a) In most cases the first letter of an element was taken as the symbol for that element. Give two examples of the same.
b) In certain cases the first letter along with its small letter from its name were used as the symbols. Give two examples of the same.
c) In some cases the symbols were derived from their Latin names. Name two metals whose symbols are derived from the same.
d) Sulphur is represented by the symbol 'S'. State how the symbol represents the elements
(i) qualitative (i.e., representation in terms of an atom)
(ii) quantitatively(i.e., representation in terms of weight).
B. Give reasons for the following:
a) In hydrogen chloride the valency of the element chlorine is considered as one.
b) Certain metals exhibit more than one valency hence showing ' variable valency'.
C. Valency
1. State the valency and name the ion or radical in each of the following cases given below (The first example is completed for you)
Electrovalent positive ions or radicals
Symbol/Valency Name
a) K¹⁺ Potassium
b) Na
c) H
d) NH₄
e) Ca
f) Mg
g) Zn
h) Ba
i) Ni
j) Co
k) Al
l) Cr
Variable valencies
a) Cu ¹⁺
b) Cu
c) Hg¹⁺
d) Hg
e) Fe²⁺
f) Fe
g) Mn²⁺
h) Mn
i) Pb²⁺
j) Pb
k) Pt²⁺
l) Pt²⁺
Electrovalent ion or radicals
Symbol/Valency Name
a) Cl¹⁻ Chloride
b) ClO₃
c) ClO
d) Br
e) I
f) OH
g) NO₂
h) NO₃
i) HCO₃
j) HSO₃
k) HSI₄
l) AlO₂
m) MnO₄
n) SO₃
o) SO₄
p) S
q) CO₃
r) O
s) CrO₄
t) Cr₂O₇
u) ZnO₂
v) PbO₂
w) PO₄
x) N
y) C
2. State the valency of each of the elements in the respective compounds in the table given below.
Valency
a) Sulphur in
i) sulphur dioxide.
ii) sulphur trioxide.
b) Nitrogen in
i) nitrogen monoxide.
ii) Nitrogen dioxide.
iii) dinitrogen oxide.
iv) diniitrogen pentoxide.
c) Copper in
i) cupric oxide.
ii) cuprous oxide.
D. Writing a Formula
1. Complete the table given below (the first example has been completed for you)
a)Cr³⁺+SO₄²⁻ -> Cr₂(SO₄)₃ Chromium sulphate
b) Mg + Cl --> ______ ______
c) Na+ ClO₃--> ______ ______
d) K+ ZnO₂ --> ______ ______
e) Ca+ PO₄--> ______ ______
f) NH₄ + SO₄--> ______ ______
g) Na+ HSO₃--> ______ _____
h) Al+ S--> _____ _____
i) Zn+ So₄--> ______. ______
j) Mg+ O--> ______ ______
2. Give the formulas of the following compounds compounds whose metallic radical exhibits variable valency.
Compound Formula
a) Cupric nitrate.
b) Cuprous chloride.
c) Iron(II) sulphate.
d) Mercuric nitrate.
e) Plumbus chloride.
f) Stannous chloride.
g) Mangannic sulphate.
h) Platinic chloride.
i) Mercurous chloride.
j) Iron(III) nitrate.
3. Give the names of the compounds whose formulas are listed below.
Formula Name of the compounds
a) HNO₂
b) HCO₃
c) H₂C₂O₄
d) H₃PO₄
e) CH₃COOH
f) Al(OH)₃
g) CaSiO₃
h) Na₂ZnO₂
i) K₂CrO₄
j) Mg₃N₂
E-F: Chemical Equation-- Chemical Reactions
A chemical equation is a shorthand form for a chemical change
a) 2KClO₃ ∆ 2KCl+ 3O₂
i) In the above reaction name the reactant and the products.
ii) State what the Arrow in between indicates.
2. Give reasons for the following:
a) All equations must be balanced.
b) A chemical equation provides useful information about a reaction.
c) All chemical equations have their limitations.
