Class 10 Science Chapter 3 Board Questions

Class 10 Science Chapter 3 Board Questions of Metal and Non-Metals including last 10 years’ board paper’s questions from CBSE Board with answers. The year of examination is mentioned in front of the questions.

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Class 10 Science Chapter 3 Board Questions From 10 Years

Class:10
Subject:Science
Contents:Board Questions & 10 Years Papers

Class 10 Science Chapter 3 Board 10 Years Questions

Class 10 Science Chapter 3 Board Questions including last 10 Years Papers answers are given below. All the questions are taken from CBSE Board Papers and CBSE Sample Papers of Previous Years Exams. These set to Board Papers Questions will provide a complete revision and preparation for board exams 2020-2021.

10th Science Chapter 3 Board Questions Set – 1 (1 Mark)

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? [CBSE 2012]

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

A non-metal X exist in two different forms Y and Z. Y is the hardest natural substance, whereas Z is good conductor of electricity. Identify X, Y and Z. [CBSE 2011]

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 is non-lustrous. [CBSE 2011]

Iodine is a non-metal which is lustrous lead is a known lustrous metal.

Why gas is liberated when a metal reacts with acid? How will you check the presence of this gas? [CBSE 2011]

Hydrogen gas is formed. Bring a burning matchstick near to it H2 will burn explosively with pop sound.

Name the metal which react with a very dilute HNO3 to evolved hydrogen gas. [CBSE 2011]

Magnesium.

What is the valency of silicon with atomic number 14? [CBSE 2010]

Its valency is equal to 4.

Calcium Float on Water

Calcium is highly reactive metal. When it react with water, hydrogen gas is formed which sticks to surface of calcium therefore it is float.

10th Science Chapter 3 Board Questions Set – 2 (1 Mark)

What is the valency of phosphorous with atomic number 15? [CBSE 2010]

Phosphorous has valency 3.

Which of the following two metals will melt at body temperature (37oC)? [CBSE 2008]

Gallium and Caesium.

Arrange the following metal in decreasing order of reactivity: Na, K, Cu, Ag. [CBSE 2009]

K> Na > Cu > Ag.

What is the valency of an element with atomic number 35? [CBSE 2010]

Its valency is 1.

Metal generally occur in solid state. Name and write symbol of a metal that exists in liquid state at room temperature. [CBSE 2009]

Mercury(Hg) exist in liquid state at room temperature.

Element M forms a chloride with the formula MCL2 which is solid with higher melting point. To which group of the periodic table does the element M belong? [CBSE 2008]

M belong to group 2.

From amongst the metals sodium, calcium, Aluminium, copper and magnesium, name the metal. (i) which react with water only on boiling and, (ii) another which does not react even with stream. [CBSE 2008]

(i) magnesium react with water only on boiling.

(ii) Copper does not react with even steam.

Do You Know

Magnesium and manganese react with very dilute HNO3 to evolve hydrogen gas.

10th Science Chapter 3 Board Questions Set – 3 (1 Mark)

Show the electronic transfer in the formation of MgCl2 from its elements. [CBSE 2008]

Mg Cl → Mg+2 Cl2-

Name any one metal which react neither with cold water nor with hot water, but react with heated steam to produce hydrogen gas. [CBSE 2006]

Iron 3Fe + 4H2O → Fe2O4 + 4H2.

Name one metal which react with very dilute HNO3 to evolve hydrogen gas. [CBSE 2010]

Magnesium and manganese react with very dilute HNO3 to evolve hydrogen gas.

Which property makes solder suitable for welding electrical wires? [CBSE 2010]

Low melting point makes solder suitable for welding electrical wires.

Give an example of a metal which is liquid at room temperature. [CBSE 2011]

Mercury.

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. [CBSE 2011]

X = Carbon
Y = Diamond
Z = Graphite

An element A forms two oxides AO and AO2. The oxides AO is neutral whereas the oxide AO2 is acidic in nature. Would you call element A a metal or a non-metal? [CBSE 2011]

Element A is a non-metal. Only non-metals form neutral and acidic oxides.

How do we know whether a given element is a non-metal if we know its electronic configuration? [CBSE 2011]

If there are four or more than four electrons in the valence cell of the given element it is a non-metal.

Silver Ornaments Lose their Shine

They get tarnished by reacting with atmospheric gases to produce Silver Sulphide.

