Wednesday, April 8, 2015

The language of chemistry class 7 Basic science soled questions

Q. What is chemistry?
Ans: Chemistry is a branch of science in which we study the composition, structure, properties and change of matter.

Q. What is matter?
Ans: Anything that is around us having some mass and occupies space is called matter.

Q. What are the different classifications of matter?
Ans: Matters are classified into element, compound and mixture.

Q. What is element?
Ans: Elements are the purest form of substance (matter) made up of same kinds of particles. The smallest unit of element is an atom. eg. Hydrogen, oxygen, carbon.

Q. What is compound?           

See full post  The language of chemistry class 7 Basic science

Class 07 Basic sciences Chapter the Language of Chemistry
A. Answer these questions

1. What does the formula of a substance tell us?

Answer: Formula of a compound or an element represents the name and number of atoms present in one molecule of that compound or element.

2. What do you mean by valancy of an element?

Answer: The number of electrons that can be donated, accepted or shared by an atom of an element during a chemical reaction is equal to the valency of that element. Thus the combining capacity of an atom is called its valancy.

3. What is a radical?

Answer: A compound radical is a group of two or more elements that acts as a single atom in a chemical reaction.
4. Name two elements having variable valancy. Give the name and formulae of compounds formed byeach of these element.

Answer: Two elements having variable valency and compounds formed by them are as follows:

(i) Copper (Cu):  
(a) Cuprous oxide [Copper (I) oxide] − Cu2O     
 (b) Cupric oxide [Copper(II)oxide] − CuO

(ii) Iron (Fe):  (a) Ferrous oxide [Iron(II)oxide] − FeO                    
(b) Ferric oxide [Iron(III)oxide] − Fe2O3

5. What is balance equations? Why should a  equation be balanced?

Answer: A reaction is in which the number of atoms on the side of the products is equal to the number of atoms on the side of the reactants is called a balanced chemical. This is known as law of the conservation of mass given by Antoine Lavoisier's 1789.  We balance a chemical reaction to represent this fact.

B. Find the vacancies of the underlined element or radicals in the following compound?

Answer:

Compound
Valency of Underlined
Compound
Valency of Underlined
BaCl2
2
 PCl3
3
MgSO4
2
CaCO3
2
Ca(OH)2
2
FeSO4
2
NaOH
1
Al(OH)3
3
Compound
Valency of Underlined
Compound
Valency of Underlined
PCl5
5
NH3
3
Na2O
1
CaO
2
FeCl3
3
Fe2O3
3
Na2CO3
1





C. What are compound radicals? Give examples of a few radicals, along with their valancies. Also mention some compound containing compound radicals. Give the valancies of the part that make up the compound?

Answer: Compound radical is a group of atoms of different elements that behave as an intact unit during a chemical reaction. Atoms in a compound radical do not break apart revealing the individual atoms but remain together forming an intact group of atoms having a valency. This unit behaves just like an atom or a molecule during a reaction.
  
Some compound radicals with their valencies are given below:

Compound Radical        Valency
OH                               1
SO4                              2
NO3                              1
CO3                              2

Some compounds containing compound radicals:

Compound
Name
Compound Radical
Valency
NaOH
Sodium hydroxide
OH
1
H2SO4
Sulphuric acid
SO4
2
Na2CO3
Sodium carbonate
CO3
2
(NH4)2SO4
Ammonium sulphate
SO4
2
KNO3
 Potassium nitrate
NO3
1

D. Complete the following

Answer :

1. A symbol is an abbreviation of the name of an element.
2. A molecule of an element or a compound is represented by its formula.
3. The valencies of the two elements of a binary compound are transposed to obtain its formula.
4. Atoms are neither lost nor gained in a chemical reaction.
E.Choose the correct options
1. Which of the following is the symbol of gold?
C. Au   
2. Which of the following is a divalent radical                                                      
(c) Sulphate                 
3. The vaancy of sulphur in sulphur dioxide                                                       
 (d) 4                
4.How many times greater is the valency of N in NH3 than that of Cl in HCl          
(b) 3
Valency of N in NH3 is 3, whereas the valency of Cl in HCl is 1.  
Hence, the valency of N in NH3 is three times greater than that of Cl in HCl.

F. Match the coloumn

Answer :

Column A
Column B
(a) Helium
(ii) He
(b) Mercury
 (i) Hg
(c) Copper
(v) Cu
(d) Calcium
(vi) Ca
(e) Phosphorus
(iv) P
(f) Lead
(iii) Pb

G. Say true and false

Answer :

1. True. The valency of hydrogen is 1.
2. True. The valency of oxygen is 2.
3. False. Symbol of iron is Fe.
4. True. The symbol of silver is Ag.
5. False. Calcium chloride is CaCl2.
6. True. The valency of both zinc and oxygen is 2. So, zinc oxide is ZnO

H. Write the formula of following compound

Answer :

Compound
Formula
Water
H2O
Calcium oxide
CaO
Carbon dioxide
CO2
Carbon monoxide
CO
Magnesium oxide
MgO
Hydrogen chloride
 H Cl
Sodium chloride
NaCl
Potassium chloride
 KCl
Magnesium chloride
MgCl2
Zinc chloride
ZnCl2
Nitric acid
HNO3
Sodium nitrate
NaNO3
Sodium carbonate
Na2CO3
Potassium carbonate
K2CO3
Calcium carbonate
CaCO3

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