CH-3 CHEMISTRY METALS AND NON METALS QUESTION ANSWER

A non-metal X exists 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: ‘X’ is carbon, ‘Y’ is diamond as it is the hardest natural substance and ‘Z’ is graphite as it is good conductor of electricity.

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.

Metals generally occur in solid state. Name and write symbol of a metal that exists in liquid state at room temperature.

ANS: Mercury(Hg) exists in liquid state at room temperature.

Which of the following two metals will melt at body temperature (37 °C) ?
Gallium, Magnesium, Caesium, Aluminium

ANS: Gallium and Caesium

Why does calcium float in water ?

ANS: It is because hydrogen gas is formed which sticks to surface of calcium, therefore it floats.

Which gas is liberated when a metal reacts with an acid ? How will you test the presence of this gas?

ANS: Hydrogen gas is formed. Bring a burning matchstick near to it, H₂ will burn explosively with ‘pop’ sound

Name the metal which reacts with a very dilute HNO₃ to evolve hydrogen gas.

ANS: Magnesium

Arrange the following metals in the decreasing order of reactivity :
Na, K, Cu, Ag

ANS: K > Na > Cu > Ag

From amongst the metals sodium, calcium, aluminium, copper and magnesium, name the metal
(a) which reacts with water only on boiling, and
(b) another which does not react even with steam.

ANS: (a) Magnesium reacts with water only on boiling.
(b) Copper does not react even with steam.

Which one of the following metals does not react with oxygen even at high temperatures ?
(a) Calcium (b) Gold (c) Sodium

ANS: (b) Gold does not react with oxygen even at high temperatures.

Name any one metal which reacts neither with cold water nor with hot water, but reacts with heated steam to produce hydrogen gas.

ANS: Iron; 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

An element forms an oxide, A₂O₃ which is acidic in nature. Identify A as a metal or non-metal.

ANS: ‘A’ is non-metal as non-metallic oxides are acidic in nature.

What is the valency of silicon with atomic number 14 ?

ANS: Its valency is equal to 4.

What is the valency of phosphorus with atomic number 15 ?

ANS: Phosphorus has valency 3.

What is the valency of an element with atomic number 35 ?

ANS: Its valency is 1.

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: It is due to the formation of basic copper carbonate [CuCO₃.Cu(OH)₂].

Give reason for the following:
(a) School bells are made up of metals.
(b) Electric wire are made up of copper.

ANS: (a) It is because metals are sonorous, i.e. produce sound when struck with a hard substance.
(b) It is because copper is good conductor of electricity.

Write one example of each of
(a) A metal which is so soft that, it can be cut with knife and a non-metal which is the hardest sustance.
(b) A metal and a non-metal which exist as liquid at room temperature.

ANS: (a) Sodium, carbon (diamond)
(b) Mercury is liquid metal, bromine is liquid non-metal.

Name the following:
(a) A metal, which is preserved in kerosene.
(b) A lustrous coloured non-metal.
(c) A metal, which can melt while kept on palm.
(d) A metal, which is a poor conductor of heat.

ANS: (a) Sodium is preserved in kerosene. (b) Iodine is lustrous coloured non-metal.
(c) Gallium (d) Lead

Give two examples each of the metals that are good conductors and poor conductors of heat respectively.

ANS: Good conductors of heat are copper and silver.
Poor conductors of heat are lead and mercury.

Name a metal/non-metal:
(i) Which makes iron hard and strong?
(ii) Which is alloyed with any other metal to make an amalgam?
(iii) Which is used to galvanise iron articles?
(iv) Whose articles when exposed to air form a black coating?

ANS: (i) Carbon makes iron hard and strong. Tungsten can also make iron hard and strong.
(ii) Mercury
(iii) Zinc
(iv) Silver

Name one metal and one non-metal that exist in liquid state at room temperature. Also name two metals having melting point less than 310 K (37 °C).

ANS: Metal in liquid state is mercury, non-metal in liquid state is bromine.
Gallium (Ga) and Cesium (Cs) have melting point below 310 K.

