CHEMICAL EQUATIONS.

            QUESTIONS:

  1. Identify the letter of the most correct answer.

   (i) It shows the total number of atoms that found in a compound.

   A: chemical equation

   B: ionic equation

   C: molecular equation

   D: empirical formula

  (ii) Express information about the proportions of atoms that constitute a particular chemical compound by using symbols.

   A: chemical equation

   B: chemical formula

   C: ionic equation

   D: chemical bonds

  (iii) Which of the following is not reduction reaction.

   A: Cl2 + 2e-  ----->2Cl-

   B: O2  + 2e-  ----> O2-

   C: H2  + 2e-  ----> 2H-

   D: Fe -----> Fe2+  + 2e-

  (iv) Insoluble salt is formed during the chemical reaction.

   A: in precipitation reaction.

   B: in neutralization reaction

   C: in double decomposition reaction

   D: in decomposition reaction

  (v) Identify the chemical equation which is not balanced:

    A: CO2 + C ----> 2CO

    B: 2H2  + O2-----> 2H2O

    C: H2O2 -----> H2O + O2

    D: CaCO3 -----> CaO + CO2

  (vi)   OH-  +  H+ -----> H2O  is

     A: ionic equation

     B: molecular equation

     C: displacement reaction

     D: precipitation reaction

  (vii) Increase of oxidation state caused by

    A: reduction

    B: increase of number of electrons

    C: oxidation

    D: carbon dioxide

   (viii) One of the following is not requirement of the chemical equation.

       A: showing nature(states) of the reactants and production.

       B: showing mole ratio

       C: using arrow to show direction of the reaction

       D: using words instead of symbols.

  (ix)  Only alkalis and acids are

involved

     A: in ionic equation.

     B: in synthesis reaction.

     C: in neutralization reaction.

     D: in displacement reaction.

   (x) One of the following chemical equations is an example of  the precipitation equation.

   A: AgNO3(aq) + NaCl(aq) ---> AgCl(s) + NaNO3(aq)

   B: NaOH(aq) + HCl(aq) ---->NaCl(aq) + H2O(l)

   C: CaCO3(s) ------> CaO(s) + CO2(g)

   D: Zn(s) + 2HCl(aq) ----> ZnCl2(aq) + H2(g)

2. Match items in list A and list B

     List  A.

(i) Decomposition reaction

(ii) displacement reaction

(iii) net ionic equation

(iv) neutralization reaction.

(v) complete ionic equation

(vi) 2H2(g) + O2(g) ----->  2H2O

(vii) spectator ions

   List  B

A: shows only chemical species that involved in the reaction.

B: F2  +  2HCl  ------> 2HF +  Cl2

C: complex chemical compound broken into simple molecules.

D: combination reaction.

E: double decomposition reaction.

F: both spectator ions and reacting species are included.

G: found both sides of the chemical equation.

H: molecular formula

I: only hydroxide ions and hydrogen ions are involved

3. Balance the following chemical equations.

     (i) Na (s) + H2O(l) ----->  NaOH(aq) +  H2(g)

     (ii) H2 (g) +  O2(g) -----> H2O(l)

    (iii) Fe (s) +  Cl2 (g)----->  FeCl2(s)

    (iv) HCl(aq)+ Na2CO3(aq)------> 2NaCl (aq)+ H2O (l)+ CO2(g)

    (v) H2O2 -------->  H2O(l) +  O2(g)

    (vi) NaOH(aq)  + H2SO4(aq)----->  Na2SO4(aq) + H2O(l)

    (vii) CuO(s) + H2(g) -------> Cu(s)  +  H2O(l)

4. Write the balanced ionic equation of the following molecular equations.

    (i) HNO3(aq) + Na2S2O3 ----> 2NaNo3(aq) + S (s) + SO2(g) + H2O(l)

  (ii) AgNO3(aq) + HCl(aq) ----> AgCl(s) + HNO3(aq)

  (iii) NaOH(aq) + H2SO4(aq) -----> Na2SO4  + H2O(l)

5. Explain the meaning of the following statements and write one example per each.

   (i) decomposition reaction

   (ii) displacement reaction

   (iii) synthesis reaction

   (iv) neutralization

   (v) redox reaction

   (vi) reduction

    (vii) oxidation.

