3. Metals and Non-metals

CHAPTER  3.
METALS AND NON-METALS
PAGE No: 40

1. Give an example of a metal which 

(i) is a liquid at room temperature

Mercury

(ii) can be easily cut with a knife

Sodium and Potassium

(iii) is the best conductor of heat

Silver and Copper

(iv) is a poor conductor of heat

Lead and Mercury

2. Explain the meaning of malleable and Ductile?

Malleable : The property of metals by which , it can be beaten into thin sheets
The most malleable metals are Gold and Silver

Ductile : The property of metals by which , it can be drawn into thin wires
The most ductile  metal is Gold . From one gram of gold a wire of 2 km can be drawn.

PAGE No: 46

1. Why is sodium kept immersed in kerosene oil?

Sodium is a highly reactive metal. It reacts vigorously with oxygen so it cannot be placed open to atmosphere.
If sodium  is kept it water it reacts with the dissolved oxygen present in it.
Hence sodium is kept in kerosene oil.

2. Write equations for the reactions of

(i) Iron with steam.

3Fe + 4H₂O  à  Fe₃O₄   + 4H₂

(ii)  Calcium and potassium with water

Ca + 2H₂O  à  Ca(OH)₂      + H₂

2K + 2H₂O  à  2KOH +  H₂ +  Heat energy

3 Samples of four metals A, B,C and D were taken and added to the following solutions one by one . The result obtained have been tabulated as follows

Metal	Iron (ll) sulphate	Copper (ll) sulphate	Zinc sulphate	Silver nitrate
A	No reaction	Displacement
B	Displacement		No reaction
C	No reaction	No reaction	No reaction	Displacement
D	No reaction	No reaction	No reaction	No reaction

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

(i) Which is the most reactive metal?

B is the most reactive metal.
According to the reactivity series the order  of reactivity is  Zinc sulphate  > Iron (ll) sulphate > Copper (ll) sulphate > Silver nitrate.
No metal has reaction with Zinc sulphate
Second is Iron (ll) sulphate, and metal B displaces it , Hence B is the most reactive metal.

* Metal A does not react with  Zinc sulphate as it has no reaction with Iron (ll) sulphate which is below zinc in the reactivity series.

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

Metal B displaces copper from its solution of Copper (ll) sulphate. Since metal B displaced iron which is above copper  in the reactivity series

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

B > A >  C > D

4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when when iron reacts with dilute H₂SO₄

Hydrogen gas is produced when  dilute hydrochloric acid is added to a reactive metal.

Fe  + H₂SO₄   à  Fe SO₄  + H₂

5. What would you observe when zinc is added to a solution of iron(ll) sulphate ? Write the chemical reaction that takes place

When zinc is added to a solution of iron(ll) sulphate zinc would displace iron from its solution.
This is because zinc is above iron in the reactivity series

Zn  + FeSO₄  à Fe  + ZnSO₄   

PAGE No: 49

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

Na₂O

Na₂O contains Sodium and oxygen as its constituent elements.
The atomic number of sodium is 11 and oxygen is 8.
The electronic configurations are 2, 8, 1  and 2, 6  respectively.
For sodium to attain stability it should either loose one electron or gain seven electrons. Gaining of seven electrons is impossible so it looses  one electron and becomes stable 

Na - 1e^-   à  Na⁺

For oxygen  to attain stability it should either loose six electron or gain two electrons. Loosing of six electrons is impossible so it gains  two  electrons and becomes stable 

O + 2e^-   à  O^2-

MgO

MgO contains Magnesium and oxygen as its constituent elements.
The atomic number of magnesium  is 12 and oxygen is 8.
The electronic configurations are 2, 8, 2  and 2, 6  respectively.
For magnesium  to attain stability it should either loose two electrons or gain six electrons. Gaining of six electrons is impossible so it looses  two electrons and becomes stable 

Mg - 2e^-   à  Mg²⁺

For oxygen  to attain stability it should either loose six electron or gain two electrons. Loosing of six electrons is impossible so it gains  two  electrons and becomes stable 

O + 2e^-   à  O^2-

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

Na₂O contains  O^2- and    Na⁺  ions  

MgO contains  O^2- and    Mg⁺²  ions  

2. Why do ionic compounds have high melting points?

The strong electrostatic force of attraction between the atoms of a molecule are responsible for the high melting points of ionic compounds.

Large amount of energy is required to overcome this force.

PAGE No: 53

1. Define the following terms

(i)  Mineral

 The elements or compounds which occurs naturally on the earths crust are known as minerals.

(ii) Ore

Minerals which contain a very high percentage of a particular metal , and the metal can be profitably extracted are known as ores.

(iii) Gangue

Ores mined from the earth are contaminated with large amount of impurities such as soil,sand etc. These impurities are called gangue

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

Gold, Platinum and Silver

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

Reduction is the process used to obtain metal from its oxide ore.

