When excess of naoh solution is added in potash alum the product is?
Answers
Potassium alum is a hydrated double salt of potassium sulphate and aluminium sulphate - K2SO4.Al2(SO4)3.24H2O. An aqueous solution of it contains K(+), Al(3+) and larger amount of SO4(2-) ions.
On adding sodium hydroxide, initially, a white precipitate of aluminium hydroxide will be formed by the reaction between the aluminium and hydroxide ions.
Al2SO4 (aq) + 6NaOH (aq) = 2Al(OH)3 (s) + 3Na2SO4 (aq)
But if NaOH is added in excess, the aluminium hydroxide so formed will dissolve to give a clear, colourless solution by forming the complex ion [Al(OH)4]-.
Al(OH)3 (s) + NaOH (aq) = Na[Al(OH)4] (aq)
Potassium sulphate does not react with NaOH in any meaningful fashion.
So, the addition of sodium hydroxide in excess will result in a colourless solution having K(+), Na(+), SO4(2-) and [Al(OH)4](-) ions. But, the use of a limited amount of the alkali will result in the separation of aluminium as insoluble aluminium hydroxide from the solution
plz Follow Me ☺️❣️
Answer:
Potash alum is K2SO4.Al2(SO4)3.24H2O.
Al2(SO4)3 reacts with NaOH to form NaAlO2 which is soluble. K2SO4 and Na2SO4 are also soluble and thus a clear solution is obtained in water.
Al2(SO4)3+6NaOH→2Al(OH)3+3Na2SO4
Al(OH)3+NaOH→NaAlO2Soluble+2H2O.