Explain why calcium metal after reacting with water starts floating on its surface. Write the chemical equation for the reaction. Name one more metal that starts floating after some time when immersed in water.

ANS: Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of metal.
Ca(s) + 2H₂O(l) → Ca(OH)₂ + H₂(g)
Magnesium reacts with hot water and starts floating due to the bubbles of hydrogen gas sticking to its surface

The way, metals like sodium, magnesium and iron react with air and water is an indication of their relative positions in the ‘reactivity series’. Is this statement true ? Justify your answer with examples.

ANS: Yes, sodium reacts explosively even with cold water, it is most reactive. Magnesium reacts with hot water, it is less reactive than Na. Iron reacts only with steam which shows it is least reactive.

X + YSO₄ → XSO₄ + Y
Y + XSO₄ → No reaction Out of the two elements, ‘X’ and ‘Y’, which is more reactive and why ?

ANS: ‘X’ is more reactive than ‘Y’ because it displaces ‘Y’ from its salt solution.

Which of the following listed metals can displace zinc from its salt solution? Give reason of your answer along with chemical equation. Copper, Lead, Magnesium, Silver

ANS: Metals which are more reactive than zinc can displace Zn from its salt solution. Therefore, Magnesium can displace zinc from its salt solution.
Mg(s) + ZnSO₄(aq) → MgSO₄(aq) + Zn(s)

When a metal X is treated with cold water, it gives a base Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z.

ANS: 2Na + 2H₂O → 2NaOH + H₂(g)
‘X’ ‘Y’ ‘Z’
‘X’ is Sodium, ‘Y’ is Sodium hydroxide, ‘Z’ is H₂ (g).

Write chemical equations that shows aluminium oxide reacts with acid as well as base.

ANS: Al₂O₃+ 6HCl → 2AlCl₃ + 3H₂O
Al₂O₃+ 2NaOH → 2NaAlO₂ + H₂O

Using the electronic configurations, explain how magnesium atom combines with oxygen atom to form magnesium oxide by transfer of electrons.

ANS:     Mg(12) = 2, 8, 2              Mg     → Mg²⁺ + 2e^–
                                      2, 8, 2      2, 8
O(8) = 2, 6                      O + 2e^– → O^2–
                                     2, 6             2, 8

Elements magnesium and oxygen respectively belong to group 2 and group 16 of the Modern Periodic Table. If the atomic numbers of magnesium and oxygen are 12 and 8 respectively, draw their electronic configurations and show the process of formation of their compound by transfer of electrons.

ANS: Mg(12) = 2, 8, 2

O(8) = 2, 6

Write the electron dot structure for sodium and chlorine atoms. How do these form a chemical bond? Name the type of bond so formed. Why does a compound so formed have high melting point ?

ANS: The electron dot diagrams of Na and Cl are as follows: form bond by transfer of an electron. Na loses one electron to form Na⁺ ion whereas Cl gains one electron to form Cl^– ion. The bond formed is ionic or electrovalent bond.
The compound (NaCl) thus formed has high melting point due to strong force of attraction between Na⁺ and Cl^– ion.

Which one of the methods given in Column I are used for extraction of each of the metals given in Column II.

Column I	Column II
(i) Electrolytic reduction	Al Zn
(ii) Reduction with carbon	Na Fe
(iii) Reduction with Al	Mn Sn

ANS: (i) Electrolytic reduction is used in case of Al, Na.
(ii) Reduction with carbon is done in case of Zn, Fe, Sn.
(iii) Reduction with Al is carried out in case of Mn.

Mention the names of the metals for the following:
(a) Two metals which are alloyed with iron to make stainless steel.
(b) Two metals which are used to make jewellary.

ANS: (a) Nickel and chromium
(b) Gold and platinum

What is an alloy? State the constituents of solder. Which property of solder makes it suitable for welding electrical wires?

ANS: Alloy is a homogeneous mixture of two or more metals. One of them can be a non-metal also. Solder consists of lead and tin. It has low melting point which makes it suitable for welding electrical wires.