3. Balance the equation.
a) CuO + NH₃--> Cu+ H₂O+ N₂
b) NH₃+ Cl₂ --> HCl+ NCl₃
c) Mg₃N₂ + H₂O--> Mg(OH)₂+ NH₃
d) Pb₃O₄ + HCl --> PbCl₂+ H₂O+ Cl₂
e) Manganese (IV)+ Hydrochloric--> Manganese (II)+ Water+ Chlorine.
f) Potassium hydroxide+ Chlorine--> Potassium chloride + Potassium hypochlorite+ water.
g) Ammonia dichromate --> Chromium oxide+ Water+ Nitrogen
h) Potassium sulphite+ Nitric acid --> Potassium nitrate+ Water+ Sulphur dioxide.
i) Iron(III) chloride+ water+ sulphur dioxide --> iron(II) chloride+ sulphuric acid + Hydrochloric acid.
j) Copper+ Sulphuric acid--> Copper sulphate+ water+ Sulphur dioxide.
k) Iron(III) oxide+ carbon monoxide--> Iron+ carbon dioxide
l) Sodium sulphite+ sulphuric acid--> sodium sulphate+ water+ sulphur dioxide.
m) Zinc+ Sodium hydroxide --> sodium zincate + hydrogen.
n) Aluminium+ Carbon dioxide--> Aluminium oxide+ carbon.
o) Sodium bicarbonate+ Aluminium sulphate--> sodium sulphate+ aluminium hydroxide+ carbon dioxide.
p) calcium hydroxide+ Ammonium sulphate---> calcium sulphate+ water+ ammonia.
q) Nitric acid+ magnesium carbonate--> magnesium nitrate+ water+ carbon dioxide
r) Iron(III) oxide+ sulphuric acid--> Iron(III) sulphate + water.
s) Zinc sulphide+ oxygen --> Zinc oxide+ sulphur dioxide.
t) Carbon+ nitric acid --> carbon dioxide+ water+ Nitrogen dioxide.
5. Match the different types of chemical reactions in column II with the meaning of the type of reactions in column I
COLUMN I
a) A chemical reaction in which two or more elements or compounds react to form one new compound as a product.
b) A chemical reaction in which a chemical compound composes or splits up into two or more simpler substances. It is generally brought about by heat.
c) A chemical reaction which takes place when an element (or radical) has replaced another element in a compound.
d) A chemical reaction in which two reactants are both the decomposed to form new substances by exchanging their radicals.
e) A chemical reaction which employs a catalyst to alter the rate of reaction.
f) A chemical reaction in which the products formed react together to form the original reactants depending on the conditions of the reaction.
g) A reaction in which a substance dissociates into two or more simpler substances on application of heat and is a reversible reaction.
h) A reaction which involves addition of oxygen or electronegative elements or removal of hydrogen or electropositive element.
i) A reaction which involves addition of hydrogen or electropositive element or removal of oxygen or electronegative element.
j) a chemical reaction which proceeds with evolution of heat energy.
k) A chemical reaction which proceeds with absorption of heat energy.
l) A chemical reaction which proceeds with absorption of light energy.
COLUMN II
1) double decomposition
2) exothermic reaction
3) reversible reaction
4) displacement reaction
5) combination or synthesis
6) Decomposition reaction
7) thermal dissociation
8) endothermic reaction
9) catalytic reaction
10) oxidation reaction
11) photochemical reaction
12) reduction reaction
6. State the type of reaction/s to which each of the following belong.
a) addition of zync to copper sulphate solution.
b) heat on a lead nitrate crystals.
c) preparation of oxygen from Potassium Chlorate
d) conversion of ferrous chloride to ferric chloride using chlorine.
e) formation of ammonia from nitrogen and hydrogen.
f) Liberation of hydrogen at the cathode from acidified water.
g) manufacture of glucose by green plants.
h) Formation of nitric oxide from Nitrogen and oxygen.
i) addition of zinc to dilute sulphuric acid.
