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351.

The metal found always in the free state , isA. AuB. AgC. CuD. Na

Answer» (a) Au is always found in free state
352.

An ore contains arsenic and antimony as impurities. How are they removed during the process of roasting?A. by conversion into `As_(2)O_(3)andSb_(2)O_(3)`B. by concersion into `As_(2)O_(5)andSb_(2)O_(5)`C. by conversion into both trioxides and pentoxidesD. by conversion into sulphides

Answer» Correct Answer - A
353.

State the main components of the following alloys : (i) Brass. (ii) Duralumin. (iii) Bronze. (iv) Stainless steel. 

Answer»

(i) Copper and zinc. 

(ii) Aluminium and magnesium. 

(iii) Copper and Tin. 

(iv) Iron.

354.

Aluminium is extracted in the electrolysis of :A. BauxiteB. AluminaC. Alumina mixed will molten cryoliteD. Molten cryolite

Answer» Correct Answer - C
355.

The metal that cannot obtained by electrolysis of an aqueous solution of its salts is `:`A. ChlorineB. BromineC. SodiumD. Aluminium

Answer» (a) Electrolysis of aqueous solution of NaCI (brine) gives `CI_(2)` at anode.
356.

The minimum voltage required to electrolyse alumina in the Hall-Heroul process is [Given, `DeltaG^(@)_(f)(A1_(2)O_(3)) =- 1520kJ//mol` and `DeltaG^(@)_(f)(CO_(2)) = 394kJ//mol]`A. `0.8 V`B. `1,60 V`C. `2.8 V`D. `3.0 V`

Answer» `(b) 2AI_(2)O_(3)+3C to 4AI + 3CO_(2)`
`Delta_(f)G^(@)=3DeltaG^(@)(CO_(2))`
`=3xx(-394)-2xx(-1520)=1859kJ`
`=1858xx10^(3)J`
`:. nFE^(@) = 1858 xx 10^(3)" "(n=12 "electrons")`
`:. E^(@)=(1858xx10^(3))/(12xx96500)=1.60 V`
357.

Name the following:i. The process of heating the sulphide ore to a high temperature in the excess of air.ii. The process of heating the carbonate ore to a high temperature in limited air.iii. The compound formed by the reaction between aluminium oxide and sodium hydroxide.iv. Two metals which are found in the free state in nature.v. A metal which has the highest melting point.vi. Two nonmetals which are lustrous.

Answer»

i. In roasting, sulphide ore is heated to a high temperature in the excess of air.

ii. In calcination, carbonated ore is heated to a high temperature in limited air.

iii. Sodium aluminate is formed by the reaction between aluminium oxide and sodium hydroxide.

iv. Gold (Au) and silver (Ag) are found in the free state in nature.

v. Tungsten has the highest melting point.

vi. Iodine and diamond are lustrous in nature.

358.

If an ore contains impurity of `SiO_(2)`, identify the appropriate flux for the removal of it

Answer» Correct Answer - A
359.

Process of heating ore is air to remove sulphur is:A. RoastingB. CalcinationC. SmeltingD. Froth-floatation

Answer» Correct Answer - A
`MS^(-2) + O_(2) overset(Delta)rarr MO^(-2) +SO_(2)`
360.

Which of the following process is related with the removal of sulphur by heating in the air ?A. SmeltingB. CalcinationC. AnnealingD. Roasting

Answer» Correct Answer - 4
Roasting is the process of heating the ore strongly in the presence of excess of air. The process is usually carried for sulphide ore and the following changes take place.
`(i)` Moisture is removed.
`(ii)` The voltatile impurities are removed.
`(iii)` Impurities of sulphur, arsenic, phosphorus etc. are removed in form of volatile oxide.
`S+O_(2)rarrSO_(2)uarr," "4As+3O_(2)rarr2As_(2)O_(3)uarr," "P_(4)+5O_(2)rarr2P_(2)O_(5)uarr`
`(iv)` Sulphide ores get oxidised in to metal oxides
`2FeS+3O_(2)rarrFeO+2SO_(2)`
361.

