27. Be sure to answer all parts. Calculate the concentrations of H2C2O4, HC2O4,

Question

27. Be sure to answer all parts. Calculate the concentrations of H2C2O4, HC2O4, C2O42, and H+ species in a 0.330 M oxalic acid solution (Ka1 = 6.5 × 102, Ka2 = 6.1 × 105). Be sure to report your answers to the correct number of significant figures. [H2C2O4] = M [HC2O4] = M [C2O42] = × 10 M Enter your answer in scientific notation. [H+] = M What are the concentrations of HSO4, SO42, and H+ in a 0.15 M KHSO4 solution? (Hint: H2SO4 is a strong acid; Ka for HSO4 = 1.3 × 102.) [HSO4] = M [SO42] = M [H+] = M

Explanation / Answer

Ka1 = 5.4x 10-2
Ka2 =5.3 x 10^-5

H2C2O4 <=> HC2O4- + H+
6.5x 10^-2 = x^2 / 0.33-x
The value of Ka1 is small ,so we can
6.5×10^-2=x^2/0.33

x = [HC2O4-]= [H+] = 0.0021M

[H2C2O4]= 0.33 - 0.0021=0.3279M

HC2O4- < = > H+ + C2O42-
6.1x 10^-5 = ( x + 0.0021) (x)/ 0.0021-x
x = [C2O42-] =6.1 x 10^-5 M
Because the first dissociation of H2SO4 is practically complete (Ka1<0) .
It is the same as having a weak monoprotic acid HA, where A is SO4(-) and we need to find the [H+], [HA] and [A-2].

.. .. .. .. .. .. HSO4(-) <=> H(+) + SO4(-2)
Initial .. .. .. .. 0.15
Dissociate.. .. x
Produce .. .. .. .. .. .. .. .. .. x .. .. .. .. x
At Equil .. .. 0.15-x .. .. .. .. x .. .. .. .. x

Ka= x^2/(0.15-x) =0.013
The vale of ka is small ,so we can
0.0 13×0.15=x^2
x=0.0195
x=0.14M

[HSO4-]=(0.15-0.14)=0.01M

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