# What are the best cleaning agents for carbon residues on glassware?

## Introduction

Recenly I wanted to isolate some ascorbic acid (Vitamin C or chemically - $\ce{C6H8O6}$). I've put the filtered solution (I had to filter it because of the binder) in a flask and heated it. It didn't go as planned because then I didn't know that ascorbic acid decomposes at high temperatures, but I still decided to keep the product of the reaction. I left it on a hotplate at a high temperature and it all went back to carbon because it was there for too long (It was dehydrated).

## The cleaning agent that I know of - $\ce{NaOH}$

I used a saturated solution of $\ce{NaOH}$ to clean it but there were still some flakes stuck on the wall that I couldn't reach.

It worked well for me - cleaned ~90% of the residue.

## The question

Are there any other cleaning agent that'll work better than aqeous Sodium Hydroxide?

## 1 Answer

Are there any other cleaning agent that'll work better than aqeous sodium hydroxide?

Yes, but I would not recommend them to anybody running experiments at home!

Back in the days in the lab we used arm-deep tanks filled with a saturated solution of potassium hydroxide in isopropanol to soak dirty flasks. You need long (!) chemical-resistant gloves and once in a while, the whole mess has to be discarded and replaced. Down the sink is not an option ;-)

And there is piranha solution, a mixture of 30% hydrogen peroxide and concentrated sulfuric acid. While is is effective, it is infamous for going off with a bang, see this report.

To sum it up: Stay with the sodium hydroxide solution. Don't risk your health and don't screw up your own environment to rescue a spoiled flask.