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CHEMICAL EQUATIONS 

Important Questions
 

1. What do you understand about Chemical equation? (AS 1) 4 Marks

A: Chemical equation is a shorthand representation of a chemical change or reaction in terms of symbols and formulae.

Chemical changes are expressed in the form of chemical equations.

The substances which take part in a chemical reaction are known as reactants.

Substances formed due to chemical change are known as products.

Reactants and products are separated by an arrow mark symbol ("  ").

Reactants are written on the left - hand side of the equation, connected by plus (+) sign.

Products are written on the right hand side of the equation, connected by plus

(+) sign.
 

Examples:

(a) Zinc metal reacts with dilute Hydrochloric acid to form Zinc chloride and Hydrogen gas.

     Zn + 2 HCl   ZnCl2 + H2

(b) Calcium oxide reacts with water to form Calcium hydroxide.

     CaO + H2O   Ca(OH)2
 

2. What do you understand about balanced chemical equation? Why should chemical equation be balanced? (AS 1) 4 Marks

A: A chemical equation in which the number of atoms of different elements on the reactants side are same as those on product side is called a balanced chemical reaction.

e.g.: Propane burns with Oxygen to form Carbon dioxide and water.

C3H8 + 5 O  3 CO2 + 4 H2O

According to the law of conservation of mass, the total mass of the products formed in chemical reaction must be equal to the mass of reactants consumed. All the chemical equations must balance, because atoms are neither created nor destroyed, in chemical reactions.
 

3. Balance the following chemical equations by mentioning their physical states. (AS1) 4 Marks
i) CO2 + H2O  C6H12O6 + O2
ii) Fe2O3 + CO   Fe + CO2
iii) NaCl + H2  NaOH + Cl2 + H2
iv) Na + H2  NaOH + H2
A: i) 6 CO2 + 6 H2O (l C6H12O6 + 6 O2
          (g)               (l)                         (s)          (g)

     ii) Fe2O3 + 3CO   2 Fe + 3 CO2
             (s)         (g)           (l)         (g)

     iii) 2 NaCl + 2 H2  2 NaOH + Cl2 + H2
             (aq)          (l)                    (aq)       (g)     (g)

     iv) 2 Na + 2 H2  2 NaOH + H2
            (s)           (l)                   (aq)       (g)

 

4. Explain how to balance the following chemical equation.                               (AS1) 4 Marks
      H2 + O2 H2O
A: ‣ Unbalanced equation H2 + O2   H2O
Compare No. of atoms of each elements on both sides of the equation.

There are two Oxygen atoms on LHS and one Oxygen atom on RHS.
To balance 'O' add a co-efficient of 2 to H2O on RHS.
       H2 + O2   2 H2O
To Balance 'H' add a co-efficient of 2 to H2 on LHS.
      2 H2 + O2  2 H2O
Now the number of atoms of different elements are same on both sides, hence equation is balanced.
∴ Balanced equation is 2 H2 + O2   2 H2O

 

4. Explain how to balance the following chemical equation.   (AS1) 4 Marks
      H2 + O2   H2O
A: Unbalanced equation H2 + O2   H2O
Compare No. of atoms of each elements on both sides of the equation.
There are two Oxygen atoms on LHS and one Oxygen atom on RHS.
To balance 'O' add a co-efficient of 2 to H2O on RHS.
       H2 + O  2 H2O
To Balance 'H' add a co-efficient of 2 to H2 on LHS.
      2 H2 + O2   2 H2O
Now the number of atoms of different elements are same on both sides, hence equation is balanced.
∴ Balanced equation is 2 H2 + O2   2 H2O

5. Explain how to balance the following chemical equation.                                (AS1) 4 Marks
     C3H8 + O2   CO2 + H2O
A: Unbalanced chemical equation is C3H8 + O2   CO2 + H2O
Compare No. of atoms of each element on both sides of the equation. Element No. of atoms