PAGE No: 55

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

Metal	Zinc	Magnesium	Copper
Zinc Oxide
Magnesium Oxide
Copper oxide

 In which case will you find displacement reactions taking place?

• Magnesium displaces zinc from its oxide
• Nothing will happen with magnesium oxide
• Copper would be displaced by zinc and magnesium  from its oxides 

2. Which metal do not corrode easily?

Gold and platinum

3. What are alloys?

An alloy is a homogeneous mixture of two or more metals or a metal and a nonmetal.
It is prepared by first melting the primary metal and then dissolving the other elements in it in definite proportion.
It is then cooled to room temperature

Eg. Amalgam, Braze, Bronze, Steel

EXERCISES  

PAGE No: 56

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

(a) NaCl solution and copper metal

(b) MgCl₂ solution and aluminium metal

(c) FeSO₄  solution and silver metal

(d) AgNO₃   solution and copper metal

2. Which of the following methods is suitable for preventing an iron frying pan from rusting?

Applying a coating of Zinc

3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. This element is likely to be

The element is likely to be calcium

4. Food cans are coated with tin and not with zinc because

Zinc is more reactive than tin.

5. You are given a hammer, a battery, a bulb, wire and a switch.

(a) How could you use them to distinguish between samples of metals and non metals? 

If we hit with a hammer the metals will get spread due to the property of malleability. On the other hand non metals  get powdered and hence we can distinguish a metal and a non metal.

If we connect the samples in a circuit containing a battery, wire , bulb and a switch, the bulb glows if it is a metal because of the property of conductivity. The bulb does not glow if it is a non metal since it is not a conductor of electricity

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

All non metals are not non conductors, for example graphite, an allotrope of carbon

Hammer test is the reliable one for some extent 

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

The metal oxides which can neutralize acids and bases 

Since it is neutralization reaction the product obtained are salt and water.

Aluminium oxide

Al₂O₃  + 6HCl  à 2AlCl₃   + 3H₂O

Al₂O₃  + 2NaOH  à 2NaAlO₂   + H₂O

Zinc oxide

ZnO  + 2HCl  à ZnCl₂   + H₂O

ZnO  + 2NaOH  à Na₂ZnO₂   + H₂O

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

All the metals above hydrogen in the reactivity series will displace hydrogen from dilute acids
Eg: Lead, Iron, Zinc, Aluminium, Magnesium , Calcium ,Sodium , Potassium etc

All the metals below  hydrogen in the reactivity series will not displace hydrogen from dilute acids

Eg: Copper, Mercury, Silver, Gold etc

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

Impure metal which is to be purified  is made as the anode.
A thin strip of pure metal (M) as the cathode.
A solution of the metal salt is used as the electrolyte

9. Pratyush took sulphur powder on a spatula and heated it. He collected the heat evolved by           inverting a test tube over it.

(a) What will be the action of gas on
(i)  Dry litmus paper

Nothing will happen to both the blue and red litmus paper , as it has no moisture content to get ionized

(ii) Moist litmus paper

With moist litmus paper sulphuric acid is produced. 

The colour of moist blue litmus chages to red. And no colour change occur to red moist litmus paper 

(b) Write the balanced chemical equation for the reaction taking place.

S + O₂ à SO₂ 

SO₂   + H₂O à H₂SO₃   ( Sulphurous acid)

10. State two ways to prevent the resting of iron

Galvanizing ,Painting , Grezing

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

Non metals reacts with oxygen to form acidic oxides or neutral oxides
 Eg: SO₂ ( acidic ) H₂O ( neutral )

12. Give Reasons

(a)  Platinum, Gold and silver are used to make jewelry.

They are at the bottom of the reactivity series and they do not have reaction with any elements.
They  have a shining surface

(b) Sodium, Potassium and Lithium are stored under oil.

They are highly reactive with oxygen and  cause fire . It is lighter than water . Hence it is kept under oil.

(c) Aluminium is a highly reactive metal , yet it is used to make utensils for cooking

When exposed to air the metal changes to oxide, aluminium oxide, this get deposited over the surface of the metal and forms a protective coating on the surface. Aluminium oxide is a non reactive compound. Hence aluminium  can be used as cooking utensils.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of                   extraction

Metals can be easily obtained from metal oxides by reduction with carbon or any other reducing agents. So metal ores of carbonate and sulphide are first converted into oxides.

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.

Copper vessel forms a greenish coat of basic copper carbonate.
Lemon and tamarind contain mild acid such as citric acid and tartaric acid respectively.
Here a neutralization reaction takes place and the basic coat of copper carbonate  is removed

14. Differentiate between metal and nonmetal on the basis of their chemical properties.

Metals	Non Metals
With Oxygen Basic oxides are formed	With Oxygen Acidic / neutral oxides are formed
Displace hydrogen from water	Do not react with  water
Displace hydrogen from dilute acids	Do not react with  dilute acids
Ionic chlorides are formed	Covalent  chlorides are formed
Very few reacts with hydrogen	Almost all reacts with hydrogen
Ionic metal hydrides	Covalent non metallic  hydrides

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 to hasty            retreat. Can you play the detective to find out the nature of the solution he had used ?  

