CBSE Class 10 Chemistry Chapter 3 Metals & Non Metals

Metals and Non-metals

3.1 PHYSICAL PROPERTIES

3.1.1 Metals

The easiest way to start grouping substances is by comparing their

physical properties

Activity 3.1

·        Take samples of iron, copper, aluminium and magnesium. Note the appearance of each sample.

·        Clean the surface of each sample by rubbing them with sand paper and note their appearance again. After rubbing with sand paper metal is shining.

Metals, in their pure state, have a shining surface. This property is

called metallic lustre.

Activity 3.2

·        Take small pieces of iron, copper, aluminium, and magnesium.

·        Try to cut these metals with a sharp knife and note your observations.

·        Hold a piece of sodium metal with a pair of tongs.

CAUTION: Always handle sodium metal with care. Dry it by pressing between the folds of a filter paper.

·        Put it on a watch-glass and try to cut it with a knife.

·        What do you observe?

All above metals are hard to cut with knife. Sodium can be cut.

Activity 3.3

·        Take pieces of iron, zinc, lead and copper.

·        Place any one metal on a block of iron and strike it four or five times with a hammer. What do you observe?

·        Repeat with other metals.

·        Record the change in the shape of these metals.

some metals can be beaten into thin sheets. Thisproperty is called malleability. Gold and silver are themost malleable metals.

Activity 3.4

·        Consider some metals such as iron, copper, aluminium, lead, etc.

·        Which of the above metals are also available in the form of wires?

Copper & Aluminium

Ductility is property of metal which defines if its thin wires can be drawn. Metals can be reshaped into useful products because of malleability & ductility.

metals that are used for making cooking vessels?

Aluminium, iron, for cooking, copper, brass is used for storing water.

Activity 3.5

·        Take an aluminium or copper wire. Clamp this wire on a stand, as shown in Fig. 3.1.

·        Fix a pin to the free end of the wire using wax. Heat the wire with a spirit lamp, candle or a burner near the place where it is clamped.

·        What do you observe after sometime?

·        Note your observations. Does the metal wire melt?

metals are good conductors of heat

and have high melting points.

best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat.

Activity 3.6

·        Set up an electric circuit as shown in Fig. 3.2.

·        Place the metal to be tested in the circuit between terminals A and B as shown.

·        Does the bulb glow? What does this indicate?

Yes Bulb Glows, It concludes most of the metals are good conductor of electricity.

Why are electric wires coated with such PVC?

PVC( Poly Vinyl Chloride) is insulator like plastic, its melted & coated over conductor during cable manufacturing.

Metals which make sound are called sonorous.

Non metals are mostly Solid or Gases except Bromine which his liquid.

Activity 3.7

Collect samples of carbon (coal or graphite), sulphur and iodine.

Carry out the Activities 3.1 to 3.6 with these non-metals and record

your observations.

Metals generally carry all these properties except a few like mercury which is soft (liquid), Sodium and lithium which are not hard. Most non-metals have contrasting features with few exceptions like coal and graphite and diamond which are hard 

 

Element	Symbol	Type of Surface	Hardness	Malleability	Ductility	Conduction Electricity	Conduction Heat
Graphite	C	Non- Lustrous	Hard	No	No	Yes	No
Coal	C	Non Lustrous	Hard	No	No	No	No
Sulphur	S	Non Lustrous	No	No	No	No	No
Iodine	I	Non Lustrous	No	No	No	No	No

 

Elements cants be grouped according to their

physical properties alone, as there are many exceptions.

1.       Metals are solid except Mercury.

2.       Metals have high melting point except gallium & cesium which have very low melting point.

3.       Non metal iodine is lustrous.

4.       Carbon is a non-metal that can exist in different forms. Each

form is called an allotrope. Diamond, an allotrope of carbon, is

the hardest natural substance known and has a very high melting

and boiling point & insulator. Graphite, another allotrope of carbon, is a

conductor of electricity, soft.

