Chapter 3 Metals and Non-Metals

(i)  Mercury is the metal which is liquid at room temperature.

(ii) Sodium & Potassium are the metals  that can be cut with a knife.

(iii) Silver is the metal which is the best conductor of heat.

(iv) Lead and Mercury are the metal that are poor conductors of heat.

Malleable: Malleable means elements when beaten turn into thin sheets called malleable. For example, gold has a maximum tendency of being malleable.

Ductile: Elements having a tendency  that they can be drawn into thin wires the tendency is called ductile. For example, gold has a maximum tendency of ductility.

Sodium is highly reactive metal so it  combines with air as well as water to form sodium oxide and hydrogen gas with heat energy.this heat is sufficient to burn hydrogen gas. That's why it catches fire if kept in open. Therefore, to prevent  sodium from combining with air and accidental fires, sodium is stored in kerosene oil.

(i) Iron reacts to steam to form ferrous oxide and hydrogen gas.

(ii) Calcium reacts with water and forms calcium hydroxide commonly known as slaked lime.

Explanation

A + FeSO₄ → No reaction, because A is less reactive than iron

A + CuSO₄ → Displacement, because A is more reactive than copper

B + FeSO₄ → Displacement, because B is more reactive than iron

B + ZnSO₄ → No reaction, because B is less reactive than zinc

C + FeSO₄ → No reaction, because C is less reactive than iron

C + CuSO₄ → No reaction, because C is less reactive than copper

C + ZnSO₄ → No reaction, because C is less reactive than zinc

C + AgNO₃ → Displacement, because C is more reactive than silver

D + FeSO₄/CuSO₄/ZnSO₄/AgNO₃ → No reaction, because D is less reactive than iron, copper, zinc, and silver

From the above equations, we get:

(i) B is the most reactive metal.

(ii) If B is added to a copper sulphate solution, then it would displace copper from its salt .

B + CuSO₄ → Displacement

(iii) The arrangement of the metals in the order of decreasing reactivity is:

B > A > C > D

Hydrochloric acid when added to a reactive metal like sodium, potassium etc.
Hydrogen gas is evolved.

When iron metal reacts with dilute H₂SO₄, iron sulphate is formed with the evolution of hydrogen gas.

Zinc is more reactive than iron. Therefore, when zinc is added to a solution of iron (II) sulphate, then it would displace iron from the solution.

Zn + FeSO₄  →  ZnSO₄ + Fe

(i) Electron dot structure is representation of elements with valence electrons as dots around the elements.

(ii)

(iii) The ions present in Na₂O are Na⁺ and O²⁻ ions and in MgO are Mg²⁺ and O²⁻ ions.

Ionic compounds are formed by strong electrostatic forces of attraction between the ions. So, it requires a lot of energy to overcome these forces. So ionic compounds have high melting points.

(i) Mineral: Minerals are the substances that are rich in particular metals and their composition is fixed.

(ii) Ore: Minerals from which particular metals can be extracted profitably are known as ores.

(iii) Gangue: The impurities like sand, silt, soil, gravel, etc. present in the ore are called gangue.

Gold, Silver are the metals that are found in free stable because these metals are least reactive, so they are present at the bottom of the reactivity series.

Metals from its oxide obtained from reduction. Metal oxide is reduced by this process, metal oxides are reduced by using suitable reducing agents such as carbon or by highly reactive metals to displace the metals from their oxides.

Example, On treating zinc oxide with carbon it reduces to metallic zinc.

Manganese dioxide is reduced to manganese when treated with aluminium powder, so aluminium displaces manganese from its oxide.

Oxides of more reactive metals are reduced by electrolysis.

Metal present at the bottom of reactivity series like gold, platinum are least reactive hence they do not corrode.

Alloys are defined as homogeneous mixtures of two or more elements or metal and non metal. An alloy is formed by melting the metal and then it dissolves in the other elements. For example, steel is an example of alloy iron and carbon.

(d) AgNO₃ solution and copper metal.

As copper is more reactive than silver it displaces silver from silver nitrate solution.

