# NCERT Solutions

## Class 10 Science

###### metals and non metals

Q1)Which of the following pairs will give displacement reactions?

• (a) NaCl solution and copper metal
• (b) MgCl2solution and aluminium metal
• (c) FeSO4solution and silver metal
• (d)AgNO3solution and copper metal.

(d) AgNO3solution and copper metal Since copper is more reactive than silver so it will displace silver from silver nitrate.

Q2)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 the above

(c) Applying a coating of Zinc.

Q3)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

(a) Calcium

Q4) 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.

(c) zinc is more reactive than tin. (refer reactivity series)

Q5) 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.

(a)
(a) If the substance can be hammered to convert into sheets then it is metal if it is broken into pieces then it is non-metal. Set up the arrangement using bulb, battery, wire and switch as shown in figure. Place the substance between Point A and B if the bulb starts glowing then the substance is a Metal otherwise it is non-metal because metals are good conductor of electricity.
(b)
Generally above methods can be used to identify metals and non-metals. But there are some exceptions also for example Sodium is metal which is not malleable in fact it is brittle. Graphite allotrope of non-metal carbon is a good conductor of electricity.

Q6)What are amphoteric oxides? Give two examples of amphoteric oxides.

Those oxides that behave as both acidic and basic oxides are called amphoteric oxides. Examples: aluminium oxide (Al2O3), zinc oxide (ZnO)

Q7)Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Iron and aluminium will displace hydrogen from dilute acids as they more reactive then hydrogen. Mercury and copper cannot displace hydrogen from dilute acids as they are less reactive than hydrogen.

Q8)Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

: During electrolytic refining, impure metal is made anode and a thin strip of pure metal M is made cathode and the electrolyte used is the soluble salt of Metal M which is to be refined.
For example -if impure copper needs to be refine then set up is in the way

Q9)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
• (b) dry litmus paper ?
• (c) moist litmus paper ?
• (d)Write a balanced chemical equation for the reaction taking place.

(a)
(i) There will be no action on dry litmus paper.
(ii) The colour of litmus paper will turn red because sulphur is a non-metal and the oxides of non-metal are acidic in nature.

(b)
$$S(s) + O_{2}(g) \rightarrow SO_{2}(g)$$

Q10)State two ways to prevent the rusting of iron.

Two ways to prevent the rusting of iron are:
? Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
? Galvanisation:An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.

Q11)What type of oxides are formed when non-metals combine with oxygen?

When non-metals are combined with oxygen then neutral or acidic oxides are formed. Examples of acidic oxides are NO2, SO2 and examples of neutral oxides are NO, CO etc.

Q12)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.

(d) AgNO3solution and copper metal Since copper is more reactive than silver so it will displace silver from silver nitrate.

1. Platinum, gold and silver are used to make jewellery because these are low reactive metals so rarely corrosion occur (In silver) and hence do not lost their shine and lustre.
2. Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water.Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.
3. (c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.
4. (d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides.

Q13)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.

Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.

Q14)Differentiate between metal and non-metal on the basis of their chemical properties.(important question)

metals Non-metals
The density of metals is usually high. Nonmetals are poor conductors of heat and electricity. Graphite and Gas carbon are exceptions.
Metals are malleable and ductile. Unlike metals, nonmetals aren’t malleable and ductile.
Metals form an alloy with other metals or non – metals. Nonmetals react more with metals than with nonmetals.
Some metals react with air and corrode. For e.g. Iron. Usually, nonmetals react with other nonmetals in high temperature.
Metals are good conductors of heat and electricity. Lead is an exception. Most nonmetals do not react with air in room temperature.
Generally, metals are in a solid state at room temperature. Except for Mercury. Mercury is in a liquid state. White phosphorus is the only nonmetal that reacts with air to form its oxide by burning.
Many metals produce metal oxide by burning in the oxygen of the air. Highly reactive metals react violently when they’re burnt in oxygen. Usually, nonmetals do not react with water. Except for Chlorine, chlorine dissolves in water to form an acidic solution.
Metals like sodium and potassium are stored in oil as they react with air in seconds. They’re highly reactive metals.
Less reactive metals like gold, silver, platinum, etc do not tarnish easily. They stay shiny and lustrous.
Nonmetals have a low density.
Metals produce metal oxide and hydrogen gas while reacting with water. They do not form alloys. However, nonmetals like carbon, silicon and phosphorous.
Soluble metal oxides dissolve in water and create metal hydroxide. Nonmetals exist in all states of matter at room temperature.
Not all metals react with water. However, highly reactive metals like sodium and potassium react with water violently and an exothermic reaction takes places where the hydrogen immediately catches fire. Salt and hydrogen are produced when a metal reacts with an acid.
Generally, a metal displaces a less reactive metal in a metal salt solution.
Different nonmetals have different reactions. Chlorine is the most reactive metal in the halogen family i.e. Chlorine (Cl), Bromine (Br), Iodine (I), and Fluorine (F). The reactivity order of the halogen family is Cl > Br > I.
Therefore, Chlorine (Cl) can displace Bromine (Br) and Iodine (I) from solutions of bromides (NaBr) and Iodides (NaI).
Ionic solids are formed when nonmetals with high electronegativity react with alkali and alkaline earth metals.

Q15)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?

Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water. $$3Fe + 4H_{2}O \rightarrow Fe_{3}O_{4}+H_{2}O$$