10th Science Chapter 3 Board Questions Set – 4 (1 Mark)

In nature Aluminium is found in combine state whereas silver, gold is found in free state. Give reason. [CBSE 2011]

Aluminium is reactive metal while silver and gold are unreactive metals.

Name one metal and one non-metal which exist in liquid state room temperature. [CBSE 2012]

Metal: Mercury
Non-metal: Bromine

Choose the amphoteric oxides amongst the following: Na2O, ZnO, Al2O3, CO2, H2O [CBSE 2012]

ZnO and Al2O3

What kind of compound are called ionic compound? [CBSE 2012]

Compounds formed by the transfer of electron from one atom to other are called ionic compound.

Name the metal which has very low melting point and can melt with the heat of your palm. [CBSE 2012]

Gallium/Caesium.

Metallurgy

The process of extraction of a metal from its ore is called metallurgy.

10th Science Chapter 3 Board Questions Set – 5 (2 Marks)

Name the following: (a) A metal, which is preserved in kerosene. (b) A lustrous coloured non-metal. (c) A metal, which can metal while kept on palm. (d) A metal, which is a poor conductor of heat. [CBSE 2012]

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

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. [CBSE 2012]

Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of metal.
Ca + 2H2O → Ca(OH)2 + H2
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 ‘reactive series’. Is this statement true? Justify your answer with examples. [CBSE 2011]

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 stream which shows it is less reactive.

X + YSO4→XSO4 + Y and Y + XSO4→ No Reaction. Out of the two element X and Y which is more reactive and why? [CBSE 2011]

X is more reactive than Y because it replaces Y from its salt solution.

What is an alloy? State the constituent of solder. Which property of solder makes it suitable for welding electrical wires. [CBSE 2011]

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 make it suitable for welding electrical wires.

Using the electronic configuration, explain how magnesium atom combines with oxygen atom to form magnesium oxide by transfer of electron? [CBSE 2011]

Mg(12) = 2, 8, 2
Mg → Mg+2 + 2e-

O(8) = 2,6
O+ 2e- → O2-

Atmospheric Ooxides

Those oxides which acidic as well as basic are called atmospheric oxides.
Example:Al2O3, ZnO.

10th Science Chapter 3 Board Questions Set – 6 (2 Marks)

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. Identifying X, Y and Z. [CBSE 2011]

2Na + 2H2O → 2NaOH + H2
X is Sodium, Y is Sodium Hydroxide and Z is H2.

Write balanced chemical equation that shows Aluminium oxide reacts with acid as well as base. [CBSE 2011]

Al2O3 + 6HCl → 2AlCl3 + 3H2O

Al2O3 + 2NaOH → 2NaAlO2 + H2O

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. [CBSE 2010]

Mg (12) = 2, 8, 2

O (8) = 2, 6

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? [CBSE 2009]

Black coating: Silver Sulphide (Ag2S)
Green coating: Basic copper carbonate (CuCO3. Cu(OH2))
By the action of the following:
(i) H2S or Sulphur compounds are present in the atmosphere.
(ii) Carbon dioxide, oxygen and water vapors present in the atmosphere.

Give reason for the following: (a) Gold and Silver ae used to make jewellery. (b) Carbonate and Sulphide ores are usually converted into oxides prior to reduction during the process of extraction. [CBSE 2008]

(a)It is because gold and silver are highly reactive.

(b) It is because reduction of oxide is easier than carbonate and Sulphide ores.

Hydrogen is not Evolved when a metal reacts with nitric acid

It is because nitric acid is oxidising agent and it provides oxygen to hydrogen released to form water. So, hydrogen is not evolved on reaction of metal with nitric acid.

10th Science Chapter 3 Board Questions Set – 7 (2 Marks)

Give reasons for the following: (a) Aluminium oxide is considered as an atmospheric oxide. (b) Ionic compounds conduct electricity in molten state. [CBSE 2012, 2008]

(a) It is because it is acidic as well as basic. ‘Al’ is less electropositive metal.
So, it forms atmospheric oxide which can react with acid as well as base.

(b) Ionic compounds can conduct electricity in molten state because ions become free to move in molten state.