5.       Metals are hard except Sodium, lithium, Potassium etc.

 

Activity 3.8

·        Take a magnesium ribbon and some sulphur powder.

·        Burn the magnesium ribbon. Collect the ashes formed and dissolve

·        them in water.

·        Test the resultant solution with both red and blue litmus paper.

·        Is the product formed on burning magnesium acidic or basic?

·        Now burn sulphur powder. Place a test tube over the burning

·        sulphur to collect the fumes produced.

·        Add some water to the above test tube and shake.

·        Test this solution with blue and red litmus paper.

·        Is the product formed on burning sulphur acidic or basic?

·        Can you write equations for these reactions?

 

Activity 3.8

Most non-metals produce acidic oxides when dissolve in water. On

the other hand, most metals, give rise to basic oxides. You

 

MgO + H2O → Mg(OH)2.

SO2 + H2O → H2SO3

sulphurous acid is weackly dibasic acid. sulphur dioxide is a major component of acid rain since it mixes with vapour in the atmosphere reacting to produce H2SO4 .

 

1. Give an example of a metal which

(i) is a liquid at room temperature.

(ii) can be easily cut with a knife.

(iii) is the best conductor of heat.

(iv) is a poor conductor of heat.

 

(i) Mercury is the metal which is liquid at room temperature

(ii) Sodium and potassium are the metals which can be cut with a knife

(iii) Silver is the best conductor of heat

(iv) Mercury is poor conductor of heat.

2. Explain the meanings of malleable and ductile.

i. Metals which can be beaten to thin sheets are called malleable

ii. Metals which can be drawn into thin wires are called ductile

 

Activity 3.9

CAUTION: The following activity needs the teacher’s assistance.

It would be better if students wear eye protection.

Hold any of the samples taken above with a pair of tongs and try

burning over a flame. Repeat with the other metal samples.

Collect the product if formed.

Let the products and the metal surface cool down.

Which metals burn easily?

What flame colour did you observe when the metal burnt?

How does the metal surface appear after burning?

Arrange the metals in the decreasing order of their reactivity

towards oxygen.

Are the products soluble in water?

 

Burning Sodium in air 

 

Metal + Oxygen → Metal oxide

2Cu + O2 → 2CuO

(Copper) (Copper(II) oxide)

4Al + 3O2 → 2Al2O3

metal oxides are basic in nature. But some metal

oxides, such as aluminium oxide, zinc oxide, etc., show both acidic as

well as basic behaviour.

Metal oxides which react with both acidic & basic solutions are known as amphoteric oxides

Al2O3 + 6HCl → 2AlCl3 + 3H2O

Al2O3 + 2NaOH → 2NaAlO2 + H2O

(Sodium

aluminate)

 

 

Activity 3.10

CAUTION: This Activity needs the teacher’s assistance.

·        Collect the samples of the same metals as in Activity 3.9.

·        Put small pieces of the samples separately in beakers half-filled

with cold water.

·        Which metals reacted with cold water? Arrange them in the increasing order of their reactivity with cold water.

·        Did any metal produce fire on water?

·        Does any metal start floating after some time?

·        Put the metals that did not react with cold water in beakers half-filled with hot water.

·        For the metals that did not react with hot water, arrange the apparatus as shown in Fig. 3.3 and observe their reaction with steam.

·        Which metals did not react even with steam?

Metals reacting with water

Metals reaction with steam

Metal + Water →Metal oxide + Hydrogen

Metal oxide + Water →Metal hydroxide

Metals like potassium and sodium react violently with cold water. In

case of sodium and potassium, the reaction is so violent and exothermic

that the evolved hydrogen immediately catches fire.

2K(s) + 2H2O(l) →2KOH(aq) + H2(g) + heat energy

2Na(s) + 2H2O(l) →2NaOH(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.

Metals like aluminium, iron and zinc do not react either with cold or

hot water. But they react with steam to form the metal oxide and hydrogen.