State whether the following statements are True or False.i. In electroplating a metal is coated with another metal using electrolysis.ii. In anodising method. the copper or aluminium article is used as anode.iii. Silver plated spoon, gold plated ornaments are the examples of alloying.iv. silver amalgam is mainly used by dentists.v. Aluminium oxide is an acidic oxide.vi. copper reacts with moist carbon form copper carbonate.vii. Corrosion is degradation of a reaction with its environment.

Answer»

i. True.

ii. True.

iii. False. 

(Silver plated spoon, gold plated ornaments are the examples of electroplating)

iv. True.

v. False. 

(Aluminium oxide is an amphoteric oxide.)

vi. True.

vii. True.

362.

Copper reacts with moist carbon-dioxide in air and slowly loses its shine to gain a green coat of ___________A. Copper oxideB. Iron oxideC. Copper carbonateD. None of the above

Answer» Copper carbonate
363.

Autoreduction process is used in the extraction ofA. `Cu & Pb`B. `Zn & Hg`C. `Cu & AI`D. `Fe & Pb`

Answer» Correct Answer - A
364.

Which of the following ores is not concentrated by froth floatation process?A. PyrolusiteB. PentlanditeC. Zinc blendeD. Copper pyrites

Answer» Correct Answer - (a)
365.

How do we separate two sulphide ores by froth floatation method?A. By adding pine oilB. By adding sodium cyanideC. By adding foaming agentD. By passing air

Answer» Correct Answer - (b)
366.

Why are non-metals called oxidizing agents ? 

Answer»

 They tend to gain electrons and act as oxidising agents.

367.

Why are metals called reducing agents ?

Answer»

 They tend to lose electrons and act as reducing agents.

368.

The table below compare some properties of metals and non-metals. Write down the missing statements (i) to (iv).MetalNon-Metal(i).........Poor conductor of heat(ii) Malleable.............(iii) Forms positive ions..............(iv) ................Form acidic oxide.

Answer»

(i) Metals are good conductor of heat. 

(ii) Non-metals are non-malleable [Brittle]. 

(iii) Non-metals form negative ions [Anions]. 

(iv) Metals form basic oxides.

369.

Poling process `:`A. reduces `SnO_(2)` to `Sn`.B. involves the liberation of reducing gases like hydrocarbons.C. uses poles of freshely cut green woodD. .all of the above are correct.

Answer» Correct Answer - 4
This method is used for the purificationo of those impure metals which contain the impurities of their own impurities for examples `CuO` in Cu and SnO in Sn.
370.

In electrorefining, the impure metal is made _____.A. anodeB. cathodeC. eletrolytic `-` tankD. none

Answer» Correct Answer - A
Impure metal is made as anode and pure metal is made as cathode.
371.

In the process of extraction of gold. Roasted gold ore `+CN^(-)+H_(2)O overset(O_(2))rarr [X]+OH^(-)` `[X]+Znrarr [Y]+Au` Identify the complexes `[X] ` and `[Y]`.A. `X=[Au(CN)_(2)]^(-),Y=[Zn(CN)_(4)]^(2-)`B. `X=[Au(CN)_(4)]^(3-),Y=[Zn(CN)_(4)]^(2-)`C. `X=[Au(CN)_(2)]^(-),Y=[Zn(CN)_(5)]^(4-)`D. `X=[Au(CN)_(4)]^(-),Y=[Zn(CN)_(4)]^(2-)`

Answer» Correct Answer - 1
`Au+2CN^(-)+H_(2)O+.^(1)//_(2)O_(2)rarr[Au(CN)_(2)]^(-)(X)+2OH^(-),2[Au(CN)_(2)]^(-)+Zn=[Zn(CN)_(4)]^(2-)(Y)+2Au`
372.

Write scientific reason.Generally the ionic compounds have high melting points.

Answer»
  • The ionic compounds exist in solid state and are hard due to strong electrostatic force of attraction between oppositely charged ions.
  • The intermolecular force of attraction is high in ionic compounds and large energy is required to overcome it. Therefore, ionic compounds have high melting points.
373.

Explain why : (a) In the electrolysis of alumina using the Hall Heroult’s Process the electrolyte is covered with powdered coke. (b) During galvanization, iron sheets are coated with zinc during galvanization.

