Answer these questions:
1. Why are musical instrument and bell made up of metal?
Ans: Musical instrument and bell are made up of metal because metal produce ringing sound when stuck by something.
2. Why are electric wire made up of copper?
Ans: Electric wire is made up of copper because copper is god conductors of electricity.
3. Why sodium and potassium stored in kerosene?
Ans: Sodium and potassium react quickly with oxygen at room temperature so they are stored in kerosene oil
4. Why is phosphorous stored under water?
Ans: phosphorous rapidly burn in air at room temperature so it is stored under water for safety.
5. Why silver and gold do not react with hydrochloric acid?
Ans: This is because silver and gold are less reactive than hydrogen.
6. Why is graphite not used for making electric cable?
Ans: Graphite is a non metal that is brittle and cannot draw into wire. This is why graphite is not used for making
7. Could you store 500 ml Zinc sulphate solution in an aluminum vessel overnight? Give reason for your answer.
Ans: Aluminium is more reactive than zinc therefore displace zinc from Zinc sulphate solution and form salt with evolution of hydrogen gas. This is why we do not store Zinc sulphate solution in an aluminum vessel overnight.
8. Describe any three properties of metal with suitable example?
(i) Metals combine with oxygen to form metal oxides.
Eg. 2Cu + O2 → 2CuO; 4Al + 3O2 → 2Al2O3
(ii) In general metals react with water to form a metal oxide or hydroxide and hydrogen gas. But all metals do not react in the same way with water.
Metals like K and Na react vigorously with cold water to form hydrogen gas.
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) + heat energy
The reaction of calcium with water is less violent. The heat evolved is not sufficient for the hydrogen to catch fire.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.
(iii) Metals react with dilute acid, like dilute HCl to give a metal salt and H2 gas.
2Na + 2HCl → 2NaCl + H2
Hydrogen gas is not evolved when a metal reacts with nitric acid (HNO3) . As HNO3 is a strong oxidizing agent, it
oxidizes the H2 to water and itself gets reduced to oxide of nitrogen (N2O, NO, NO2).
Magnesium and Manganese react with very dil.HNO3 to give H2 gas.
Mg(s) + 2HNO3(aq) → Mg(NO3)2 + H2 ;
Mn(s) + 2HNO3(aq) → Mn(NO3)2 + H2
9. What is aqua regia?
Ans: Aqua regia, (Latin for ‘royal water’) is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and platinum.
For rest questions visit link : class 8 Chapter Metals and Non metal
Q. If x = 1 + 2 ^1/3 + 2 ^2/3 then show that x^3 – 3x^2 – 3x – 1 = 0
Q. If x = 1 + root 2 + root 3 then show that x^4 – 4x^3 – 4x^2 + 16x – 8 = 0
For more questions: http://jsuniltutorial.weebly.com/ix-number-system.html
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