6. What mass remained when 100g of calcium carbonate is strongly heated to a constant  mass?

     ANSWERS:

1. (i) C      vi) A

    (ii) B     vii) C

    (iii) D    viii) D

     (iv)A      ix) C

      (v)C        x) A

2. i) C

   ii) B

  iii) A

  iv) I

   v) F

  vi) D

  vii) G

3. (i) 2Na(s) +  2H2O -------> 2NaOH (aq)  + H2 (g)

   (ii) 2H2 (g)  +  O2(g) -------> 2H2O(l)

  (iii) It is balanced.

  (iv) 2HCl(aq)  +  Na2CO3(aq) -----> 2NaCl(aq) + H2O(l)  + CO2(g)

   (v) 2H2O2  ------> 2H2O(l)  + O2(g)

  (vi) 2NaOH(aq) + H2SO4(aq) -----> Na2SO4 (aq) + 2H2O(l)

 (viii) It is balanced.

4. (i) 1st  step.

        Balance the chemical equation

 2HNO3(aq) +Na2S2O3(aq) -----> 2NaNO3(aq) + S(s) + H2O(l) + SO2(g)

     2nd step.

  Write the ions present separately

  2H+  +  2NO3-  +  2Na+  +  S2O3  2+  -----> 2Na+  + 2NO3 -  + S  + SO2 + H2O

  3rd step.

 Cancel spectator ions.

  Spectator ions are 2Na+ and 2NO3 -

  4th step.

  Write the remaining ions at reactants side and products formed at products side.

    2H+(aq)  +  S2O3 2- (aq) -----> S  + SO2(g)  +  H2O(l)

*steps in 4(i) applied in (ii) and (iii)

 (ii) Ag+(aq)  +  Cl- (aq) -------> AgCl(s)

(ii 2OH -(aq)  +  2H+(aq)  -------> 2H2O(l)

5. i) Decomposition reaction:- is a type of chemical reaction in which a single compound breaks into its components.

2PbNO3 ----------> 2PbO  +  4NO2

   ii) Displacement reaction:- is a type of chemical reaction in which a more reactive substance takes the place of a less reactive substance in a compound.

       Fe. + CuSO4 -----> FeSO4  + Cu.

      Cu is displaced by Fe

  iii) Synthesis reaction:- is a type of chemical reaction in which two or more substances combine to form a single and more complex compound.

     2Mg + O2 -------> 2MgO

  iv) Precipitation reaction :- is a type of chemical reaction in which two soluble compounds combine to form soluble compound and insoluble compound.

     AgNo3(aq)  + NaCl (aq) -----> AgCl(s) + NaNo3(aq)

       AgCl is insoluble salt.

  v) Redox reaction :- is a type of chemical reaction involve both of reduction and oxidation.

        For example:

        CuO + H2 -----> Cu +  H2O

        Cu formed as result of reduction reaction in which oxygen removed from CuO.

        Addition of oxygen to hydrogen to form water is oxidation reaction.

  (vi) Reduction defined as:-

                - the process of adding hydrogen to the substance.

                     C + 4H -----> CH4

                    It means carbon is reduced after gaining hydrogen atoms.

               - the removal of oxygen from the substance.

                  CuO + H2 ------>  Cu  + H2O

       

                   Cu is reduced.

                - the process of adding electron(s) to the substance.

                  3Cl2  + 6e-  ------> 6Cl-

               - the process of decrease in oxidation number

                   Cl  + e-  ------> Cl-

                  Cl has decreased in oxidation number from zero to negative one.

      vii) Oxidation defined as:-

                 -addition of oxygen to the substance.

               

                   2Ca. +  O2  ------> 2CaO

               - Removal of hydrogen from the substance.

                 Cu  + 2HCl --------> CuCl2  + H2

                    Cl is oxidized by removing hydrogen from it.

            -reaction where electrons are lost.

              2Fe --------> 2Fe 3+   +  6e-

       

            - the increase in oxidation number.

                 2Fe -------> 2Fe 3+   +  6e-

                  Iron has increased in oxidation state from zero to three.

     NB.

             An oxidizing agent is a substance that make another substance to be oxidized and reducing agent is a substance that make another substance to be reduced.

 6. solution.

   Given data:

       Mass of CaCO3 =100g.

                        Ca=40

                        C=12

                         O=16

    Heating of CaCO3 is decomposition reaction.

       CaCO3  ---------> CaO  +  CO2.

       Mass reduced is that which used to form carbon dioxide gas.

      There fore

    Remaining mass = Total mass - mass of  carbon dioxide

    Total mass=100g

    Mass of CO2= 12+(16x2)

                            =44

     Remaining mass= 100 - 44

                                    =56g