2Al(s) + 3H2O(g) →Al2O3(s) + 3H2(g)

3Fe(s) + 4H2O(g) →Fe3O4(s) + 4H2(g)

Metals such as lead, copper, silver and gold do not react with water at all.

Metal + Dilute acid →Salt + Hydrogen

 

Activity 3.11

·        Collect all the metal samples except sodium and potassium again.

·        If the samples are tarnished, rub them clean with sand paper.

CAUTION: Do not take sodium and potassium as they react vigorously even with cold water.

·        Put the samples separately in test tubes containing dilute hydrochloric acid.

·        Suspend thermometers in the test tubes, so that their bulbs are dipped in the acid.

·        Observe the rate of formation of bubbles carefully.

·        Which metals reacted vigorously with dilute hydrochloric acid?

·        With which metal did you record the highest temperature?

·        Arrange the metals in the decreasing order of reactivity with dilute

acids.

Metal with Sulfuric acid

Metals with HCl

Write equations for the reactions of magnesium, aluminium, zinc

and iron with dilute hydrochloric acid.

Hydrogen gas is not evolved when a metal reacts with nitric acid. It is

because HNO3 is a strong oxidising agent. It oxidises the H2 produced to

water and itself gets reduced to any of the nitrogen oxides (N2O, NO,

NO2). But magnesium (Mg) and manganese (Mn) react with very dilute

HNO3 to evolve H2 gas.

The reactivity decreases in the

order Mg > Al > Zn > Fe. In the case of copper, no bubbles were seen and

the temperature also remained unchanged 

Aqua regia, (Latin for ‘royal water’) is a freshly prepared 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.

 

Activity 3.12

·        Take a clean wire of copper and an iron nail.

·        Put the copper wire in a solution of iron sulphate and the iron

nail in a solution of copper sulphate taken in test tubes (Fig. 3.4).

·        Record your observations after 20 minutes.

·        In which test tube did you find that a reaction has occurred?

·        On what basis can you say that a reaction has actually taken place?

·        Can you correlate your observations for the Activities 3.9, 3.10

and 3.11?

·        Write a balanced chemical equation for the reaction that has taken

place.

·        Name the type of reaction.

 

Metal A + Salt solution of B → Salt solution of A + Metal B

 

3.2.5 The Reactivity Series

K Potassium Most reactive

Na Sodium

Ca Calcium

Mg Magnesium

Al Aluminium

Zn Zinc Reactivity decreases

Fe Iron

Pb Lead

H Hydrogen

Cu Copper

Hg Mercury

Ag Silver

Au Gold Least reactive

1. Why is sodium kept immersed in kerosene oil?

Solution: Sodium is a reactive metals, if kept open it will react with oxygen to explore and

catch fire. Sodium metal is kept immersed in kerosene to prevent their reaction with oxygen,

moisture and carbon dioxide of air.

2. Write equations for the reactions of

 3 Metals and Non-metals

(i) iron with steam

(ii) calcium and potassium with water

Solution: (i) Iron reacts with steam to form a magnetic oxide of Fe with the liberation of H2.

3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

(ii) Calcium reacts with water to form calcium hydroxide and hydrogen.

Ca(s) + 2H2O(I) → Ca(OH)2(aq) + H2(g)

Potassium reacts with cold water violently immediately with evolution of H2 which catches

fire.

2K(s) + 2H2O(I) → 2KOH(aq) + 2H2(g)

3. Samples of four metals A, B, C and D were taken and added to the following

solution one by one. The results obtained have been tabulated as follows

Use the Table above to answer the following questions about metals A, B, C and D.

(i) Which is the most reactive metal?

(ii) What would you observe if B is added to a solution of Copper (II)

sulphate?

(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.

 3 Metals and Non-metals

Solution:

(i) Metal B is the most reactive as it gives displacement reaction with iron (II) sulphate.

