Having trouble predicting the reactants for this question. I understand to conve

Question

Having trouble predicting the reactants for this question. I understand to convert the volume and molarity given into moles, then to setup the products of the reaction. However I need help getting the reactants. I would appreciate full steps for the entire question though.

In three 250 ml beakers, add 50 ml solution of 0.1 M Na2HPO4 to each beaker. HP042-(aq) + H2O (I) H3O+ (aq) + PO43-(aq) Record the pH of the solution after addition of each of the following solution: pH-9.10 (initial) 1) Beaker 1: Add 10 ml of 0.1 M ZnCl2 and record the pH. pH-7.50 2) Beaker 2: Add 10 ml 0.1 M NasPO4 and record the pH, pH=10.84 3) Beaker 3: Add 20 ml of 1 M NaCl and record the pH. pH=8.82 In your data sheet and for each of those steps, write a balanced chemical equation and identify the direction of the chemical equilibrium shift. Explain the rationale for the shift and identify the spectator ions.

Explanation / Answer

HPO4- (aq) + H2O (l) <---------------> H3O+ (aq) + PO43- (aq) pH = 9.10

1) Add 10 ml of 0.1M ZnCl2 : pH = 7.50

Adding ZnCl2, the follwoing reaction takes place:

2 Cl- (aq) + 2 H3O+ (aq) ----------> 2 HCl (aq) + 2H2O

Adding Cl- leads to the above reaction and consumes H3O+ ions on the right. Decrease in H3O+ ions on the right, pushes the equilibrium to the right and production of HCl reduces the pH to 7.50

2) Add 10 ml of 0.1M Na3PO4 : pH = 10.84

Adding Na3PO4, leads to tan increase in the concentration of PO43- ions on the right. Increase in PO43- ions on the right, pushes the equilibrium to the left, increasing the reactant concentration and hence pH = 10.84

3) Add 20 ml of 1M NaCl: pH = 8.82

Adding NaCl, the follwoing reaction takes place:

Cl- (aq) + H3O+ (aq) ----------> HCl (aq) + H2O

Adding Cl- leads to the above reaction and consumes H3O+ ions on the right. Decrease in H3O+ ions on the right, pushes the equilibrium to the right and production of HCl reduces the pH to 8.82

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