Aqua regia

It is a highly corrosive mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3: 1

 This is the only solution where gold dissolves.

16 . Give reason why copper is used to make hot water tanks and not steel ( an alloy of iron)

Copper is better conductor of heat than steel which is an alloy of iron.
Copper do not react with hot water but iron does

3Fe + 4H₂O  à  Fe₃O₄   + 4H₂

2. Acids , Bases and Salts

CHAPTER  2.
ACIDS , BASES AND SALTS
PAGE No: 18

1. You have been provided with three test tubes. One of them contains distilled water and the           other two contain an acidic solution and a basic solution respectively. If you are given only         red litmus paper , how will you identify the contents of each test tube?

Take the red litmus paper and cut it into three pieces. Dip  the pieces one each in one test tube.
Note the difference in colour

(a) The test tube in which the red litmus turns blue is a basic solution

 The blue litmus obtained from the first test is dipped in the rest of the two test tubes
(b)The test tube in which the blue litmus turns red is an acidic solution

(c)The test tube in which no change in colour occurs to the litmus is distilled water

PAGE No: 22

1. Why should curd and sour substances not be kept in brass and copper vessels ?

The curd and sour substances contains acids which reacts with metals.
Metals + Acids  gives  Salt + Hydrogen
This may spoil the food and even turns poisonous.

2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example.       How will you test for the presence of this gas?

Hydrogen gas is produced when a metal reacts with acids
Zinc granules reacts with hydrochloric acid to produce Zinc chloride and hydrogen

   Zn + 2HCl   à  ZnCl₂ + H₂

We can test  the presence of hydrogen by passing it through a delivery tube to  a container containing soap solution.
Introduce a lighted candle while the bubbles arises. The bubbles burns with a pop sound indicates hydrogen gas

3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reactions if one of the compounds formed is calcium chloride

Since the gas evolved extinguishes the burning candle,. the gas evolved is carbon dioxide

The products are calcium chloride and carbondioxide.
The given reactant is Hydrochloc acid , hence the other reactant is calcium carbonate 

CaCO₃   + 2HCl  à  CaCl₂  +   CO₂ + H₂O

     

PAGE No: 25

1. Why do HCl ,  HNO₃ etc show acidic character s in aqueous solutions , while solutions of compounds like alcohol and glucose do not show acidic character? 

When acids are made dilute with water     H⁺   ions are produced  which combines with water to form hydronium ions ( H₃O⁺ )

This is responsible for the acidic character  of acids in aqueous solution

While alcohol and glucose in aqueous solution do not produce ions hence do not show acidic or basic character

2. Why does an aqueous solution of an acid conduct electricity?

Acids produce H⁺  ions in aqueous solution. This is responsible for the conduction of electricity.

3. Why does dry HCl gas not change the colour of dry litmus paper?

Dry HCl gas does not have H⁺  ions. Hence dry HCl gas not change the colour of dry litmus paper.
If we dilute it with water  H⁺   ions are produced  which combines with water to form hydronium ions ( H₃O⁺ ) and hence the colour of  blue litmus paper change to red

4. While diluting an acid why is it recommend that the acid should be added to water and not         water to the acid?

If we dilute an acid  with water  H⁺   ions are produced  which combines with water to form hydronium ions ( H₃O⁺ ) . This reaction is highly exothermic.

If we add water to the acid  all the molecules of water take part in reaction and excess heat is produced , causing the acid to splash out and may cause burns.
Also the container may break due to high temperature

On the other hand if we add acid to water drop by drop we can control the reaction and hence avoid danger.  

5. How is the concentration of hydronium ions ( H₃O⁺ ) affected when a solution of an acid is diluted?

When a solution of acid is diluted with water H₃O⁺ ions per unit volume decreases. 

6. How is the concentration of hydroxide ions (OH^- ) affected when excess base is dissolved in a solution of sodium hydroxide?  

If excess base is dissolved in a solution of sodium hydroxide, the concentration of  OH^-
 ions increases.
 This is because when another base dissolve in the solution another set OH^-  ions are produced

PAGE No: 28

1. You have two solutions, A and B, the  p^H   of  solution A is 6 and  p^H  of solution B is 8. Which solution have more hydrogen ion concentration ? Which of this is acidic and which one is basic?

 Solution A 
 More hydrogen ion concentration, since its p^H  is below seven.
 Solution is acidic

Solution B
 Less hydrogen ion concentration, since its p^H  is above seven
Solution is basic

2. What effect does the concentration of  H⁺  (aq) ions have on the nature of the solution?

The H⁺   ion  concentration determines the power of an acid. Higher the   H⁺   ion  concentration higher is its acidic character and vice versa.