There are three Carbon atoms on LHS and one Carbon atom on RHS. To balance 'C' atoms add a co-efficient of 3 to CO2 on RHS.
   C3H8 + O  3 CO2 + H2O
There are eight Hydrogen atoms on LHS and two Hydrogen atoms on RHS. To balance 'H' atoms add a co-efficient of 4 to H2O in RHS.
   C3H8 + O2   3 CO2 + 4 H2O
There are two Oxygen atoms on LHS and ten Oxygen atoms on RHS. To balance 'O' atoms add a co-efficient of 5 to O2 on LHS.
   C3H8 + 5 O2   3 CO2 + 4 H2O
Now the number of atoms of different elements are same on both sides, hence equation is balanced.
∴ Balanced equation is C3H8 + 5 O  3 CO2 + 4 H2O
There are two Oxygen atoms on LHS and ten Oxygen atoms on RHS. To balance 'O' atoms add a co-efficient of 5 to O2 on LHS.
   C3H8 + 5O2 3CO2 + 4H2O
Now the number of atoms of different elements are same on both sides, hence equation is balanced.
 Balanced equation is C3H8 + 5O2 3CO2 + 4H2O

6. If a chemical reaction occurs then mention the changes.                                 (AS1) 4 Marks
A: ¤ The original substance lose their characteristic properties. Hence these may be products with different physical states and colours.
Chemical changes may be exothermic or endothermic i.e, evolve liberated or absorb heat.
They may form an insoluble substance known as precipitate.
Gas may be evolved.

7. Write the balanced chemical equations for the following reactions.                (AS1) 4 Marks
i) Calcium hydroxide + Carbondioxide  Calcium carbonate + Water
ii) Zinc + Sodium hydroxide  Sodium Zincate + Hydrogen
iii) Magnesium + Hydrochloric acid  Magnesium chloride + Hydrogen
iv) Sodium hydroxide + Sulphuric acid  Sodium sulphate + Water
A: i) Ca(OH)2 + CO2 CaCO3 + H2O
     ii) Zn + 2NaOH  Na2ZnO2 + H2
     iii) Mg + 2HCl  MgCl2 + H2
     iv) 2 NaOH + H2SO4  Na2SO4 + 2H2O

8. What is the additional information can we get from a chemical equation?
A: Chemical equation can be made more informative by expressing the following characteristics of the reactants and products.
i) Physical state
ii) Heat Exchange (Exothermic or endothermic change)
iii) Gas evolved (if any)
iv) Precipitate formed (if any)
i) Expressing the Physical state: The Physical state of the substances may be mentioned along with their chemical formulae. The different states i.e. gaseous, liquid and solid states are represented by the notations (g), (l) and (s) respectively. If the substance is present as a solution in water it is represented as (aq).
e.g.: Fe2O3 + 2Al   2 Fe + Al2O3
           (s)          (s)               (s)         (s)
ii) Expressing the Heat Exchanges: Heat is liberated in exothermic reactions and it is absorbed in endothermic reactions.
e.g.: C  +  O2  CO2 + Q (exothermic reaction)
        (s)    (g)             (g)
        N2 + O2 2NO - Q (endothermic reaction)
       (g)     (g)               (g)
iii) Expressing the Gas evolved: If a gas is evolved in a reaction it is denoted by an upward arrow ↑ or (g).
e.g.: Zn + H2SO4 ZnSO4 + H2 ↑
        (s)      (aq)                 (aq)        (g)
iv) Expressing precipitate formed: If a precipitate is formed in the reaction it is denoted by a downward arrow () (or) the physical state (S) is written subscript for precipitate substance.
e.g.: AgNO3 + NaCl  AgCl↓  + NaNO3
           (aq)        (aq)              (s)           (aq)

v) Some times the reaction conditions such as temperature, pressure, catalyst etc, are indicated above and/or below the arrow in the equation.
Sunlight
e.g.: 2 AgCl  2Ag + Cl2
           (s)                 (s)       (g)

9. Interpret about a balanced chemical equation.                                                 (AS1) 4 Marks
A: ¤ A chemical equation gives information about the reactants and products through their symbols and formulae.
¤ It gives the ratio of molecules of reactants and products.
¤ As molecular masses are expressed in "unified masses (U)'', the relative masses of reactants and products are known from the equation.
¤ If the masses are expressed in grams then the equation also gives the molar ratios of reactants and products.
¤ If gases are involved, we can equate their masses to their volumes and calculate the volumes or those gases liberated at given condition of temperature and pressure using molar mass and molar volume relationship.
¤ Using molar mass and Avagadro's number we can calculate the number of molecules and atoms of different substances from the equation. It gives information about relative masses of reactants and products. From the equation we get
    a) Mass - mass relationship
    b) Mass - volume relationship
    c) Volume - volume relationship
    d) Mass - volume - number of molecules relationship etc.