(ii) When metal B is added to copper (II) sulphate solution, a displacement reaction will take

place because of which the blue colour of copper (II) sulphate solution will fade and a redbrown

deposit of copper will be formed on metal B.

(iii)Metal B is the most reactive because it displaces iron from its salt solution. Metal A is less

reactive because it displaces copper from its salt solution. Metal C is still less reactive because it

can displace only silver from its salt solution and metal D is the least reactive because it cannot

displace any metal from its salt solution. Hence, the decreasing order of reactivity of the metals

is B > A > C > D.

4. Which gas is produced when dilute hydrochloric acid is added to a reactive

metal? Write the chemical reaction when iron reacts with dilute H2SO4.

Solution: Hydrogen gas is liberated when dilute HCl is added to a reactive metal.

Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)

5. What would you observe when zinc is added to a solution of iron (II) sulphate?

Write the chemical reaction that takes place.

Solution: Zinc is more reactive (more electro positive) than iron. Therefore Zinc displaces

Iron from its salt solution. The colour of ferrous sulphate is pale green, which turns colourless.

FeSO4 + Zn → ZnSO4 + Fe(s)

Light green Zinc sulphate(Colourless)

 

Activity 3.13

·        Take samples of sodium chloride, potassium iodide, barium chloride or any other salt from the science laboratory.

·        What is the physical state of these salts?

·        Take a small amount of a sample on a metal spatula and

·        heat directly on the flame (Fig. 3.7). Repeat with other samples.

·        What did you observe? Did the samples impart any colour to the flame? Do these compounds melt?

·        Try to dissolve the samples in water, petrol and kerosene.

·        Are they soluble? Soluble in water only

·        Make a circuit as shown in Fig. 3.8 and insert the electrodes into a solution of one salt. What did you observe? Test the other salt samples too in this manner.

·        What is your inference about the nature of these Compounds? 

Salt solubility test

Electrical conductivity test of salts

 

1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.

(ii) Show the formation of Na2O and MgO by the transfer of electrons.

(iii)What are the ions present in these compounds?

Solution: (i) Sodium:

 3 Metals and Non-metals

Oxygen:

Magnesium:

(ii) Formation of Magnesium oxide:

When magnesium reacts with oxygen, the magnesium atom transfers its two outermost

electrons to an oxygen atom. By losing two electrons, the magnesium atoms form a magnesium

ion (Mg2+) and by gaining two electrons, the oxygen atom forms an oxide ion (O2-).

Mg: +  → MgO

Formation of Sodium oxide:

Two sodium atoms transfer their 2 outermost electrons to an oxygen atom. By losing two

electrons, the two sodium atoms form tow sodium ions (2Na+). And by gaining two electrons,

the oxygen atom forms an oxide ion (O2-).

(iii) The ions present in sodium oxide compound (Na2O) are sodium ions (2Na+) and oxide

ions (O2-).

 3 Metals and Non-metals

The ions present in Magnesium oxide compound (MgO) are magnesium ions Mg2+ and oxide ions (O2-).

2. Why do ionic compounds have high melting points?

Solution: Ionic compounds are the ones which has both positive and negative charges. Hence there will be strong force of attraction between them. This make expenditure of lot of heat to break this force of attraction hence ionic compounds have high melting points.

 

Copper Electrolysis Purification

 

1. Define the following terms.

(i) Mineral (ii) Ore (iii) Gangue

2. Name two metals which are found in nature in the free state.

3. What chemical process is used for obtaining a metal from its oxide?

(i) Minerals are compounds (also known as elements) which are found naturally in the

earth’s crust. E.g. Alums, K2SO4.Al2(SO4)3.24H2O, etc.

(ii) Ores are minerals from which metal can be extracted Ex: Bauxite Al2O3.2H2O is the ore

of Al, copper pyrite CuFeS2.All minerals are not considered as ores but all ores are also

minerals.

(iii) Ores mined from the earth are naturally contaminated with sand, rocky materials. There

are impurities present in the ore which are known as gangue.

