Question

0.0012 mol of sodium carbonate (Na2CO3) are added to 1 L of pure water.

a) If the solubility of sodium carbonate is 215 g/L, would you expect all of the sodium carbonate to dissolve?

b) Would the resulting solution be acidic, basic, or neutral? Explain your answer with showing the equilibrium reactions involved.

c) Using your answer from part b), what assumption can you make about the concentration of dissolved CO2and carbonic acid, [H2CO3 * ]?

d) Calculate the pH of the solution.

Answer 1

A. All sodium carbonate are dissolved. Sodium bicarbonate is ionic and would therefore be considered polar. Most polar and ionic solutes dissolve in water because water is a polar solvent.

B. Basic in nature.

EQUATION 1: Na₂CO₃+ 2H₂O = 2NaOH+H₂CO₃  

C.   The carbonic acid is a weak acid, and it can dissociate to form bicarbonate ion (HCO3-) and (in basic solution) carbonate ion: (CO32-):

H2CO3(aq) H+(aq) + HCO3-(aq)
HCO3-(aq) H+(aq) + CO32-(aq)

Because the carbonic acid forms slowly, adding a base to carbonated water causes the pH to jump up (as the small amount of carbonic acid is quickly neutralized) and then, slowly down again (as new carbonic acid forms from hydrated carbon dioxide)

D. PH=14-(-log0.0024) In the equation 1.. 1M Sodium carbonate dissociate gives 2 moles of Sodium hydroxide SO 0.0012 moles multiply into 2 so it gives 0.0012×2=0.0024

     PH=11.38