Chemistry FBISE SSC-1 Keybook Chapter 8

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  1. Define electro positivity? Also write trends

Ans.     Electro positivity:

The tendency of a metal to lose electrons is called electropositivity.

Trend:

Electropositve character increases down a group

Electropositive character decreases across a period

 

Example 8.1

In each of the following pairs of elements, identify which element is more metallic

  • Na, K

As electropositive character increases down a group. So K is more metallic.

  • Be, K, Na

As electropositive character decreases across a period.So Na is more metallic

 

  1. In each of the following pairs identify, which element is more metallic?
  • Be, B

As electropositive character decreases across a period. So Be is more metallic

  • Si, Al

As electropositive character decreases across a period. So Al is more metallic

  • K, Li

As electropositive character increases down a group. So K is more metallic.

 

  1. Using the periodic table, rank each set of elements in order of decreasing metallic character.

(a)        Na, Li, K

As electropositive character increases down a group. So

K > Na > Li

(b)        Al, Na, Mg

As electropositive character decreases across a period. So

Na >    Mg >   Al

 

  1. Which is more basic Li2O or Na2O?

Ans.     As basic character increases down a group. So Na2O is more basic than Li2O.

 

  1. What is the position of Alkali metals and Alkaline earth metals?

Ans.     The group IA elements except hydrogen are known as alkali metals.

The group II A elements are known as alkaline earth metals.

 

 

Identify the position of Mg and Ca in the periodic table.

Ans.     Mg is alkaline earth metal in group IIA.

Ca is alkaline earth metal in group II A.

 

  1. Write down the uses of sodium and calcium?

Ans.     Uses of Sodium:

  1. i) Sodium-potassium alloy is used as a coolant in nuclear reactors.
  2. ii) It is used to produce yellow light in sodium vapour lamps.

iii)   It is used as a reducing agent in the extraction of metals like Ti.

Uses of Calcium:

  1. It is used to remove sulphur from petroleum products.
  2. It is used as reducing agent to produce Cr, U and Zr.

 

  1. Compare the reactivity of Alkali and Alkaline earth metals?

Ans.     Reactivity of metals depend on ionization energy. Alkali metals have low ionization energies than Alkaline earth metals. So alkali metals are more reactive than alkaline earth metals.

 

  1. Write down importance of silver and gold?

Ans.     Silver:

  1. It is used for making utensils.
  2. Silver allows are used for making coins.
  • The light sensitive silver halides are used in photographic process.
  1. It is used in mirror industry.
  2. It is used in dental preparation.

 

Gold

  1. Gold alloys are used in dentistry.
  2. It is used in jewelry
  • It is used in making coins

 

  1. Define electronegative character. Also write trend

Ans.     Electronegativity:

It is the tendency to gain electrons to form anions

            Trend:

Electronegative character decreases down a group

Electronegative character increases across a period

 

Example 8.1(a)

In each of the following pairs of elements, identify which elements is more non-metallic

(a)        N or O

Ans.     As electronegative character increases across a period. So O is more non-metallic.

(b)        F or Cl.

Ans.     As electronegative character decreases down a group. So F is more non-metallic.

 

  1. In each of the following pair, identify which element is less metallic.

(a)        B or C

As electronegative character increases across a period. So B is less non-mettalic.

(b)        C or Si

As electronegative character decreases down a group. So Si is less non-metallic.

(c)        Cl or Br

As electronegative character decreases down a group. So Br is less non-metallic

 

 

  1. Using periodic table rank each set of elements in order of increasing non-metallic character.

(a)        N, F, O

As electronegative character increases across a period So

N   <   O   <   F

(b)        Cl, Br, I

As electronegative character decreases down a group so

Cl   <   Br   <   I

(c)        Si, S, P

As electronegative character increases across a period. So

Si   <   P   <   S.

  1. What are halogens?

Ans.     The element in group VIIA are called halogens. The name halogen is derived from the Greek words “halous” meaning salt and “gen” meaning former. All halogens are reactive non-metals. They all exist as diatomic molecular substance.

 

            Which of the following displacement reaction will occur?

 

  1. Cl2 (g) + 2NaF (aq) →        2NaCl (aq) + F2(g)

Ans.     Will not occur because reactivity of halogens decreases down the group

F2   >   Cl2

                Therefore Cl2 cannot oxidized Fe2.

 

  1. Br2 (g) +2KI (aq)      → 2KBr (aq) + I2 (g)

Will occur because reactivity of halogens devreases down the group

Br2   >   I2

Therefore Br2 can oxidized I2 .

 

  1. I2 (g) + 2KBr (aq) 2KI (q) + Br2 (l)

Ans.     Will not occur because reactivityof halogens decreases down the group

Br2 > I2

Therefore I2 cannot oxidized Br2.

 

  1. Cl2 (g) + KBr (aq)   → 2KCl (aq) + Br2 (l)

Ans.     Will occur because the reactivity of halogens decreases down the group

Cl2   >   Br2

Therefore Cl2 can oxidized Br2

 

  1. Cl2 (g) + 2NaI (aq) →        2NaCl (aq) + I2 (s)

Will occur because the reactivity of halogens decreases down the group

Cl2   >     I2

Therefore Cl2 can oxidized I2

 

 

 

Exercise

Review Questions

Q.1      Encircle the correct answer:

  • Which of the following oxides is the most basic oxide?
  1. MgO
  2. BaO
  3. CaO
  4. SrO
  • Which of the following oxides is amphoteric oxide?
  1. Na20
  2. Al2O3
  3. MgO
  4. SO2
  • Which of the following element: is most metallic?
  1. Al
  2. Na
  3. Mg
  4. Li
  • Valence shell electronic configuration of alkaline earth metals is:
  1. ns1
  2. ns2np1
  3. ns2
  4. ns2np6
  • Which of the following metals is not noble metal?
  1. Au
  2. Cu
  3. Hg
  4. Ag
  • Which of the following elements is the least non-metallic?
  1. Si
  2. S
  3. P
  4. CI
  • Oxidizing power of ________ is the highest.
  1. I2
  2. Cl2
  3. Br2
  4. F2
  • Chlorine cannot oxidize _____ ion.
  1. Iodide
  2. Flouride
  3. Bromide
  4. Astatine
  • Na is more reactive than Li, but less reactive than
  1. Mg
  2. Al
  3. Rb
  4. All of these
  • Which of the following is the strongest acid?
  1. HI
  2. HCl
  3. HF
  4. HBr

Answers:

        i.            A      ii.            B    iii.            A    iv.            C      v.            C
    vi.            A  vii.            Dviii.            B    ix.            C      x.            A

 

 

Q.2      Give short answers

(i)         In a group the reactivity of metals with oxygen increases? Give example

Ans.     In a group the reactivity of metals with oxygen increases. For instance, alkali metals on exposure to air show an increase in affinity for oxygen as we move down the group. Lithium forms normal oxide

4Li(s) + O2(g)   →        2Li2 O (s)

Sodium forms per oxide.

2Na (s) + O2 (g)           →        Na2O2 (s)

K, Rb and Cs form super oxides

K (s) + O2 (g)   →        KO2 (s)

  1. ii) Which element is more metallic Mg or Al? Explain

Ans.     Reactivity of metals decreases from left to right. So Mg is more metallic than Al.

 

iii)        What is the importance of Mg?

Ans.     Magnesium has relatively low density and it is used in making light weight alloy with aluminum that are used for making frames of automobiles, aircraft and spaceship, cameras etc. Since magnesium burns brilliantly, it is used in photo flash guns Mg (OH) 2 called milk of magnesia is commonly used as antacid.

 

  1. iv) Arrange the following in order of increasing acidic strength.

            HF, HI, HBr, HCl

Ans.     HF   < HCl   < HBr   < HI

 

  1. v) Can F2 oxidize all the halides ions to free halogen?

Ans.     Oxidizing power of F2 is the highest. Due to the relative strength as oxidizing agent, it is possible for a free halogen to oxidize the ion of halogen next to it in the group. This means F2 can oxidize all the halide ions to free halogen.

 

Q.3      Arrange the following oxides in order of decreasing basic character

BeO, CaO, MgO, SrO

Ans.                 SrO   >   CaO   >   MgO   >   BeO

 

Q.4      Rank the each set of elements in order of increasing metallic character.

(a)        Al, Na, Mg

Ans.     Na   <   Mg   <   Al

(b)        Na, Li, K

Ans.     Li   <   Na   <   K

 

Q.5      Which of the following displacement reaction will not occur? Give reason

(a)        Cl2 + 2NaF2    →        2NaCl + F2

Ans.     Will not occur because reactivity of halogens decreases down the group

F2         >          Cl2

Therefore Cl2 cannot oxidize F2

 

(b)        Br2 + 2KI        →        2KBr + I2

Ans.     Will occur because reactivity of halogens decreases down the group

Br2       >          I2

Therefore Br2 can oxidize I2

 

(c)        I2 + 2KBr        →        2KI + Br2

Ans.     Will not occur because the reactivity of halogens decreases down the group

Br2       >          I2

Therefore I2 cannot oxidize I2

 

Q.6      Give some important applications of platinum.

Ans.     Important applications of platinum.

  1. Platinum is used as catalyst for many industrial process.
  2. Platinum is used as electrode as a part of hydrogen electrode and in fuel cells.
  • New cars are equipped with catalytic converters. These converters contain platinum.
  1. A platinum compound called Cis-platin is useful as an anti-cancer agent.
  2. Platinum is used to make jewelry items.
  3. Platinum is used in the production of hard disk drive coatings and fiber optic cables.

 

Q.7      Identify the position of potassium and calcium in the periodic table

Ans.     Potassium is alkali metal in group 1A calcium is alkaline earth metal in group IIA.

 

Q.8      What is aqua regia?

Ans.     Aqua regia is a mixture of 3 parts by volume of conc. HCl and one part by volume of conc. HNO3. Gold and platinum react only with aqua regia.

ThinkTank

  1. Why it is advisable not to pick sodium metal with fingers.

Ans.       Sodium reacts violently with water (moisture of fingers), often catching fire and exploding. This reaction produces sodium hydroxide, a strong and caustic base.

  1. Arrange the following elements in order of increasing non-metallic character.

Si, Al, P

Ans.      Since Si, Al and P lies in period 3 and in period from left to right non-metallic character increases therefore:

Al < Si < P

Therefore Phosphorus (P) is more non-metallic in character.

  1. Design an experiment to show that iron is more reactive than copper.

Ans.      When iron is added to copper sulphate solution the copper is displaced by the iron. Copper metal cannot be used to displace iron because in reactivity series

  1. Design an experiment to differentiate between Cl and I.

Ans.      Take salts whose ions need to be identified in separate dry test tubes. Add few drops of H2SO4 solution. Note the test tube in which gas evolves.

  1. If the salt gives colourless gas with pungent smell. Dip glass rod dipped in Ammonia or Ammonium Hydroxide solution.. It will give white dense fumes. This indicates Clions.
  2. If the salt gives violet fumes with pungent smell. Dip starch paper in these vapours, it must turn blue this indicates I ions.
  1. An iron bar is to be silver plated which metal would be the anode and which the cathode?

Ans.      Pure Silver is made the anode and iron bar to be electroplated is made the cathode.