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

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

and 點解

thanks

eg,唔查表,可否分到佢地的先後次序?

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

thanks!!!!!!!!!!!!!!

### 2 個解答

• 1 十年前
最愛解答

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&#39;s a kind of p.p.t

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

it&#39;s difficult to tell you that why &quot;oh-會走去同那一個ions form bond&quot;

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