j) NH₄Cl <=> NH₃ + HCl.
k) 2KNO₃ ∆ --> 2KNO₂ + O₂.
l) PbBr ₂ --> Pb²⁺ + 2Br¹⁻ (ions)
m) 2HgO ∆--> 2Hg + O₂
n) N₂O₄ ∆ <=> 2NO₂
o) AgNO₃ + KCl --> AgCl+ KNO₃
p) Fe + S --> FeS
q) H₂ + Cl₂ sunlight--> 2HCl
r) C+ H₂O --> CO+ H - ∆
s) Cl₂ + 2KI --> 2KCl + I₂
t) 3Fe+ 4H₂O ∆--> Fe₃O₄ + 4H₂
u) 2Cu + O₂ --> 2CuO
v) Fe₂O₃ + 2Al --> Al₂O₃+ 2Fe
w) KNO₃ + H₂SO₄--> HNO₃ + KHSO₄
x) 2FeCl₂ + Cl₂ --> 2FeCl₃
y) Fe+ H₂SO₄ --> FeSO₄ + H₂
z) SO₂ + Cl₂ --> SO₂Cl₂
a') 3Ca + N₂ --> Ca₃N₂
b') CuSO₄ + Fe --> FeSO₄ + Cu
c') 4HNO₃ --> 2H₂O + 4NO₂ + O₂
7. Oxidation and reduction reactions are generally termed as redox reactions. In the examples given below underline the oxidised product or reduced product in the respective reactions. The underline substances is the oxidising or reducing agent respectively.
Oxidation Reaction
1) Cu+ O₂ --> 2CuO
2) H₂S + Cl₂ --> S + 2HCl
3) 2FeCl + Cl₂ --> 2FeCl₃
4) SO₂ + H₂O + Cl₂ -> H₂SO₄ + 2HCl
5) H₂S + 2FeCl₃ --> 2FeCl₂+ 2HCl + S
6) Zn+ H₂SO₄ --> ZnSO₄ + H₂
7) Fe + S --> FeS
8) 2Mg + SO₂ --> 2MgO + S
9) 2H₂S + SO₂ + 3S + 2H₂O
10) S + 2H₄SO₄ --> 3SO₂ + 2H₂O.
Reduction reactions
1) CuO+ H₂ --> Cu+ H₂O
2) Br₂ + H₂S --> 2HBr + S
3) 2FeCl₃ + H₂S --> 2FeCl₂ +2HCl+ S
4) 2HgCl₂ + SnCl₂ --> Hg₂Cl₂ + SnCl₄
5) 2FeCl₃ + SO₂ + 2H₂O --> 2FeCl₂ + 2HCl + H₂SO₄
6) Fe₂(SO₄)₃+ 2H₂O + SO₂ --> 2FeSO₄ + 2H₂SO₄
7) Cl₂ + 2H₂O + SO₂ --> 2HCl + H₂SO₄
8) 2HNO₃ + SO₂ --> 2NO₂ + H₂SO₄
9) 2kMnO₄ + 2H₂O + 5SO₂ --> 2MnSO₄ + K₂SO₄ + 2H₂SO₄
10) K₂Cr₂O₇+ H₂SO₄ + 3SO₂ --> Cr₂(SO₄)₃ + K₂SO₄ + H₂O.
8) Name the following:
a) A coloured gaseous oxidising agent.
b) A liquid oxidizing agent which on thermal decomposition in presence of a catalyst liberates oxygen.
c) A gaseous reducing agent containing oxygen.
d) An acid other than nitric and Sulphuric Acid which is an oxidising agent.
e) A gaseous reducing agent neutral in nature other than carbon monoxide.
f) An oxidizing agent which liberates chlorine on heating with concentric hydrochloric acid.
g) Two neutral gases which react to give a basic gas and the reaction is exothermic.
h) Two neutral gases which react to give a neutral oxide and the reaction is exothermic.
i) A substance which decomposes by absorption of sound energy.
j) Two substances which react explosively on close physical contact.
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