3. Do basic solutions also have H⁺  (aq) ions? . If yes , then why are these basic?

Yes. Basic solution contain H⁺ ions. But in a basic solution the concentration of OH^-  ions is higher than that of H⁺  ions

4. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime ( calcium oxide) or slaked lime ( calcium hydroxide) or chalk ( calcium carbonate)?

Plants grow well between the p^H  range of 6  to 8  . If the soil become too acidic , to reduce the acidicity the farmers use bases like quick lime ( calcium oxide) or slaked lime ( calcium hydroxide) or chalk ( calcium carbonate)

PAGE No: 33

1. What is the common name of the compound CaOCl₂  ? 

Bleaching Powder

2. Name the substance which on treatment with chlorine yields bleaching powder

Dry slaked lime  Ca(OH)₂   

3. Name the sodium compound which is used for softening hard water

Washing soda   (Na₂CO₃.10H₂O )

4.What will happen if a solution of sodium hydrocarbonate is heated?  Give the equation of the reaction involved

When a solution of sodium hydrocarbonate is heated sodium carbonate, water and carbon dioxide are formed

2NaHCO₃   à  Na₂CO₃  + H₂O  + CO₂

5. Write an equation to solve the reaction between Plaster of Paris and water

The product is gypsum

CaSO₄ .½H₂O   +  1½H₂O   à   CaSO₄ .2H₂O   

EXERCISES 

PAGE No: 34

1. A solution turns red litmus blue, its p^H  is likely to be

10, since the solution is basic . All other option given are below seven.

2. A solution reacts with crushed egg shells to give a gas that turns lime water milky. The solution contains

HCl.  All other options are basic.

3. 10 mL of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution ( the same solution as before) required to neutralize it will be

10 mL NaOH  neutralize  8 mL  HCl

20 mL NaOH  neutralize X mL  HCl

HCl  required  is    ( 8 x 20 )  /  10 

        =  16 mL

4. Which one of the following types of medicines is used for treating indigestion?

Antacid.  Antacid contain mild base,  normally sodium hydrogen carbonate ( NaHCO₃ )

5. Write word equations and then balanced equations for the reaction taking place when

(a)  Dilute sulphuric acid reacts with zinc granules

Zinc  +  Sulphuric acid ( dil)  à  Zincsulphate  + Hydrogen

Zn  + H₂SO₄   à  Zn SO₄  + H₂

(b) Dilute hydrocholoric acid reacts with  magnesium ribbon

Magnesium + Hydrochloric acid (dil)  à Magnesium chloride + Hydrogen

Mg  + 2HCl  à  MgCl₂  + H₂

(c) Dilute sulphuric acid reacts with aluminium powder

Aluminium + Sulphuric acid ( dil)  à  Aluminium sulphate  + Hydrogen

2Al  + 3 H₂SO₄  à  Al₂(SO₄) ₃  + 3H₂

(d) Dilute hydrochloric acid reacts with iron filings

Iron  + Hydrochloric acid (dil)  à Ironchloride + Hydrogen

Fe  + 2HCl  à  FeCl₂  + H₂

6. Compounds such as alcohols and glucose also contain hydrogen, but are not categorized as acids. Describe an activity to prove it

Materials required : dilute solution of ethanol and glucose solution
Apparatus required : beaker , a cork ,2 iron nails ,battery , bulb ,key , ethanol ,glucose solution , connecting wire
Procedure :

• take a cork
• fix two iron nails with a space between them 
• take the beaker and place this in the middle of the beaker
• now connect the two nails to the circuit containing a key a dry cell and a bulb
• now fill the beaker with glucose solution 
• note down the observation 
• drain the solution out and fill it with ethanol solution 
• note down your observation 

Observation : you would observe that the bulb does not glow in both the solution
Conclusion :from the above experiment we come to a conclusion that both the solution does not conduct electricity and this implies that both the solution does not contain any ions therefore it does not contain  H⁺  ions  thus it is not an acid

7. Why does distilled water not conduct electricity, where as rain water does?

 Rain water:
  Rain water contains impurities like mud acid etc therefore rain water is acidic thus it contains H⁺  ions and other charged particle   so it conducts electricity
Distilled water:
 Distilled  water does contain any  impurities or charged particles are not present  so it does not conduct electricity

8. Why do acids not show acidic behavior in the absence of water ?

Acids cannot produce H⁺  ions in the abscence of water . Only by diluting with  water it produces H⁺  ions

9. Five solutions A,B,C, D and E when tested with universal indicator showed  p^H   as 4 ,  1,  11,  7  and 9  respectively . Which solution is

(a) Neutral ?

D , since its p^H is 7

(b) Strongly alkaline ?

C, since its p^H is 11

(c) Strongly acidic ?

B , since its p^H is 1

(d) Weakly acidic ?

A , since its p^H is 4

(e)  Weakly alkaline ?

E , since its p^H is 9

The increasing order is C<E< D< A< B

10. Equal length of magnesium ribbons are taken in test tube A and B . Hydrochloric acid ( HCl )is added to test tube A, while acetic acid  (CH₃COOH ) is added to test tube B..Amount and concentration taken for both the acids are same.In which test tube will the fizzing occur more vigorously and why ?

