Monday, August 6, 2012

X Chemical reactions and Chemical Equation:FA-Evaluation Assignments

Very short answer questions (V.S.A) : X Chemical reactions  and Chemical Equation:FA
1. Arrange the following metals in the decreasing under of reactivity or electro positive character.
K Zn Na Fe Pb Cu
2. Which of them will be a reducing agent a metal or non metal?
3. Balance the chemical equation            Na(s) + H2O     ®   NaOH + H2
4. Select the combination reaction from following
(i)KClO3 ® KCl + 3 O2                   (ii) S + O2 ®  SO2
5. Select the decomposition reaction from following
(i) 2H2O   +  O2  ® 2H2 O        
(ii) CaCO3   ------Heat------® CaO + CO2
6. Select the double displacement reaction
(i) BaCl2  + H2SO4 ---® Ba SO4        +    H2   
(ii) 2KBv + Cl2        ®  K Cl2               + Bv2
7. Fill in the following about reactivity series of metal
 (a) the …………………. Metal replaces the ………………. Metal from its salt solution.
8. Which of the following is not the necessary condition for rusting
(i) Presence of oxygen (ii) Presence of catalyst (iii) Presence of moisture
9. Which of the following is required for prevention of corrosion?
(i) coating of less electropositive metal
(ii) coating of move electropositive metal
10. Choose the correct about rancidity
(i) Rancidity is a reduction process   (ii) Rancidity is an oxidation process
Answers
1. K > Na > Zn > Fe > Pb > Cu
2. Non metal
3. 2 Na(s) +2 H2O         ® 2NaOH + 2H2
4. S + O2 ® SO2
5. CaCO3   ------Heat®  CaO + CO2
6. BaCl2  + H2SO4 ® Ba SO4        +    H2
7. Strong, Weak
8. Presence of catalyst
9. Coating with move electropositive metal
10. Rancidity is an oxidation process
See some questions:  Short Answer type Question (2 marks)
1. (i) What happens when aqueous solution of barium chloride is added to aqueous sodium sulphate solution?
(ii) When silver coloured metal (A) is added to dilute sulphuric acid, solution (B) is formed which is colourless solution and a gas (c) is evolved which is colourless name ‘A’, ‘B’ and ‘C’ and write the equation?
(iii) An ‘A’ blue coloured crystalline salt on heating decomposes to ‘B’ white substance. W hen in
blue salt solution, a metal (Zinc) is added, its gives rise to colourless solution ‘C’ wth leaving behind ‘D’ reddish brown metal.
2. Name the compounds ‘A’, ‘B’, ‘C’ and ‘D’
(iv)  A reaction mixture of chromium Oxide is heated with aluminum powder on strong heating
3. a. Write the reaction?
b. Give one application of this reaction?
(v) Define Rusting?
4. Give two methods of protection of metal trans rusting.
5. (i) Rusting is a slow electrochemical process in which hydrated oxide of metal in formed from metal when it comes in with air moisture (ii) By Painting, by galvanization, by tinning
6. (i) Explains the term ‘corrosion’?
(ii) Write the chemical reaction of corrosion of Iron?
(iii) Name two metals which corrodes easily?
(iv) Aluminum corrodes in moist air but is widely used is making utensils.
(v) what is galvanization and why do we use Zn for it?\
7. (i) What is rancidity? Where does it happen
(ii) what are anti oxidants? Why are they added fat and oil containing food to prevent from rancidity?
(iii) why do most items puffed with nitrogen.
Solution:
1. White precipitate of BaSO4 is obtained. Reaction will be as
Na2SO4        + BACl2    ----------------® BaSO4 + 2NaCl
2. A is Zinc, B is ZnSO4 solutions C is H2gas and reactions will be
Zn (s) + H2SO4 (d)         ------------® Zn SO (aq)   + H2 (g)
3. A, B, C, and D are respectively-
CuSO4, 5 H2O, CuSO4, ZnSO4 (aq), Cu (s)
4. (i)Cr2O3   + 2Al ------® Al2O3 + 2 Cr
(ii) This reaction is used in termite welding
5. (i) The process of slow destruction of metals when exposed to air, moisture and pollutant gases , in called as corrasim
(ii) Fe + 3H2 + 2H2O ------------® Fe2O3 x H2O
(iii) Formation of green coating on copper and formation of thin layer of oxide on aluminum are example of corrosion.
(iv) Aluminum forms oxide layer on exposure to air, this oxide layer further checks corrosion.
(v) Galvanization is a process in which Zinc layer is applied on Iron. It is used to protect iron from rusting.
6. (i) The oxidative deterioration of oils and fats leading to stinking smell or stale taste is known as rancidity.
(ii) Anti Oxidants are those chemicals which an addition to fat and oil checks it from rancidityan addition of anti oxidants fatty food is protected from stale.
(iii) Nitrogen is filled in potato chips & other food to create anaerobic (air free atmosphere) which avoids rancidity.

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