(a) Sodium carbonate, Na2CO3, is used in processing paper, making glass, and som

ID: 783462 • Letter: #

Question

(a) Sodium carbonate, Na2CO3, is used in processing paper, making glass, and some types of soap.

This important compound is mined in large deposits in Wyoming. In water, Na2CO3 completely

dissociates into sodium ions and the dibasic carbonate ion (CO3 2-).

(Possibly useful information: For H2CO3; Ka1 = 4.5 x10-7; HCO3-Ka2 = 4.7 x 10-11.)

(i) Complete the reaction that shows CO3 2- acting as a base in water:

CO3 2-+ H2O %u2190%u2192 ________________

(ii) What is the value for the Kb for that reaction?

Kb= ______________________

(iii) What then would be the pH of a 0.010 M solution of Na2CO3?

(i) CO32- + H2O <----> HCO3- + OH-

(ii) Kb = 10^ -14/4.7x10^-11 = 2.1277 x10^ -4

(iii) Kb = 2.1277x10^ -4 = x^2/( 0.01-x)

x =[OH-] = 0.001356 , pOH = 2.868 , pH = 11.132

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