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. Give 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
(i) H₂S or sulphur compounds present in the atmosphere.
(ii) Carbon dioxide, oxygen and water vapours present in the atmosphere.

What is 24 carat gold ? How will you convert it into 18 carat gold ?

ANS: 24 carat gold is pure gold. It is converted into 18 carat gold by adding 6 parts of Copper to 18 parts of Gold, i.e. 75% Au and 25% Cu.

You are given samplies of there metals: Sodium, magnesium and copper. Suggest any two activities to arrange them in order of decreasing activity.

ANS:     Activity 1: Sodium reacts with cold water to form sodium hydroxide and hydrogen gas.
2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)
      cold Magnesium does not react with cold water but with hot water to form magnesium hydroxide and hydrogen gas.
Mg (s) + 2H₂O → Mg(OH)₂ (aq) + H₂ (g)
     (hot)
Hence sodium is more reactive than magnesium.
Activity 2: Mg (s) + CuSO₄ (aq) → MgSO₄ (aq) + Cu (s)
Cu (s) + MgSO₄ (aq) → No reaction
So magnesium is more reactive than copper. Concluding from activity 1 and 2 Na > Mg > Cu.

State three reasons for the following facts:
(a) Sulphur is a non-metal (b) Magnesium is a metal
One of the reasons must be supported with a chemical equation.

ANS:

(a) Sulphur is a non-metal	(b) Magnesium is a metal
(i) Poor conductor of heat and electricity.	(i) Good conductor heat and electricity.
(ii) Neither malleable nor ductile.	(ii) Malleable and ductile
(iii) S+ O₂ → SO₂ SO₂ + H₂O → H₂SO₃ (Sulphurous acid) Sulphur dioxide is acidic oxide.	(iii) 2Mg + O₂ → 2MgO MgO + H₂O → Mg(OH)₂ (Magnesium hydroxide) Magnesium oxide is basic in nature.

Write balanced equations for the reaction of :
(a) aluminium when heated in air. Write the name of the product.
(b) iron with steam. Name the product obtained.
(c) calcium with water. Why does calcium start floating in water ?

ANS: (a) 4Al + 3O₂ $Description: C:\fake\image7.png$ 2Al₂O₃.
The product formed is aluminium oxide.
(b) 3Fe + 4H₂O (Steam) → Fe₃O₄ + 4H₂
The product obtained is iron(II) iron (III) oxide.
(c) Ca + 2H₂O → Ca(OH)₂ + H₂
The bubbles of hydrogen stick to the surface of metal that is why it floats.

Write balanced chemical equations for the following reactions :
(a) Dilute sulphuric acid reacts with aluminium powder.
(b) Dilute hydrochloric acid reacts with sodium carbonate.
(c) Carbon dioxide is passed through lime water.

ANS: (a) 2Al(s) + 3H₂SO₄(dil.) → Al₂(SO₄)₃ (aq) + 3H₂(g)
(b) Na₂CO₃(s) + 2HCl(dil.) → 2NaCl(aq) + H₂O(l) + CO₂(g)
(c) Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
Lime water (White ppt.)

What is meant by reactivity series of metals? State which of the following chemical reactions will take place giving suitable reason for each.
(a) Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
(b) Fe(s) + ZnSO₄(aq) → FeSO₄(aq) + Zn(s)
(c) Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s)

ANS: Reactivity series is a series of metals arranged in the order of their decreasing reactivities (activities).
(a) Reaction will take place because Zn is above Cu in the activity series and is more reactive than Cu.
(b) Reaction will not take place as Fe is below Zn in the activity series and cannot displace Zn from its solution.
(c) Reaction will take place because Zn is more reactive than Fe.

Observe the two test tubes A and B in the diagram given below and answer the following questions:

(a) In which test tube will the reaction take place ?
(b) Write a balanced equation for the reaction.
(c) Name the type of reaction.