10. Al + Fe2O3  Al2O3 + Fe
      (s)       (s)                  (s)        (s)
(Atomic masses of Al = 27 U, Fe = 56 U, and O = 16 U)
Then calculate the amount of Aluminium required to get 336 kg of iron by the above reaction.                                                                                                                      (AS1) 4 Marks

Sol: 2 Al + Fe2O3  Al2O3 + 2Fe
          (s)         (s)                  (s)         (s)
(2 × 27)U + (2 × 56 + 3 × 16)U  (2 × 27 + 3 × 16)U + (2 × 56)U
54U + 160U  102U + 112U
54g + 160g  102g + 112g
As per the balanced equation
Aluminium  Iron
54 g  112 g
Xg  (336 × 1000)g

= (3 × 1000) × 54
= 162000 g (or) 162 kg
To get 336 kg of Iron we have to use 162 kg of Aluminium

11. How many grams of Carbondioxide is liberated when 16 grams of Calcium carbonate is heated?                                                                                                                       (AS1) 4 Marks
(Atomic weight of Ca = 40 U, C = 12 U and O = 16U)
Sol: CaCO3  CaO + CO2 (is a balanced equation)
            (s)                  (s)      (g)
[40 + 12 + (3 × 16)U  (40 + 16)]U + [12 + (2 × 6)]U
(40 + 12 + 48)U  56U + (12 + 32)U
100U  56U + 44U
100g  56g + 44g
As per the balanced equation Calcium carbonate  Carbondioxide
100g  44 g
16g  ?

 = 7.04 g
16 grams of CaCO3 gives 7.04 grams of CO2.

12. Calculate the volume of Oxygen required for complete burning of 36 grams of Carbon. (AS1) 4 Marks
(Atomic weight of O = 16U, C = 12U)
Sol: C + O2 CO2
        (s)   (g)             (g)
Step-1: Convert 36 grams of Carbon into moles.

                                         = 3 moles.
Step-2: From the equation, it is clear that one mole of Carbon requires one mole of Oxygen to yield one mole of Carbondioxide.

Step-3: Calculation of required volume of Oxygen.
At STP, 1 mole occupies 22.4 litres.
At STP, 3 moles occupies 22.4 × 3 = 67.2 litres.
At STP, 3 moles of Oxygen occupies 67.2 litres.

13. Calculate the volume, mass and number of molecules of Hydrogen liberated when 92 g of Sodium reacts with excess of water at STP. (atomic masses of Na = 23U, O = 16U and H = 1U)                                                                                                                         (AS1) 4 Marks
Sol: 2 Na + 2 H2O  2 NaOH + H2 is balanced equation.
           (s)         (l)                     (aq)       (g)
(2 × 23)U + 2(2 × 1 + 1 × 16)U  2(23 + 16 + 1)U + (2 × 1)U
46U + 36U  80U + 2U
46g + 36g  80g + 2g
As per the balanced equation
46 g of Na gives 2g of Hydrogen.
92 g of Na gives ....? g of Hydrogen

2g of Hydrogen occupies 22.4 litres at STP
4g of Hydrogen occupies 44.8 litres at STP
2g of Hydrogen i.e., 1 mole of H2 contains 6.02 × 1023 molecules.
4g of Hydrogen contain ....?

= 2 × 6.02 × 1023
= 12.04 × 1023
= 1.204 × 1024 molecules.