Answer»

(a) It prevents burning of carbon anodes and prevents heat loss from the molten electrolyte. 

(b) Zinc forms a protecting coating on the surface of iron and hence prevents it from rusting. Zinc by itself form a protective layer of zinc oxide and hence does not tarnish. 

374.

Which of the following contain both calcium and magnesium:-A. MagnesiteB. CalamineC. CarnaliteD. Dolomite

Answer» Correct Answer - D
Dolomite: `CaCO_(3). MgCO_(3)`
375.

Explain the reactivity series of the metals.

Answer»

The arrangement of metals in decreasing order of their reactivity in the form of a series is called the reactivity or activity series of the metals. The most reactive metal is placed at the top of the list and least reactive metal is placed at the bottom of the list.

On the basis of reactivity, we can classify metals into the following categories:

1. High reactivity metals 

2. Moderately reactive metals 

3. Less reactive metals.

1. Extraction of High reactivity metals: The metals which are placed at the top of the reactivity series are very reactive. They are never found in nature as free elements, e.g., sodium, potassium, calcium and aluminium. These metals are obtained by electrolytic reduction.

2. Extraction of Moderately reactive metals: The metals in the middle of reactivity series such as iron, zinc, lead, copper are moderately reactive. These elements are present as sulphides or carbonates in nature. Generally metals are obtained from their oxide as compared to their sulphides and carbonates.

3. Extraction of Less reactive metals: The metals which are placed at the bottom of the reactivity series are least reactive. They occur in free state, e.g. gold, silver and copper. Copper and silver are also found in the combined state as sulphide and oxide ores. These metals are obtained from their ores by just heating the ores in air.

376.

The reactivity of metals increase down to reactivity series.

Answer» Correct Answer - False.
The reactivity of metals decreases down the reactivity series
377.

Name the categories into whcich metals can be classified based on their reactivity.

Answer» Based on reactivity, metals can be classified into three groups ,
(i) metals of high reactivity
(ii) mnetals of moderate reactivity
(iii) metals of low reactivity
378.

The least stable oxide among the following isA. `Sb_(2)O_(3)`B. `Ag_(2)O`C. `CuO`D. `ZnO`

Answer» (b) the least stable oxide is `Ag_(2)O`.
379.

Which of the following statements about the reduction is not true ?A. `Delta_(f)G^(@) "of the sulphide is greater than those of "CS_(2) ""and"""H_(2)S`B. `Delta_(f)G^(@)` is megative for roasting of sulphide ore to oxideC. Roasting of sulphide to oxide is thermodynamically feasibleD. Carbon and hydrogen are suitable reducing agents for metal sulphides

Answer» (d) both C and `H_(2)` are not suitable for reducing sulphide ore because `Delta_(f)G^(@)` of metal sulphide is more than that of `CS_(2)` and `H_(2)S` which will be formed as a result of reduction.
380.

Write the equation for the action of heat on aluminium hydroxide.

Answer» When aluminium hydroxide is heated upto `1000^(@)C` , it forms alumina and water.
`2Al (OH)_(3) overset("heat") underset(1000^(@)C)to Al_(2)O_(3)+3H_(2)O`
381.

Match the following:Column IColumn II(1) Copper and zinc(a) Stainless steel(2) Copper and tin(b) Zinc amalgam(3) Iron, nickel and chromium(c) Bronze(4) Mercury and zinc(d) Brass(e) Steel

Answer»

(1) Copper and zinc – Brass 

(2) Copper and tin – Bronze 

(3) Iron, nickel and chromium – Stainless steel 

(4) Mercury and zinc – Zinc amalgam.

382.

`{:(Column-I(Ore),Column-II),((A)"Iron",(p)"Carbon reduction method"),((B)Lead,(q)"Self reduction"),((C)Copper,(r)"Thermite process"),((D)"Chromium",(s)"Hydrometallurgical process"):}`

Answer» Correct Answer - `(A) rarr p; (B) rarr p,q; (C) rarr q,s; (D) rarr r`
383.

Write chemical equation for the following events.A reaction was brought about between ferric oxide and aluminium.

