Metals And Non-metals

(i) Mercury is liquid at room temperature.

(ii) Sodium can be easily cut with a knife.

(iii) Silver is the best conductor of heat.

(iv) Lead is a poor conductor of heat.

(a) Metals can be beaten into thin sheets, hence they are called malleable.

(b) Metals can be turned into thin wires by stretching, hence they are called ductile.

Sodium is very reactive metal which react with the atmospheric moisture when kept in the open and produces fire as well. So, it is always kept immersed in kerosene oil to prevent its reaction with air and to prevent accidental fires.

(i) Equation for the reaction of iron with steam is given below:

(ii) Equation for the reaction of calcium with water is as follows:

(iii) Equation for the reaction of potassium with water can be written as:

(i) Metal B gives the displacement reaction with the iron (II) sulphate, hence it is the most reactive metal.

(ii) When metal B is added to copper (II) sulphate solution, it displaces the copper.

(iii) Metal B is the most reactive metal whereas metal D is the least reactive metal as it cannot displace any metal from its salt solution. Hence, the decreasing order of reactivity of the metals is:

B > A > C > D.

Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal. The chemical equation for reaction when iron reacts with dilute sulphuric acid is as follows.

Fe (s) + H₂SO₄ FeS0₄ (aq) + H₂ (g)

When zinc is added to iron (II) sulphate solution, zinc displaces iron from iron (II) sulphate solution. This is because zinc is more reactive than the iron. The reaction can be shown as follows:

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

(i) The electron-dot structure of sodium (Na):

The electron-dot structue of oxygen(O):

The electron-dot structue of magnesium(Mg):

(ii) (a) Formation of Na₂O

Na₂O is sodium oxide. Sodium atom has one electron in its outermost shell whereas oxygen atom has six electrons in its outermost shell. In the formation of sodium oxide, two sodium atoms transfer their two outermost electrons to an oxygen atom. Thus, sodium atoms form two sodium ions (2Na⁺) by losing two electrons while oxygen atom forms an oxide ion (O^2-) by gaining two electrons.

Sodium ions and oxide ion, being oppositely charged, attract each other and are held together by strong electrostatic forces of attraction to form the ionic sodium oxide compound 2Na⁺O^2- or Na₂0.

(b) Formation of MgO

MgO is magnesium oxide. Magnesium atom has two electron in its outermost shell whereas oxygen atom has six electrons in its outermost shell. In the formation of magnesium oxide, magnesium atom transfer its two outermost electrons to an oxygen atom. Thus, magnesium atom forms magnesium ion (Mg²⁺) by losing two electrons while oxygen atom forms an oxide ion (O^2-) by gaining two electrons.

Magnesium ion and oxide ion, being oppositely charged, attract each other and are held together by strong electrostatic forces of attraction to form the ionic magnesium oxide compound Mg²⁺ O^2- or MgO.

(iii) The ions present in sodium oxide (Na₂O) compound are sodium ions (Na⁺) and oxide ions (O^2-).

The ions present in magnesium oxide (MgO) compound are magnesium ions (Mg²⁺) and oxide ions (O^2-).

In ionic compounds, oppositely charged ions are held together by strong electrostatic force of attraction. This is because a considerable amount of energy is required to break this force of attraction. That’s why ionic compounds have high melting points.

(i) Mineral: The elements or compounds, which occur naturally in the earth’s crust, are known as minerals

(ii) Ore: Minerals from which the metals can be extracted profitably are called ores.

(iii) Gangue: Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue.

Gold and Platinum are found in nature in the free state.

A metal can be extracted from its oxide by the process of reduction.

When a more reactive metal displaces a less reactive metal from its oxide, a displacement reaction takes place. In the given metals, magnesium is the most reactive metal whereas copper is the least reactive metal.

Metals which are at the bottom of the reactivity series are highly unreactive. They are not affected by air, moisture or ordinary chemicals. Therefore, they do not corrode easily. Gold and platinum do not corrode easily.

Alloys are a homogeneous mixture of two or more metals or a metal and a non-metal. It is prepared by first melting the primary metal, and then, dissolving the other elements in it. It is then cooled to room temperature. For example, brass is an alloy of copper and zinc.