(c) Applying a coating of zinc

(Rusting can be prevented by applying grease and oil. But, in case of an iron frying pan, grease and paint cannot be applied because when the pan is heated and washed again and again, the coating of grease and paint gets destroyed. Therefore Zinc coating is done i.e. galvanisation to prevent rusting.)

(a) The element is calcium.

Because calcium oxide is an ionic compound, as these compounds have a high melting point.

(c) Zinc is more reactive than tin therefore food cans are coated with tin and not with zinc.

(a) Suppose on hammering or beating the sample it converts into sheets, then it is a metal otherwise a non-metal because metals are malleable whereas non metals are not. If we use the battery, bulb, wires, and a switch to make up a circuit. If these  samples conduct electricity, then it is a metal, otherwise a non-metal.

(b) As these tests are based on the physical properties. No chemical reactions occurs or are required in these tests. Therefore, the above tests are useful in distinguishing between metals and nonmetals.

Those oxides that behave both as acidic and basic oxides are called amphoteric oxides.

Examples: Aluminium oxide (Al₂O₃), zinc oxide (ZnO)

Metals that are present at the top reactivity series are more reactive like potassium and sodium. So hydrogen displaced from dilute acids. Metals that are less reactive than hydrogen do not displace it that are present at the bottom of reactivity series like copper and silver.

While electrolytic refining of a metal M:

Impure metal M will be taken as anode.

Thin strips of pure metal M will be taken as cathode.

Solution of salt of the metal M as electrolyte.

(a) (i) No change will be on dry Litmus paper.

(ii) The gas is sulphur dioxide (SO₂), which turns moist blue litmus paper to red because sulphur dioxide reacts with moisture to form sulphurous acid.

(b)  S_(s)   +   O_2(g)   →   SO_2(g)
                                   Sodium dioxide

       SO_2(g)   +   H₂O_(f)   →   H2SO_3(aq)
                                        Sulphurous acid

The rusting of iron can be prevented by:

(i) Painting or Oiling: By applying paint or oil on the surface becomes waterproof and the moisture and oxygen present in the air cannot come into contact with iron. Therefore, rusting can be prevented.

(ii) Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron from coming in contact with oxygen and moisture. So, rusting is prevented.

Non-metals when combine with oxygen form acidic oxides.

For example:

S_(s)   +   O_2(g)   →   SO_2(g)
                            (Acidic in nature)

(a) Platinum, gold, and silver are used to make jewellery because they are very lustrous as well as they are very less reactive and do not corrode easily.

(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air and water. So, they are kept in kerosene oil in a way to prevent their direct contact with air and moisture.

(c) Aluminium is a reactive metal, yet it can resistant to corrosion. This is because aluminium reacts with oxygen present in air to form aluminium oxide. This oxide layer is quite stable and which further prevents reaction of aluminium with oxygen. Also, it is lightweight and a good conductor of heat. Therefore why it is used to make cooking utensils.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be more easily extracted from their oxides than from their carbonates and sulphides.

Copper metal reacts with atmospheric carbon dioxide and forms copper carbonate and as a result, which copper vessel loses its shiny brown surface and forms a green layer of copper carbonate. Lemon or tamarind contain acid that neutralises the base copper carbonate and dissolves the layer. So, tarnished copper vessels using lemon and tamarind, copper vessels retain their shine.

The gold metal is dipped in the solution of aqua regia i.e. 3:1 mixture of conc. HCl and conc. HNO₃. Aqua regia is a fuming, highly corrosive liquid. It dissolves gold in it. When the gold ornaments are dipped into aqua regia, the outer layer of gold gets dissolved and the inner shiny layer appears. That is why the weight of gold ornaments drastically decreases.

Iron react with steam, whereas copper does not reat with cold water, hot water, or steam. So, hot water tanks are made of steel (an alloy of iron), then iron reacts with the steam formed by hot water.

     3Fe       +       4H₂O       →       Fe₃O₄       +       4H₂
     Iron               Steam           Iron(II,III)oxide      Hydrogen

Therefore copper is used to make hot water tanks, and not steel.