Metal and nonmetals
1. Why are metals good conductors of electricity?
Metals are good conductors of electricity because they contain free electrons. These free electrons move easily through the metal and conduct electric current.
2. Which property of graphite is utilised in making electrodes?
Graphite is a good conductor of electricity. Due to this property, graphite is utilised in making electrodes.
3. Which of the following metals will melt at body temperature?
Gallium, Magnesium, Caesium, Aluminium
Gallium and caesium will melt at 37°C (body temperature).
4. Name two metals that do not react with water at all.
Lead and copper.
5. What happens when calcium is treated with water?
Calcium reacts less violently with water and bubbles of hydrogen gas stick to its surface.
6. Generally, non-metals are not lustrous. Name a non-metal which is lustrous.
Iodine
7. What is the nature of non-metal oxide?
Non-metal oxides are acidic or neutral in nature.
8. What is the nature of metal oxides?
Metal oxides are basic in nature.
9. Why does calcium float in water?
[CBSE Delhi 2011]
When calcium reacts with water, hydrogen gas is produced which sticks to the surface of calcium, so it floats in water.
10. What is flux?
Flux is a substance which is added to the ore, during reduction, for removing the non-fusible impurities.
11. Why do copper objects develop a green coating in air?
Copper reacts with moist carbon dioxide in the air and gains a green coating of basic copper carbonate.
12. Why do silver articles become black on prolonged exposure to air?
Sulphur compounds such as hydrogen sulphide gas (H2S) present in the air when combine with the silver articles, form a black coating of silver sulphide (Ag2S).
13. Which oxide of iron could be obtained on prolonged reaction of iron with steam?
Fe3O4
3Fe(s)+4H2O(g)→Fe3O4(s)+4H2(g)
14. Why are ionic compounds usually hard?
In all ionic compounds, their positive and negative ions are attached to each other by a strong ionic bond. So, they are rigid and hard solids.
15. Why does aluminium not react with water under ordinary conditions?
Aluminium does not react with water under ordinary conditions because of the presence of a thin layer of aluminium oxide on its surface.
16. In nature, metal A is found in a free state while metal B is found in the form of its compounds. Which of these two will be nearer to the top of the activity series of metals?
Metal B will be nearer to the top of the activity series of metals as it is so reactive that it is found in combined state.
17. Arrange the following metals in decreasing order of their reactivity:
Fe, Zn, Na, Cu, Ag
Na > Zn > Fe > Cu > Ag.
18. Why cannot aluminium be obtained by reduction of its oxide with carbon?
Aluminium has more affinity for oxygen than carbon.
19. Why does a little addition of carbon in iron make it more useful?
Pure iron is very soft and stretches easily when hot. When it is mixed with a small quantity of carbon (0.05%), it becomes hard and strong and hence becomes more useful.
20. Give an example of a sulphide ore which is reduced to metal by heating alone, i.e., by roasting.
Cinnabar (HgS) on roasting is first changed to mercuric oxide which on further heating is reduced to mercury.
2HgS(s)+3O2(g)→Heat2HgO(s)+2SO2(g)2HgO(s)→Heat2Hg(l)+O2(g)
21. Metals are refined by using different methods. Name two metals refined by electrolytic refining.
Copper and gold.
22. What is rust?
The coating of brown, flaky substance on the surface of iron when it is kept exposed in moist air is called rust.
23. What is corrosion?
When the surface of a metal is attacked by air, water and some other substances, it is said to be corroded. This phenomenon is known as corrosion.
24. What is aqua regia?
It is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1. It can dissolve gold. It is a highly corrosive liquid.
25. Which metals are mixed with iron to get stainless steel?
Nickel and chromium
26. Why is stainless steel preferred for making household utensils?
Stainless steel is preferred as it is non-reactive and so the milk or food is not spoiled in it.
27. What is galvanisation?
Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
28. Name an alloy of
aluminium used in the construction of aircraft.
Duralium
lead used in joining metals for electrical work.
Solder