Answer»

The reaction between ferric oxide and iron produces aluminium oxide and iron. It is a thermite reaction and is highly exothermic.

It produces a large amount of heat, which is released to melt oxygen and aluminium. This reaction is used in welding of machineries. It is also used in warfare to make grenades.

The chemical reaction for the above is as follows:

3Fe3O2 + 4Al → 2Al2O3 + 6Fe

384.

What is principle of magnetic separation method ?

Answer» Magnetic separation method used the principle of difference in the magnetic propertiesof the ore and the gangue.
385.

A reaction was brought about between ferric oxide and alumininum.

Answer» When Ferrix xide react with aluminium, aliminium oxide and iron are formed. This reaction is known as 'Thermit Reaction' .
` underset("Oxide") underset("Ferric")(Fe_(2)O_(3))+ underset("Aliminium")(2Al) to underset("Iron")(2Fe)+ underset("Oxide") underset("Aluminium")(Al_(2)O_(3)+"heat")`
386.

 Write a note on thermite welding?

Answer»

Thermite is a mixture of 3 parts of ferric oxide and one part of aluminium powder. On the top of the thermite mixture, an irgnition mixture of potassium chlorate and magnesium powder is placed. A burning Mg riboon is inserted into the ignition mixture, which catches the fire and ignite the thermite. During this reaction ferric oxide is converted into iron and a large amount of heal is evolved and about 3000°C temperature is achieved.

Fe2O, + 2Al ⟶ 2Al2O3 + 2Fe + Heat

The formed liquid iron is allowed to drop over the gap between the broken piece and thus they join together. This process is termed as boldschmidts aluminothermic process.

387.

Aluminium powder is used in thermite welding because, (A) it is a strong reducing agent (B) it is a strong oxidising agent (C) it is corrosion resistant (D) it is a good conductor of heat.

Answer»

Aluminium powder is used in thermite welding because, it is a strong reducing agent.

388.

Mention one reason for the use of aluminium in thermite welding?

Answer»

Aluminium is a strong reducing agent. As such its reaction with Fe2O3 is highly exothermic. the white not iron not iron so produced not fills the gap but also welds it.

389.

Give reasons for the following – pertaining to Hall Herault’s process. It is preferred to use a number of graphite electrodes as anode, instead of a single graphite electrode.

Answer»

The graphite[carbon] anodes are continously replaced during the electrolysis because : 

(a) The oxygen evolved at the anode escapes as a gas or reacts with the carbon anode. 

(b) The carbon anode is thus oxidised to carbon monoxide which either bums giving carbon dioxide or escapes out through an outlet. 

2C + O2 → 2CO [2CO + O2 → 2CO2

(c) The carbon anode is hence consumed and renewed periodically after a certain period of usage,

390.

To obtain pure germanium which of the following methods of refining is preferred?A. LiquationB. Zone-refiningC. Electrolytic methodD. Poling

Answer» (b) Elements such as Ge,Si Ga ,etc., which are used as semiconductors, are refined by zone-refining.
391.

Why is brass preferred to stainless steel for door settings?

Answer» Composition of brass of and stainless steel.
(ii) Relation between the composition and the property of the alloy.
(iii) Comparison among the given properties of alloys.
(iv) Requisite for door settings.
392.

 What is froath floatation process and for, what purpose it is used ?

Answer»

In this process, the heavy material containing metal, is floated upward with froath to separate it from,waste material present in ore or mineral. Hence it is called froath floatation process. 

393.

What are the various alloys used in daily life? Where are those used?

Answer»
Various alloysUses
1. BronzeIt is used to prepare: Coins, utensils, medals, statues
2. BrassPipes, condenser tubes, utensils worshipping God.
3. Stainless steelUtensils, tools, dairy equipment, boilers.
4. SteelConstruction of bridges and buildings, cutting tools, blades.
5. Tungsten steelHigh speed cutting tools
6. AmalgamSilver amalgam used by dentists
7. DuraluminBodies of aircraft, buses, kitchenwares
8. Aluminium bronzePigment in ink and paint
9. German silverElectrical heaters, resistors
10. Gun metalGuns, boiler fittings
11. MagneliumBeams of scientific balances, aircraft parts.
12. Gold with copper or nickel or silver or platinumJewellery

394.

