Question

Part A Calculate H3 Oof the following polyprotic acid solution: 0.130 MH2 CO3 Express your answer using two significant figures. AD H3O]= М Submit Request Answer

Answer 1

Ionization equation for H2CO3 is

H2CO3_(aq) + H2O_(l)$\rightarrow$ HCO3^-_(aq) + H3O⁺_(aq)

Ionization constant (Ka) value for this equation is 4.3×10^-7.

Use ICE table to find [H3O⁺]

The equation is

H2CO3_(aq) + H2O_(l)$\rightarrow$ HCO3^-_(aq) + H3O⁺_(aq)

	H2CO3	H20	HCO3-	H3O+
Initial	0.130M	-	0	0
Change	(-x)	-	(+x)	(+x)
Equilibrium	(0.130-x)	-	x	x

Use Ka value to find x value which gives [H3O⁺].

Ka = [HCO3^-] [H3O⁺] / [H2CO3]

4.3×10^-7= (x)(x)/(0.130-x)

4.3×10^-7 = x² / (0.130-x)

Because of small value of Ka, we will assume that the value of x in denominator is negligible. So the above equation becomes

4.3×10^-7 = x² / 0.130

x² = 4.3 × 10^-7 × 0.130

x² = 5.59 × 10^-8M

x = 2.36 × 10^-4M

x = [HCO3^-] = [H3O⁺] = 2.36×10^-4 M