2. Name two metals which are found in nature in the free state

Solution: Gold and platinum are the two metals found in Free State in nature.

3. What chemical process is used for obtaining a metal from its oxide?

Reduction method is used to obtain metal from its oxide. Ex: Zinc oxide is reduced to metallic

zinc by Heating with carbon.

ZnO + C → Zn + CO

 3 Metals and Non-metals

Ex: Lead oxide is reduced to lead by heating with carbon

PbO +C → Pb + CO

CORROSION:

Corrosion is when a refined metal is naturally converted to a more stable form such as its oxide, hydroxide or sulphide state this leads to deterioration of the material.

Silver articles become black after some time when exposed to air.

This is because it reacts with sulphur in the air to form a coating

of silver sulphide.

Copper reacts with moist carbon dioxide in the air and slowly loses

its shiny brown surface and gains a green coat. This green

substance is copper carbonate.

Iron when exposed to moist air for a long time acquires a coating

of a brown flaky substance called rust.

Anhydrous Calcium Chloride 94-97% is a purified inorganic salt produced by removing water from a naturally occurring brine solution.

solutions of calcium chloride can prevent freezing at temperatures as low as −52 °C

 

1. Metallic oxides of zinc, magnesium and copper were heated with the following

metals.

Metal	Zinc	Magnesium	Copper
Zinc Oxide
Magnesium Oxide
Copper Oxide

 

Answer:

A more reactive metal can displace a less reactive metal from its oxide. Among Zinc,

Magnesium, and Copper metals, magnesium is the most reactive, copper is the least reactive metal and zinc is less reactive. The displacement reaction will take place in the following cases

 

 

Metal	Zinc	Magnesium	Copper
Zinc Oxide	-	Displacement	-
Magnesium Oxide	-	-	-
Copper Oxide	Displacement	Displacement	-

 

 

 

 

2. Which metals do not corrode easily?

Answer: Gold and platinum are the metals which do not corrode easily

3. What are alloys?

Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal.

 

Exercise questions

1. Which of the following pairs will give displacement reactions?

(a) NaCl Answer and copper metal

(b) MgCl2 Answer and aluminium metal

(c) FeSO4 Answer and silver metal

(d) AgNO3 Answer and copper metal

Answer: Option d i.e AgNO3 Answer and copper is correct answer. Copper displace the

silver cations (reducing them to the elemental metal), in the process copper itself being

oxidised to Copper II cations (Cu2+) and going into Answer. So silver metal precipitating out and a copper II nitrate Answer will be remaining.

Cu(s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag (s)

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: Answer is (c) Applying a coat of Zinc

Though applying grease and applying paint prevents iron from rusting but we cannot apply these methods on frying pan hence applying a coat of Zinc is most appropriate method to prevent an iron pan from rusting.

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: Correct answer is option (a) i.e Calcium.

Calcium reacts with oxygen to give calcium oxide. Calcium oxide is soluble in water to give Calcium Hydroxide. Carbon forms carbon-oxide with oxygen which is gas hence option B is wrong Silicon reacts with oxygen and forms silicon dioxide. This is insoluble in water. So option C is not correct. Iron reacts with oxygen and forms Iron dioxide. This is insoluble in water. So option D is not correct.

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: Answer is c. Food cans are coated with tin and not with zinc because Zinc is more reactive that is electro positive than tin.

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 nonmetals?

(b) Assess the usefulness of these tests in distinguishing between metals and nonmetals.

Answer:

(a) Metals are malleable and can be easily drown into sheets by hitting with hammer. On the other hand if we beat non-metals they break down and they cannot be drawn into sheets as they are non-malleable. Metals of good conductors of electricity hence they make bulb when you connect metals with a battery, wire and bulb. Similarly If non metals are bad conductors of electricity chance they fail to lit up the bulb on connecting with wire and battery.(b) These experiments can be helpful to demonstrate the malleability and electric

conductivity of the metals and non-metals

6. What are amphoteric oxides? Give two examples of amphoteric oxides

Answer: Oxides that react with both acids and bases to form salt and water are known as amphoteric oxides. Examples: PbO and Al2O3.Amphoteric oxides are the one which reacts with both acids and bases to form salt and water.Examples: Lead oxide - PbO and Aluminium oxide - Al2O3.

