KENDRIYA VIDYALAYA INS MANDOVI

SCIENCE WORKSHOP

GOA CLUSTER

14 OCTOBER 2017

STUDY MATERIAL

CLASS : X SUBJECT-SCIENCE

COURSE DIRECTOR & VENUE PRINCIPAL

MR. PARVEZ ASLAM

KV INS MANDOVI GOA

TEAM MEMBERS

MRS. REKHA DEVAN KV PONDA MRS. SANGEETA KV INS MANDOVI

MRS. RUPA SIDDHU KV NO. 1 VASCO MRS. SHAHANA RIZVI KV NO. 1 VASCO

MRS. SANTOSH YADAV KV BAMBOLIM MS. NIKITA KV NO. 2 VASCO

MRS. SEJAL PALIENKAR KV BAMBOLIM

ACIDS, BASES AND SALTS

1 Mark QUESTIONS

Q. How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?

Ans. Bring a burning matchstick near the gas. It burns with 'pop' sound showing that it is hydrogen.

Q. Which bases are called alkalies? Give an example of alkalies.

Ans. Soluble bases are called alkalies, e.g. sodium hydroxide (NaOH).

Q. Dry ammonia gas has no action on litmus paper, but a solution of ammonia in water turns red litmus paper blue. Why is it go?

Ans. Ammonia dissolves in water, forms ammonium hydroxide which is base and turns red litmus blue.

NH3+ H2O NH 4+¿ ¿ + OH−¿¿

Dry ammonia gas does not change into OH- ions.

Q. Name tow synthetic indicators which are used to test acids and bases.

Ans. (i) Phenolphthalein (ii) Methyl orange.

Q. What is aqua regia?

Ans. It is a mixture of conc. HCl and conc. HNO3 in the ratio of 3:1.

Q. What are antacids? Give one example.

Ans. Those compounds which neutralise excess of acid in stomach , e.g. NaHCO3.

2 Marks Questions

Q. 15 mL of water and 10 mL of sulphuric acid are to be mixed in a beaker.

(a) State the method that should be followed with reason.

(b) What is this process called?Ans. (a) The acid is to be added slowly in water to prevent the mixture to be splashed. The reaction is highly exothermic, therefore, constant cooling should be done.

(b) The process is called dilution.

Q.What happens when chlorine is passed over slaked lime at 313K ? Write chemical equation of the reaction involvedd and state two uses of the product obtained.

Ans. Bleaching powder is formed.

Ca (OH)2 (S) + Cl2 (g) 313K CaoCl2(S) + H2O(l)

Slaked lime Bleaching powder ( Calcium oxychloride)

Uses:

(i) It is used as bleaching agent in paper and textile industries.(ii) It is used as disinfectant in purification of drinking water.

Q. Answer the following questions:

(a) State the colour of phenolphthalein in soap solution.

(b) Name one indicator which specifies the various levels of H+ ion concentration

Ans. (a) Pink

(b) Universal indicator.

Q. What happens when chlorine is passed over slaked lime at 313 K? Write chemical equation of the reaction involved and state two uses of the product obtained.

Ans. Bleaching powder is formed.

Ca(OH)2 +Cl2 CaOCl2 + H2O

Uses:

i) It is used as bleaching agent in paper and textile industries.ii) It is used as disinfectant in purification of drinking water.

3 Marks Questions

Q. (a) Define olfactory indications. Name two substances which can be used as olfactory indicators.

(b) Choose strong acids from the following:

CH3COOH, H2SO4, H2CO3, HNO3

Ans. (a) Those substances whose smell (odour) changes in acidic or basic solution are called olfactory indicators, e.g. onion and vanilla.

(b) H2SO4 and HNO3 are strong acids.

Q. (a) How is tooth decay related to pH? How can it be prevented?

(b) Why does bee sting cause pain and irritation? Rubbing of baking soda on the sting area gives relief. How?

Ans. (a) Lower the pH, more will be tooth decay. Acid reacts with Ca3(PO4)2 and cause tooth decay. It can be prevented by brushing our teeth after every meal.

(b) It is due to formic acid. Sodium hydrogencarbonate (Baking soda) neutralises formic acid giving relief.

Q. A white powder is added while baking breads and cakes to make them soft and fluffy. Write the name of the powder? Name its main ingredients. Explain the function of each ingredient. Write the chemical reaction taking place when the powder is heated during baking.

Ans. Baking powder.

It consists of sodium hydrogencarbonate and tatric acid.

Sodium hydrogencarbonate gives CO2 which makes cake soft and fluffy. Tatric acid neutralises the bitterness due to sodium carbonate produced.

2NaHCO3 (s) Heat Na2CO3 (s) + CO2 (g) + H2O (l)

Q. On passing excess carbon dioxide gas through lime water, it first turns milky then becomes colourless. Explain why? Write all the chemical equations of the reactions involved.

