Q  1. Choose amphoteric oxides from the following: Na₂O, ZnO, Al₂O₃, SO₂.

Solution

Amphoteric oxides = ZnO, Al₂O₃
Q  2. Ionic compounds dissolve in water. Explain.

Solution

Ionic compounds dissolve in water because water is a polar compound, it decreases the electrostatic forces of attraction, resulting in free ions in aqueous solution. Hence they dissolve.
Q  3. Why is gold mixed with other metals for making jewellery? Name two metals mixed with gold.

Solution

Gold is a malleable metal and is extremely soft. So, mixing it with other metals makes it stronger for its use in making jewellery. Commonly used metals to mix with gold while making jewellery are copper and silver.
Q  4. Why is carbon not used for reducing aluminium from aluminium oxide?

Solution

Because aluminium has greater affinity for oxygen than for carbon, therefore carbon cannot reduce alumina (Al₂O₃) to aluminium.
Q  5. Why are metals good conductor of electricity?

Solution

The metals are good conductors of electricity because they have free mobile electrons which can move easily through the metal and conduct electricity.
Q  6. What is aqua regia?

Solution

Aqua regia is the freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3:1. It can even dissolve metals like gold and platinum.
Q  7. How will you prove that a given salt is a carbonate of a metal?

Solution

To the salt, add few drops of dilute HCl or H₂SO₄, if colourless gas is evolved with brisk effervescence and when the gas is passed through lime water and if lime water turns milky, then the gas is CO₂ and salt is carbonate of the metal.
Q  8. State any two properties of alloys in comparison to the constituent metals.

Solution

1. Alloys are stronger than the metals from which they are made. 2. Alloys are more resistant to corrosion.
Q  9. What is ‘corrosion’? Name the compound formed when:   (i) silver corrodes (ii) copper corrodes

Solution

When the surface of a metal is exposed to air, moisture or any other substance around it, the metal is said to corrode, and the phenomenon is known as corrosion.   (i) Silver sulphide (ii) Basic Copper carbonate (mixture of copper carbonate and copper hydroxide).  
Q  10. Answer the following question: (i) Are all pure liquids bad conductors of electricity? Justify your answer with one example. (ii) Why ionic compounds are always hard? (iii) Name the cathode and anode in the electrolytic refining of copper.

Solution

(i) No, all pure liquids are not bad conductors of electricity. There are many pure liquids which are good conductors of electricity. For example, solutions of acids like sulphuric acid, nitric acid are good conductors of electricity. (ii) Ionic compounds are hard solids because they have strong electrostatic forces of attraction between their ions, which cannot be separated easily. (iii) Cathode: A thin strip of pure copper metal      Anode: A thick block of impure copper metal

Q  11. Metals high up in the reactivity series cannot be obtained from their compounds by heating with carbon. Why?

Solution

Carbon cannot reduce the oxides of sodium and aluminium because these are highly reactive metals; have more affinity towards oxygen than carbon.  
Q  12. Define corrosion. What is the condition required for corrosion to take place?

Solution

Corrosion is the eating away of metals by the action of air, water, acids present on its surface. Corrosion requires presence of air and water.
Q  13. Name the metal which has very low melting point and can melt with the  heat of your palm.

Solution

Gallium and Cesium have very low melting points.
Q  14. Why ionic compounds are soluble in polar solvents and insoluble in non-polar solvents?

Solution

Ionic compounds are soluble in polar solvents and insoluble in non-polar solvents. Polar solvents like water decrease the electrostatic forces of attraction, resulting in free ions in aqueous solution. Hence, ionic compounds dissolve in polar solvents. Non-polar solvents like kerosene, benzene are not capable of dissolving ionic solids since they can not decrease the forces of attraction between the ions.
Q  15. Why do silver articles become black after some time when exposed to air?

Solution

Silver articles get tarnished by reacting with atmospheric air to form black coating of silver sulphide.
Q  16. What is sonority?

Solution

When we strike a metal, it produces a metallic pop sound. This property of metals is called sonority.
Q  17. What is the total number of ions produced by one molecule of Na₂O and MgBr₂ in their aqueous solution?

Solution

The total number of ions produced by one molecule of Na₂O in its aqueous solution is 3. The total number of ions produced by one molecule of MgBr₂ in its aqueous solution is 3.
Q  18. What do you understand by enrichment of ores?

Solution

Ores mined from the earth are usually combined with impurities. These impurities must be removed from the ore before the extraction of metal. The removal of impurities from the ore depends on the difference in physical and chemical properties of impurities and metals. This method of removal of impurities from metal ore is called enrichment of ores.
Q  19. Define: (i) Minerals (ii) Ores (iii) Gangue

Solution

(i) Minerals: The naturally occuring compounds of metals which are generally mixed with other matter such as soil, sand, limestone and rocks are known as minerals. (ii) Ores : The minerals from which metals are extracted commercially at a comparatively low cost and with minimum effort are called ores. (iii) Gangue : The earthly impurities including silica, mud etc. associated with the ore are called gangue.
Q  20. “All ores are minerals but all mineral are not ores”. Justify the statement with examples.

Solution

All ores are minerals while all minerals are not ores as some of them might have a large amount of unwanted substances such as sand, stones and earthly impurities. For example: Aluminium occurs in earth’s crust in the form of two minerals bauxite and clay. Out of these, aluminium can be easily and profitably extracted from bauxite only. So, we can infer that bauxite is an ore of aluminium.On the other hand, it has not been possible to obtain aluminium from clay by some easy and cheap method. So, clay remains only as mineral and not as ore of aluminum.
Q  21. Name two allotropes of carbon. Which is the hardest natural substance known?

