Solutions of Metals and Non-metals (Page No - 193) - Chemistry Lakhmir Singh, Class 10 | Extra Documents, Videos & Tests for Class 10 PDF Download

Question 45:
Explain how, a reduction reaction of aluminium can be used for welding cracked machine parts of iron. Write a chemical equation for the reaction involved.
Solution :
A mixture of Iron (III) oxide and aluminium powder is ignited with a burning magnesium ribbon. Aluminium reduces iron oxide to produce iron metal with the evolution of lot of heat. Due to this heat, iron metal is produced in the molten state. This molten iron is poured between broken iron parts of the machine to weld them (to join them).

Question 46:
(a) What is corrosion ?
(b) Name any two metals which do not corrode easily.
(c) What is the corrosion of iron known as ?
(d) Explain why, aluminium is a highly reactive metal, still it is used to make utensils for cooking.
Solution :
(a) The eating up of metals by the action of air, moisture or a chemical (such as an acid) on their surface is called corrosion.
(b) Gold and Platinum
(c) Rusting
(d) Aluminium begins to corrode quickly when it comes in contact with moist air. The action of moist air on aluminium metal forms a thin layer of aluminium oxide all over the metal. This aluminium oxide is very tough and prevents the metal underneath from further corrosion. Therefore, aluminium is used for making utensils irrespective of its highly reactive property as its corrosion leads to the non-corrosion of the metal in the longer run.

Question 47:
What is meant by ‘rusting of iron’ ? With the help of labelled diagrams, describe an activity to find out the conditions under which iron rusts.
Solution :
When an iron object is left in damp air (or water) for a considerable time, it gets covered with a red-brown flaky substance called rust. This is called rusting of iron .
Experiment to show that rusting of Iron requires both, air and water :
We take three test-tubes and put one clean iron nail in each of the three test-tubes:

1. In the first test-tube containing iron nail, we put some anhydrous calcium chloride and close its mouth with a tight cork . Anhydrous calcium chloride absorbs water moisture from the damp air present in the test-tube and make it dry. In this way, the iron nail in the first test-tube is kept in dry air (having no water vapour in it).
2. In the second test-tube containing iron nail , we put boiled distilled water. Boiled water does not contain any dissolved air (or oxygen) in it (this is because the process of boiling removes all the dissolved air from it). A layer of oil is put over boiled water in the test-tub e to prevent the outside air from mixing with boiled water. In this way, the iron nail in the second test-tube is kept in air free boiled water.
3. In the third test-tube containing an iron nail, we put unboiled wa ter so that about two-thirds of nail is immersed in water and the rest is a bove the water, exposed to damp air. In this way , the iron nail in the third test-tube has been placed in air and water together.
The mouth of all three test tube s is cl osed with a cork and it is kept aside for about one week.
After one week, we observe the iron nails kept in all the three test-tubes, one by one. We find tha t (i) No rust is seen on the surface of iron nai l kept in dry air (water-f ree air) in the first test-tube. This tells us that rusting of iron does not take place in air alone.
(ii) No rust is seen on the surface of iron nail kept in air-free, boiled water in the second test-tube. This tells us that rusting of iron does not take place in water alone.
(iii) Red-brown rust is seen on the surface of iron nail kept in the presence of both air and wat er together the third test-tube. This tells us that rusting of iron takes pla ce in the presence of both air and water together.

Question 48:
(a) What is an alloy ? How is an alloy made ?
(b) What elements are present in steel ? How are the properties of steel different from those of pure iron ?
(c) Give the constituents and one use of brass.
Solution :
(a) An alloy is a homogeneous mixture of two or more metals (or a metal and small amount of non-metals). An alloy is prepared by mixing the various metals in molten state in required proportions, and then cooling their mixture to the room temperature.
(b) Steel contains iron and carbon.
This alloy of iron (steel) is hard and strong. It also rusts less readily than pure iron.
(c) Brass contains copper and zinc.
Brass is used for making cooking utensils.

Question 49:
(a) Name two metals which resist corrosion due to the formation of a thin, hard and impervious layer of oxide on their surface.
(b) Name five methods of preventing rusting of iron.
(c) What are the constituents of stainless steel ? What are the special properties of stainless steel ?
Solution :
(a) Aluminium and Zinc resist corrosion due to the formation of a thin, hard and impervious layer of oxide on their surface.
(b)(i) Painting (ii) Applying grease or oil (iii) Galvanisation (iv) Tin and chromium plating (v) Alloying to form stainless steel.
(c)Stainless steel contains i ron, chromium and nickel.
Stainless steel does not rust at all and is strong and tough.

Question 50:
(a) Name an alloy of copper. State its chemical composition and any one use.
(b) Explain why, when a copper object remains in damp air for a considerable time, a green coating is formed on its surface. What is this process known as ?
Solution :
(a) Brass:It contains Copper (Cu)-80% and Zinc(Zn) – 20%. It is used for making cooking utensils.
(b) When a copper object remains in damp air for a considerable time, then copper reacts slowly with the carbon dioxide and water of air to form a green coating of basic copper carbonate on the surface of the object. The formation of this green coating of basic copper carbonate corrodes it. This process is known as corrosion of copper.

Question 51:
(a) How does the painting of an iron object prevent its rusting ?
(b) How does the electrical conductivity of copper alloys, brass and bronze, differ from that of pure copper ?
(c) What is meant by 22 carat gold ? Name the metals which are usually alloyed with gold to make it harder.
Solution :
(a) When a coat of paint is applied to the surface of an iron object, it prevents air and moisture to come in contact with the object; hence no rusting takes place.
(b) The electrical conductivity of copper alloys like brass and bronze is less than that of pure copper.
(c) It means that 22 parts pure gold is alloyed with 2 parts of either silver or copper for making ornaments; Silver and copper are usually alloyed with gold to make it harder .