Ans. Ca(OH)2 + CO2 CaCO3 (s) + H2O

CaCO3 (s) + CO2 (g) + H2O (l) Ca(HCO3)2

Lime water turns milky due to the formation of calcium carbonate. It becomes colourless when excess of CO2 is passed due to formation of Ca(HCO3)2 which is soluble in water.

Q. (a) What is universal indicator?

(b) Write the chemical equation involved in the preparation of sodium hydroxide. Name the process.

Ans. (a) Universal indicator is mixture of synthetic indicators which is used to find pH of solutions.

(b) 2NaCl (aq) + 2H2O (l) electrolysis 2NaOH (aq) + H2 (g) + Cl2 (g)

Q. (a) Name the compound which is obtained from baking soda and is used to remove permanent hardness of water.

(b) Write its chemical formula.

(c) What happens when it is recrystallised from its aqueous solution?

Ans. (a) Sodium carbonate is obtained from baking soda and is used to remove hardness of water.

(b) Na2CO3

(c) It changes to washing soda, Na2CO3, 10H2O.

Q. A compound which is prepared from gypsum has the property of hardening when mixed with proper quantity of water.

(a) Identify the compound.

(b) Write the chemical equation for its preparation.

(c) Mention one important use of this compound.

Ans. (a) Plaster of Paris.

(b) CaSO4 . 2H2O 373 K CaSO4.12 H2O +

32 H2O. .

(c) It is used for plastering fractured bones.

5 Marks Questions

Q.(a) State the chemical properties on which the following uses of baking soda are based:

(i) As an antacid

(ii) As a soda acid fire extinguisher.

(iii)To make bread and cake soft and spongy.

(b) How is washing sada obtained from baking soda? Write balanced chemical equation.

Ans. (a) (i) It is weakly basic in nature and naturalize hyperacidity.

(ii)It liberates CO2 with H2SO4, which extinguish fire.

(iii)It liberates CO2 on heating which makes bread and cakes soft and sponge.

(b) 2NaHCO3 Heat Na2CO3 + CO2 + H2O

Baking soda on heating gives sodium carbonate which on crystallization from hydrated washing soda

Na2CO3 + 10H2O Na2CO3.10 H2O

Q. State reason for the following statements:

(a) Tap water conducts electricity whereas distilled water does not.

(b) Dry hydrogen chloride gas does not turn blue litmus red whereas dilute HCl does.

(c) During summer season, a milkman usually adds a very small amount of baking soda to fresh milk.

(d) For a dilution of acid, acid is added into water and not water into acid.

(e) Ammonia is a base but does not contain hydroxyl group.

Ans. (a) Tap water contains ions which conduct electricity, distilled water does not contain ions.

(b) Dry HCl does not form ions but HCl gives H+ and Cl-.

(c) Baking soda does not allow milk to change to lactic acid which makes milk sour.

(d) Adding water to acid is highly exothermic. Therefore, water is added to acid very slowly with cooling.

(e) Ammonia dissolves in water forms OH-. Therefore, it is basic.

NH3+ H2O NH 4+¿ ¿ + OH−¿¿.

CARBON AND ITS COMPOUNDS

ONE MARK QUESTION

1. In which form is carbon found in the earths crust?

Ans: Carbon is found is the earths crust as carbonates,hydrogen carbonates, coal and petroleum.

2. In which form is carbon fond in the atmosphere?

Ans: Carbon is found in the atmosphere as carbon dioxide.

3. Most of the carbon compounds are poor conductors of electricity. Give reason

Ans: Most of the carbon compounds are poor conductors of electricity as it shows covalent bonding which does not give rise to ions.

4. Carbon compounds have low boiling and melting point . Give reason .

Ans: Carbon compounds have low boiling and melting point as they have covalent bonds which are weak forces of attraction.

5.Write the atomic number of carbon and show its electronic configuration?

Ans. Atomic no. of carbon: 6

Electronic configuration: 2,4.

6. Name the allotrope of carbon which is a good conductor of electricity.

Ans. Graphite

7. What is catenation?

Ans.The ability of an atom of an element to form covalent bond with the atoms of same element is called catenation.

8.Give the name of the functional group.

i) –OH ii)-CHO

9.Name the following compound.

i) ii)

10.Arrange the following in increasing order of boiling point.

C4H9OH, CH3OH, C3H7OH, C2H5OH

11. Burning of which of the following fuel will give a flame. LPG or Coal.?Why?

Ans: LPG gives flame as it vapourises easily.

