Double+Displacement+R.Stacey

Double Displacement

A double-displacement reaction is when the positive ions of 2 compounds switch places to form 2 new compounds.  v  Another way to think of it is as if there are two couples, and the girls switch dates, forming two new couples. This is well represented in a general sense by the following: ** AX + BY ** ** à **** AY + BX **  v  One of the compounds is usually a precipitate and insoluble gas that bubbles out of the solution or molecular compound, usually water. The other is soluble and stays dissolved.  v  An example would be: Silver Nitrate and Sodium Chloride react to form Sodium Nitrate and Silver Chloride 1.  So first, you find the elements and the products  v  So you see Silver Nitrate, Sodium Chloride, Silver Chloride and Sodium Nitrate  v  The symbols are AgNO3, NaCl, NaNO3, and AgCl  v  Since you see NO3 on both sides, you keep the compound, and the charge is -1.  v  Ag is a transition metal, but the charge is +.  v  The charge of Na is +1 as well because it is in group 1.  v  The charge of Cl is -1 because it is in Group 17. 2. So now you have all of the charges, and you need to balance the reactants and products.  v  So AgNO3 is fine, with a +1 and -1 charge.  v  Na and Cl are also fine because of the +1 and -1 charge again. Since all of the cations are +1 and all of the anions are -1, all of the reactants and products are neutral and balanced. So the final equation is AgNO3 + NaCl  à NaNO3 + AgCl.  This is from <chloridehttp://genchem.chem.wisc.edu/demonstrations/ Gen_Chem_Pages/15precippage/silverchloridedissolvesinxs.htm> They describe this pictures as: 'A small amount of saturated sodium chloride solution is added to about 200 mL of 0.01M silver nitrate, and the expected precipitate forms. Addition of a large excess of the same sodium chloride solution redissolves the precipitate.'

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