14. Calculate the volume of Oxygen (O2) needed for the combustion of 100 ml Acetylene. It is an unsatured hydrocarbon with the molecular formula C2H2. What would be the volume of Carbondioxide produced in this reaction ?                                                              (AS1) 4 Marks
Sol: Step-1: 2 C2H2 + 5 O2  2 H2O + 4 CO2 (balanced equation)
                           (g)         (g)                  (l)           (g)
Step-2: 2 vol (ml) of Acetylene + 5 vol (ml) of Oxygen  2 vol (ml) of H2O + 4 vol (ml) of CO2
Step-3: 2 ml of C2H2 requires 5 ml of O2 for combustion.
1 ml of C2H2 requires 2.5 ml of O2 for combustion
100 ml C2H2 required 2.5 × 100 = 250 ml of O2 for combustions
Step - 4: 2 ml of C2H2 produces 4 ml of CO2
1 ml of C2H2 produces 2 ml of CO2
100 ml of C2H2 produces 2 × 100 = 200 ml of CO2

15. Give some examples to chemical changes occurring in our daily life. (AS1) (AS6) 2 Marks
A: ¤ Burning of fuels
Rusting of Iron
Digestion of food in our body
Coal is burnt
Crackers are burnt
Ripening of fruits
Milk is converted into curd
Fermentation of grapes.

16. What are the important characteristics of chemical reactions?                   (AS1) 2 Marks
A: The important characteristic of chemical reactions are
Change in state
Evolution of a gas
Formation of a precipitate
Change in colour
Change in temperature

17. Observe the following equations and answer the questions given below.
a) Zn + HCl  ZnCl2 + H2  ↑                                                                      (AS4) 2 Marks
b) AgNO3 + NaCl  AgCl ↓ + NaNO3
i) Mention the products in equation 'a'.
ii) Which is the precipitate in equation 'b'.
A: i) ZnCl2, H2
     ii) AgCl

18. Why the white washing gives shiny finish to the walls?                      (AS1) (AS6) 2 Marks
A: Slaked lime is prepared by adding water to quick lime.
     CaO + H2O  Ca(OH)2
A solution of slaked lime is used to white wash the walls.
Calcium hydroxide reacts with the Carbondioxide in air to form thin layer of Calcium carbonate on the walls. It gives a shiny finish to the walls.
     Ca(OH)2 + CO2 CaCO3 + H2O

19. Balance the following chemical equations.                                                     (AS1) 2 Marks
i) NH3 + Cl2 N2H4 + NH4Cl
ii) NH3 + Cl2 NCl3 + HCl
A: i) 4 NH3 + Cl2 N2H4 + 2 NH4Cl
ii) NH3 + 3 Cl2 NCl3 + 3 HCl

20. Balance the following chemical equations including the physical states.      (AS1) 2 Marks
i) CaCO3 + HCl  CaCl2 + H2O + CO2
ii) Fe2O3 + Al  Fe + Al2O3
A: i) CaCO3 + 2 HCl  CaCl2 + H2O + CO2
            (s)           (aq)              (aq)        (l)       (g)
     ii) Fe2O3 + 2 Al  2 Fe + Al2O3
            (s)          (s)              (s)         (s)

21. KMnO4 + H2SO4  K2SO4 + MnSO4 + H2O + O2
       Balance the above chemical equation.                                                                (AS1) 1 Mark
A: 4 KMnO4 + 6 H2SO4  2 K2SO4 + 4 MnSO4 + 6 H2O + 5 O2

22. Ca3(PO4)2 + SiO2 + C  CaSiO3 + P + CO
      Balance the above equation.                                                                                 (AS1) 1 Mark
A: Ca3(PO4)2 + 3 SiO2 + 5 C  3 CaSiO3 + 2 P + 5 CO

23. Balance the chemical equation
      Zn(NO3)2  ZnO + NO2 + O2                                                                                               (AS1) 1 Mark
A: 2 Zn(NO3)2  2 ZnO + 4 NO2 + O2

24. Cr2O3 + NaOH + O2  Na2CrO4 + H2O
     Balace the above chemical equation.                                                                    (AS1) 1 Mark
A: 2 Cr2O3 + 8 NaOH + 3 O2  4 Na2CrO4 + 4 H2O

25. FeCl3 + H2 Fe(OH)3 + HCl
      Balance the above chemical equation.                                                               (AS1) 1 Mark
A: FeCl3 + 3 H2Fe(OH)3 + 3 HCl

26. NH3 + Cl2  NH4C+ N2 Balance the equation.                                       (AS1) 1 Mark
A: 8 NH3 + 3 Cl2  6 NH4C+ N2


Short Questions

1. Which law state that total mass of the products formed in a chemical reaction must be equal to total mass of the reactants consumed? (AS 1) 1 Mark
A: Law of conservation of mass.

