Aluminum sulfate, known as cake alum, has a remarkably wide range of uses, from

Question

Aluminum sulfate, known as cake alum, has a remarkably wide range of uses, from dyeing leather and cloth to purifying sewage. In aqueous solution, it reacts with base to form a white precipitate.

(a) Write balanced total and net ionic equations for its reaction with aqueous NaOH. (Type your answer using the format (NH4)2CO3 for (NH4)2CO3, [NH4]+ for NH4+, and [Ni(CN)4]2- for Ni(CN)42-. Use the lowest possible coefficients. Type the cation before the anion.)

1 Al2(SO4)3 (aq) + 6 NaOH(aq)---> 3 Na2SO4 (aq) + 2 Al(OH)3 (s)
1 Al3 (aq) + 3 [OH]- (aq) ---> 1 Al(OH)3 (s)

(b) What mass of precipitate forms when 150.0 mL of 0.638 M NaOH is added to 517 mL of a solution that contains 13.4 g aluminum sulfate per liter?_______

Explanation / Answer

a) 2Al 3+ (aq) + 3SO4 2- (aq) + 6Na+ (aq) + 6OH- (aq) --> 2Al(OH)3 (s) + 6Na+ (aq) + 3SO4 2- (aq) we get, 2Al 3+ (aq) + 6OH- (aq) --> 2Al(OH)3 (s) b) moles of NaOH = 150/1000 * 0.638 = 0.0957 mass of Al2(SO4)3 = 517/1000 * 13.4 = 6.9278 grams moles = 6.9278/342.1 = 0.0202 mass of precipitate = 0.0957/3 * 78 = 2.488 grams

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