Metals and Non-metals - Q&A
1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper metal
Answer: (d) AgNO3 solution and copper metal
Explanation: A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution. Copper is more reactive than silver (Ag), so it can displace silver from silver nitrate solution. In the other options, the metal added is less reactive than the metal in the salt solution.
2. Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) All of the above
Answer: (c) Applying a coating of zinc
Explanation: While grease and paint prevent rusting, they are not suitable for a frying pan because they will burn or peel off when the pan is heated. Coating with zinc (galvanization) is the most suitable method here as it protects the iron even at high temperatures.
3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
(a) calcium
(b) carbon
(c) silicon
(d) iron
Answer: (a) calcium
Explanation: Calcium reacts with oxygen to form calcium oxide (CaO), which is an ionic compound with a high melting point. Calcium oxide is also soluble in water (forming lime water). Carbon forms a gas (CO2), silicon forms silica (sand, insoluble), and iron oxide is insoluble in water.
4. Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin.
(b) zinc has a higher melting point than tin.
(c) zinc is more reactive than tin.
(d) zinc is less reactive than tin.
Answer: (c) zinc is more reactive than tin.
Explanation: Zinc is a more reactive metal than tin. If food cans were coated with zinc, it might react with the organic acids present in the food to form toxic substances. Tin is less reactive and safe for food storage.
5. You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
Answer:
(a) Using the hammer: Take the sample and beat it with the hammer. If the sample flattens into a thin sheet without breaking, it is malleable and likely a metal. If it breaks into pieces (brittle), it is a non-metal.
Using the circuit (battery, bulb, wires, switch): Set up an electric circuit with the battery, bulb, and switch. Insert the sample into the circuit between the wires. If the bulb glows, the sample conducts electricity and is a metal. If the bulb does not glow, it is a non-metal.
(b) These tests are generally very useful because malleability and electrical conductivity are characteristic properties of metals. However, there are exceptions (e.g., Graphite is a non-metal but conducts electricity; Zinc is a metal but is brittle at room temperature). Therefore, using both tests together gives a more reliable conclusion.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer: Amphoteric oxides are metal oxides that react with both acids and bases to produce salt and water. They show properties of both acidic and basic oxides.
Examples:
1. Aluminium oxide (Al2O3)
2. Zinc oxide (ZnO)
7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer:
Metals that displace hydrogen: Magnesium (Mg) and Zinc (Zn). (These are more reactive than hydrogen).
Metals that do not displace hydrogen: Copper (Cu) and Silver (Ag). (These are less reactive than hydrogen).
8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer:
Anode: A thick block of the impure metal M.
Cathode: A thin strip of the pure metal M.
Electrolyte: A water-soluble salt solution of the metal M (e.g., if M is copper, use copper sulphate solution).
9. Pratyush took sulphur powder on a spatula and heated it. 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 is heated, it reacts with oxygen to form sulphur dioxide gas (SO2).
(i) Dry litmus paper: There will be no change in colour because acids only show their property in the presence of water.
(ii) Moist litmus paper: The blue litmus paper will turn red. This is because sulphur dioxide dissolves in the moisture to form sulphurous acid (H2SO3), which is acidic.
(b) Reactions:
Burning of sulphur: S(s) + O2(g) → SO2(g)
Reaction with moisture: SO2(g) + H2O(l) → H2SO3(aq) (Sulphurous acid)
10. State two ways to prevent the rusting of iron.
Answer:
1. Painting or Greasing: Applying a layer of paint, oil, or grease cuts off the contact between iron and moist air, preventing rust.
2. Galvanization: Coating the iron object with a layer of zinc. Zinc is more reactive than iron and protects it from oxidation even if the coating is scratched.
11. What type of oxides are formed when non-metals combine with oxygen?
Answer: Non-metals combine with oxygen to generally form acidic oxides (e.g., SO2, CO2). Some non-metals also form neutral oxides (e.g., CO, H2O).
12. Give reasons
(a) Platinum, gold and silver are used to make jewellery.
(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) They are used for jewellery because they are highly lustrous (shiny) and very unreactive (noble metals). They do not tarnish or corrode easily when exposed to air or moisture.
(b) These metals are highly reactive. They react vigorously with oxygen and moisture in the air and can even catch fire. Storing them under oil prevents contact with air and moisture.
(c) Although aluminium is reactive, it forms a thin, stable layer of aluminium oxide on its surface when exposed to air. This layer prevents further corrosion. Also, aluminium is a good conductor of heat and is lightweight.
(d) It is chemically easier to extract a metal from its oxide (by reduction) than from its carbonate or sulphide. Therefore, these ores are first converted into oxides by calcination or roasting.
13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Answer: Copper vessels tarnish due to the formation of a layer of basic copper carbonate (greenish colour) on their surface. Lemon and tamarind juice contain natural mild acids (citric acid and tartaric acid). These acids react with the basic copper carbonate layer to form soluble salts, which are then washed away, restoring the shine of the copper vessel.
14. Differentiate between metal and non-metal on the basis of their chemical properties.
Answer:
| Property | Metals | Non-Metals |
|---|---|---|
| Nature of Oxides | Form basic oxides (e.g., Na2O, MgO). | Form acidic or neutral oxides (e.g., SO2, CO). |
| Reaction with Water | Active metals displace hydrogen from water. | Do not react with water. |
| Reaction with Dilute Acids | Displace hydrogen gas from dilute acids. | Do not displace hydrogen from dilute acids. |
| Electronegativity | Electropositive (lose electrons to form cations). | Electronegative (gain electrons to form anions). |
15. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. 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: The solution used by the impostor was Aqua Regia. It is a freshly prepared mixture of concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO3) in the ratio of 3:1. Aqua regia is one of the few reagents capable of dissolving gold. When the bangles were dipped in it, the outer layer of gold dissolved, revealing the shiny inner layer, but this process caused a significant loss in the weight of the gold bangles.
16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer:
1. Conductivity: Copper is a better conductor of heat than steel, which makes it more efficient for transferring heat in hot water tanks.
2. Reactivity with Steam: Iron (in steel) reacts with steam (hot water vapour) to form iron oxide and hydrogen gas, leading to corrosion of the tank.
Equation: 3Fe + 4H2O(steam) → Fe3O4 + 4H2
Copper does not react with water or steam at any temperature.