ANS: (a) In first test tube reaction will take place.
(b) Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
(c) Displacement reaction

(a) What are amphoteric oxides? Choose the amphoteric oxides from amongst the following oxides:
Na₂O, ZnO, Al₂O₃, CO₂, H₂O
(b) Why is that non-metals do not displace hydrogen from dilute acids?

ANS: (a) Those oxides which are both acidic as well as basic are called amphoteric oxides, e.g. Al₂O₃, ZnO.
(b) It is because non-metals do not supply electrons to change H⁺ ions into hydrogen gas.

A student was given Mn, Zn, Fe and Cu metals. Identify which of them
(a) will not displace H₂ from dil. HCl.
(b) will react only with steam to give H₂(g).
(c) will give H₂ with 5% HNO₃.
Write the chemical reactions involved.

ANS: (a) Copper will not displace hydrogen from dil. HCl.
(b) Iron will react only with steam to liberate H₂(g).
3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
(c) Manganese will react with 5%. HNO₃ to give hydrogen.
Mn(s) + 2HNO₃(5%) → Mg(NO₃)₂(aq) + H₂(g)

(a) Write the electron dot structures for potassium and chlorine.
(b) Show the formation of KCl by the transfer of electrons.
(c) Name the ions present in this compound, KCl.

ANS:

(a) State the electron-dot structure for calcium and sulphur.
(b) Show the formation of CaS by the transfer of electrons.
(c) Name the ions present in this compound CaS. [Atomic number of Ca = 20, O = 16.]

ANS:

(a) Explain the formation of ionic compound CaO with electron dot structure. Atomic number of calcium and oxygen are 20 and 8 respectively.
(b) Name the constituent metals of bronze.

ANS:

(a) Show the formation of Na₂O by the transfer of electrons between the combining atoms.
(b) Why are ionic compounds usually hard?
(c) How is it that ionic compounds in the solid state do not conduct electricity but they do so when in molten state?

ANS:
(b) It is due to strong force of attraction between oppositely charged ions.
(c) In solid state, ions are not free to move whereas in molten state ions are free to move, therefore, they conduct electricity in molten state.

Suggest a method of reduction for the following metals during their metallurgical processes:
(a) metal ‘A’ which is one of the last second or third position in the reactivity.
(b) metal ‘B’ which gives vigorous reaction even with water and air.
(c) metal ‘C’ which is kept in the middle of activity series.

ANS: (a) ‘A’ can be obtained by chemical reduction by using carbon or carbon monoxide as reducing agent.
(b) ‘B’ can be obtained by electrolytic reduction.
(c) ‘C’ can be reduced by reducing agent like ‘Al’.

What is cinnabar? How is metal extracted from cinnabar? Explain briefly.

ANS: Cinnabar is HgS.
Mercury is obtained by roasting cinnabar. HgO formed is thermelly unstable and gives mercury.
2HgS(s) + O₂(g)→ HgO(s) + SO₂(g)

2HgO(s)→Hg(l) + O₂(g)

or HgS(s) + O₂(g) → Hg(l) + SO₂(g)
Mercury can be purified by distillation.

An ore on heating in air produces sulphur dioxide. Which process would you suggest for its concentration ? Describe briefly any two steps involved in the conversion of this concentrated ore into related metal.

ANS: It is concentrated by froth-floatation process.
(i) Roasting : The concentrated sulphide ore is heated strongly in the presence of oxygen to convert it into its oxide.
2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g)
(ii) Reduction : This oxide of metal is reduced with suitable reducing agent to get free metal.
ZnO(s) + C(s)

ZnO(s) + C(s) →

Zn(s) + CO(g)

Write one example of each of the following:
(a) Most malleable metal and most ductile metal.
(b) The best conductor of heat and the poorest conductor of heat.
(c) A metal with highest melting point and a metal with lowest melting point.

ANS: (a) Gold is the most malleable and ductile metal.
(b) Silver is the best conductor, whereas lead is poor conductor of heat.
(c) Tungsten has highest melting point, Mercury has the lowest melting point.