TWO MARKS QUESTIONS

1. Diagrammatically explain the bonding in hydrogen molecule.

Ans:

2. Why does carbon form covalent compounds? / Why carbon is tetravalent?

Ans: Carbon has 4 valence electrons. It cannot lose 4 electrons because very high amount of energy is needed . It also cannot gain 4 electrons because 6 protons cannot hold 10 electrons. Therefore carbon shares 4 electrons ton form 4 covalent bonds.

3. Explain the two factors which allow carbon to form large number of compounds.

Ans.1. Catenation: The ability of an atom of an element to form covalent bond with the atoms of same element .

2.Tetravalency: Ability to bond with four other atoms of carbon or atoms of other elements.

4.Differentiate between Saturated and unsaturated carbon compounds.

Ans Saturated carbon compounds Unsaturated carbon compound

1. Those compounds in which valency of carbon is satisfied by single bond.

1. Those compounds in which valency of carbon is satisfied by double or triple bonds.

2.Less reactive 2.More reactive.

5.Draw the structure of following molecules

i) Ethanoic acid ii) Butanone

6.What happens when a piece of sodium is dropped in ethanol? Write the chemical reaction.

Ans: Ethanol reacts with sodium leading to evolution of hydrogen and formation of sodium ethoxide.

2Na + 2CH3CH2OH ------------------------> 2CH3CH2O-Na+ + H2

THREE MARKS QUESTIONS

1. Draw the electron dot structure of oxygen,nitrogen and carbon dioxide molecules.

Ans:

2. Write the molecular formula of the following compounds and draw their electron dot structure.

i)Ethane ii) Ethene iii) Ethyne

Ans:

C2H6 C2H4 C2H2

3. What are structural isomers? Why can’t ethane have an structural isomer? Draw the possible structures of butane(C4H10) .

Ans: Isomers are those compounds which have same molecular formula but different structures.

In ethane branching is not possible therefore isomers are not possible.

4) What is homologous series? List the properties of homologous series? Write the general formula for alkynes.

Ans. Homologous series is a series of organic compounds which have same functional group and similar chemical properties,

Each member of series is differ by –CH2—in its m molecular formula and 14 u in its molecule mass, as the molecular mass increase in any homologous series a gradation in physical properties will increase.

Alkynes - CnH2n-2

5. What are oxidizing agents? Give one example.Write an oxidation reaction.

Ans: Oxidising agents are capable of adding oxygen to others.

Example :Alkaline potassium permanganate and Acidified potassium dichromate

CH3CH2OH -----------------------------------------------> CH3COOH

6.”Shama’s mother prefers using vegetable oil over ghee in cooking.”

i)How can vegetable oil be converted to saturated hydrocarbon?Name the process and write the equation.

ii)What value does Shama’s mother exhibit?

Ans. I) The process is hydrogenation.

ii) The value exhibited by Shama’s mother is utilizing scientific knowledge for betterment of health.

FIVE MARKS QUESTIONS

Alkaline KMnO4 + heat

Acidified K2Cr2O7 + heat

1. a)What is the difference between the chemical composition of soap and detergents.

b) State in brief the action of soap in removing an oily spot for cloth with the help of suitable diagram.

c) Which of the two -soap /detergent would you prefer for washing clothes in well water? Why?

Ans: a)Soaps are sodium and potassium salts of long chain carboxylic acids(--COONa). While detergents are generally ammonium or sulphonate salts of long chain carboxylic acid(--SO3Na).

b) When a dirty cloth is placed in soap solution, the long hydrophobic hydrocarbon tail of soap molecules points towards the oily dirt particles and the hydrophilic ionic end point towards the water. This forms a spherical structure with hydrophillic parts of the molecule towards outside and hydrophobic parts in the center. This spherical structure is called micelle. This micelle is attracted towards water and carries the oily dirt particles along with it. This causes the dirt particles to detach from the fibres of the cloth. In this manner, clothes become free from dirt or dust.

c) I would prefer detergents for washing clothes in the well water as it is hard water. The soap reacts with calcium and magnesium salts present in hard water and forms insoluble scum thus it does not lather and reduce the cleaning capacity. While detergent does not form scum and is effective in hard water.

2. An organic compound X on heating with conc.H2SO4 forms a compound Y which on adding of one molecule of hydrogen in the presence of nickel forms a compound Z. one molecule of Z on combustion forms two molecules of CO2 and three molecules of H2O. identify X,Y,Z. and also write their chemical equations and state the type of reaction.

Ans.  X is ethanol(C2H5OH) X combines with conc. Sulphuric acid.  C2H5OH + conc. H2SO4---C2H4+ H2O (dehydration reaction)

Y is ethene.(C2H4) 

Ethene when added to H2:

C2H4+H2-------------------C2H6  (hydrogenation)

Z is ethane(C2H6) 

Ethane when combusted: 

C2H6+O2--------------2CO2 + 3H2O (combustion)

3. An organic compound A is widely used as a preservative in pickles and has a molecularformula C2H4O2. This compound reacts with ethanol to form a sweet smelling compound B?

