Metals and Non-metals

AgNO₃ solution and copper

Reason — In reactivity series, Na is above Cu, Mg is above Al and Fe is above Ag so displacement reaction does not occur in these pairs. Ag is below Cu, hence only AgNO₃ solution and copper metal will give displacement reaction.

Applying a coating of zinc

Reason — Applying grease is not suitable as it will contaminate the food cooked in the frying pan making it inedible. Applying paint is not suitable as heating and washing the pan several times will cause the paint to peel off very soon. Hence, galvanisation i.e., applying a coating of zinc is the most suitable method to prevent an iron frying pan from rusting.

Calcium

Reason — The resulting compound must be ionic as it has a high melting point which means that it must be formed by the reaction of a metal with oxygen. So, it will be either Calcium or Iron.
As oxide of Calcium is soluble in water but oxides of Iron are not, hence the element is likely to be Calcium.

Zinc is more reactive than tin

Reason — Zinc is more reactive than tin. It reacts with food acids to form poisonous compounds hence, it is not used to coat food cans.

(a) Method 1 — On striking with hammer if the sample takes the shape of a sheet, it is a metal. A non-metal will break into pieces, hence, the two can be distinguished.

Method 2 — Set up an electric circuit using a battery, a bulb, wires and switch as shown in the figure below.

Place the element to be tested between the terminals A and B. If the bulb glows, then the sample is a metal, if not, then it is a non-metal.

(b) Method 1 — When struck by hammer, metals being malleable turn into sheets whereas non-metals being brittle break into pieces.
Method 2 — Metals are good conductors of electricity, hence the bulb glows whereas non-metals are poor conductors of electricity.

Amphoteric oxides are those compounds which react with both acids and alkalis to form salt and water.

Example: Zinc Oxide (ZnO), Lead Oxide (PbO)

Two metals which will displace hydrogen from dilute acids
Zinc and Iron (as they are placed above hydrogen in reactivity series)

Two metals which will not displace hydrogen from dilute acids
Copper and Silver (as they are placed below hydrogen in reactivity series)

Impure metal M is made the anode, thin strips of pure metal is made the cathode. A solution of metal salt is used as electrolyte.

(a) The gas collected is sulphur dioxide. It is acidic in nature.

(i) No change in colour is seen with dry litmus paper.

(ii) moist blue litmus paper turns red, confirming that the acidic nature of the gas.

(b) S (s) + O₂ (g) ⟶ SO₂ (g)

Two ways to prevent the rusting of iron are:

(i) Applying grease or paint.

(ii) Galvanization.

Acidic oxides are formed when non-metals combine with oxygen.

(a) Platinum, gold and silver are low reactive metals so they rarely corrode and hence do not lose their shine and lustre. Additionally, they are very malleable and ductile so they can be easily crafted into beautiful jewellery having fine design.

(b) Sodium, potassium and lithium react so vigorously with oxygen that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are stored under oil.

(c) Aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide on its surface. This oxide layer is very stable and acts as a protective coating by preventing further reaction of aluminium. This combined with aluminium's excellent heat conductivity, easy and cheap availability, malleability and ductility makes it a good choice to make utensils for cooking.

(d) As metals can be easily extracted by the reduction of their oxides rather than from their carbonates and sulphides therefore carbonate and sulphide ores are usually converted into oxides during the process of extraction.

When copper vessels come into contact with moist carbon dioxide in the air, copper carbonate is formed that gets deposited as a green layer on the surface of these copper vessels and tarnishes them. The citric acid present in lemon or tamarind juice acts to neutralize the basic copper carbonate, effectively dissolving this layer. This restores the characteristic luster of the copper vessels.

The man's actions and the outcome suggest that he used aqua regia to clean the gold bangles. Aqua regia is a mixture of one part by volume of concentrated nitric acid and three parts by volume of concentrated hydrochloric acid. It is known for its ability to dissolve noble metals like gold and platinum.
When the man dipped the bangles in aqua regia, outer layer of gold dissolved in it. So, although the bangles sparkled like new but their weight was reduced drastically.

Copper being below hydrogen in the reactivity series does not react with cold water, hot water or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water as shown in the reaction below:
3Fe (s) + 4H₂O (g) ⟶ Fe₃O₄ (s) + 4H₂ (g)
Thus, to prevent corrosion, copper is used to make hot water tanks and not steel.

(i) Mercury

(ii) Sodium

(iii) Silver

(iv) Lead

Malleable — Ability of metals to be beaten into thin sheets is called Malleability. Gold and silver are the most malleable metals.

Ductile — Ability of metals to be drawn into thin wires is called ductility. Gold is the most ductile metal.

Sodium reacts so vigorously with oxygen present in air that it catches fire if kept in the open. Hence, to protect it and to prevent accidental fires sodium is kept in kerosene oil.

1. 3Fe (s) + 4H₂O (g) ⟶ Fe₃O₄ (s) + 4H₂ (g)
2. Ca (s) + 2H₂O (l) ⟶ Ca(OH)₂ (aq) + H₂ (g)
   2K (s) + 2H₂O (l) ⟶ 2KOH (aq) + H₂ (g) + heat energy

(i) B is showing displacement reaction with iron (II) sulphate and no reaction with silver nitrate, hence, the metal lies above iron and below zinc. As we know metals at the top of the metal reactivity series are most reactive, therefore, B is the most reactive metal.

(ii) When B is added to a solution of copper (II) sulphate, displacement reaction will take place. Blue colour of copper sulphate will fade and reddish brown copper will settle down.

(iii) The decreasing order of reactivity is:

B > A > C > D

Hydrogen gas

Fe (s) + H₂SO₄ (aq) ⟶ FeSO₄ (aq) + H₂ (g)

The bluish-green colour of iron (II) sulphate solution changes to colourless when zinc is added to it, as zinc, being higher in the reactivity series than iron, displaces iron from the solution.

Zn (s) + FeSO₄ (aq) ⟶ ZnSO₄ (aq) + Fe (s)

(i) Electron-dot structures for sodium, oxygen, and magnesium are shown below:

(ii) Formation of Na₂O

$\underset{\text{2,8,1}}{\text{Na}} \longrightarrow \underset{\text{2,8}}{\text{Na}^+} + \text{e}^-$

$\underset{\text{2,6}}{\text{O}} + 2\text{e}^- \longrightarrow \underset{\text{2,8}}{\text{O}^{2-}}$

Formation of MgO

$\underset{\text{2,8,2}}{\text{Mg}} \longrightarrow \underset{\text{2,8}}{\text{Mg}^{2+}} + 2\text{e}^-$

$\underset{\text{2,6}}{\text{O}} + 2\text{e}^- \longrightarrow \underset{\text{2,8}}{\text{O}^{2-}}$

(iii) Ions present in these compounds are:

Ionic compounds have high melting points because a considerable amount of energy is required to break the strong inter-ionic attraction between the oppositely charged ions of the compound.

(i) Mineral — Minerals are naturally occurring, homogenous solid inorganic substance that have a definite chemical composition with its own chemical and physical properties.

(ii) Ores — Ores are minerals from which metals are extracted commercially at a comparatively lower cost and with minimum effort.

(iii) Gangue — The earthly impurities like soil, mud, sand, silica (SiO₂), limestone, rocks, etc. that are mixed with valuable minerals in an ore deposit are called gangue or matrix.

Gold and silver.

Reduction.

The displacement reactions will take place as below:

Metals which are placed at the bottom of activity series like silver, gold, platinum do not corrode easily.

An alloy is a homogeneous mixture of two or more metals or of one or more metals with certain non-metallic elements.