A student adds 0.1 mol of oxalic acid and 0.1 mol of sodium dihydrogen phosphate

Question

A student adds 0.1 mol of oxalic acid and 0.1 mol of sodium dihydrogen phosphate to enough water to make 1.0 L of solution. The following equilibrium is established with the concentrations of the products greater than the concentrations of the reactants. Which of the statements about the equilibrium system is correct?

H2C2O4(aq) + H2PO4-(aq) HC2O4-(aq) + H3PO4(aq)

A) Oxalic acid is a weaker acid than phosphoric acid.

B) The hydrogen oxalate anion, HC2O4-, is a stronger base than the dihydrogen phosphate anion, H2PO4- .

C) Phosphoric acid is a weaker acid than oxalic acid.

D) The dihydrogen phosphate anion, H2PO4-, is a stronger acid than oxalic acid.

E) Water is a stronger acid than either oxalic or phosphoric acids.

can someone give me explanations why EACH one isn't or is the right answer. I'm studying for a test but want to understand the concept. the answer is C

Explanation / Answer

H2C2O4(aq) + H2PO4-(aq)------> HC2O4-(aq) + H3PO4(aq)

the above reaction ia a acid base reaction. Here you can see that H2C2O4 giving H+ and H2PO4- accepting H+ . You know in a acid base reaction stronger acid gives H+ and weaker acid or base accepts tis H+. conjugate base( HC2O4-) of a strong acid(H2C2O4) is weak and vice versa. conjugate acid(H3PO4) of a strong base( H2PO4-) is weak.

As The above equilibrium is established with the concentrations of the products greater than the concentrations of the reactants, as H2C2O4 forcefully giving H+ to H2PO4- leading to greater forward reaction, Hence H2C2O4 is stronger than H3PO4.(Ans C)

As water doesn't perticipate in the reaction so Water is niether a stronger acid than oxalic nor phosphoric acid.

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