Ni,heat

i)Identify the compound A ii)) Write the chemical equation for this reaction with ethanol to form compound B. Name compound B iii) How can we get back the compound A from B? Name the process . iv)Which gas is produced when compound A reacts with baking soda? Write the chemical reaction.

Ans: i) compound A – CH3COOH (Ethanoic acid)

ii) CH3COOH + C2H5OH -----------------> CH3COOC2H5 + H2O

compound B- ethyl ethanoate

iii) CH3CH2OH -----------------------------------------------> CH3COOH

Oxidation reaction

iv)The gas produced when compound A reacts with baking soda is carbon dioxide

CH3COOH + NaHCO3 -----------------> CH3COONa + H2O + CO2

CHEMICAL EQUATIONS AND REACTIONS

ONE MARK QUESTIONS

1. State one difference between physical and chemical change.

Ans. in physical change no new substance is formed whereas in a chemical change a new substances are formed.

2. AgNO3 + NaCl AgCl ↓ + NaNO3

FeS+ H2SO4 FeSO4 +H2S ↑

in above chemical reaction what does two different kinds of arrows (↑ &↓) indicate ?

Ans. ↓ shows the insoluble substance (precipitate ) formed and ↑ shows the gas evolved.

3. On what basis is a chemical equations balanced?

Ans. It is based on law of conservation of mass.

Conc H2SO4

Acidified K2Cr2O7 + heat

4.Name the gas collected on cathode and anode respectively in electrolysis of water.

Ans. In electrolysis of water hydrogen gas is formed at cathode and oxygen gas is formed at anode.

5. What happens when dilute hydrochloric acid is added to iron fillings?

Ans. Hydrogen gas and iron chloride are prepared.

6. Name the phenomenon responsible for the black coating on silver and green coating on copper .

Ans. Corrosion (atmospheric oxidation)

7. Balance the following chemical equation.

Al (s) + CuCl2(aq) AlCl3(aq) + Cu (s)

Ans. 2 Al (s) +3 CuCl2(aq) 2 AlCl3(aq) +3 Cu (s)

8. What happens chemically when quicklime is added to water filled in a bucket ?

Ans. Slaked lime is produced with lot of heat and hissing sound.

9. Write two observations that help us to determine whether a chemical reaction has taken place.

Ans. Change in state , change in color , evolution of gas ,change in temperature(any two)

10.Write the type of reaction for each-

(i) burning of magnesium ribbon

(ii) heating of cooper powder

11. What is a redox reaction?

Ans. The reaction in which oxidation and reduction take place simultaneously is called a redox reaction.

TWO MARKS QUESTIONS

1. A solution of substance ‘X’ is used for white washing. What is the substance ‘X’.? write the chemical reaction of ‘X’ with water.

Ans. ‘X’ is calcium oxide (CaO).

CaO(s) + H2O (l) Ca(OH)2 (aq) + HEAT

2. Define combination reaction. Give one example of combination reaction which is also exothermic.

Ans. A reaction in which two elements or compound combine together to form a single compound is called a combination reaction.

2Mg (s)+ O2 (g)2 MgO(s) + heat +light

It is an example of combination and exothermic reaction both.

3. Give two examples from daily life where redox reactions are taking place.

Ans (i) rusting of iron

(ii) combustion reaction (burning of coal)

4.Identify the substance that are oxidized and the substance that are reduced in the following reaction-

(i) CuO + H2 Cu + H2O

(IIMnO2 + HCl MnCl2 + H2O +Cl2

Ans. (I) substance oxidized is H2 and reduced is CuO.

(II) substance oxidised is HCl and reduced is MnO2.

5. What is corrosion? Write the formula for rust of iron.

Ans. Slow eating up of metal surface due to the attack of atmospheric factors ( oxygen , moisture etc) is known as corrosion .

Rust of iron is Fe2O3 .X H2O

6. What happens when white silver chloride is placed in sunlight ? Write the type of reaction and chemical equation involved .

Ans. White silver chloride turns grey.

This is a photo decomposition reaction .

2AgCl (s) 2Ag (s)+ Cl2 (g)

7.What is a precipitation reaction ? Give one example .

Ans. A reaction in which one insoluble substance (precipitate) is produced can be called a precipitation reaction.

Na2SO4 (aq) + BaCl2 (aq) --> BaSO4(s) + 2NaCl(aq)

In above reaction a white ppt of barium sulphate is formed.

8. we should not store copper sulphate solution in container made of iron.Why?

Ans. Iron is more reactive than copper so displacement reaction will take place .

Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

9. Why should a magnesium ribbon be cleaned before burning in air ?

Ans. When magnesium ribbon is kept open in air slowly it reacts with atmospheric oxygen to form a layer of magnesium oxide.Magnesium oxide hinders the efficient burning of magnesium ribbon so that layer of magnesium ribbon should be cleaned before burning.

THREE MARKS QUESTION

1. Why is respiration considered as exothermic reaction ? Explain.

Ans. In cellular respiration glucose breaks down in presence of oxygen to release energy.Due to the release of energy respiration is considered as exothermic reaction.

C6H12O6 +6O2 6CO2 +6H2O + energy

2.What happens when iron nail is dipped in copper sulphate solution? Write the type of reaction and equation for the above chemical change.

Ans. When iron nail is dipped in copper sulphate solution-

(I) Blue color copper sulphate solution turns green ( due to the formation of iron sulphate)

(II) Brown deposition on iron nail ( due to copper deposition )

It is a displacement reactionCuSO4 (aq) + Fe(s) FeSO4(aq) + Cu(s)↓

Q3. State the type of chemical reactions with chemical equations that take place in the following:

(a) Magnesium ribbon is burnt in air.

(b) Electric current is passed through water.

(c) When lime stone is heated.

Ans. (a) 2Mg (s) +O2 (g) 2MgO(s)

Combination reaction ( Redox reaction).

(b) 2H2O (l) electrolysis 2H2(g) + O2 (g)

Electrical decomposition reaction.

(c) CaCO3(S) CaO (s) +CO2(g)

Thermal decomposition reaction.

Q.4 2 g of ferrous sulphate crystals are heated in a dry boiling tube.

(a) List any two observations.

(b) Name the type of chemical reaction taking place.

(c) Write the chemical equation for the reaction.

Ans. (a) Green colour of FeSO4 disappears and reddish brown Fe2O3 is formed.

Smell of burning sulphur .

(b) Decomposition reaction.

(c) 2FeSO4 (s) Heat Fe2O3 (s) +SO2 (g) + SO3 (g)

Q.5 When you have mixed the solutions of lead(II) nitrate and potassium iodide.

(a) What was the colour of the precipitate formed and can you name the precipitate?

(b) Write the balanced chemical equation for this reaction.

(c) Is this also a double displacement reaction?

Ans. (a) The colour of the precipitate is yellow. The name of the compound formed as a precipitate is lead iodide (PbI2).

(b) Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq)

(c) Yes, it is also a double displacement reaction.

Q.6 A reddish brown colored metal, used in electrical wires, when powdered and heated strongly in an open china dish, its color turns black. When hydrogen gas is passed over this black substance, it regains its original color. Based on the above information answer the following questions.

(a) Name the metal and the black color substance formed.

(b) Write balanced chemical equations for both the reactions.

Ans. Reddish brown metal is copper. When it is heated in china dish in presence of oxygen, black colored copper oxide is formed.

(b) 2Cu (s) + O2 (g) 2CuO (s)

When hydrogen gas is passed over heated copper oxide reddish brown copper metal is formed, e.g.

CuO (s) + H2 (g) Heat Cu (s) + H2O (g)

Q7. What is rancidity? Mention any two ways by which rancidity can be prevented.

Ans. The process in which taste and smell of food gets spoiled is called rancidity. It happens due to oxidation .

Prevention from rancidity.

a) Antioxidants are added to fatty acids to prevent oxidation , e.g. chips are packed in presence of nitrogen gas which prevents spoilage by oxidation .

b) Food should be kept in airtight container in refrigerator .

Q.8 Write three methods to prevent corrosion.

Ans. (i) oiling or greasing

(ii) painting

(iii) electroplating ( galvanization for iron )

5 Marks Questions

Q.1 (a) Write one example for each of decomposition reaction

(i) Electricity (ii) Heat (iii) Light

(b) Which of the following statements is correct give reason in support of your answer –

copper can displace silver from silver nitrate

OR

silver can displace copper from copper sulphate solution.

Ans. (a) (i) 2H2O Electrolysis 2H2 (g) + O2

(ii) CaCO3 Heat CaO + CO2

(iii) 2AgBr Sunlight 2Ag + Br2

(b) Copper can displace silver from AgNO3 because copper is more reactive than Ag, e.g.

Cu + 2AgNO3 (aq) Cu (NO3)2 (aq) + 2Ag (s)

Q2.(a) A metal nitrate ‘A’ on heating gives yellowish brown colored metal oxide along with brown gas ‘B’ and a colorless gas ‘C’. Identify ‘A’ ‘B’ and ‘C’.

(b) Write the type of reaction.

(c) Write balanced chemical equation for the reaction taking place.

(d)How is a decomposition reaction is different from combination reaction ?

Ans. (a)Metal nitrate ‘A’ is lead nitrate ( Pb(NO3)2) , ‘B’ is nitogen dioxide(NO2) and ‘C’ is oxygen gas.

