Chemistry (Ionic equation)

[匿名]

2010-07-31 9:33 pm

I've just finished reading my textbook about acid.
And I found something that's really cofusing for me.

from the book:
Dilute acid - Reaction with carbonates:
e.g. Sodium carbonate:
chemical formula
Na2CO3(s or aq) + 2HCl (aq) --> 2NaCl (aq) + H2O (l) + CO2(g)
the ionic equation:
CO3^2- (aq) + 2H^+ (aq) --> H2O (l) + CO2 (g)

I thought that the ionic equation should be:
Na2CO3(s or aq) + 2H^+ (aq) --> 2Na^+ (aq) + H2O (l) + CO2 (g)

The book explains that solid Na2CO3 dissolves in water to give CO3^2- (aq) ions, so we write it that way.
But, I just don't understand it.

I really appreciate it if you can give me further explanations. Thanks :)

回答 (1)

andrew

2010-07-31 10:11 pm

✔ 最佳答案

This should be divided into two cases:

The first case is using solid sodium carbonate, the full equation is
Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
Write all reactants and products that are ionized in water in ionic form, i.e.
Na2CO3(s) + 2H⁺(aq) + 2Cl¯(aq) → 2Na⁺(aq) + 2Cl¯(aq) + H2O(l) + CO2(g)
Cancel all dummy ions (which appear on the both sides, i.e. 2Cl¯). The ionic equation of the reaction is
Na2CO3(s) + 2H⁺(aq) → 2Na⁺(aq) + H2O(l) + CO2(g)

The second case is using solid sodium carbonate, the full equation is
Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
Write all reactants and products that are ionized in water in ionic form, i.e.
2Na⁺(aq) + 2CO3²¯(aq) + 2H⁺(aq) + 2Cl¯(aq) → 2Na⁺(aq) + 2Cl¯(aq) + H2O(l) + CO2(g)
Cancel all dummy ions (which appear on the both sides, i.e. 2Na⁺ and 2Cl¯). The ionic equation of the reaction is
CO3²¯(aq) + 2H⁺(aq) → H2O(l) + CO2(g)

Somebody thinks that Na2CO3(s) dissolves in water to give Na2CO3(aq), and thus write the ionic equation is the second case even when Na2CO3(s) is used. However, this is NOT a good practice.

參考: andrew

👍 0 👎 0