[radeon4u]

is mixture of NaOH and CO2 in water buffer?

[Mitch]

No, read your book.

[AWK]

In some cases - yes, but on the condition that molar ratio CO2/NaOH is greater then 0.5. Mixtures H2CO3/NaHCO3 (ratio .GT. 1) or NaHCO3/Na2CO3 (ratio between 0.5 and 1) form buffer solutions

[Borek]

Genral idea is that you must have acid and conjugated base in the solution. In the case of the carbinc acid there are two such pairs. When you dissolve CO2 in NaOH - depending on the CO2 and NaOH amounts - you will get mixtures containg all three possible forms of carbonic acid - H2CO3, HCO3(-) and CO3(2-). As AWK stated whether they will form a buffer depends on their ratio, which in turn depends on the ratio of NaOH and CO2 used at the beginning.