Fizzing  occurs more frequently in the test tube in which  HCl was added this is because HCl is strong acid and CH3COOH is a weak acid

11. Fresh milk has a p^H   of 6. How do you think the p^H  will change as it turns into curd ? Explain your answer

when the milk changes to curd its p^H would decrease this is because the acidic character increases as lactic acid is formed when it changes into curd

12. A milkman added a very small baking soda to fresh milk

(a) Why does he shift the  p^H  of milk from 6 to slightly alkaline?
This is to prevent the milk from changing to curd . the formed lactic acid would get neutralized

(b) Why does this milk take a long time to set as curd?
this is because the baking soda reacts with the formed lactic acid and thus get neutralizes the effect . thus the milk which is added with baking soda takes a long time to set as curd


13. Plaster of Paris should be stored in a moister  proof container . Explain Why?

plaster of paris must be stored in moisture proof container because plaster of paris reacts with water to form gypsum which o not posses the property of setting

CaSO₄ .½H₂O   +  1½H₂O   à   CaSO₄ .2H₂O   

14. What is neutralization reaction? Give two examples.

the reaction between an acid and base to produce salt and water is called neutralization reaction

HCl + NaOH  à NaCl +H₂O

HCl + KOH  à KCl +H₂O

15. Give two important uses of washing soda and baking soda

Washing soda 

• can be used as a cleaning agent for domestic purposes 
• removing permanent hardness of water 

Baking Soda  

• used in soda acid fire extinguisher 
• An active ingredient in antacids  

10. Light - Reflection and Refraction

CHAPTER  10.
LIGHT - REFLECTION AND REFRACTION
PAGE No: 168

1. Define the principal focus of a concave mirror.

Rays of light falling parallel to the principal  axis of a concave mirror  after reflection converges at a common fixed point on the principal axis .
This common fixed point on the principal axis is known as the principal focus of a concave mirror

2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Radius of curvature = 2  x  focal length
20  = 2 x f
f   =   20/2
f  =10.cm
Focal length is 10 cm

3. Name a mirror that can give an erect and enlarged image of an object?

A concave mirror can give an erect and enlarged image when the object is placed between the principal focus and the pole.

4. Why do we prefer a convex mirror as a rear-view mirror in vehicles?

We prefer a convex mirror as a rear view mirror because of
1. It gives an erect and diminished image of a large area in front of the mirror.
2. It gives a wider field of view as it curved outwards than a plane mirror

PAGE No: 171

1.Find the focal length of a convex mirror whose radius of curvature is 32 cm ?

For a convex mirror
Radius of curvature and focal length are positive
Radius of curvature = 2  x  focal length
32  = 2 x f
f   =   32/2
f  =16.cm
Focal length is  + 16 cm

2. A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Where is the image located?

m =  - 3 ( since image is three times magnified and negative sign since  the image is real)
u =  -10 ( Negative sign indicates the object is in front , that is to the left of the mirror)
v = ?
Magnification  m  = -v/u
                        -3  = -v / -10

        -v   =  -10 x -3  =  + 30cm

          v =  -30 cm
The image is located at a distance of 30 cm in-frond of the mirror.

PAGE No: 176

1.A  ray of light travelling in air enters obliquely into water. Does the light ray bent towards the normal or away from the normal why ?

The light ray bents towards the normal .
Air is a rarer medium and the speed of light is greater  in a rarer medium than a denser medium.
Water is a denser medium compared to air, hence the speed of light is less in water
Hence the light ray slows down when entering obliquely from air to water and bend towards the normal.

But if the ray incident along the normal the ray undergo no deviation

2. Light enters from air to glass having refractive index 1.50. What is the speed of light in the          glass ? The speed of light in vacuum is 3 x 10⁸ m /s

Refrative index of glass  n  = 1.50
Speed of light in vaccum  c = 3 x 10⁸ m /s
 Speed of light in medium   v = ?


n = c / v
  1.50 = 3 x 10⁸  / v

  v = 3 x 10⁸  / 1.50
       =  2 x 10⁸  m/s

3. Find out ( from table 10.3) the medium having highest optical density Also find the medium        with lowest density  

Air has the lowest refractive index of 1.0003
This implies that air has the lowest optical density

Diamond has the highest refractive index of 2.4
This implies that diamond has the highest optical density

4. You are given kerosene, turpentine, and water. In which of these does the light travel fastest?       Use the information given in table 10.3

Kerosene has a refractive index of 1.44 

Turpentine has a refractive index of  1.47

Water  has a refractive index of  1.33

From these information  turpentine has the highest optical density and water has the lowest

As water has the lowest optical density, light travels the fastest in water than the other two.

