Class 10 Science Chapter 3 Board Questions

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

X is carbon, Y is diamond as it is the hardest natural substance and Z is graphite as it is good conductor of electricity.

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

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

Magnesium.

Its valency is equal to 4.

Phosphorous has valency 3.

Gallium and Caesium.

K> Na > Cu > Ag.

Its valency is 1.

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

M belong to group 2.

(i) magnesium react with water only on boiling.

(ii) Copper does not react with even steam.

MgCl₂ → Mg²⁺ (Cl₂)²⁻

Iron 3Fe + 4H₂O → Fe₂O₄ + 4H₂.

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

Low melting point makes solder suitable for welding electrical wires.

Mercury.

X = Carbon
Y = Diamond
Z = Graphite

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

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

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

Metal: Mercury
Non-metal: Bromine

ZnO and Al₂O₃

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

Gallium/Caesium.

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

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.

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

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.

Mg(12) = 2, 8, 2
Mg → Mg⁺² + 2e-

O(8) = 2,6
O + 2e- → O²⁻

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

Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

Mg (12) = 2, 8, 2

O (8) = 2, 6

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.

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

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

(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.

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

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

(a) Ca → Ca⁺² + 2e-
O + 2e- → O²⁻

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

(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.

(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.

(a) 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂

(b) Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

(c) Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

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.

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

(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.

(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.

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

(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.

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.

(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

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.

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

(a) Magnesium burns with a dazzling light producing white ash of magnesium oxide.
2Mg + O₂ → 2MgO
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.

(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-

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

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)

(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.

(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) 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.

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

(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.

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.

Brass: Copper(Cu) and Zinc(Zn)

Bronze: Copper(Cu) and Tin(Sn)

Solder: Lead(Pb) and Tin(Sn)

(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) 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) 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(OH)₂ + H₂

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

(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) 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.↓