State reasons for the following:
(a) Electric wires are covered with rubber like material.
(b) From dilute hydrochloric acid, zinc can liberate hydrogen gas but copper cannot.
(c) Sulphide ore of a metal is first converted to its oxide to extract the metal from it.

ANS: (a) It is because rubber is an insulator and does not allow current to flow through it.
(b) Zinc is more reactive than hydrogen. Therefore, it can displace hydrogen from dilute HCl whereas copper cannot, because, it is less reactive than hydrogen.
(c) It is because it is easier to reduce oxide ore as compared to sulphide ore.

A metal ‘X’ acquires a green colour coating on its surface on exposure to air.
(a) Identify the metal ‘X’ and name the process responsible for this change.
(b) Name and write chemical formula of the green coating formed on the metal.
(c) List two important methods to prevent the process.

ANS: (a) Metal is copper. The process is corrosion.
(b) Basic copper carbonate [CuCO₃.Cu(OH)₂]
(c) • It should be coated with tin.
• It should be mixed with other metals to form alloys.

Write one example of each of the following:
(a) A metal and a non-metal which are liquids at room temperature.
(b) A metal which is very soft and a non-metal which is very hard.
(c) A metal which has very low melting point and a non-metal which has very high melting point.

ANS: (a) Mercury is a metal, bromine is non-metal, liquid at room temperature.
(b) Sodium is very soft metal, diamond is very hard non-metal.
(c) Gallium has low melting point, diamond has very high melting point.

What is meant by ‘rusting’? With labelled diagrams, describe an activity to find out the conditions under which iron rusts.

ANS: The process in which iron reacts with oxygen in the presence of moisture to form reddish brown coating of hydrated ferric oxide [Iron (III) oxide].Fe₂O₃ · xH₂O
ACTIVITY
Aim : To show that air and water are necessary for rusting to take place.
Materials Required : Three boiling tubes, iron nails, cork, anhy. CaCl₂, oil.
Procedure : 1. Take three boiling tubes A, B and C.
2. Pour some water in test tube A . Put iron nails in it and cork it.
3. Pour boiled distilled water in another test tube B and put iron nails in it. Add 1 mL of oil over it such that oil floats over it and prevents the air from entering.
4. Take some iron nails in test tube C and put some anhydrous calcium chloride in and cork it.
5. Leave all the three test tubes for one day and then observe.

Observation : Iron nails get rusted in test tube A because both air and water are present in it. Iron nails do not get rusted in B because there is water but no air. In C, rusting will not take place because there is neither air nor water.

Conclusion : Iron gets rusted in the presence of air and water.

Give reasons for the following observations:
(a) Ionic compounds in general have high melting and boiling points.
(b) Highly reactive metals cannot be obtained from their oxides by heating them with carbon.
(c) Copper vessels get a green coat when left exposed to air in the rainy season.

ANS: (a) Ionic compounds have high melting and boiling points due to strong force of attraction between
oppositely charged ions.
(b) It is because these metals, themselves are strong reducing agents. Therefore, cannot be reduced
by reducing agent like carbon.
(c) Copper vessels react with CO₂, O₂ and moisture to form green coloured basic copper carbonate [CuCO₃.Cu(OH)₂].

Explain the following statements:
(a) Most metal oxides are insoluble in water but some of these dissolve in water. What are these
oxides and their solutions in water called?
(b) At ordinary temperature the surface of metals such as magnesium, aluminium, zinc, etc. is
covered with a thin layer. What is the composition of this layer? State its importance.
(c) Some alkali metals can be cut with a knife.

ANS: (a) Solution of metal oxides in water is called alkali (soluble base), e.g. sodium hydroxide (NaOH),
potassium hydroxide (KOH).
(b) This layer is oxide layer. It makes the metal less reactive (passive) and makes it more useful
because it cannot get corroded and remains as it is.
(c) It is because these metals are very soft, e.g. sodium metal can be cut with a knife.

(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 into green coloured ferrous sulphate solution.