Solution

The two allotropes of carbon are diamond and graphite. Diamond is the hardest natural substance.Q  22. What makes aluminium resistant to further corrosion? How can we improve it?

Solution

Aluminium develops a thin layer of aluminium oxide when exposed to air. This aluminium oxide prevents it from further corrosion. This can be improved further by making the oxide layer thicker.
Q  23. What is percentage of gold in 18 carat gold?

Solution

18 carat gold contains 75% gold and remaining 25% is copper and silver.
Q  24. State two physical properties of gold which are of extreme use to jewellers.

Solution

Ductility and lustre are the properties of gold which makes it useful in making jewellery.
Q  25. Define an amalgam. How are amalgams important to us?

Solution

A mixture or an alloy of mercury with a number of metals or alloys such as sodium as well as with some non-metals is known as amalgam. Uses: 1. Sodium is highly reactive metal and therefore it is difficult to transport. To lower its reactivity, it is mixed with mercury. 2. Dental amalgam is a mixture of mercury and a silver-tin alloy and is used for fillings in teeth.
Q  26. What are the four main steps involved in metallurgy?

Solution

The main steps involved in metallurgy are- 1)      Extraction of ore. 2)      Crushing and grinding of ore. 3)      Concentration or enrichment of ore. 4)      Extraction of metal from concentrated ore.Q  27. Name any two metals that occur free in nature.

Solution

The two metals that occur free in nature are gold and silver.
Q  28. Give an example of a metal which is the best conductor of heat.

Solution

Silver is the best conductor of heat.
Q  29. “The way metals like sodium, magnesium and iron react with air and water is an indication of their relative positions in the reactivity series”. Is this statement true? Justify your answer with examples.

Solution

The statement is correct because they react with air and water at different rates and in different conditions. While sodium reacts spontaneously and violently with air and cold water, magnesium reacts with air less vigorously and with water when heated. Iron reacts with air very slowly and reacts with steam to form iron oxide and hydrogen being the least reactive among sodium, magnesium and iron.
Q  30. Make a distinction between metals and non – metals with respect to the nature of their oxide.

Solution

Metallic oxides are basic but few are amphoteric. Non-metallic oxides are acidic but some are neutral.
Q  31. Describe tin plating and chromium plating. What kind of materials are protected using these methods?

Solution

Tin and chromium metals are resistant to corrosion. So, a thin layer of tin metal (or chromium metal) is deposited on iron and steel objects by electroplating to protect these objects from rusting. Tin plating is used for tiffin boxes because it is non-poisonous and hence does not contaminate the food kept in them. Chromium plating is done on taps, bicycle handle bars and car bumpers made of iron and steel to protect them from rusting and give them a shiny appearence.
Q  32. What are alloys? How are they made? Name the constituents and uses of brass, bronze and solder.

Solution

Alloys are homogeneous mixtures of two or more metals or a metal and a non metal. They are prepared in the following ways: (i) Melting the primary metal. (ii) Dissolving the other elements in a definite proportion and then cooling them to room temperature. Constituents and uses of the alloys are: 1. Brass: It is an alloy of copper and zinc     Uses: In making utensils and scientific instruments. 2. Bronze: It is an alloy of copper and tin     Uses: In making statues and medals. 3. Solder: It is an alloy of lead and tin     Uses: In soldering (welding) electrical wires together.
Q  33. Name a non-metal which is lustrous and a metal which is non-lustrous.

Solution

(a) Non-metal which is lustrous = Iodine (I) (b) Metal which is non-lustrous = Sodium (Na)
Q  34. How do various metals occur in nature?

Solution

Most of the metals are reactive so, they occur in combined state in the form of their oxides, carbonates, halides, sulphides, suphates etc. For example, sodium and potassium occur mainly as their chlorides, calcium and magnesium as carbonates, aluminium as its oxide while zinc, lead, copper are found as sulphides. Metals which have low chemical reactivity are found in free state. e.g. gold, platinum.
Q  35. Differentiate metals and non-metals on the basis of their physical properties.

Solution

Metals Non-metals Metals are good conductors of heat and electricity. Non-metals are bad conductors of heat and electricity. Metals are malleable that is they can be beaten into sheets. Non-metals are not malleable. Metals are ductile that is they can be drawn into wires. Non-metals are not ductile. Metals are sonorous. Non-metals are not sonorous. Metals have high tensile strength due to high  attraction between molecules. Non-metals have low tensile strength due to low attraction between molecules. Metals have high density. Non-metals have low density.
Q  36. An element X forms an oxide which turns red litmus blue. Identify whether X is a metal or non-metal.

Solution

X is a metal since metal oxides are basic in nature.
Q  37. Give reason : (i) A magnesium ribbon should be cleaned before burning it in air. (ii) The blue colour of copper sulphate solution changes when iron nails are dipped in it.

Solution

(i) Magnesium ribbon should be cleaned before burning it in air to remove the layer of basic magnesium carbonate or magnesium oxide from its surface.   (ii) The colour of blue copper sulphate changes due to displacement reaction in which a more reactive iron has displaced less reactive copper from its solution.
Q  38. In the formation of a compound XY, atom ‘X’ gives one electron to an atom of ‘Y’. What is the nature of bond in XY?

Solution

Nature of the bond will be ionic. Ionic bonds are formed by the transfer of electrons from one atom to another.
Q  39. Name any one metal which is found in its free state in nature.

Solution

Metal which is found in its free state in nature – Gold or Platinum.
Q  40. State the constituents of solder and their percentage composition. Which property of solder makes it suitable for welding electrical wires?

Solution

The constituents of Solder – Lead (Pb), Tin (Sn). It contains 50% lead and 50% tin. Being a low melting solid, it is used for soldering electrical wires together.