7. Name two metals which will displace hydrogen from dilute acids, and two

metals which will not.

Answer: Zinc (Zn) and Magnesium (Mg) are the two metals which will displace Hydrogen from dilute acids as they are very reactive metals. Gold (Au) and Silver (Ag) are the metals which will not replace Hydrogen from dilute acids as these metals are less reactive.

8. In the electrolytic refining of a metal M, what would you take as the anode, the

cathode and the electrolyte?

Answer: In the process of electrolytic refining of metal called ‘M’, An impure and thick block of metal M. is considered as anode, Thin strip or wire of pure metal M is taken as anode A suitable salt Answer of metal M is considered as the electrolyte.

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 powder is burnt in the air sulphur-di-oxide is formed.

(i) Sulphur-di-oxide does not have any effect on dry litmus paper.

(ii) Sulphur-di-oxide turn the moist litmus paper from blue to red as contact of SO2 with water turns to sulfurous acid.

(b) S(s) + O2(g) → SO2(g)

SO2(g) + H2O →H2SO3

10. State two ways to prevent the rusting of iron.

Answer:

1. Iron can be prevented from rusting by coating the surface of the iron with rust proof

paints

2. By applying Oil/grease on the surface of iron objects as it will prevent the iron

surface to get in contact with air consisting of moisture.

11. What type of oxides are formed when non-metals combine with oxygen?

Answer: When non-metals combine with oxygen it forms either acidic or neutral oxides. Ex:

N2O5 or N2O3 is an acidic oxide; CO is a neutral oxide.

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) Platinum, gold and silver are used to make jewellery for these metals are very less

reactive hence they are not affected by air, water or most chemicals. These metals have a

lot of lustre and they are malleable and ductile in nature.

(b) Sodium, potassium and lithium readily reacts with water to produce a lot of heat. As a result Hydrogen evolved in the reaction results in fire. On exposure to water they react

with moisture (water droplets) present in the atmosphere, In order to prevent contact

with water hence these metals are stored under oil.

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: Tarnished copper vessels being cleaned with lemon or tamarind because these sour substance contains acids which dissolve the coating of copper oxide or basic copper carbonate present on the surface or tarnished copper vessels. This makes them shining red-brown again. Hence they are very effective in cleaning tarnished copper vessels.

14. Differentiate between metal and non-metal on the basis of their chemical

properties.

Answer:

 

 

Metals	Non-metals
When metals are heated with oxygen, they form ionic oxides which are basic in nature and form bases on dissolving with water. This turn red litmus paper to blue.	When non-Metals are heated with oxygen, they form covalent oxides which are acidic in nature which form acid on dissolving with water. This turn blue litmus paper to red.
They are electro positive, lose electrons readily and become a positive ion	They are electro negative, gain electrons and become negative ions.
Metals are lustrous	Non-metals are non-lustrous; graphite is the exception
Reducing agents	Good oxidizing agents.
Metals are the good conductors of electricity and heat.	Non-metals are non-conductors of electricity and heat; graphite is the exception
All metals are solids except mercury	Non-metals are in solid-liquid and gaseous States

 

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: Goldsmith used the solution called Aqua regia which is called as royal water in Latin. . It is the mixture of concentrated Hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua regia is capable of dissolving noble metals like gold and platinum. When upper-layer of dull gold ornament is dissolved they lose their weight.

 

16. Give reasons why copper is used to make hot water tanks and not steel (an

alloy of iron).

Answer: Copper is used to make hot water tanks and not steel (an alloy of iron) because copper does not reacts with either water or steam whereas iron reacts with steams to corrode the tank.