Answers
Assignment – 2
Chemical Reactions and Equations

Ans 16. Magnesium ribbon is cleaned before burning to remove the protective layer of basic magnesium carbonate from the surface of magnesium ribbon.
Ans 17. Balance chemical reaction with state symbols are as follows-
i. BaCl2(aq) + Na2SO4 (aq)  →  BaSO4 (s) + 2NaCl (aq)
ii. NaOH (aq) + HCl (aq)   →  NaCl (aq) + H2O

Ans 18. (i). The substance whose solution is water is used for white washing is calcium oxide. Its formula is CaO.
    (ii). CaO (s) + H2O   →  Ca(OH)2 (s)

Ans 19. The reaction involved is:
              Cu (s)  +  2 AgNO3 (aq) →  Cu(NO3)2  (aq)  +  2 Ag (s)

Ans 20. A chemical reaction in which an insoluble substance (precipitate) is formed is called precipitation reaction. For example
              AgNO3 + NaCl  →  AgCl + NaNO3

Ans 21. The brown coloured element ‘X‘ is copper. On heating in air it forms copper oxide, which is black in colour.
              2CuS + O2  →  2CuO

Ans 22. We apply paint on iron articles to prevent rusting. Iron articles do not come in contact of atmospheric oxygen and moisture and thus the rusting is prevented.

Ans 23. Oil and fat containing items get rancid due to oxidation with atmospheric oxygen. To prevent rancidity food items are flushed with nitrogen. Nitrogen do not reacts with oil and fat containing items.

Ans 24.  BaCl2 (aq)   +   Na2SO4  (aq)   →    BaSO4 (s)  +   2 NaCl (aq)
                                                      Barium Sulphate    
          White Precipitate
    NaOH (aq)   +   HCl (aq)   →   NaCl (aq)   +   H2O (l)

Ans25. (a) 2 HNO3  +  Ca(OH)2   →   Ca(NO3)2   +   2 H2O
  (b) 2 NaOH  +   H2SO4    →    Na2SO4    +   2 H2O
  (c)  NaCl   +   AgNO3      →    AgCl   +   NaNO3
  (d)  BaCl2   +   H2SO4     →   BaSO4   +   2 HCl


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