Class 10 Science Chapter 3 Important Questions

(i) Sodium and Potassium react so vigorously if it kept in open it catches fire that’s why it is kept immersed in Kerosene.
(ii) Magnesium, Aluminium, Zinc, Lead are the metals which covered with a thin layer of Oxide on the surface of it which prevent it from the further oxidation.
(iii) Iron does not burn on heating but iron fillings burn on heating.
(iv) Copper does not burn but it is coated with a black copper oxide.
(v) Silver and Gold are the metals which does not react with oxygen because it is very low reactive metal.

Metals combine with oxygen to forms metal oxide.
Metal + O₂ → Metal oxide
For example:
Na + O₂ → NaO₂
2Cu + O₂ → 2CuO
K + O₂ → K₂O
4Al + 3O → 2Al₂O₃

Amphoteric oxide is a type of metal oxide which react with both acids as well as base.

For example:
Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O
Al₂O₃ + 6HCl → 2AlCl₃ + H₂O

(i) K, Na, Ca react with cold H₂O.

(ii) Al, Fe, Zn react with steam.

(iii) Fe, Sn react with hot H₂O.

(iv) Pb, Cu, Ag, Au are the metals which does not react with H₂O.

(v) Ca and Mg float as bubble H₂ stick to their surface.
Examples:
3Fe + 4H₂O → Fe₃O₄ + 4H₂
2Na + 2H₂O → 2NaOH + H₂ + Heat
Ca + 2H₂O → Ca(OH)₂ + H₂

When metal react with acid salt and water will produces.
For example:
Fe + 2HCL → FeCl₂ + H₂
Mg + 2HCL → MgCl₂ + H₂
Zn + 2HCL → ZnCl₂ + H₂

Metal A + Salt of metal B → Salt solution A + metal B
If a metal is more reactive than so it displaces the less reactive metal.
For example:
Na + HCl → NaCl + H₂
Ca + H₂SO₄ → CaSO₄ + H₂
These two reaction are exothermic.

Ionic compound are those compound which contain both metal and non-metal ions in this compound strong compound strong force of attraction take place between ions.

Properties of ionic compound are:
(i) Ionic compound conduct electricity in aqueous solution but it cannot cannot conduct electricity in dry or solid form.
(ii) Physical Nature: It is solid in nature and also very hard because strong force of attraction between the positive and negative ions.
(iii) Melting and boiling: It has high melting point and boiling point.
(iv) It is soluble in water but it does not dissolve in organic solvent like: Petrol, Oil etc.

It is the only reactant that is capable of dissolving metals like gold and platinum. It is obtained by mixing concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua Regia is also known as Royal water.

(i) Reactivity of the element is the tendency to attain a completely filled balanced shell.
(ii) Atom of the metal lose electron from their balance shell to form cation. Atom of the non-metal gain electron in the valence shell to form anion.

On the basic of reactivity series we can group the metals into three group:
(i) Metals of high reactivity: For example, potassium, sodium, calcium, magnesium and Aluminium.
(ii) Metals of medium reactivity: For example, zinc, iron, lead etc.

Ores are generally contaminated with impurities, such as soil, sand, etc., called gangue. These impurities must be removed from the ores before proceeding to extraction. The method used for removing gangue depend upon the physical and chemical properties of the gangue and the ores.

Low reactive are very unreactive. For example, cinnabar(HgS) is an ore of mercury. When heated it is first converted to mercury oxide which on further heating changes to metallic mercury.
2HgS + 3O₂ → 2HgO + 2SO₂
2HgO → 2Hg + O₂
Similarly copper which occurs in nature as Cu2S can be obtained by just heating in air.
2CuS + 3O₂ → 2Cu₂O + 2SO₂
2Cu₂O + Cu₂S → 6Cu + SO₂

It is a type of process in which a metal oxide are reduced to corresponding metal by using reducing agent like carbon.
ZnO + C → Zn + CO

It is a type of process in which a metal oxide are reduced to corresponding metal by using reducing agent like carbon.
ZnO + C → Zn + CO

The reaction of iron oxide Fe2O3 with Aluminium is an exothermic process. Iron is obtained in molten state which is used to join railway tracks or cracked machine parts. This reaction is known as thermit reaction and the process is known as thermit process.
Example: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + Heat

The surface of some metal get corrode when they exposed in the contact of moist air for a very long period so this is called corrosion.
For examples:
(i) Silver articles turn black when exposed to air. This is because it reacts with Hydrogen Sulphide in air to form Silver Sulphide which is black.
(ii) Similarly copper articles turn green due to reaction with atmospheric carbon dioxide forming green copper carbonate.
(iii) Iron gets rusted when exposed to moist air from brown oxide of iron.

Rusting of iron metal can be preventing by the following method:
(i) by painting the surface.
(ii) by oiling or greasing the surface.
(iii) galvanizing, chrome plating, anodising or making alloy.

It is a method of protecting steel and iron from rusting. The article is coated with a thin layer of zinc. Galvanized article is protected against rusting even if coating is broken.

Pure gold which is 24-carat gold is very soft and is not suitable for making ornaments. It is alloyed with either copper or silver to make it hard. Generally, in India 22carat gold is good for making jewellery, it means 22 part of gold is alloyed with 2 part of copper or silver.

Basic oxide: Those oxides which react with acids or acidic oxide to form salt and water are called basic oxide. Metal react with oxygen to form metallic oxide which are generally basic in nature example Na₂O (sodium oxide) CaO (calcium oxide) K₂O (potassium oxide) MgO (magnesium oxide) are basic oxide.
MgO + 2HCl → MgCl₂ + H₂O
Acidic oxide: Those oxides which react which react with bases or basic oxide to form salt and water are called acidic oxides. Non-metals react with oxygen to form non-metallic oxide which are generally acidic in nature example CO₂ (carbon dioxide), SO₂(Sulphur dioxide), K₂O (potassium oxide), SO₃ (Sulphur trioxide), P₂O₅ (phosphorus pentoxide) SiO₂ (silicon dioxide) are acidic oxides.
CO₂ + 2NaOH → Na₂CO₃ + H₂O

It is process in which crushed (powdered) ore is washed with stream of water. The light gangue particle is washed away in a stream of water whereas heavy mineral particle is settle down at the bottom. It is based on difference in density of an ore and impurities.

This process is used to concentrate some ores especially Sulphide ores. In this process the finely powdered ores is mixed with water and a suitable oil like pine oil, in a large tank. It is based on the principal that the mineral particle is more wetted by oil, whereas the gangue particle is more wetted by water. Compressed air is bubbled through the mixture. As a result of agitation oil froth is formed which contain mineral which float on the top of water and can be separated easily. Impurities are left behind at the bottom.

It is a process in which a magnetic ore is separated from non-magnetic impurities with the help of electromagnet. The ore is crushed and electromagnet are brought near it which attract the mineral particle leaving behind the gangue particle. Magnetite (iron ore Fe3O4) pyrolusite (magnesium ore MnO2), chromite (chromium ore Cr2O3) are enriched by magnetic separation.

Alloy of a metal with mercury is known as amalgam. It has been observed that melting point and electrical conductivity of an alloy are lower than those of the constituent metals. For example, brass which is an alloy of copper and zinc and bronze which is an alloy of copper and tin are not as good conductor of electricity as copper. Solder which is an alloy of lead and tin has a low melting point and it is used for welding electrical wires.