Hand Sanitiser Ratio problem

[flawless101]

Hi,

I am trying to make some Hand Sanitiser at home.
The ingredients I am using are as follows:
70% Rubbing Alcohol.
Glycerin
Alo Vera Gel.

If the level of alcohol drops below 60% then the Hand Sanitiser won't kill germs.
I need to add the Glycerin and the Alo Vera gel (to make it less runny and as a moisturiser).

What volume of each can I use to make sure that the alcohol level in the final solution is at least 60%.

Can anyone help please?

 

[tkhunny]

Okay, one for free, just to help save society from COVID-19

If your alcohol is 70% of the mixture, that leaves 30% for other stuff. Your task is to add more "other stuff" and keep the alcohol over 60%.

It might be easier with am example.

100 units of Alcohol Mixture contains
----- 70 units of alcohol and
----- 30 units of other stuff.

Thus, if you are shooting for 60%, we get (70 units Alcohol)/(100 units mixture + ??? Units of New stuff) = 0.60

Algebra: 70 alcohol = 0.60*(100 + ???) = 60 + 0.60???
More algebra: 70 - 60 = 10 = 0.60???
Still more: ??? = 10 / 0.60 = 16.66 (rounding DOWN so we don't accidentally go under.)

In case that doesn't quite make enough sense: If you have 1 litre of 70% alcohol mixture, you can add 1/6 litre of the other stuff and hit 60% right on. Less than 1/6 litre and you're over 60%

Check: 70 / (100 + 16.66) = 70 / 116.66 = 0.60003428767358134750557174695697 -- Just BARELY over 60%.

Word of Warning: Material density and physical interaction may be problematic. If you mix equal amounts of water and alcohol, you DON'T get a total volume equal to the sum of the individual volumes; it's less! Will the same thing happen with your ingredients? Will it go the other way? In any case, I'd stay away from 60% on purpose, just to avoid any question. Maybe keep it to 10 units of Glycerin and Aloe Vera Gel. If you wish to get particularly precise, you should consult a real chemist. That would not be me.

 

[flawless101]

You're a star
Thank you.
When I did the maths I got something similar but became thoroughly confused when I saw a few Youtube videos.
In these videos they were adding two cups of 70% rubbing alcohol to one cup of Aloe Vera gel (I think they confused 70% for 99%).
When I did the maths I worked out that the percentage alcohol was around 46% than 50% for these videos and did wonder whether my maths had let me down.