ANS: (a) The series of metals in which metals are arranged in decreasing order of their reactivity.
Au < Cu < Fe < Mg is increasing order of 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) Ag (s) + FeSO₄ (aq) → No reaction
Reaction will not take place because ‘Ag’ is less reactive than iron.

A metal (E) is stored under kerosene. When a small piece of it is left open in the air, it catches fire.
When the product formed is dissolved in water, it turns red litmus to blue.
(a) Name the metal (E).
(b) Write the chemical equation for the reaction when it is exposed to air and when the product
is dissolved in water.
(c) Explain the process by which the metal is obtained from its molten chloride.

ANS: (a) ‘E’ is sodium which catches fire in presence of moisture.
(b) 4Na + O₂ → 2Na₂O
Na₂ O + H₂ O → 2NaOH
(c) Electrolytic reduction: Electric current is passed through molten NaCl. Sodium is formed at
cathode and Cl₂ (g) is liberated at anode.

2NaCl →		2Na + Cl₂
Molten

(a) Write two differences between calcination and roasting.
(b) No reaction takes place when granules of a solid ‘A’ are mixed with a powder of solid ‘B’. However when the mixture is heated, a reaction starts with evolution of much heat. Product ‘C’ of the reaction settles down as a liquid metal and solid product ‘D’ keeps floating over the liquid ‘C’. This reaction is sometimes used for making metals for ready use in odd places.
(i) Based on this information, make assumptions about ‘A’ and ‘B’ and corresponding deductions about ‘C’ and ‘D’ and write a balanced chemical equation for the reaction. Include in the chemical equation about physical states of the reactants and products, need of heating for starting the reaction and the reaction being exothermic.
(ii) Name two types of chemical reactions to which this reaction can belong.

ANS:

(a)

Calcination	Roasting
(i) It is carried out by heating ore in the absence of air. (ii) It converts carbonate ores into oxides.	(i) It is carried out by heating ore in the presence of air. (ii) It converts sulphide ores into oxides.

(b) (i) ‘A’ is aluminum, ‘B’ is ferric oxide (Iron(III) oxide).
(ii) This reaction is displacement reaction because ‘Al’ is displacing ‘Fe’. It is also a redox
reaction because ‘Al’ is reducing agent and Fe₂O₃ is oxidising agent.

(a) Write electron dot structure for chlorine (At No. 17) and calcium (At No. 20). Show the formation of calcium chloride by the transfer of electrons.
(b) Identify the nature of the above compound and explain three physical properties of such compounds.

ANS: (b) It is ionic compound.
Physical properties
1. It is hard and solid.
2. It has high melting and boiling point.
3. It is soluble in water.

(a) In the formation of compound 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 in the molten state. Why ?
(d) Why is melting point of NaCl high ?

ANS: (c) Na⁺ and Cl^– are free to move in molten state but not in solid state.
(d) It is due to strong force of attraction between Na⁺ and Cl^–.A

Write the names and symbols of two most reactive metals. Explain by drawing electronic structure how any one of the two metals react with a halogen. State any four physical properties of the compound formed.

ANS: K(Potassium) and Na(Sodium) are two highly reactive metals.
K^· and Na^· are electronic structures as they have one valence electron.
KCl will be the compound formed.
K → K⁺ + e^–
Cl + e^– → Cl^–
(i) It has high melting point.
(ii) It is soluble in water.
(iii) It conducts electricity in molten state not in solid state.
(iv) It is solid and some what hard.

(a) An ore on treatment with dilute hydrochloric acid produces brisk effervescence. What step 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 balanced chemical equation of the reaction involved.

ANS: (a) Carbonate ore:
Steps
(i) Calcination: Carbonate ore is heated in limited supply of air and oxide is obtained, e.g.
(ii) Reduction with carbon: Oxide ore is heated with carbon
ZnO (s) + C (s) → Zn (s) + CO (g)
(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, e.g.
Cu (s) + 2AgNO₃ (aq) → Cu(NO₃)₂ (aq) + 2Ag (s)

(a) Differentiate between roasting and calcination. Explain the two with the help of suitable chemical equations. How is zinc extracted from its ore ?
(b) Name two metals that can be used to reduce metal oxides to metals.

