\"What is the net ionic equation for the reaction HCl(aq) withNa 2 HPO 4 (aq)?\"

Question

"What is the net ionic equation for the reaction HCl(aq) withNa2HPO4(aq)?"
This is my answer..
H3O+(aq) + HPO42-(aq)<--> H2PO4-(aq) +H2O(l)
is the charge on "HPO4" correct, or should it be just1-?
also, does charge balance matter in net ionic equations, or only incomplete reactions?
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"What is the pH of 1.0 x 10-10 M HCl?"
Since this is a strong acid, it dissociates completely. Sinceproducts are in a 1:1 ratio with reactants, the initialconcentration of HCl is equal to the final concentration ofH+.
pH = -log[1.0 x 10-10] = 10.
correct?
Thank you for all your help!
-Andrea

Explanation / Answer

     HCl + Na2HPO4 -----> 2NaH2PO4 + NaCl    The ionic equation for the above reactionis      H+(aq) +Cl-(aq)  + 2Na+(aq) +HPO42-(aq) ---->  2Na+(aq) + H2PO4-(aq) + Cl-(aq)       In the above equation Na+ions and Cl- ions are spectator ions. They are unchangedin the chemical reaction .So they can be cancelled and the netionic equation is      The netionic equation is       H+(aq) +   HPO42-(aq) ---->   H2PO4-(aq)   (or)       H3O+(aq)+ HPO42-(aq) -->H2PO4-(aq) +H2O(l)       The charge is balanced inthe net ionic equation b )   [HCl] = 1.0 x 10-10M          HCl   ----> H+(aq) + Cl-(aq)       Since HCl is a strong acid itis completetly dissociated .          [H+] = 1.0 x 10-10 M        Here we have toconsider the contribution of water ,          H2O   <------> H+(aq) + OH-(aq)            [H+] =10-7 M       Total [H+ ] = 10-10 M + 10-7M          pH = - log( 10-10 + 10-7)M                        = 6.99                               

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