9 Chem Unit 8 New

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CHEMISTRY FOR 9TH CLASS (UNIT # 8)

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SHORT QUESTIONS

QUESTIONS ANSWERS

In a group the reactivity of metals with

oxygen increases? Give example.

In a group, the reactivity of metals with

oxygen increase because of increase of atomic size and increase in affinity on

exposure to air e.g. Lithium form normal

oxide with oxygen.

Which element is more metallic Mg or Al?

Explain

Al is more metallic than Mg because Al

atom release three valence electron and change into AL+3 while Mg loses two

electrons so formed Mg+2. High the net charge more will be the metallic nature.

What is the importance of Mg? Mg has relatively low density and used

in making light weight alloy with Aluminum that are used for making

frames of automobiles, air craft and spaceship etc.

Mg burns brilliantly with white smoke, it is used in Photoflash guns.

Mg(OH)2 called milk of magnesia is commonly used as antacid.

Arrange in order of increasing acidic

strength HF, HI, HBr, HCl

HF < HCl < HBr < HI

Can F2 oxidize all the halides ions to free

halogen?

Yes F2 oxideze all the halides ions to free

halogen

Arrange the following oxides in order of

decreasing basic character. BeO, CaO,

MgO, SrO

SrO > CaO > MgO > BeO

Rank the each set of elements in order of

increasing metallic character. a) Al, Na, Mg

b) Na, Li, K

a) NA < Mg < Al so Al will be more

metallic b) Li < Na < K because down the

group reactivity increases due to decreases of Ionization of Energy.

Which of the following displacement

reaction will not occur? Give reason. A) Cl2+2NaF ---> 2NaCl + F2

B) Br2+ 2KI ---> 2KBr + I2 C) I2 + 2KBr ---> 2KI + Br2

A. Cl2 cannot displace F ions from NaF

because oxidizing power of Cl2 is lesser than F2.

B. Br2 can displace I-1 from KI because oxidizing power of Br2 is more than

that of I2 C. I2 cannot displace Br- ions from KBr

because oxidizing power of I2 is lesser than Br2.

Give some important applications of

platinum

Platinum has many applications in

electrical and medical fields.




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It is used in spinneret nozzles.

Its alloys is used in dentistry and jewellery manufacture.

It is used in industrial processes as catalysis.

It is used as electrode as a part of Hydrogen electrode and in fuel cells.

Cis-Platin is useful as an anticancer agent.

Identify the position of potassium and

calcium in the periodic table.

Potassium belongs to Alkali metal and its

atomic number is 19. Its electron distribution is 1s2, 2s2, 2p6, 3s2, 3p6, 4s1

In calcium electron distribution is 1s2, 2s2, 2p6, 3s2, 3p6, 4s2 .So: -

Name Period Group Potassium 4th I-A

Calcium 4th II-A

What is aqua region? It is a mixture of two acids HCl and HNO3 with proportion 3:1 respectively. It is also

called royal water because it is used to dissolve all metals (Gold, Pt etc.)

Name the most electronegative and electropositive elements

Fluorine is most electronegative and Caesium is the most electropositive.

How physical states of halogens change

down the group

F2 and Cl2 are gases. At radioactive solid.

Br2 liquid while I2 is solid.

Colour of halogen intensity increases

down the group. How

F2 = yellow gas

Cl2 = greenish yellow gas Br2 = reddish brown liquid

I2 = deep violet solid

How the solubility of halogens in water change down the group.

Halogens are slightly so label in water. Their solution decreases down the group.

F2 cannot be dissolved in water because it decomposes water.

Differentiate between Soft metals and Hard metals

Soft Metals: They have low MP and BP

They have low binding energy Their compounds are white

Hard Metals:

They have high MP and BP They have high binding energy

Their compounds are coloured

Why mercury is liquid at room

temperature?

Mercury metal is liquid at room

temperature because its melting point is very low (-38.83oC)

Why metals can be easily converted into Because metals have low ionization




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cations? energies and are more electropositive in

characters.

Why Non-Metals can be easily converted

into anions?

Non-metals have high electron affinity or

light electro negativity. They have tendency to gain electron and hence form

anions (-ev ions).

Define Chemical Reactivity The easiest way in which an atom (metal) loses an electron from outermost shell or

an atom (non-metal) gain an electron in an outer most shell is called chemical

reactivity.

Define Metals, Non-Metals and Metalloids. Elements which conduct heat and

electricity and can easily loss electrons

are called metals. E.g. Iron, Gold, Silver etc.

Elements which don’t conduct heat and electricity and can easily gain electrons

are called non-metals. E.g. Carbon, Sulphur etc.

Elements which have both properties of metals and non-metals are called

Metalloids. E.g. Silicon, Boron etc.

Define Minerals The form of soil or rock stone which

contains different compounds of metals

and non-metals is called minerals.

Define Ores Minerals which have sufficient amount of

metals are called ores.

Define Metallurgy The science that deals with the

extraction, working and use of metals and

their alloys from their ores is called metallurgy.

What is meant by electropositive character

The tendency of an element to lose electron(s) and form positive ions

(cations) is called electropositive character or electro positivity.

Why electro positivity increases in group

and decreases in a period

In group it increases because of increase

of atomic size and decrease of ionization energy.

In period it increases because tendency to lose electron decreases as we move from

left to right in period.

Define Alkali Metals The elements of group I-A except

hydrogen are called alkali metals. E.g.

sodium, potassium, rubidium etc.

Define Akaline Earth Metals The elements of group IIA are called




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Alkaline Earth Metals. E.g. Calcium,

Barium, and Radium etc.

Why Alkali metals are kept under a

kerosene oil?

The alkali and alkaline earth metals show

increased reactivity down the group. They are all so reactive that they may react

with air or moist air at room temperature, so they are kept under inert atmosphere

or liquid such as kerosene oil.

What are halogens? The element in group VII-A are called halogens. Halogens means salt former.

Describe Inertness of Nobel metals The chemistry of metals is characterized by their ability to lose electrons to form

cations. Some metals such as copper,

gold, silver and platinum are relatively difficult to oxidize. Therefore these metals

are often called Nobel Metals.

Write about Strontium-90 It is radioactive isotope. It is major

product of an Atomic Bomb explosion. Its constant exposure of the body to high

energy radiations emitted by Sr-90 can lead to anaemia, leukemia and other

chronic illnesses.

Why copper, silver and gold have used for jewllery

These metals have beautiful high luster and malleability, therefore these are used

as jewllery.

What is Carat? Carat is standard purity of gold. The

purity of gold is expressed in Carat. 22 Carat = 92% Gold

LONG QUESTIONS Question: Compare the Properties of Metals and Non-Metals.

Metals Non-metals

Metals are hard and strong Non-Metals are mostly liquid and gases.

Metals can be moulded into wires and sheets.

They are difficult to mould.

Atoms are bonded by metallic bonding Atoms are bonded with covalent bonding.

Metals can transfer heat easily Non-metals do not transfer heat.

Metals reflect light Non-metals absorb light.

Melting and boiling points are high Melting and boiling points are low

Oxides of metals are basic Oxides of non-metals are acidic

Metals have tendency to lose electrons Non-metals have tendency to gain electrons

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9 Chem Unit 8 New