Copper metal is more reactive than silver metal (Ag), so a displacement reaction will take place between AgNO₃ solution and Copper metal.

The most suitable method for preventing an iron frying pan from rusting is applying a coat of zinc. This is called galvanization. Grease and paint are also used for prevent rusting from iron. However, in case of iron frying pan, grease and paint cannot be applied because when fan will be heated and washed again and again, the coating of grease and paint would get destroyed.

The element is likely to be calcium. When calcium reacts with oxygen to give an ionic compound, calcium oxide, having a high melting point. This calcium oxide compound is soluble in water. When carbon reacts with oxygen, carbon dioxide is formed which is a gas. Silicon reacts with oxygen to form a compound silicon dioxide which has high melting point but insoluble in water. Similarly, iron reacts with oxygen to form iron (III) oxide compound which has a high melting point but ' insoluble in water

Food cans are coated with tin and not with zinc because zinc is more reactive than tin. Hence, being more reactive, zinc may react with acidic food and form toxic products which may be harmful for our health.

(a) (i) Metals are malleable because they can change into a thin sheet on hammering whereas non-metals are brittle as they are broken into pieces on hammering. When we beat the samples, if sample turns into a thin sheet, then it is a meatal otherwise it is a non-metal.

(ii) We can use battery, bulb, wires and switch to set up an electric sample. Now place the given samples to be tested in the circuit between the terminals one by one. The sample which allows the current to pass through it making the bulb to light up, will be a metal. On the other hand, the sample which does not allow the current to pass through it and hence does not make the bulb to light up, will be a non-metal.

(b) Metals are malleable as they can turn into thin sheets. The metal sheets can be used for various purposes such as iron sheets are used for making buckets, roofing material and boxes.

Metals are good conductor of electricity. Therefore, the metal wires are used as electric wires for various purposes.

Those oxides which act as both basic and acidic oxides are called amphoteric oxides. Aluminium oxide and zinc oxide show the properties of both basic as well as acidic oxides.

Zinc and iron will displace hydrogen from dilute acids because they are more reactive than hydrogen. While copper and silver cannot displace hydrogen from dilute acids because they are less reactive than hydrogen.

In the electrolytic refining of metal M:

Anode- The impure metal M is made the anode.

Cathode- a thin strip of pure metal M is made the cathode.

Electrolyte- A solution of salt of the metal M is used as an electrolyte.

(a) When sulphur is burnt in air, then sulphur dioxide(SO₂) gas is formed.

(i) There will be no action on dry litmus paper.

(ii) Sulphur dioxide gas turns moist blue litmus paper to red.

(b) S (s) + O₂ (g) SO₂ (g)

(i) Rusting of iron can be prevented by galvanization. In this process, iron articles are coated with a thin layer of zinc metal which prevent the iron to come in contact with air and moisture. Hence, rusting is prevented.

(ii) Rusting of iron can be prevented by applying oil, grease, or paint. These are applied all over the surface of iron object to keep the air and moisture away.

When non-metals combine with oxygen, then neutral or acidic oxides are formed.

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

(b) Sodium, potassium and lithium are very reactive metal which react with the atmospheric moisture when kept in the open and produce fire as well. So, these are always kept in kerosene oil to prevent their reaction with air and to prevent accidental fires.

(c) Although aluminium is a highly reactive metal, it is resistant to corrosion. This is because when aluminium metal react with oxygen present in air it forms a protective layer of aluminum oxide on its surface. This oxide layer is very stable and makes the aluminium metal resistant to corrosion.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because it is much easier to obtain metals from its oxide as compared to its sulfides and carbonates ores.

Tarnished copper vessels are cleaned with lemon or tamarind juice as the acids contained in them dissolves the coating of copper oxide or basic copper carbonate present on the surface of the vessels and makes them shining red-brown again.

Differences between metals and non-metals on the basis of their chemical properties:

The solution used by the goldsmith was aqua-regia solution which contains concentrated nitric acid and concentrated hydrochloric acid in the ratio 1:3. When the gold bangles were dipped into this solution, considerable amount of gold was dissolved in it. Thus the weight of the bangle was reduced.

Copper is used to make hot water tanks because it is resistant to corrosion and is a good conductor of heat than steel.