5. The refractive index of diamond is 2.42. What is the meaning of this statement?

The refractive index of diamond  is  2.42 indicates that the ratio of the speed of light in vacuum / air to that of   diamond is 2.42

PAGE No: 184

1.Define 1 dioptre of power of a lens

One dioptre is the power of a lens having a focal length of 1 meter

2.A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it.             Where is the needle placed in front of the convex lens if the image is equal to the size of the          object? Also find the power of the lens 

Convex lens.
Real and inverted image
v = + 50 cm  ( positive for the image is real and formed along the direction of incident ray )

m = -1 ( size of the image and size of the object are equal, negative sign since the image is real)

m = v/u


-1 = 50 /u

u = -50 cm

Negative sign indicates that the object is placed in the opposite direction of the incident ray
The needle is placed at a distance of 50 cm in-front  of the convex lens


To find the power of lens

1/f  = 1/v - 1/u


     = 1/(+50 )   -    1/( -50)

  1/f     =  2/50  =  1/25

f =25 cm  = 0.25 m 

Power  P = 1/f  ( in meter )

              = 1/0.25
              = + 4 D     ( Dioptre)

The power of the lens is 4 Diopter

3.Find the power of a concave lens of focal length 2m

EXERCISES

PAGE No: 185

1.Which one of the following materials cannot be used to make a lens?

2.The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?

3.Where should an object be placed in front of a convex lens to get a real image of the size of the object?

4.A spherical mirror and a thin spherical lens have each a focal length of -15 cm . The mirror and the lens are likely to be-

5. No matter how far you stand from a mirror , your image appears erect . The mirror is likely to be -

6.Which of the following  lenses would you prefer to use while reading small letters found in a dictionary?

7.We wish to obtain an erect image of an object, using a concave mirror of focallength 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the immage? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case

8.Name the type of mirror used in the following situations

(a)Headlight of a car

(b) Side / Rear view mirror of a vehicle.

(c)  Solar furnace

9.One half of a convex lens is covered with a black paper . Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations

10.An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position size and nature of the image formed

11.A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram

12.An object is placed at a distance of 10cm from a covex mirror of focal length 15 cm. Find the position and nature of the immage

13.The magnification produced by a plane mirror is +1. What does this mean?

1. Chemical Reactions and Equations

CHAPTER  1.
CHEMICAL REACTIONS AND EQUATIONS
PAGE No: 6

1. Why should a magnesium ribbon be cleaned before burning in air ?

Magnesium reacts slowly with  oxygen present in the atmosphere and forms a thin layer of coating of magnesium oxide.

This has to be removed before burning , otherwise the magnesium oxide coating resist further oxidation

2. Write the balanced equation for the following chemical reaction

(i) Hydrogen  + Chlorine    à    Hydrogen chloride

       H₂ + Cl₂    à   2HCl

(ii)  Barium chloride  + Aluminium sulphate  à Barium sulphate + Aluminum chloride

      3BaCl₂   +  Al₂ (SO₄)₃   à      3BaSO₄   + 2AlCl₃

(iii)  Sodium  + Water  à  Sodium hydroxide  + Hydrogen

       2Na  +  2H₂O    à     2NaOH  + H₂

3.  Write a balanced chemical equation with state symbols for the following reactions

(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride

      BaCl₂ (aq)  + Na₂SO₄ (aq)  à    BaSO₄ (s)  + 2NaCl  (aq)

(ii)  Sodium hydroxide solution ( in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water

      NaOH(aq)  + HCl (aq)  à  NaCl (aq)  + H₂O(l)

PAGE No: 10

1. A solution of a substance'X' is used for white washing ?

(i) Name the substance "X" and write its formula

Calcium oxide  CaO

(ii) Write the reaction of the substance "X"  with water

CaO (s)      +      H₂O(l)   à     Ca(OH)₂

_{Quick lime                                         Slaked lime}

2. Why is the amount of gas collected in one of the testtubes in activity 1.7 double of the amount collected in the other? Name this gas

In activity 1.7, by the electrolytic decomposition of water, we get hydrogen at cathode and oxygen at anode . This can be given by the chemical equation

2H₂O(l)    à     2H₂(g)  + O₂(g)

Hydrogen combines with oxygen  in the ratio 2: 1 to form water.
Hence the volume of hydrogen produced  is double the volume of oxygen produced

There for the amount of gas collected at cathode is double the amount of gas collected in the anode

The gas produced  at the cathode which is double the other one is hydrogen

PAGE No: 13

1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

When an iron nail is dipped in copper sulphate solution which is blue in colour , its colour changes to green
This is because iron which is  comparatively more reactive than copper displaces copper from its solution.

The overall reaction can be written as

Fe (s)  + CuSO₄(aq) à       FeSO₄ (aq)  + Cu(s)

And hence this is a displacement reaction.

2. Give an example of a double displacement reaction other than the one given in activity 1.10

Lead nitrate reacts with hydrochloric acid to give lead chloride and nitric acid

Pb(NO₃)₂ (aq)  + 2HCl(aq)   à   PbCl₂ (s)  +  2HNO₃(aq)

 The precipitate of lead chloride is formed when Pb⁺⁺   ions from lead nitrate combines with 2Cl^- ions of hydrochloric acid.

