Understanding Metals and Non-Metals – Maharashtra Board Class 10 Solutions for Science and Technology (English Medium)
Cryolite (AlF3, 3NaF) and fluorspar (CaF2)
- Characteristics which are relevant to metals:
- Conduct electricity
- (1, 2, 3) valence electrons
- Characteristics which are relevant to their compounds:
- Basic oxides
- Discharged at the cathode
- Metal as a sulphide: FeS (iron sulphide)
- Metal as a carbonate: CaCO3 (calcium carbonate)
- Metal as an oxide: Al2O3 (aluminium oxide)
The naturally occurring compounds of metals along with other impurities are known as minerals.
Examples: Granite, talc
Ores contain metal compounds with impurities such as soil, sand and rocky material. These impurities are called gangue.
Minerals from which metals are expected profitably and conveniently are called ores.
Examples: Bauxite (Al2O3.H2O), Cinnabar (HgS)
The process used for the extraction of metals in their pure form from their ores is called metallurgy.
The process of heating an ore to a high temperature in excess of air and converting it into its oxide is called roasting.
Example: ZnS (zinc blende) is roasted to get ZnO (zinc oxide).
- Sodium cannot be kept in the open as it reacts with oxygen in the air and catches fire.
- It does not react with kerosene and sinks in it, so it does not come in contact with air.
- Hence, to protect sodium and to prevent it from catching fire, sodium is stored under kerosene.
- Gold and silver both have natural lustre. They are malleable and ductile, so it is good for delicate designs in jewellery.
- Gold and silver are noble metals. They are not affected by air, water and acids under normal conditions. Hence, gold and silver are used to make jewellery.
- Calcium reacts with water less vigorously, so the heat generated is not sufficient for hydrogen to catch fire.
- Instead the bubbles of hydrogen gas formed stick to the surface of the metal making it lighter to float on the water. Hence, calcium floats on water during the reaction with water.
- Ionic compounds are solids and due to strong electrostatic attraction between oppositely charged ions, they are hard too.
- To break the strong ionic bonds, a large amount of energy is required. Hence, ionic compounds have high melting and boiling points.
- Copper reacts with oxygen in the air to form black copper oxide. Copper oxide slowly reacts with CO2 in the air which forms a green coat of copper carbonate.
- Lime juice and tamarind contain acid. The green coating of basic copper carbonate which is present on the surface of a tarnished copper utensil dissolves in acid. Thus, it becomes shiny again.
- Hence, tarnished copper utensils are cleaned with lime juice or tamarind.
Copper is more reactive than silver. So, when a copper coin is dipped in a silver nitrate solution, copper displaces silver from it. Thus, liberated silver gets deposited on the copper coin.
Cu(s) + 2AgNO3(aq)→ Cu(NO3)2(aq) + 2Ag(s)
- The metal is more reactive if the number of electrons in the outermost orbit is less. Metal A has 1 electron in the outermost orbit shell, while metal B has 2 electrons. Therefore, metal A is more reactive than metal B.
- Metal A is sodium and metal B is calcium.
- Reactions of Na and Ca with dil. HCl are
- 2Na + 2HCl →2NaCl(aq) + H2(g)
- Ca + 2HCl → CaCl2 + H2(g)
4. In both reactions, hydrogen gas is liberated and the respective salts are formed.
Reactions involved in obtaining zinc from zinc sulphide:
A: 2ZnS + 3O2→ 2ZnO + 2SO2
B: ZnO + C → Zn + CO
2Al(s) + 3H2O → Al2O3(s) + 3H2(g)
2Cu2S(s) + 3O2 2Cu2O + 2SO2(g)
2Cu2O(s) + Cu2S(s) 6Cu(s) + SO2(g)
Fe2O3 + 2Al → 2Fe + Al2O3 + Heat
Mg(s) + 2H2O → Mg(OH)2(aq) + H2(g)
Al2O3 + 2NaOH →2NaAlO2 + H2O
The process of concentration of bauxite is known as Bayer’s process.
At the cathode: Al3 + 3e–→ Al
Function: Cryolite is added to the molten mixture of alumina to reduce the melting point.
The formula of cryolite is (Na3AlF6).
2Al(OH)3 Al2O3 + 3H2O
During the electrolysis of alumina, oxygen liberated at the carbon anode reacts with it. So, the anode gets oxidised. Thus, it erodes continuously. Hence, it is necessary to replace the anodes from time to time.
When aluminium ore is heated with a caustic soda solution under high pressure for 2 to 8 hours and at 140°C to 150°C, aluminium oxide from aluminium ore dissolves in caustic soda as it is amphoteric in nature and forms sodium aluminate.
Al2O3 + 2NaOH → 2NaAlO2 + H2O.
Two methods of preventing the rusting of iron:
- By oiling, greasing or varnishing its surface.
- Galvanisation, i.e. by coating the iron surface with a thin layer of zinc.
A homogeneous mixture of two or more metals or a metal and a non-metal in a definite proportion is called an alloy.
Brass: Copper (60-90%) and Zinc (40-10%)
Bronze: Copper (81-90%) and Tin (19-10%)
Metals can be arranged in the decreasing order of chemical reactivity as
Na > Ca > Mg > Zn > Fe > Cu.
- Magnesium has atomic number 12, so its electronic configuration is 2, 8, 2.
- It loses 2 electrons from its outermost shell M, and the L shell becomes its outermost shell with a stable octet.
- Its atomic number is 17, so its electronic configuration is 2, 8, 7. Thus, the chlorine atom has 7 electrons in its outermost shell. It requires 1 electron to complete the octet.
- Thus, magnesium loses two electrons and gets two unit positive charge, giving the magnesium cation (Mg++). These are gained by two chlorine atoms, one each which gives two chloride ions with one unit negative charge each, i.e. 2 (Cl–).
Magnesium and chloride ions with opposite charges get attracted to each other and form an ionic bond. Thus, the ionic compound magnesium chloride (MgCl2) is formed.
Element X is a metal because its oxide is basic in nature.
It is a metal like Na or K.
Sodium combines with oxygen and forms sodium oxide (Na2O). When this oxide dissolves in water, it forms an alkali, sodium hydroxide (NaOH), which turns red litmus blue.
2Na + O2→ Na2O
Na2O + H2O → 2NaOH