2. In an experiment mixing of sodium sulphate solution to Barium Chloride solution, which precipitate is formed, and write chemical equation for it?
                                                                                                                              (AS 3) 2 Marks
A: Barium Sulphate precipitate is formed.
     Na2SO4 + BaCl2 
BaSO4 ↓+ 2 NaCl

3. Addition of Dry CaO to the water, what type of thermo chemical reaction takes place? (AS 3) 1 Mark
A: Exothermic reaction.

4. Which product formed in an experiment by mixing Dry CaO with water which can changes Red litmus to blue litmus? (AS 3) 1 Mark
A: Calcium Hydroxide.


5. Write a chemical reaction, when dil. HCis added to Zinc granuels?  (AS 1) 1 Mark
A: Zn + 2 HC ZnCl2 + H2


6. Write balanced chemical equation for burning of propane in air. (AS 1) 1 Mark
A: C3H8 + 5 O2 3 CO2 + 4 H2O

7. Fe2O3 + 2 A Al2O3 + 2 Fe
    Identify the reactants in the above reaction. (AS 4) 1 Mark
A: Fe2O3 and Al.

8. Which additional information can be shown by a chemical equation?
A: 1. Physical State                                                                                   (AS 1) 2 Marks
     2. Heat Changes
    3. Gas evolved
    4. Precipitate formed

What is indicated by Δ in the above reaction? (AS 4) 1 Mark
A: Δ represents heating.


10. N2 + O2 + Q   2 NO
       Identify above reaction is either endothermic or exothermic reaction.
                                                                                                                         (AS 1) 1 Mark
A: Exothermic reaction.


11. Which sign can be used for evolution of gas in a chemical reaction? (AS 1) 1 Mark
A: 


12. Name the precipitate formed in the following reaction. (AS 1) 1 Mark
         AgNO3 + NaCl 
 AgC + NaNO3
           (aq)         (aq)               (s)        (aq)
A: AgC

13. Write the physical state of reactants and products in the following reaction.
       6 CO2 + 6 H2
 C6H12O6 + 6 O2                                    (AS 1) 1 Mark
A: 6 CO2 + 6 H2
 C6H12O6 + 6 O2   
        (g)           (l)                     (s)            (g)

14. How much volume can occupy by 1gm of Hydrogen at S.T.P.? (AS 1) 1 Mark
A: 11.2 Litres

15. How many molecules present in 1 mole of Hydrogen at S.T.P.? (AS 1) 1 Mark
A: 6.023 × 1023 molecules.

16. What temperature and pressure can represent S.T.P.? (AS 1) 1 Mark
A: 0°C (or) 273 K and 760 mm (or) of Hg (or) 1 bar pressure.

17. How much volume is occupied by 1 mole of gas at S.T.P? (AS 1) 1 Mark
A: 22.4 litres

18. How much volume in ml. can be occupied by 0.5 moles of O2 at S.T.P.? (AS 1) 1
Mark
A: 11,200 ml

19. Balance the following equations. (AS 1) 2 Marks
      (i) BaCl2 + H2SO4  BaSO4 + HCl
      (ii) Cu2S + O2   Cu2O + SO2
A: (i) BaCl2 + H2SO4  BaSO4 + 2 HCl
     (ii) 2 Cu2S + 3 O2  2 Cu2O + 2 SO2

20. Complete and balance the following equations (AS 1) 2 Marks
       (i) C3H+ O2 .......... + .........
      (ii) Na + H2 ......... + .........
A: (i) C3H8 + 5 O2  3 CO2 + 4 H2O
     (ii) 2 Na + 2 H2 2 NaOH + H2

Posted Date : 09-10-2021

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.

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