Percent concentration of 500 μM of H2O2

Question

What is the percent concentration of hydrogen peroxide which has a concentration of $500~\mu\mathrm{M}$?

Is $500~\mu\mathrm{M}$ $\ce{H2O2}$ toxic to the eyes?

A particular honey has a concentration of $\ce{H2O2}$ of $500~\mu\mathrm{M}$ after a 24-hour incubation time, after it has been diluted. I am trying to figure out what the concentration is in percent (%).

I recalculated and the result is actually $0.00153\%$ for $500~\mu\mathrm{M}$. $0.0012\%$ is the equivalent to $400~\mu\mathrm{M}$, but I need someone to confirm this. Someone on researchgate wrote that $30\%$ of $\ce{H2O2}$ is $9.8~\mathrm{M}$.

Answer 1

I will assume you are asking for percent mass/volume, $\mathrm{g/ml}$, since to calculate percent mass/mass you need the density of the liquid (unless you assume it is water which is $1~\mathrm{g/ml}$ so will give the same answer).

We have $500~\mu\mathrm{M}$ of hydrogen peroxide, which means we have $500~\mu\mathrm{mol}$ of hydrogen peroxide per 1 litre of solution. $500~\mu\mathrm{mol} = 0.0005~\mathrm{mol}$. Now you can work out the molar mass of hydrogen peroxide and multiply it by the number of moles to get the mass of hydrogen peroxide per litre of solution. This gives $0.017~\mathrm{g}$. There are $1000~\mathrm{ml}$ in 1 litre. So you have $0.017~\mathrm{g}/1000~\mathrm{ml} = 0.000017 = 0.0017\%$.

For your question about whether hydrogen peroxide is toxic to the eyes, you can search the internet for the Materials Safety Data Sheet (MSDS) of hydrogen peroxide (Sigma-Aldrich is a good site to search). This contains all the hazards associated with this chemical, and when you do laboratory work you always have to look these up for each chemical before you start a reaction. The MSDS states that hydrogen peroxide can cause severe eye damage, among other hazards.

Answer 2

Regarding toxicity: Honey solutions are actually sometimes used in ophthalmology. There is a company called Optimel that sells 16% manuka honey eye drops OTC for treating dry eye syndrome but note that very little or almost nothing H2O2 is released in manuka honey. Another example is this case report in which they used a 25% w/v silver fir honey solution as eye drops for the treatment of a corneal ulcer with success.

I found an article in which the use of H2O2 in the eyes in various concentrations is outlined. At the concentration below 60 ppm (the lowest safe point) the eye’s natural enzyme mechanisms can break down the small amount of H2O2 making it safe.

So a 25% w/v (silver fir) honey solution contains around 0.00085% or 8.5 ppm of H2O2 which would make it safe for the use in eyes.