ANS: (a) Roasting: It is process in which sulphide ore is heated in presence of oxygen to convert into oxide.
2ZnS + 3O₂ → 2ZnO + 2SO₂
Calcination. It is a process in which carbonate ore is heated in absence of air to form oxide.

By reduction process, Zn can be extracted from its ore.
Reduction. ZnO + C → Zn + CO₂
(b) Aluminium, Magnesium.

(a) Carbon cannot be used as reducing agent to obtain Mg from MgO. Why?
(b) How is sodium obtained from molten sodium chloride? Give equation of the reactions.
(c) How is copper obtained from its sulphide ore? Give equations of the reactions.

ANS: (a) It is because ‘Mg’ is stronger reducing agent than carbon.
(b) Sodium is obtained from molten NaCl by electrolysis. (c) Copper ore is concentrated by froth-floatation process.
Roasting 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
Bassemerisation: Copper oxide reacts with Cu₂S on heating to form Blister copper and SO₂.
Cu₂S + 2Cu₂O → 6Cu + SO₂
Blister Copper is purified by electrolytic refining.

How is the method of extraction of metals high up in the reactivity series different from that for metals in the middle ? Why the same process cannot be applied for them? Explain giving equations, the extraction of sodium.

ANS: Metals high up in the series are obtained by electrolytic reduction because these metals are strong reducing agents and therefore cannot be obtained by chemical reduction. Metals in middle of series are less reactive and can be obtained by chemical reduction. The same process can’t be used for both them as highly reactive metals can’t be obtained by chemical reduction. Extraction of Sodium is done by electrolysis of molten sodium chloride.

(a) Write the chemical name of the coating that forms on silver and copper articles when these are left exposed to moist air.
(b) Explain what is galvanisation. What purpose is served by it?
(c) Define an alloy. How are alloys prepared? How do the properties of iron change when:
(i) small quantity of carbon,
(ii) nickel and chromium are mixed with it.

ANS: (a) Ag₂S (silver sulphide) is formed on silver, Basic copper carbonate CuCO₃.Cu(OH)₂ is formed on copper.
(b) The process of coating zinc over iron is called galvanisation. It is used to prevent rusting of iron.
(c) Alloy is a homogeneous mixture of two or more metals. One of them can be non-metal. Alloys are prepared by melting two or more metals together.
(i) Iron does not rust on adding small quantity of carbon.
(ii) When we form alloy of iron with nickel and chromium we get stainless steel which is malleable and does not get rusted.

Give reasons for the following:
(a) Silver and copper lose their shine when they are exposed to air. Name the substance formed on their surface in each case.
(b) Tarnished copper vessels are cleaned with tamarind juice.
(c) 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) These metals get corroded. Silver forms black Ag₂S (silver sulphide) and copper form greenish layer of basic copper carbonate CuCO₃.Cu(OH)₂.
(b) Tamarind contains acid which reacts with basic copper carbonate and product gets dissolved and removed from copper vessel.
(c) Aluminium forms oxide layer on its surface which does not further react with air.

(a) How the metals at the top of the reactivity series can be extracted from their ores ? Explain with an example.
(b) Name any one alloy made from
(i) a metal and a non-metal, and
(ii) two metals.

ANS: (a) These metals are extracted by electrolytic reduction e.g., aluminium is obtained from bauxite by electrolytic reduction.
(b) (i) Steel is made up of Iron and Carbon.
(ii) Brass is made up of Copper and Zinc.

(a) Give two methods to prevent the rusting of iron.
(b) Name the ores of the following metals:
(i) mercury, and
(ii) zinc
(c) Explain with the help of a diagram, how copper metal can be refined ? Label the important arrangements in the experimental set up.

ANS: (a) (i) Painting (ii) Galvanisation
(b) (i) Cinnabar (ii) Zinc Blende
(c) Impure copper is taken as anode whereas pure copper is taken as cathode.
Copper sulphate solution (CuSO₄) is taken as electrolyte. When electric current is passed, impure copper changes to ions which gain electrons at cathode and change into pure copper. Impurities are left behind as anode mud.

