Answers
Assignment – 4
Chemical Reactions and Equations

Ans 1. The colour of magnesium is silvery-white. And after Burning in the presence of Oxygen the colour changes to white (MgO → Magnesium oxide).

Ans 2. The important reasons are:
§  Because, If the Concentration of the Acid will be higher than it will be a More Exothermic Reaction and if the activity will not be completed in the presence of the right Mentor then it can be very harmful.
§  To prevent the danger. Because you all know how Acids are harmful If the concentration will be higher it can Even burn the skin. And to prevent Danger, we use the highly dilute Acid.

Ans 3. SO2 and SO3 are the colourless gases which are colourless and pungent smell. These gases are harmful to health.

Ans 4. As you know now, AgCl is a photolytic Decomposing material that’s why when we kept AgCl in a black colour bottle to protect it from the Sunlight.

Ans 5. 2 AgBr(s) + Sunlight → 2 Ag(s) + Br2(g)

Ans 6. 2 AgBr(s)  +  Sunlight  →  2 Ag(s) + Br2(g), This reaction is also Similar to the Above one(2 AgCl  → 2 Ag + Cl2). And this Reaction is used for the Black and white Photography.

Ans 7. In this reaction, the Iron nail becomes brownish in colour and the blue colour of copper sulphate solution fade Because Iron displaces Cu (Copper) from its Position (CuSO4) Copper Sulphate. Because Iron is more reactive than Copper and it easily displaces Cu (Copper) from Copper Sulphate (CuSO4).
And that’s why the colour of CuSO4 solution changes from Blue colour to fade and finally the solution of Copper sulphate is converted into Iron Sulphate (FeSO4).
Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)

Ans 8. NH4Cl, NH4NO3, Cl2, HCl(dil), Fe, Pb(NO3)2, MnO2, AgNO3, NaNO3, NaNO2, CaCO3, Ca(OH)2, H2SO4, HNO3, CuSO4, CaSO4.

Ans 9. Strong, Weak

Ans 10. (ii) Presence of catalyst

Ans 11.  (ii) Rancidity is an oxidation process

Ans 12. A is Zinc, B is ZnSO4 solution, C is H2 gas and reactions will be
         Zn  +  H2SO4 (aq)   →  ZnSO4 + H2

Ans 13. A, B, C, and D are CuSO4, H2O, CuSO4, ZnSO4 and Cu respectively-.

Ans 14. (i) Cr2O3 + 2 Al   →  Al2O3  + 2Cr
              (ii) This reaction is used in termite welding

Ans 15. True or False
ü  In exothermic reaction heat is evolved. True / False
ü  Decomposition is possible by thermal decomposition, electrolytic decomposition and by photo chemical decomposition. True / False
ü  Displacement reaction of metals is based on reactivity series of metals. True / False
ü  Oxidising agent is a substance which causes addition of oxygen or removal of hydrogen from other substance. True / False
ü  Reduction is a process which involves removal of hydrogen and addition of oxygen. True / False

Q16. Give a word to fill in the blank
ü  Substance which causes addition of oxygen or removal of hydrogen from other substance is …Oxidising…….. agent.
ü  Presence of air, presence of moisture, presence of salt in water, electropositive metals leads a metal to ………Rusting…
ü  ……Noble or Ag, Au, Pt…………metals are less electropositive and hence they do not corrode in moist air.
ü  A reaction in which an insoluble product formed during the reaction of two ionic compounds in aqueous solution is called …Precipitation. reaction.
ü  A substance which causes addition of Hydrogen or removal of Oxygen from other substance is called …Reducing Agent…… .
ü  The arrangement of elements in decreasing order of their electro positive character is called ……Reactivity Series...
ü  When sodium metal is added to water, it gets …Oxidised… .
ü  In the order of decreasing order of reactivity in Ca > Al > Zn > H > Ag > Pt The most reactive metal is ………Ca…….
ü  In the order of decreasing order of reactivity as stated above the least reactive metal is .......Pt..............
ü  In the order of Ca > Al > Zn > H > Ag > Pt Choose the metal which from above can react with all the salt solutions. ……Ca………

Ans 17. Sodium does not react with kerosene oil but reacts in water and air.

Ans 18. Blue coloured copper sulphate crystals CuSO4.5H2O loses water molecules on heating and turn to white.

Ans 19. Hydrogen librates at cathode and hydrogen ion takes electrons from cathode.

Ans 20. Quick lime (CaO) in water forms lime water Ca(OH)2 milky white substance by a combination reaction.