Ng 發問於 科學及數學化學 · 1 十年前

點解naoh可以precipitate metal ion

naoh在aq狀態時佢會以ions form

但點解if在aq內有其他metal ions eg mg

佢會走去bind with mg而not na,form compound?

另外if naoh在aq,而aq內有幾種ions

mg2+, zn2+, pb2+, fe2+, fe3+

咁oh-會走去同那一個ions form bond先呢

and 點解



咁請問solubility product depend on wht呢


定係其他呢,洗唔洗睇個cation positive charge density?


naoh + fe(no3)2 + fe(no3)3 + cu(no3)2 + zn(no3)2 + al(no3)3


更新 2:


2 個解答

  • 1 十年前

    OH- ion is movable in aqueous solution, it will form bond with metals ions

    eg. A solution contains K+, Mg2+, Fe2+, Fe3+ ions, when you added NaOH drop by drop.

    The OH- ion will bond with Na+, K+, Mg2+, Fe2+, Fe3+ ions to form hydroxide compound.

    NaOH, KOH, Mg(OH)2, Fe(OH)2, Fe(OH)3, however NaOH, KOH are very soluble in water, so no NaOH, KOH ppt formed. Only Mg(OH)2, Fe(OH)2, Fe(OH)3 formed since they are sparingly soluble in water.

    There is a term called solubility product, Ksp, to determine the solubility of compound.

    For example, Ksp of X(OH)2 is 1.2*10^ (-12), Ksp of A(OH)2 is 6*10^ (-5), that mean when you add NaOH in a solution contain X2+, A2+; X(OH)2 will ppt out first then A(OH)2 when all X2+ used up.

  • 1 十年前

    not all the metal can be p.p.t when combine with naoh

    only a few metal will undergo reaction and form p.p.t

    just like Cu(OH)2

    it's a kind of p.p.t

    in NaOH(aq):Na+,OH-,H+,O2-

    it's difficult to tell you that why "oh-會走去同那一個ions form bond"

    i can only tell you that is OH- have a strong contraction and pull a ion from other compound

    2006-11-30 21:59:34 補充:

    點解呢係好難解點解H 和 O 係可以燒和助燃但H2O點解又剛剛相反,就係無得解不過係有表背的要的可以寫上來