An aqueous solution of nitric acid is formed H⁺ ions combines with NO₃^- ions

3. Identify the substances that are oxidized and the substances that are reduced in the following reactions  

(i)    4Na(s)  + O₂(g)     à             2Na₂O (s)

Sodium is oxidized and oxygen is reduced 

Oxygen atom is added to sodium and hence oxidized.
From a molecule of oxygen one atom is released and hence reduced.

 (ii)  CuO (s) + H₂( g)       à              Cu (s)  + H₂O (l)

Hydrogen is oxidized and copper oxide is reduced

Copper oxide looses oxygen atom to form copper , hence reduced.
Hydrogen gains oxygen atom to form water and hence oxidized

EXERCISES

PAGE No: 14

1. Which of the statements about the reaction below are incorrect?

2PbO(s)  + C (s)  à    2Pb(s) + CO₂(g)

(a) Lead is getting reduced
(b) Carbon dioxide is getting oxidized
(c) Carbon is getting oxidised
(d) Lead oxide is getting reduced


(a) and (b) are incorrect  and both (c) and (d) are correct.
Carbon gains oxygen and hence oxidized.
Lead oxide looses hydrogen and reduced

2. Write the balanced equation for the following chemical reaction

Fe₂O₃   +  2Al    à     Al₂O₃  + 2 Fe

The above reaction is an example of  displacement reaction

Here aluminium is comparatively more reactive than iron.
In the reactivity series aluminium is above iron
Hence it displaces iron from its  solution.

3. What happens when dilute hydrochloric acid is added to iron filings?

Hydrogen gas and iron chloride are produced

It is a displacement reaction.

In the reactivity series chlorine is above hydrogen
Hence it displaces hydrogen from its  solution.

4. What is a balanced chemical equation? Why should chemical equation be balanced?

A chemical equation in which the number of atoms of each element in the reactant and the product side are equal , then the chemical equation is said to be balanced.

Principle of balancing a chemical equation is based on the law of conservation of mass

The number of atoms of each element remains the same before and after a chemical reaction, so we need to balance a skeletal chemical equation

5. Translate the following statements into chemical equations and then balance them

(a)  Hydrogen gas combines with nitrogen gas to form ammonia

       3H₂(g)  + N₂ (g)   à   2NH₃(g)

(b)  Hydrogen sulphide gas burns in air to give water and sulpur dioxide

       2H₂S(g) + 3O₂(g)   à 2H₂O(l)  + 2SO₂(g)

(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of          barium sulphate

        3BaCl₂ (aq)  +  Al₂ (SO₄)₃ (aq)  à     3BaSO₄ (s) + 2AlCl₃(aq)

(d) Potassium metal react with water to give potassium hydroxide and hydrogen gas

      2K (s)  +  2H₂O(l)      à      2KOH (aq) + H₂(g)

6. Balance the following chemical equations?

(a)   2HNO₃  + Ca(OH)₂   à  Ca(NO₃)₂  + 2H₂O


(b) 2NaOH  + H₂SO₄    à Na₂SO₄  + 2H₂O


(c) NaCl  + AgNO₃  à AgCl  + NaNO₃



(d) BaCl₂  + H₂SO₄   à BaSO₄ + 2HCl

7. Write the balanced chemical equations for the following reactions?

(a) Calcium hydroxide  +  Carbon dioxide  à   Calcium carbonate + Water

      Ca(OH)₂   + CO₂     à  CaCO₃  + H₂O

(b)  Zinc   +  Silver nitrate à Zinc nitrate  + Silver

      Zn  + 2AgNO₃   à   Zn(NO₃)₂  + 2Ag

(c)  Aluminium + Copper chloride  à  Aluminium chloride  + Copper

       2Al + 3CuCl₂  à 2AlCl₃ + 3Cu

(d)  Barium chloride + Potassium sulphate  à  Barium Sulphate + Potassium chloride

       BaCl₂ + K₂SO₄    à BaSO₄  + 2KCl

8. Write the balanced chemical equations for the following and identify the type of reaction in each case

(a) Potassium bromide (aq) + Barium iodide (aq) à Potassium iodide (aq) + Barium bromide(s)

      2KBr (aq)  + BaI₂ (aq) à  2KI (aq)  + BaBr₂(s)

       Double displacement reaction

(b) Zinc carbonates(s)   à Zinc Oxide (s) +Carbon dioxide  (g)

      ZnCO₃ (s)  à ZnO(s) + CO₂(g)

      Decomposition reaction

(c) Hydrogen (g) + Chlorine (g)     à    Hydrogen chloride (g)

      H2(g)  + Cl₂(g)    à    2HCl (g)

     Combination Reaction

(d) Magnesium (s) + Hydrochloric acid (aq)   à  Magnesium chloride (aq) + Hydrogen (g)

