For what purpose it is used? (ii) Two solutions A and B have pH values of 3.0 and 9.5 respectively. Which of these will turn litmus solution from blue to red and which will turn phenolphthalein from colourless to pink? (iii) What is a neutral substance. WHat colour will you get when you add a few drops of universal you get when you add a few drops of universal indicator of a test tube containing distilled water?

Answer»

Solution :(i) Universal indicator is a mixture of many different indication (or dyes) which give different colours at different PH values of the entire pH scale. The colour produced by universal indicator is used to FIND the pH value of acid or base by matching the colour with the colours on pH colour chart.
(II) Solution A is acidic and will turn litmus solution from blue to RED.
Solution B is basic and will turn phenolphthalein from colourless to pink.
(iii) Green colours will be obtained.
Discussion
5194.

(i) Define the term functional group. Identify the functional group present in (a) H-overset(O)overset(||)(C)-H, (b) H-underset(H)underset(|)overset(H)overset(|)H-overset(OH)overset(|)(C)=O (ii) What happens when 5% alkaline KMnO_(4) solution is added drop by drop to warm ethanol taken in a test-tube ? State the role of alkaline KMnO_(4) solution in this reaction.

Answer»

Solution :(i) Functional group-Hetero atom or group of ATOMS attached to the carbon chain, which GIVES specific properties to the compounds, is called a functional group.
(a) Aldehyde group, (B) Carboxylic acid
(ii) Acetic/Ethanoic acid is formed. It is an OXIDIZING AGENT.
Discussion
5195.

(i) Define corrosion . (ii) What is corrosion of iron called? (iii) How will you recognisethe corrosion of silver? (iv) Why corrosion of iron is a serious problem ?

Answer»

Solution :(i) CORROSION is a process in which metals aredeteriorated byaction of AIR, moisture, chemicals, etc.
(ii) Corrosion of iron is CALLED Rusting.
(iii) Silver turns black as it reacts with `H_(2)S` present in airand forms a LAYER of `Ag_(2)S`.
(iv) Corrosion of iron is a serious problem beause it leads to wastage of tonnes of iron every year and lot of money is spent to repair or REPLACE it .
Discussion
5196.

{:("i.Cuprite",,"(a)Halilde ore"),("ii. Marble",,"(b)Oxide ore"),("iii. Fluorspar",,"(c) Sulphate"),("iv. Galena",,"(d) Carbonate ore"):}

Answer»

SOLUTION :i-b, ii-d, iii-a, iv-c
Discussion
5197.

(i) Crystals of copper sulphate are heated in a test tube for some time. (a) What is the colour of copper sulphate crystals before heating, and after heating? (b) What is the source of liquid droplets seen on the inner upper side of the test tube during the heating process? (ii) A metal 'X' when dipped in aqueous solution of aluminium sulphate no reaction is observed whereas when it is dipped in an aqueous solution of ferrous sulphate, the pale green solution turns colourless. Identify metal 'X' with reason.

Answer»

Solution :(i) (a) The colour of copper sulphate crystals before heating is blue and TURNS white after heating.
(b) The liquid droplets are actually the water droplets. The source of water droplets is the water of CRYSTALLISATION of hydrated copper sulphate crystals `(CuSO_(4).5H_(2)O)`.
(ii) When metal .X. is DIPPED in aqueous solution of ALUMINIUM sulphate no reaction is observed, it means it is less reactive than aluminium. But when it is dipped in ferrous sulphate solution, the solution turns from pale green to colourless, so .X. is more reactive than iron and thus displaces it from its solution.
Therefore, .X. must be zinc. It reacts with ferrous sulphate to form colourless zinc sulphate solution by displacing iron.
`Zn(s)+FeSO_(4)(aq)rarrZnSO_(4)(aq)+Fe(s)`
Discussion
5198.

(i) "Covalent compounds have low melting and boiling points". Justify this statement. (ii) What is an ester ? Describe an activity to form an ester in a school laboratory.

Answer»

Solution :(i) The force of attraction between the molecules of covalent compounds are not strong as ionic compounds. So, they have low melting and low boiling points.
(ii) Esters are organic compounds which have sweet SMELL.
Activity:
Aim: To demonstrate esterification process using ethanol and acetic acid.
Materials Required : Beakers, water, test-tube, ethanol, ethanoic acid, conc. `H_(2)SO_(4)`.

Procedure:
(a) Take 2 ml of ethanol in a test-tube.
(b) Add 2 ml of ethanoic acid into it.
(C) Add few drops of conc. `H_(2)SO_(4)`
(d) Warm it in a beaker containing water.
(e) Observe the smell of the products formed.
OBSERVATION : Pleasant fruity SMELLING compound (called ester) is formed.
Chemical Reaction :

Conclusion: Carboxylic acid reacts with ALCOHOL in presence of conc. `H_(2)SO_(4)` which act as a dehydrating agent to from esters.
Discussion
5199.

{:("i. Copper",,"(a) Lustrous greyish white metal"),("ii. Iron",,"(b) Cn 112"),("iii. Aluminium",,"(c) Reddish brown metal"),("iv. Copernicium",,"(d) Silvery white metal"):}

Answer»

SOLUTION :I-c, ii-a, iii-d, iv-b
Discussion
5200.

(i) Carbonate and sulphide ores are usually converted into oxides during the process of extraction of metals. (ii) Ionic compounds have generally high melting points. (iii) Hydrogen is not a metal but is has been assigned a place in the reactivity series of metals. (iv) The galvanised iron article is protected against rusting even if the zinc layer is broken.

Answer»

Solution :(i) It is easy to REDUCE metal oxide to the metallic form than metal carbonate or metal sulphide.
(II) In ionic compounds, oppositely charged ions are closely packed and the attractive forces are very strong. Therefore, ionic compounds have high melting POINTS.
(iii) Hydrogen has been assigned a place in the reactivity SERIES of metals because just LIKE metals, it behaves as an electropositive element.
Discussion