Choose a metal out of the following which reacts with hot water but not with cold water: Sodium, Magnesium, Iron. Mention the products formed during the reaction. [CBSE 2006]

Magnesium
The products formed are magnesium hydroxide and hydrogen gas.
Mg + 2H2O → Mg(OH)2 + H2

Choose the metal (from the list given below) which can displace zinc from zinc sulphate solution-Lead, Copper, Magnesium, Silver. Write the equation of the chemical reaction involved. [CBSE 2006]

Magnesium, because it is more reactive than zinc.
Mg + ZnSO4 → MgSO4 +Zn

(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. [CBSE 2012]

(a) Ca → Ca+2 + 2e-
O + 2e- → O2-

(b) bronze is made up of copper and tin.

A metal X acquires a green colour coating on its surface on exposure to air. (i) Identify the metal X and name the process responsible for this change. (ii) Name and write chemical formula of the green coating formed on the metal. (iii) List two important methods to prevent the process. [CBSE 2012]

(i) Metal is copper. The process is corrosion.

(ii) Basic copper carbonate(CuCo3.Cu(OH)2)

(iii)
(a) It should be coated with tin.
(b) It should be mixed with other metals to form alloy.

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10th Science Chapter 3 Board Questions Set – 8 (3 Marks)

Write balanced equations for the reaction of: (i) Aluminium when heated in air. Write the name of the product. (ii) Iron with steam. Name the product obtained. (iii) Calcium with water. Why does calcium start floating in water? [CBSE 2012]

(i) 4Al + 3O2 → 2Al2O3.
The product formed is Aluminium oxide.

(ii) 3Fe + 4H2O → Fe3O4 + 4H2
The product obtained is iron and iron oxide.

(iii) 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. [CBSE 2012]

(a) 2Al + 3H2SO4 → Al2(SO4)3 + 3H2

(b) Na2Co3 + 2HCl → 2NaCl + H2O + CO2

(c) Ca(OH)2 + CO2 → CaCO3 + H2O

What is meant by reactivity series of metals? State which of the following chemical reactions will take place giving suitable reasons for each. (I) Zn + CuSO4 → ZnSO4 + Cu (II) Fe + ZnSO4 → FeSO4+ Zn (III) Zn + FeSO4 → ZnSO4 + Fe [CBSE 2009]

Reactivity series is a list of metals arranged in the order of their decreasing reactivity (activities).

(i) Reaction will take place because Zn is above Cu in the activity series and is more reactive then Cu.

(ii) Reaction will not take place as Fe is below Zn in the activity series and cannot displace Zn from its solution.

(iii) Reaction will take place because Zn is more reactive than Fe.

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. [CBSE 2009]

It is concentrated by froth floatation process.
(i) Roasting: The Sulphide ore is converted into oxide are by heating strongly in the presence of excess air. This process is known as roasting.
For example: 2ZnS + 3O2 → 2ZnO + 2SO2

(ii) Reduction: This oxide of metal is reduced with suitable reducing agent to get free metal
For example: ZnO + C → Zn+ Co

Rusting

The process in which iron reacts with oxygen in the presence of moisture to form reddish brown coating hydrated ferric oxide, iron oxide [Fe2O3.XH2O].

10th Science Chapter 3 Board Questions Set – 9 (3 Marks)

Give reasons for the following observations: (i) Ionic compounds in general have high melting and boiling points. (ii) Highly reactive metals cannot be obtained from their oxides by heating them with carbon. (iii) Copper vessels get a green coat when left exposed to air in the rainy season. [CBSE 2009]

(i) Ionic compounds have high melting and boiling points due to strong force of attraction between oppositely charged ions.

(ii) It is because these metal, themselves are strong reducing agents. Therefore, cannot be reduced by reducing agent like carbon.

(iii) Copper vessels react with Co2, O2 and moisture to form green coloured basic copper carbonate.

State reasons for the following observations: (i) The shining surface of some metals becomes dull when exposed to air for a long time. (ii) Zinc fails to evolve hydrogen gas on reacting with dilute nitric acid. (iii) Metal Sulphide occur mainly in rocks but metal halides occur mostly in sea and lake waters. [CBSE 2009]

(i) It is because metal reacts with substance present in atmosphere to form surface compound which make it dull.

(ii) It is because Dil. HNO3 is an oxidising agent therefore zinc gives No and not H2 with Dil. HNO3.

(iii) It is because sea water contains sodium chloride due to which metal halides are formed whereas Sulphur is found below rocks. Therefore, metal Sulphide are formed in rocks.

