Chapter 3– Metals and Non Metals Solutions
Question - 21 : - What are amphoteric oxides? Give two examples of amphoteric oxides
Answer - 21 : -
Oxides that react with both acids and bases to form salt and water are known as amphoteric oxides. Examples: PbO and Al2O3.
Amphoteric oxides are the one which reacts with both acids and bases to form salt and water. Examples: Lead oxide – PbO and Aluminium oxide – Al2O3.
Question - 22 : - Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer - 22 : - Zinc (Zn) and Magnesium (Mg) are the two metals which will displace Hydrogen from dilute acids as they are very reactive metals. Gold (Au) and Silver (Ag) are the metals which will not replace Hydrogen from dilute acids as these metals are less reactive.
Question - 23 : - In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer - 23 : - In the process of electrolytic refining of metal called ‘M’, An impure and thick block of metal M. is considered as anode, Thin strip or wire of pure metal M is taken as cathode. A suitable salt solution of metal M is considered as the electrolyte.
Question - 24 : - Pratyush took sulphur powder on a spatula and heated it.
Answer - 24 : -
He collected the gas evolved by inverting a test tube over it, as shown in figure below.
(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
Answer
a) When sulphur powder is burnt in the air sulphur-di-oxide is formed.
(i) Sulphur-di-oxide does not have any effect on dry litmus paper.
(ii) Sulphur-di-oxide turn the moist litmus paper from blue to red as contact of SO2 with water turns to sulfurous acid.
(b) S(s) + O2(g) → SO2(g)
SO2(g) + H2O →H2SO3
Answer - 25 : -
1. Iron can be prevented from rusting by coating the surface of the iron with rust proof paints
2. By applying Oil/grease on the surface of iron objects as it will prevent the iron surface to get in contact with air consisting of moisture.
Question - 26 : - What type of oxides are formed when non-metals combine with oxygen?
Answer - 26 : - When non-metals combine with oxygen it forms either acidic or neutral oxides. Ex: N2O5 or N2O3 is an acidic oxide; CO is a neutral oxide.
Question - 27 : - Give reasons
(a) Platinum, gold and silver are used to make jewellery.
Answer - 27 : -
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction
Answer
(a) Platinum, gold and silver are used to make jewellery for these metals are very less reactive hence they are not affected by air, water or most chemicals. These metals have a lot of luster and they are malleable and ductile in nature and also high corrosion resistance in nature.
(b) Sodium, potassium and lithium readily react with water to produce a lot of heat. As a result, Hydrogen evolved in the reaction results in a fire. On exposure to water they react with moisture (water droplets) present in the atmosphere, In order to prevent contact with water hence these metals are stored under oil.
(c) Aluminium forms on its surface a nonreactive surface of aluminium oxide. Such coating prevents other compounds from reacting to aluminium. So aluminium is being used to produce utensils for cooking.
(d) Reducing metal oxide into free metal is easy. Additionally, because it is easier to obtain metals directly from their oxides than from their carbonates or sulphides, the carbonate and sulphide ores are first transformed to oxides to obtain the metals.
Question - 28 : - You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice.
Answer - 28 : - Explain why these sour substances are effective in cleaning the vessels.
Answer
Tarnished copper vessels being cleaned with lemon or tamarind because this sour substance contains acids which dissolve the coating of copper oxide or basic copper carbonate present on the surface or tarnished copper vessels. This makes them shining red-brown again. Hence they are very effective in cleaning tarnished copper vessels.
Question - 29 : - A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments.
Answer - 29 : - An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Answer
Goldsmith used the solution called Aqua regia which is called as royal water in Latin. . It is the mixture of concentrated Hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua regia is capable of dissolving noble metals like gold and platinum. When upper-layer of dull gold ornament is dissolved they lose their weight.
Question - 30 : - Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer - 30 : - Copper is used to make hot water tanks and not steel (an alloy of iron) because copper does not reacts with either water or steam whereas iron reacts with steams to corrode the tank.