Na2CO3 同 acid react 時算係alkali?

2008-05-15 6:24 am

1) Na2CO3 +2HCl → 2NaCl + H2O + CO2
2) Na2CO3 + H2O → 2Na+ + HCO3- + OH-
呢2條eqt都無錯,,

(2)證明左Na2CO3係alkali,, 因為放OH- (p.s. 維基也找到..)
問題黎啦... 共3題

a) 點解(1)唔係純neutralization (i.e. 放左CO2)??
b) NaHCO3也是alkali?? 還是只是alkaline?? (請附eqt.)
c) CaCO3 / Ca(HCO3)2又算alkali嗎?? (請附eqt.)

回答 (1)

cheungwaito

2008-05-19 5:47 am

✔ 最佳答案

(a) I am not sure....but it is an alkaline neutralization

sodium carbonate is a weak base, which do not dissociate completely
also, the system is a buffer system,
for the first euqtion it involves 2 steps, both are neutralization
1st carbonate + acid = hydrogencarbonate + salt
2nd hydrogencarbonate + acid = CO2 + salt

carbonate and hydrogencarbonate forms a buffer system, which, can resist
pH change, therefore it is not a pure neutralization.

(b) yes, hydrogencarbonate is an alkali. (pH above 7)
it is a proton acceptor, thus it is a base
HCO3 - + H+ = CO2 + H2O
the above is a neutralization

(c) yes, they are alkali. Their pH are above 7, both can react with acid , i.e.
both can be neutralized

the equation is the same as above

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