(b) this is a decomposition reaction

(c) 2Pb(NO3)2 (s) Heat 2PbO (s) + 4NO2 (g) + O2 (g) ……

Lead Nitrate Lead (II) oxide Nitrogen dioxide Oxygen

‘A’ (yellowish colour) (Brown) (Colourless)

‘B’ ‘C’

(d) in decomposition reaction a single reactant breaks down to form two or more products whereas in combination reaction two or more reactants react to form a single product.

Q.3 Aqueous solution of ‘A’ on reaction with potassium iodide forms a yellow precipitate of compound ‘D’.

(a)Indentify ‘A’ and D.

(b)Also identify the types of reactions and write chemical equation for the reaction.

(c) Metal present in ‘A’ is used in alloy which is used for soldering purposes.Write the constituent metals of solder.

(d)

A.(a) ‘A’ is lead nitrate solution ‘D’ is lead iodide.

(b) this is a double displacement reaction.

Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq) … ‘A’ lead nitrate Potassium iodide Lead iodide Potassium nitrate ( yellow ppt) ‘D’(c) Lead and Tin are the constituting metals of solder.

METALS AND NON METALS

ONE MARK QUESTIONS

1 Name a non metal which is lustrous and a metal which is non – lustrous. Ans:- Iodine is a non metal which is lustrous . lead is a non lustrous metal .

2 Name a metal and a non metal and write their symbols that exists in liquid state at room temperature.Ans:- Mercury (Hg) , Bromine(Br) exists in liquid state at room temperature.

3 Why does calcium float in water?Ans:- Calcium reacts with water to form calcium oxide and hydrogen gas. Released Hydrogen gas sticks to the surface of calcium therefore it floats.

4 Which metal neither reacts with cold water nor with hot water , but reacts with steam to produce hydrogen gas.Ans:- Iron / Aluminium/Zinc.3Fe + 4H2O(g) Fe3O4 +4H2

5 An element forms an oxide , A2O3 which is acidic in nature. Identify ‘A’ is a metal or a non metal.Ans:- ‘A’ is non metal as non metallic oxides are acidic in nature.

6 A green layer is gradually formed on a copper plate left exposed to air for a week in a bathroom. What could this green substance be?Ans:- This green colour is due to the formation of copper carbonate due to the corrosion of copper.

7 What is the formula of rust?Ans :- Fe2O3.xH2O

8 Give composition of the alloys – brass and bronze.Ans :- Brass – Cu and Zn Bronze – Cu and Tin

9 Name two metals which have very low melting point.Ans :- Gallium and Caesium.

10 Why oxides of high reactive metals cannot be reduced by carbon ?Ans:- Oxides of high reactive metals cannot be reduced by carbon because these metals have more affinity for oxygen than carbon.

TWO MARKS QUESTIONS

1. Write two examples each of metals that are good conductors and poor conductors of heat.

Ans: Copper and silver – Good conductors of heat . Lead and Mercury – poor conductors of heat.

2. Name two metals which are purified by electrolyte refining. Mention the anode , cathode and the electrolyte used in the refining process. At which electrode would the pure metal be deposited?Ans:- Copper , Zinc are purified by electrolyte refining.Anode is made of Impure metal and cathode is made of thin strip of pure metal. A solution of the metal salt is used as an electrolyte. Pure metal from electrolyte is deposited on the cathode.

3. a. Name two metals which are alloyed with iron to make stainless steel.Ans: Nickel and Chromium.b. Name two metals which are used to make jewellery.Ans : - Gold and Platinum.

4. A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and green coating on copper coins. State the chemical name of black and green coating. How are they formed.Ans:- Black coating-silver sulphide (Ag2S) Green Coating- Basic copper carbonate [CuCo3.Cu(OH)2]By the action of H2S or sulphur compounds present in the atmosphere black coating on silver coins are formed.By the action of carbon dioxide , oxygen and water vapour present in the atmosphere green coating is formed on copper coins.

5. Define an alloy. How is an alloy prepared?Ans:- Homogeneous mixture of two or more metals or a metal and a non metal is known as an alloy.It is prepared by first melting the primary metal and then dissolving the other elements in it in definite proportions.

6. Give reasons for the following-a. School bells are made up of metals.b. Electrical wires are made up of copper.

Ans a:- School bells are made up of metals because metals are sonorous-produce ringing sound. b:- Copper is very good conductor of electricity therefore used in making of electrical wires.

7. Define the term ‘ anode mud’.Ans:- The insoluble impurities which settles down at the bottom of the anode are known as anode mud.

8. What is 24 carat gold? How will you convert into 18 carat gold?Ans:- 24 carat gold is pure gold. It is converted in to 18 carat gold by adding 6 parts of copper to 18 parts of gold i.e 75% Au and 25% Cu.

