Question

when a 12.7 g chunk of zinc dissolves in 500. ml of 1.450 m hcl, what is the concentration of hydrogen ions remaining in the final solution? (asume the volume does not change during the reaction)

Answer 1

Concentration of hydrogen ions remaining in the final solution is $.673 M$

In original solution we have 1.450M of HCl

1.450 M means 1.450 moles of HCl in 1 liter of water

Therefore, number of moles of HCl in 500ml of water will be

                                                           =  $1.450*0.5$ moles

                                                           =  0.725 moles of HCl

Reaction between HCl and Zn happens when zinc is added -

         $Zn(s) + 2HCl$     →      $ZnCl_{2} + H_{2}$

Therefore two moles of HCl is needed for 1 mole of zinc

Thus number of moles of HCl needed to react with 12.7g of Zinc will be

                                   =  $(12.7/ 65.38 moles of Zn )* (2moles of HCl/mole of Zn)$

                                   = .388 Moles

So moles of HCl left  = $0.725 - .3888$

                                  =  0.3365 moles

In 1 Mole of HCl there is 1 mole of H because

                                    $HCl$  →  $H^{+} + Cl^{-}$

Therefore in 0.3365 mole HCl there will be 0.3365 moles of H

Thus final concentration of H ions in final solution is =

                                      =  $0.3365mole/0.5 L$

                                      = 0.673M

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