Question 52:
Explain giving equation, what happens when :
(a) ZnCO₃ is heated in the absence of air ?
(b) a mixture of CU₂O and CU₂S is heated ?
Solution :
(a) When zinc carbonate is heated strongly in the absence of air, it decomposes to form zinc oxide and carbon dioxide.

(b) When copper (I) oxide reacts with copper (I) sulphide, it forms copper metal and sulphur dioxide.

Question 53:
(a) For the reduction of a metal oxide, suggest a reducing agent other than carbon.
(b) Explain why, an aqueous solution of sodium chloride is not used for the electrolytic extraction of sodium metal.
Solution :
(a) Aluminium can be used a reducing agent other than carbon.
(b) We cannot use an aqueous solution of sodium chloride to obtain sodium metal because if we electrolyse an aqueous solution of sodium chloride, then as soon as sodium metal is produced at cathode, it will react with water present in the aqueous solution to form sodium hydroxide. Hence, electrolysis of an aqueous solution of sodium chloride will produce sodium hydroxide and not sodium metal.

Question 54:
How are metals refined by the electrolytic process ? Describe the electrolytic refining of copper with the help of a neat labelled diagram.
Solution :
For the refining of an impure metal by the process of electrolysis, a thick block of impure metal is made anode (connected to +ve terminal of the battery) and a thin strip of the pure metal is made cathode (connected to -ve terminal of battery). A water soluble salt (of the metal to be refined) is taken as electrolyte. On passing current, impure metal dissolves from the anode and goes into the electrolyte solution. And pure metal from the electrolyte deposits on the cathode.
Electrolytic refining of copper: In an electrolytic tank, acidified copper sulphate (CuSO₄⁺ dilute H₂O₄) solution forms the electrolyte. A block of impure copper is made into an anode by connecting the positive terminal of a power supply (battery). A thin strip of highly pure copper metal is the cathode of the cell. The negative terminal of the power supply is connected to it.

A small electric curr ent is passed through the cell. Atoms from the anode enter the electrolyte. The copper from the anode gets converted into copper sulphide. An equal number of copper atoms from the solution get deposited on the cathode. This is to keep the concentration of the solution constant. Impurities from the anode block either remain in solution or collect below the anode, as they are unable to displace copper form the sulphate solution. The insoluble impurities remain in the electrolyte and are called anode mud.
Copper sulphate solution contains ions of Cu⁺⁺ and SO₄^— . The following reactions take place at the anode and cathode when an electric current is passed.

Pure copper is scraped or removed from the cathode. Anode becomes thinner as the electrolysis process proceeds. Some important metals like gold and silver are present in the anode mud. These can be recovered separately.

Question 55:
(a) Name the chemical compound which is electrolysed in molten state to obtain aluminium metal. Which gas is evolved during this process ?
(b) Name the chemical compound which is electrolysed in molten state to obtain sodium metal. Which gas is produced in this process ?
(c) Name the gas produced when calamine ore is calcined.
(d) Name the gas evolved when cinnabar ore is roasted.
Solution :
(a) Aluminium oxide is electrolysed in molten state to obtain aluminium metal. Oxygen gas is evolved during the process.
(b) Sodium chloride is electrolysed in molten state to obtain sodium metal. Chlorine gas is evolved during this process.
(c) Carbon dioxide is produced when calamine ore is calcined.
(d) Sulphur dioxide gas is evolved when cinnabar ore is roasted.

Question 56:
(a) Name two metals which are found in nature mainly in the free state (as metallic elements).
(b) Name two metals which are always found in combined state.
(c) What iron compound is present in haematite ore ? Also write its chemical formula.
Solution :
(a) Gold and Platinum are found in nature mainly in the free state.
(b) Sodium and Magnesium are always found in combined state.
(c) Iron (III) oxide; Fe₂O₃ is present in haematite ore.

Question 57:
(a) What is the difference between a mineral and an ore ?
(b) Which metal is extracted from cinnabar ore ?
(c) Name one ore of sodium. Name the sodium compound present in this ore and write its chemical formula.
(d) How is sodium metal extracted ? Explain with the help of equation of the reaction involved.
(e) Name three other metals which are extracted in a manner similar to sodium.
Solution :
(a)The natural materials in which the metals or their compounds are found in earth are called minerals. Those minerals from which the metals can be extracted conveniently and profitably are called ores.
(b) Mercury.
(c)Rock salt – Sodium chloride, NaCl.
(d)Sodium metal is extracted by the electrolytic reduction of molten sodium chloride. When electric current is passed through molten sodium chloride, it decomposes to form sodium metal and chlorine gas.

(e) Potassium, Calcium and Magnesium .

Question 58:
(a) Name the metal which is extracted from haematite ore.
(b) Name one ore of aluminium. Name the aluminium compound present in this ore and write its chemical formula.
(c) How is aluminium metal extracted ? Explain with the help of an equation.
(d) Name the electrode at which aluminium metal is produced.
(e) Which gas is produced during the extraction of aluminium ? At which electrode is this gas produced ?
Solution :
(a)Iron is extracted from haematite ore .
(b)Bauxite; Aluminium oxide, Al₂O₃.2H₂O
(c)Aluminium metal is extracted by the electrolytic reduction (electrolysis) of molten aluminium oxide. When electric current is passed through molten aluminium oxide, it decomposes to form aluminium metal and oxygen gas.

(d) A luminium metal is produced at Cathode (Negative electrode).
(e) Oxygen gas is produced; at anode (Positive electrode).