Statement-I : Thermite mixture `Fe_(2)O_(3) +AI` (powder) is used in the welding. Statement-II : Al is a good reductantA. Statement-I is True, Statement-II is True, Statement-II is a correct explanation for Statement-IB. Statement-I is True, Statement-II is True, Statement-II is NOT a correct explanation for Statement-IC. Statement-I is True, Statement-II is False.D. Statement-I is False, Statement-II is True.

Answer» Correct Answer - B
395.

Why are alumininum alloys widely used in aircrafts and ships?

Answer» (i) Property of aluminium.
(ii) Comparison of properties of metal and its alloy.
396.

Match the properties & uses of alloys in List 1 – with the correct answer from List 2.1.Contains pb & Sn, has low melting point & is used in electrical fuseA. Duralumin2. Contains Cu,Zn & Sn is hard, takes up steel polish & used in statues & medalsB. Stainless3. Contains Cu & Zn is hard,malleable & ductile & is used in electrical fittingsC. solder4. Contains Al & Cu is light & is used in air crafts & pressure cooker.D. Brass5. Contains Fe, Ni & Cr is corrosion resistent & is used in cutlery steel.E. Bronze

Answer»
List 1List 2
1.Contains pb & Sn, has a low melting point & is used in electrical fuseC. Solder
2. Contains Cu, Zn & Sn is hard, takes up polish & used in statures & medalsE. Bronze
3. Contains Cu & Zn is hard,malleable & ductile & is used in electrical fittingsD. Brass
4. Contains Al & Cu is light & is used in air crafts & pressure cooker.A. Duralumin
5. Contains Fe, Ni & Cr is corrosion resistent & is used in cutlery steel.B. Stainless

397.

(i) composition (ii) reason for alloying (iii) one use of each of the following alloys. 1. Brass 2. Bronze 3. Duralumin 4. Solder [fuse metal] 5. Stainless steel

Answer»
CompositionReason for alloyingUse
(i) Brass: Cu -60 -80% Zn 40 - 20%Hard, lustrousElectrical fittings
(ii) Bronze : Cu -80% Zn-1%; Sn -19%Hard,attractionStatues,medals
(iii) Duralumin : Al-95% Mg -0.3% Cu =4%very light Aircrafts
(iv) Solder : pb -50% Sn -50%Low m.p,High tensile strengthwelding, electrical fase.
(v) Stainless : Fe -75% N -10%)
Steel : Cr -15%, C-5%
Lustrous,hardsurgical instruments.

398.

Why L-D process is preferred to Bassemer process?

Answer» (i) Comparison of the type of fuel used.
(ii) Comparison of the composition of gases passed thruogh the charge in L-D and Bessemer process.
(iii) Comparison of the process of passing the gases in L-D and Bessemer converter.
(iv) Reactions that takes place in L-D and Bessener coverter.
(v) Change in the rates of reactions due to difference in abvoe two processes.
(vi) Effect of the presence of the non-reacative component of the gas blasted in Bessemer process on the property of steel.
399.

Statement-I : `CuFeS_(2)` is concentrated by froath floatation method Statement-II : `CuFeS_(2)` is main ore of copper.A. Statement-I is True, Statement-II is True, Statement-II is a correct explanation for Statement-IB. Statement-I is True, Statement-II is True, Statement-II is NOT a correct explanation for Statement-IC. Statement-I is True, Statement-II is False.D. Statement-I is False, Statement-II is True.

Answer» Correct Answer - B
400.

Statement-I : Extraction of iron metal from iron oxide ore is carried out by heating with coke. Statement-II : The reaction `Fe_(2)O_(3) (s) overset(Delta)rarr Fe(s) +3//2O_(2)(g)` is a spontaneous process at standarde condition.A. Statement-I is True, Statement-II is True, Statement-II is a correct explanation for Statement-IB. Statement-I is True, Statement-II is True, Statement-II is NOT a correct explanation for Statement-IC. Statement-I is True, Statement-II is False.D. Statement-I is False, Statement-II is True.

Answer» Correct Answer - C