State the main components of the following alloys : (i) Brass (ii) Duralumin (iii) Bronze.
(i) Brass — Cu [60-80%], Zn [40-20%] (ii) Duralumin — Al [95%], Mg [0.5%], Mn [0.5%], Cu [4%] (iii) Bronze — Cu [80%], Zn [1%], Sn [19%]
Aluminium powder is used in thermite welding because : (1) it is strong reducing agent (2) it is strong oxidizing agent (3) it is corrosion resistant (4) it is a good conductor of heat.
1. it is strong reducing agent. Reason — Aluminium is a strong reducing agent, it reduces Fe2O3, to Fe which fills the gap. Hence it is used for thermite (Fe2O3) welding.
The following questions relate to the extraction of aluminium by electrolysis : (i) Name the other aluminium containing compound added to alumina and state it’s significance. (ii) Give the equation for the reaction that takes place at the cathode. (iii) Explain why is it necessary to renew the anode periodically.
(i) The compound is cryolite [Na3AlF6]. It — lowers the fusion point of the mixture i.e., mixture fuses around 950°C instead of 2050°C. enhances the mobility of the fused mixture…
The amphoteric metallic oxide is : (1) Calcium oxide (2) Barium oxide (3) Zinc oxide (4) Copper (II) oxide
Zinc oxide is an amphoteric oxide. It reacts with acids and alkalis giving salt and water.
The following questions are relevant to the extraction of Aluminium : (i) State the reason for addition of caustic alkali to bauxite ore during purification of bauxite. (ii) Give a balanced chemical equation for the above reaction. (iii) Along with cryolite and alumina, another substance is added to the electrolyte mixture. Name the substance and give one reason for the addition.
(i) Bauxite is reacted with a conc. solution of NaOH (caustic alkali) under pressure for 2 hrs as a first step in obtaining Al2O3. The impurities present in bauxite mainly…
Match the properties and uses of alloys in List 1 with the appropriate answer from List 2. List 1:- The alloy contains Cu and Zn, is hard and is used in decorative articles.
- It is stronger than Aluminium, light and is used in making light tools.
- It is lustrous, hard, corrosion resistant and used in surgical instruments.
- Tin lowers the melting point of the alloy and is used for soldering purpose.
- The alloy is hard, brittle, takes up polish and is used for making statues.
List 2 : (A) Duralumin (B) Brass (C) Bronze (D) Stainless steel (E) Solder
The alloy contains Cu and Zn, is hard and is used in decorative articles. (B) Brass It is stronger than Aluminium, light and is used in making light tools. (A)…
The metallic oxide/s which cannot be reduced by normal reducing agents ? 1. Magnesium oxide 2. Copper (II) oxide 3. Zinc oxide 4. Iron (III) oxide
Magnesium oxide Reason They are most electropositive and have strong affinity for oxygen. Hence, they cannot be reduced by normal reducing agents