your answer. When a sample of pure Na COs is placed in distilled water, the stud
ID: 1037526 • Letter: Y
Question
your answer. When a sample of pure Na COs is placed in distilled water, the student observes that the pH of the solution increases significantly. This process is represented by the balanced net-ionic equation shown below. (e) The student prepares a 0.10 M Na COs(aq) solution and measures the pH of the solution to be 11.65. (i) Calculate [OH] in the Na2COs(aq) solution. (ii) Write the expression for Kb for the carbonate ion. (ii) Calculate the value of K, for the carbonate ion. The student adds some 1.0 M Sr(NOs)(ay) to the 0.10 M Na CO,(aq) and observes the formation of a precipitate. 0 Write the balanced net-ionic equation for the reaction between Sr(NO,)y and Na CO, that produces the precipitateExplanation / Answer
e)
pH = 11.65
pOH = 2.35
[OH-] = 4.47 x 10^-3 M
CO32- (aq) + H2O (l) --------------> HCO3- (aq) + OH- (aq)
0.10 0 0
0.10 - x x x
Kb = [HCO3-] [OH-] / [CO32-]
Kb = x^2 / 0.10 - x
x = OH- = 4.47 x 10^-3
Kb = (4.47 x 10^-3 )^2 / 0.10 - 4.47 x 10^-3
Kb = 2.09 x 10^-4
i)
concentration of [OH-] = 4.47 x 10^-3 M
ii)
Kb expression :
Kb = [HCO3-] [OH-] / [CO32-]
iii)
Kb = 2.09 x 10^-4
f)
Net ionic :
Sr+2 (aq) + CO32- (aq) --------------> SrCO3 (s)
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