State reasons for the following: (i) Electric wires are covered with rubber like material (ii) From dilute hydrochloric acid, zinc can liberate hydrogen gas but copper cannot. (iii) Sulphide ore of a metal is first converted to its oxide to extracted the metal from it. [CBSE 2009]

(i) It is because rubber is an insulator and does not allow current to flow through it.

(ii) Zinc is more reactive than hydrogen. Therefore, it can displace hydrogen from Dilute HCL whereas copper cannot because it is less reactive than hydrogen.

(iii) It is because it is easier to reduce oxide ore as a compound to Sulphide ore.

(a) Why are ionic compound are usually hard? (b) How is it that ionic compound in the solid state do not conduct electricity but they do so when in molten state? [CBSE 2012, 2008]

(a) It is due to strong force of attraction between oppositely charged ions.

(b) 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.

(a) Name the solvent in which ionic compound are generally soluble? (b) Why are aqueous solution of ionic compound able to conduct electricity? [CBSE 2012, 2008]

(a) Ionic compound are soluble in water. (b) It is because is consist of ions which can move freely in aqueous solution and carry current.

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10th Science Chapter 3 Board Questions Set – 10 (3 Marks)

(a) What are amphoteric oxides? Choose the amphoteric oxide from amongst the following oxides: Na2O, ZnO, Al2O3, CO2, H2O. (b) Why is that non-metal do not displace hydrogen from dilute acids? [CBSE 2008]

(a) Those oxides which are both acidic as well as basic solution called amphoteric oxides, example Al2O3, ZnO.

(b) It is because non-metals do not supply electrons to change H+ Ions into hydrogen gas.

Name two metal which react with violently with cold water. Write any three observations you would make when such a metal is dropped into water. How would you identify the gas evolved if any during the reaction? [CBSE 2008]

Sodium, Potassium
When these metals are dropped in water, Bubbles will be evolved due to evolution of hydrogen gas.

The gas will catch fire and the solution will be alkaline i.e. it will turn red litmus blue. Test: When a burning match stick is brought near it burns explosively with a POP sound and splinter is extinguished.

A metal M found in nature as Sulphide ore (M2S) is one of the good conductor of heat an electricity and used in making electric wires. (i) Identify the metal M. (ii) Write the balanced chemical equation involved in the process of extraction of the metal. [CBSE 2010]

(i)The metal M is copper Cu.

(ii) Balanced chemical equations for the extraction of copper are:
(a) Cu2S + 3O2 → 2Cu2O + 2SO2
(b) 2Cu2O + Cu2S → 6Cu + SO2

A substance X which is an oxide of a metal is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reaction involved. [CBSE 2011]

The substance X is calcium oxide, CaO.
The element calcium is present in bones.
On treatment with water, it produces a calcium hydroxide as under:
CaO + H2O → Ca(OH)2
Calcium hydroxide is a base. It turns red litmus blue.

A metal A which is used in thermite process, when heated with oxygen gives an oxide B, which is atmospheric in nature. Identify A and B. Write down the reactions of oxide B with HCl and NaOH. [CBSE 2011]

The metal A is Aluminium Al.
The substance B is Al2O3 which is atmospheric because it react with both acid and base.
Al2O3 + 6HCl → 2Al2O3 + 3H2O
Al2O3 + NaOH → 2NaAlO2 + H2O

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10th Science Chapter 3 Board Questions Set – 11 (3 Marks)

(a) What do you see when a magnesium ribbon is burn? Is magnesium oxidised reduced in this reaction? (b) Define corrosion? [CBSE 2011]

(a) Magnesium burns with a dazzling light producing white ash of magnesium oxide.
2Mg + O2 → 2 MgO
Magnesium is oxidised because it combines with oxygen.

(b) Corrosion is defined as the combination of a metal with atmospheric oxygen, carbon dioxide and moisture to form an oxide, carbonate etc. corrosion causes damage to car body, bridges, etc.

With reference to the electro refining of impure copper, Answer the following? (a) What is the electrolyte used? (b) name the cathode and anode used. (c) What happens at cathode and anode. [CBSE 2011]

(a) The electrolyte used in the refining of copper is acidified CuSo4 solution.

(b) Anode consist of impure copper.
Cathode consist of a strip of pure copper.

