Question 1106365
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A 20% v/v solution of HCl is diluted by a ratio of 1:2, and then by a ratio of 1:4. Find the concentration of the resulting HCl solution. 
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0.  The initial composition is 1:4 :  1 volume of HCl to 4 volumes of water; 
                                      5 elementary volumes in all.



1.  First dilution:                   They add 2*5 = 10 volumes of water.
                                      We have now 1 elementary volume HCl and 4+10 = 14 volumes of water. 
                                      In all, there are 1 + 14 = 15 elementary volumes of the solution.



2.  Second dilution:                  They add 4*15 = 60 volumes of water.
                                      We have now 1 elementary volume HCl and 14+60 = 74 volumes of water. 
                                      In all, the final composition is 1 volume HCL and 74 volumes of water, 
                                      which gives the concentration {{{1/75}}} =  0.013333 = 1.3(3)%.
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