# NaOH Normality Slowly Changing

Our lab uses a sodium hydroxide solution of a (theoretically) known normality (0.8000 - 1.0000) to titrate product samples for quality control. However, we suspect that the normality of the $\ce{NaOH}$ left in the burette/tubing connected to our container is changing if we let it sit (our tests come out wrong, and the answers seem to get better if we run a couple of burettes worth of $\ce{NaOH}$ out first). I expect it's absorbing moisture from the air, but I don't know for sure.

We've tried different container types and we've put a desiccant in line with the tubing to absorb stray moisture (which it seems to be doing, there's been an observable color change), but the situation remains that we need to just throw out up to 200mL of $\ce{NaOH}$ any time we need to run a test. Does anyone on here have any recommendations for countering this normality drift?

• As @iad22agp said, it's most definitely absorption of CO2; NaOH is known to do this. Maybe instead of throwing it out, you could titrate the NaOH before using it? – orthocresol Jul 30 '15 at 19:21