9. Name the ore of mercury . How is mercury extracted from its ore?Ans:- ore – cinnabar into HgS First HgS is converted into HgO

2HgS+ 3O2 2HgO+ 2SO2

Then HgO is reduced to mercury on further heating

2Hg O 2Hg + O2

3 MARKS QUSETIONS

1. When a metal X is treated with cold water it gives a basic salt Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X,Y and Z and also write the reaction involved

Ans:- The base with molecular mass is NaOH Hence metal X is sodium Na. it reacts with H2o to form the base NaOH and liberates H2 gas which easily catches fire.

2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

Sodium(X) Sodium hydroxide Hydrogen gas

(Y) (Z)

2. A non metal X exist in two different forms Y and Z . Y is the hardest natural substance , whereas Z is a good conductor of electricity. Identify X,Y and Z

Ans: Non metal ‘X’ must be carbon. It exist in two forms diamond (Y) and graphite (z). diamond (Y) is the hardest natural substance and graphite (Z) is good conductor of electricity.

3. What are the constituents of solder alloy? Which property of solder makes it suitable for welding electrical wires?

Ans: Solder is an alloy of lead (50%) and tin(50%) , it has lower melting point that lead as well as tin. So it is suitable for welding electric wires.

4. A metal ‘A’ which is used in thermite process , when heated with oxygen gives an oxide B which is amphoteric in nature. Identify A and B. write down the reactions of oxide ‘ B’ with Hcl and NaOH.Ans: ‘A’ is Aluminium‘B’ is Aluminium oxide Al2O3

Al2O3(s) + 6 HCL(aq) 2AlCl3 (aq) + 3H2O(l)Aluminium oxide hydrochloric acid Aluminium chloride Water

Al2O3(s) + 2NaAlo2(aq) 2NaAlO2(aq) + H2O(l)Aluminium oxide sodium hydroxide Sodium aluminate water

5. A non-metal ‘A’ is an important constituent of our food and forms two oxides ‘B’ and ‘C’ . Oxide B is toxic whereas c causes global warming.a. Identify A, B and Cb. To which group of periodic table ‘A’ belongs

Ans. a. ‘A’ is Carbon

‘B’ is carbon monoxide (CO)

‘c’ is Carbon dioxide (CO2)

b. Carbon (A) belongs to the group 14 of the periodic table.

6. What happens when-

a. ZnCO3 is heated in the absence of oxygen.

b. A mixture of Cu2O and Cu2S is heated.

Ans. a. ZnCO3 ZnO + CO2

b. 2Cu2O + Cu2S 6Cu +SO2

7. Two ores ‘A’ and ‘B’ were taken. On heating ore ‘A’ gives CO2 whereas ore ‘B’ gives SO2. What steps will you take to convert them into metals?

Ans. Ore ‘A’ is carbonate of any metal (MCO3). It can be converted into metal by calcinations followed by smelting or electrolytic reduction depending upon the nature of a metal.

MCO3 MO + CO2 Calcination

MO + C M + CO Reduction

Ore ‘B’ is any metal sulphate. To obtain metal from this ore , first roasting then reduction is done.

2MS + 3 O2 2 MO +2 SO2 Roasting

MO + C M + CO Reduction

8. Explain the following-

a. Reactivity of aluminium decreases if it id dipped in HNO3.

b. Carbon cannot reduce the oxides of Na or Mg.

c. Iron articles are galvanized.

Ans. a. When aluminium reacts with HNO3 , aluminium oxide (AL3O3) is formed which further gets deposited on aluminium metal. Hence more aluminium metal is not available for the reaction because Al3O3 layer is passive in nature.

b. Sodium and magnesium both metals are very reactive. These metals have more affinity towards oxygen than carbon. Hence carbon cannot reduce the oxides of these metals.

c. Galvanization is a process to protect the iron from rusting , iron articles get rusted when come in contact with air and moisture.

9. Define aqua regia.

Ans:- Aqua regia (Latin for ‘royal water’) is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1. It can dissolve gold. It is a highly corrosive and fuming liquid.

5 MARKS QUESTIONS

1.A. In the formation of compounds between two atoms A and B , A loses two electrons and B gains one electron.

(i) What is the nature of bond between A and B?

(ii) Suggest the formula of the compound formed between A and B .

B. On similar lines explain the formation of MgCl2 molecule.

C. Common salt conducts electricity only at molten state. Why?

D.Why is melting point of Nacl high?

Ans:- A(i) Bond is ionic bond.

(ii) (A 2+) ( B ) 2 i.e. AB2

B. Mg Mg 2+ + 2e-

2Cl + 2e- 2Cl-

(Mg2+) (Cl)2 i.e. Mg Cl2

C. In the molten state or aqueous solution ions are (Na + , Cl- ) are free to move where as in solid state ions cannot move.