(c) Pure copper is deposited at cathode.
Cu+2 + 2e- → Cu
Copper dissolves into the solution at the anode.
Cu → Cu+2 + 2e-

What are atmospheric oxides? Give two examples of atmospheric oxide with balanced chemical equation. [CBSE 2011]

An oxide which reacts with acids as well as bases to produce salt and water is called atmospheric oxide.
Al2O3 + 6HCl → 2AlCl3 + 3H2O
Al2O3 + 2NaOH → 2NaAlO2 + H2O

What is concentration of an ore? Why is it necessary to concentrate an ore before processing? Name an ore of mercury and copper? [CBSE 2012]

The process of removing unwanted impurities like sand, soil etc present in an ore is called concentration of an ore.
We need to concentrate the ore so that the impurities do not interfere in the extraction of the metal.
Ore of mercury: Cinnabar (HgS)
Ore of copper: Copper Pyrite (Cu2S)

Give reasons: (i) Silver metal does not easily combine with oxygen but silver jewellery tarnished after sometime. (ii) Iron grills are frequently painted. (iii) Gold ornaments retain their luster even after several years of use. [CBSE 2013]

(i) Silver meatal react with the H2S gas present in traces in the atmosphere to form silver sulphide which tarnish is a metal.

(ii) Iron forms a layer of rust (Fe2O3.XH2O) on combination with oxygen and moisture present in the atmosphere. This weakens the metal. To prevent this loss iron gills are frequently painted.

(iii) Gold is an unreactive metal it does not react with atmospheric oxygen and acids so the luster of gold jewellery is retained even after several years.

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10th Science Chapter 3 Board Questions Set – 12 (3 Marks)

(a) Compare the properties of a typical metal and a non-metal on the basis of the following: (i) Nature of the oxide formed by them. (ii) Conductivity. (b) name a non-metal which is lustrous and metal which is liquid at room temperature. [CBSE 2013]

(a)
(i) Sodium is a metal, it forms basic oxide while carbon is a non-metal. It forms acidic oxide.
(ii) Copper is a metal. It is a good conductor of heat and electricity. Sulphur is a non-metal it is non conductor of heat and electricity.

(b) Graphite, a form of carbon is a non-metal and is lustrous. Mercury, (Hg) a metal is a liquid at room temperature.

A Non-metal A is an important constituent of food and forms two oxides B and C. Oxide of B is Toxic whereas C causes global warming. (a) Identify A, B, C. (b) To which group of periodic table does A belong? [CBSE 2011]

(a) The non-metal A is carbon. Carbon is a constituent of carbohydrate, proteins and fats.
B = Carbonmonooxide (CO)
C = Carbon dioxide (CO2)
CO is a poisonous gas and CO2 causes global warming.

(b) 14th group.

Write the chemical name and formula of gypsum. What happens when gypsum is heated at 373K write chemical equation for the reaction? [CBSE 2015]

Chemical name: calcium sulphate hydrated.
Formula: CaSo4. 2H2O

On heating gypsum at 373K, gypsum changes to plaster of Paris.
CaSO4. 2H2O → CaSO4. 1/2H2O + 1.1/2 H2O

Mention the names of the metal for the following; (a) Two metals which are alloyed with iron to make stainless steel. (b) Two metals which are used for making jewellery. (c) Metals present in bronze. [CBSE 2016]

(a) Nickel and chromium are alloyed with iron to make stainless steel.

(b) Gold and silver are used for making jewellery.

(c) Copper and tin are present in bronze.

Give reason for the following: (a) Sodium is kept immersed in kerosene oil. (b) Iron the most widely used metals is never used in its pure state. (c) Hydrogen is not evolved when a metal reacts with nitric acids. [CBSE 2015]

Sodium is reactive metal.
Na + 2H2O → NaOH + H2
Kerosene does not react with sodium.

(b) Iron is soft metal. It is alloyed with other elements for different uses.

(c) This is because hydrogen gas first evolved react with HNO3 to form oxide of nitrogen.

Write the name and symbols of constituents present in the following alloy: (a) Brass (b) Bronze (c) Solder [CBSE 2016]

Brass: Copper(Cu) and Zinc(Zn)

Bronze: Copper(Cu) and Tin(Sn)

Solder: Lead(Pb) and Tin(Sn)

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10th Science Chapter 3 Board Questions Set – 13 (5 Marks)
Explain the following: (a) Reactivity of Al decreases if it is dipped in HNO3. (b) Carbon cannot reduce the oxides of Na or Mg. (c) NaCl is not a conductor of electricity in solid state whereas it conducts electricity in aqueous as well as in molten state. (d) Iron articles are galvainished. (e) Metal like Na, K, Ca, N, Mg are never found in their free state in nature. [CBSE 2014]

(a) When Al is dipped in HNO3 a layer of AL2O3 is formed on Aluminium which decreases the activity of Al.