(a) Define corrosion.
(b) What is corrosion of iron called?
(c) How will you recognise the corrosion of silver?
(d) Why corrosion of iron is a serious problem?
(e) How can we prevent corrosion of iron?

ANS: (a) It is a process in which a metal reacts with substances present in air to form surface compounds.
(b) Rusting.
(c) Black layer on its surface due to formation of Ag₂S.
(d) It makes the metal weak and brittle, which is serious problem.
(e) Oiling, painting, greasing, galvanisation, alloying can prevent iron from corrosion.

74	Ram singh is a villager who uses underground water for drinking. Fluoride ion, iron levels, salinity and arsenic levels are high in ground water. Underground water also contains microorganism which cause diseases like typhoid, cholera. His son Himanshu advised his father to use boiled water and add one tablet of bleaching powder to one bucket of water. (a) What are harmful effects of F^– in water? (b) What can we do for preservation of underground water? (c) What values are possessed by Himanshu?	4

	ANS: (a) It may cause fluorosis leading to tooth decay. (b) Rain harvesting. (c) Himanshu is helping his family to remain free from water-borne disease.

75	Seema cooks and sometimes overcooks food to make it tender irrespective of the fact that it destroys some nutrients. She adds spices, sugar and/or salt to make it tastier and enjoyable. Geeta uses plant roots and fruits which have enough sugar. She uses food of a vegetable origin is better than animal origin. Seema enjoy spicy food but also takes one tablet for heart burn, one for digestion and another to release constipation. She uses stale food or the food repeatedly warmed which loses its nutritive value. She uses frozen and preserved food which have a shelf life, after which it is inedible. (a) Why should we prefer food from vegetable origin and not from animal origin? (b) Why should we not take spicy food? (c) Why should we not overcook food? (d) Why should we not take frozen and preserved food and always prefer fresh food? (e) What values are possessed by Geeta?	4

	ANS: (a) Food from vegetable origin is less complex and easily digestible as compared to food from animal origin. (b) It leads to indigestion and sometimes constipation and heartburn. (c) It will lead to loss of nutrients. (d) It has shelf life and is not fit for use after sometimes it becomes stale. Fresh food is rich in nutrients. (e) Geeta has good eating habits and she keeps her family healthy.

76	Sonu filled helium gas which is lighter than air in party balloons which float up to ceiling on her birthday. There is shortage of the helium which is threatening to disrupt critical research projects. Helium is the second most abundant element in the universe. It is used to inflate airships as it is non-inflammable. It is used to cool magnets used in semiconductors and in mobile phones. It is mixed with oxygen in deep sea diving. It is used for cooling magnets needed for super conductivity. It is used in cryosurgery. Monu does not use helium in party balloon and also asked sonu not to use it due to its usefulness in medicines and other fields. (a) Why is helium so useful? (b) Why is helium used in cryosurgery? (c) Why is there a shortage of helium? (d) How can we overcome shortage of helium? (e) What values are possessed by Monu who does not use helium gas in party balloons?	4

	ANS: (a) It is inert, non-inflammable, lighter and has low boiling point which make it very useful. It is cheap and readily available. (b) Liquid helium at low temperature can destroy microorganism causing infections. (c) Cheap helium drives misuse as 8% of world’s helium supply is currently used for filling party balloons. (d) We should not fill party balloons with helium gas. (e) Monu is saving most important gas which can be better used for cryosurgery. He is sensible person and takes care of others.

77	Shivam helps his friend Rohan in studies. Shivam is topper in the class. Rohan also improved his performance. They like each other and they are good friends. (a) What values are possessed by Shivam? (b) What type of bond exists between Rohan and Shivam? (c) Why are ionic bonds strong?	4

	ANS: (a) Shivam has helping nature. (b) It is like ionic bond. (c) Ionic bond are strong due to strong force of attraction between oppositely charged ions.

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