D. Melting point is high due to strong force of attraction between Na+ and Cl- .

2.a An ore on treatment with dilute hydrochloric acid produces brisk effervescence. What steps will be required to obtain metal from the enriched ore?

b. Copper coin is kept immersed in silver nitrate solution for some time. What change will take place in coin and colour of the solution? Write balance chemical equation of the reaction involved ?

Ans: a. Ore- Carbonate ore

Steps- calcination : carbonate ore is heated in limited supply of air and oxide is obtained.

e.g. ZnO + c Zn + CO

b. Copper being more reactive than silver will displace silver from silver nitrate solution and there will be deposition of silver on copper coin. The colour of solution will turn to blue.

Cu + 2 Ag NO3 Cu(NO3)2 + 2Ag

3.a. List two differences between calcinations and roasting in tabular form.

b. Which method will you use to reduce the following? Explain by giving a suitable example.

(i) Oxides of less reactive metals

(ii) Oxides of moderately reactive metals.

(iii) Oxides of highly reactive metals.

Ans.a.

Roasting Calcination

Heating in presence of excess heat Heating in limited supply of air

Done for sulphide ores Done for carbonate ores

b.i) Oxide of less reactive metals by self reduction (in the presence of heat)

2HgO 2Hg + O2

2Cu2O +Cu2S 6Cu + SO2

heat

heat

ii)oxides of moderately reactive metals by reduction using carbon

ZnO + C Zn + CO

Highly reactive metals are also used as reducing agents.

3MnO2 + 4Al 3Mn + 2Al2O3 + Heat

Fe2O3 + 2Al 2 Fe + Al2O3 + Heat

(iii) Oxides of highly reactive metals by electrolytic reduction e.g. Na ,Mg , Ca are obtained by electrolysis of their molten chlorides.

4. Write Chemical equation when zinc granules react with

i) Sulphuric acid ii) Hydrochloric acid

iii) Aluminium Chloride iv) Sodium hydroxide

v) Nitric acid.

Ans : 1) Zn + H2SO4 ZnSO4 +H2

2)Zn + 2HCL ZnCl2 +H2

3)Zn + AlCl3 No reaction

4) Zn + 2NaOH NaZnO2 +H2

5) Zn + 4 HNO3 Zn(NO3)2 + 2 NO2 + 2H2O

5.a Define activity series of metals. Arrange the metals gold , copper , iron and magnesium in order of their increase in reactivity.

b. What will you observe when-

i) Some Zinc pieces are put in copper sulphate solution

ii) Some silver pieces are put in to green coloured ferrous sulphate solution.

Ans. A. The series of metals in which metals are arranged in decreasing order of their reactivity Gold(Au)<Copper(Cu)<Iron(Fe)<Magnesium(Mg) increasing order of their reactivity.

B(i) The blue solution will become colourless and reddish brown copper metal will be deposited.

Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s)

Blue colourless (reddish brown)

ii) No reaction will take place because silver is less reactive then iron

Ag(s) + FeSO4(aq) No reaction

Green colour

6.a. What are amphoteric oxides? Give two examples.

b. State reasons for the following-

(i) Silver and copper lose their shine when they are exposed to air. Name the substance formed on their surface .

(ii) Tarnished copper vessels are cleaned with tamarind juice.(iii) Aluminium is more reactive than iron yet there is less corrosion of aluminium as

compared to iron when both are exposed to air.

Ans. A. Those oxides which reacts with both acid as well as base to produce salt and water are called amphoteric oxides

e.g. Aluminium oxide – Al2O3

Zinc Oxide ZnO

(i) Silver and copper gets corroded when exposed to air silver forms black silver sulphide (Ag2S) and copper forms greenish layer of basic copper carbonate (CuCO3.Cu(OH)2)

(ii) Tamarind contains acid which reacts with basic copper carbonate and the product gets dissolved and removed from the copper vessel.

(iii) Aluminium forms oxide layer on its surface which does not further reacts with air and prevents corrosion

VALUE BASED QUESTION

1. Nidhi and Nishi were visiting Qutub Minar along with their classmates . After seeing Qutub Minar they went tosee iron pillar nearby . Nidhi said to Nishi “Look this pillar was made around 400 BC as history says but this has not rusted. What could be the technology behind this? “ Nishi replied “ yes this is amazing. Let us ask madam , how could the technicians of that era made such a wonder”

A. What possibly was stated by madam to the queries of nidhi and nishi?

B. How do the electrical conductivity and melting point of metals change when they are mixed to form alloy?

Ans A thin layer of iron oxide was formed on the surface as a result of finishing treatment given to the pillar. The pillar was pointed with a mixture of different salts then heated quenched.

b. the electrical conductivity and melting point decreases an alloying the metals.