(b) Carbon is less reactive element than Na or Mg.

(c) In the solid state the ions Na+ and Cl- are not free to move about. In aqueous solution and molten state the ions can move and conduct electricity.

(d) Galvanization is a coating of surface with zinc this is done to prevent corrosion of iron and zinc as has smaller tendency to oxidised.

(e) Na, K, Ca, Mg are highly reactive metals they react with oxygen and carbon dioxide to form oxides carbonates etc.

(a) Describe an activity to show that metals are good conductor of electricity. (b) Account for the following: (i) Hydrogen gas is not evolved when a metal reacts with nitric acid. (ii) For storing sodium metal it is kept immersed in kerosene. (iii) The reaction of iron oxide with Aluminium. [CBSE 2015]

(a) Activity:
1. Set up an electric circuit.
2. Place the metal to be tested in the circuit between terminals A and B.
3. We find that the bulb glows. This shows that metal is good conductor of electricity.

(b)
1. This is because the hydrogen gas first evolved reacts with HNO3 to produce oxides of nitrogen.
2. We cannot store it under water because sodium reacts with water to produce hydrogen gas.
2Na + 2H2O → 2NaOH + H2
3. Fe2O3 + 2Al →Al2O3 + 2Fe + Heat
This is exothermic reaction. The molten iron is used to join cracked iron parts of machine.

(a) When calcium metal is added to water, the gas evolved does not catch fire but the same gas evolved on adding potassium metal to water catches fire. Explain why? (b) Name a metal for each case: (i) It displaces hydrogen gas from nitric acid. (ii) It does not react with any physical state of water. (iii) It does not react with cold as well as hot water but reacts with steam. [CBSE 2015]

(a) Reaction of potassium with water is so violent and exothermic that the evolved hydrogen catches fire.
2K + 2H2O→ 2KOH+ H2
The reaction of calcium with water is less violent. The heat evolved is not sufficient for hydrogen to catch fire.
Ca + 2H2O → Ca(OH02 + H2

(b) (i) Magnesium
(ii) Copper
(iii) Aluminium

Give reasons for the following: (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 it has been assigned a place in the reactivity series of metals. (iv)The galvanized iron articles is protected against rusting even if the zinc layer is broken. (v) The wires carrying current in homes have a coating of PVC. [CBSE 2016]

(i) It is easier to convert metal oxides to metals as compared to carbonates and Sulphide. Therefore, Carbonates are calcinated and Sulphide are roasted to oxides.

(ii) There are electrostatic forces of attraction between the cations and anions in ionic compounds which are difficult to break. Therefore, ionic compounds have high melting points.

(iii) Metals above hydrogen evolve hydrogen gas and metals below hydrogen do not evolve hydrogen when treated with an acid. That is when hydrogen has been assigned a place in the reactivity series of metals.

(iv) Even if zinc layer is broken, It will preferentially oxidised because it is more reactive than iron.

(v) The wires carrying current in homes have a coating of PVC. This is because PVC is an insulting substance and protects from electric shock.

(a) Define corrosion, what name is given to the corrosion of iron? (b) Name the colour of coating formed on silver and copper articles, when exposed to air? (c) List two damages caused by corrosion and suggest how corrosion can be prevented. [CBSE 2016]

(a) When a metal is attacked by substances around it, such as moisture, acids, etc, it is said to corrode and this process is called corrosion. Corrosion of iron is called rusting.

(b) Coating formed on silver is black and that formed on copper is green.

(c) Damages caused by corrosion:
(i) It causes damage to car bodies and bridges.
(ii) It damages iron railings and ships.

Prevention of corrosion:
(i) Corrosion can be prevented by oiling, painting, greasing and galvanizing.
(ii)Corrosion can be prevented by galvanizing and alloying.↓

Properties of Ionic Compounds

Ionic compounds have high melting and boiling points. Ionic compounds are generally soluble in water and insoluble in kerosene and petrol.

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