      Mg(s) + 2HCl (aq) à MgCl₂(aq) + H₂(g)

     Displacement reaction

9. What does one mean by exothermic and endothermic reactions ? Give examples.

Exothermic Reaction:

The reaction in which heat is liberated along with the formation of products is known as exothermic reaction
Burning of natural gas

CH₄  + 2O₂  à CO₂ + 2H₂O  + heat

Endothermic Reaction:

The reaction in which heat is absorbed during the formation of products is known as exothermic reaction 

Heating of calcium carbonite

CaCO₃  + heat   à CaO + CO₂

10. Why is respiration considered an exothermic reaction? Explain

During respiration carbohydrates are converted into glucose.
And further glucose gets oxidized to simpler substances such as carbon dioxide and water along with the liberation of energy in the form of heat

Hence respiration is considered as an exothermic reaction

11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions

Decomposition reaction: 

Here the compound splits into two or more simpler compounds or elements
Eg: While heating calcium carbonate decomposes to form calcium oxide and carbondioxide

CaCO₃  + heat   à CaO + CO₂

Combination Reaction:
Here two or more reactants combines to form a single product
Eg: Carbon combines with oxygen to form carbondioxide

C + O₂ à CO₂

12. Write one equation each for decomposition reaction where energy is supplied in the form of        heat, light or electricity

Heat :
Calcium carbonite when heated decomposes to form calcium oxide and carbondioxide.
CaCO₃  + heat   à CaO + CO₂

Here energy is supplied in the form of heat

Sunlight :
Silver chloride in the presence of sunlight turns gray . This is due to the decomposition of silver chloride to silver and chlorine. This reaction was utilized in was used in old black and white photography

2AgCl   + sunlight    à 2Ag + Cl₂

Electricity:

Electrolysis of water. Here electricity is used to decompose  water molecule into hydrogen and oxygen

2H₂O  à H₂  + O₂

13. What is the difference between displacement and double displacement reactions? Write equations for these reactions

Displacement Reaction:

The reaction in which a highly reactive metal displaces a less reactive from its solutions

Fe (s)  + CuSO₄(aq)   à     FeSO₄ (aq)  + Cu(s)    

Double displacement Reaction:

The reaction in which there is an exchange of ions between the reactants

BaCl₂ (aq)  + Na₂SO₄ (aq)  à    BaSO₄ (s)  + 2NaCl  (aq)

14. In the refining of silver , the recovery of silver from silver nitrate solution involved                      displacement by copper metal. Write down the reactions involved

Here copper displaces silver from its nitrate solution and the products are copper nitrate   and silver. Hence silver get refined

Cu + 2AgNO₃   à   Cu(NO₃)₂  + 2Ag

15. What do you mean by a precipitation reactions?

Those reactions in which the reactants combines to form an insoluble substance called precipitate 

Eg: BaCl₂ (aq)  + Na₂SO₄ (aq)  à    BaSO₄ (s)  + 2NaCl  (aq)
Here is the BaSO₄  precipitate

16. Explain the following in  terms of gain or loss of oxygen with two examples each?

(a) Oxidation

The process by which a molecule gains  oxygen atom or atoms

C + O₂ à CO₂

2Mg + O₂   à   2MgO

(b)  Reduction

The process by which a molecule lose  oxygen atom or atoms
2H₂O(l)    à     2H₂(g)  + O₂(g)    
2MgO   à   2Mg + O₂

17. A shiny brown colored element "X" on heating in air becomes black in colour. Name the element "X" and the black coloured compound formed

Element "X" is Copper
Black coloured compound is copperoxide

2Cu  +   O₂   à   2CuO

18. Why do we apply paint on iron articles?

When iron is exposed to air which is humid, the iron reacts with oxygen to form iron oxide.
This is a brown flaky substance. Hence it  corrodes.

So iron articles can be protected by applying paint, to prevent direct contact with atmosphere

19. Oil and fat containing items are flushed with nitrogen. Why?

The food containing oil and fat get rancid.
This is due to the oxidation of food in the presence of oxygen.
Rancid food is not good for consumption
Hence oil and fat containing items are flushed with nitrogen.

20. Explain the following terms with one example each

(a) Corrosion

Metals when exposed to air which is humid, reacts with substances of atmosphere  to form various surface compounds. Corrosion causes damage to the metal articles like car bodies, iron bridges, ships , iron railings etc
Chemical formula of rust is  Fe₂O₃.2H₂O  

(b) Rancidity

Rancidity is due to the oxidation of food containing oil and fat  in the presence of oxygen.
Rancid food is not good for consumption because the smell and taste changes

It can be reduced by

 Keeping in air tight containers
 Refrigerating the food.
 Flushing packets of foods with nitrogen.
Storing food in vacuum packets
Antioxidants such as Butylated hydroxy anisole ( BHA)  and  Butylated hydroxy toluene ( BHT)