6 ms·

If I have a 91% currently, can I just add water to dilute it? Do I need some kind of special water vs what’s from my tap?

tldmanagement 7y ago
It’s preferable to used sterile distilled water or water that has been boiled according to the WHO. https://www.who.int/gpsc/5may/Guide_to_Local_Production.pdf https://www.who.int/gpsc/5may/Guide_to_Local_Production.pdf
- azinman2 7y ago
  Thank you!
deleted 7y ago
[deleted]
p1mrx 7y ago
If you mix cheap booze (e.g. 40% vodka) with 91% isopropyl, you can make a larger quantity of 70% sanitizer than you could with pure water. Mixing on a scale can be pretty confusing, though, because the percentages are (I think) by volume, and water and alcohol have different densities.
- mdturnerphys 7y ago
  It can also be confusing if you check the volumes after mixing, since the water-alcohol interaction decreases the molecular spacing and the total volume. V_(water + alcohol) < V_water + V_alcohol. https://en.wikipedia.org/wiki/Alcohol_by_volume#Volume_change https://en.wikipedia.org/wiki/Alcohol_by_volume#Volume_chang...
- hutzlibu 7y ago
  Any booze you buy has a huge tax on it, so you would be better of, with cleaning alcohol.
  - mokus 7y ago
    Normally, yes. Today, I’m not even able to find isopropyl at many stores. I’m actually thinking about ordering flux cleaner for my soldering, for the first time in my life.
    - ficklepickle 7y ago
      You can get methanol pure and cheap from auto stores (in regions that get cold, anyway). Just try not to get it on your skin or breath the fumes too much. It's quite a bit more toxic. Definitely don't use it to make hand sanitizer.
- azinman2 7y ago
  But then don’t you lose the qualities that make water important in disinfecting?
  - p1mrx 7y ago
    What do you think the other 60% of vodka is?
- vikramkr 7y ago
  And also ethanol vs isopropanal, might add a bit of complexity
Wistar 7y ago
Diluting Down 99% IPA to the desired concentration: A Lesson in Math & Chemistry https://onsenlabs.com/blogs/blog/isopropyl-alcohol-ipa-aka-iso-shortage-how-labs-dilute-99-ipa-with-water-for-a-more-efficient-conservative-cleaning-experience https://onsenlabs.com/blogs/blog/isopropyl-alcohol-ipa-aka-i... Also includes a dilution table for 91%.
- beervirus 7y ago
  Their table seems reasonable, but the first example they work through is wrong. >Example 1: >Suppose a scientist has a bottle of 99% IPA (C1) that they want to dilute down to 70% (C2). To end with 50mL of 70% IPA (V2), how much volume of 99% IPA should they use and dilute with distilled water to create the final solution? >99% x V1 = 70% x 50mL = 35.35mL >Thus, adding 35.35mL of distilled water to 14.65mL of 99% IPA creates a 50mL solution of 70% IPA. (They reversed the water and IPA quantities.)
  - Wistar 7y ago
    Good catch!
  - Dylan16807 7y ago
    The table's garbage. It's showing the total volume as exactly equal to water volume plus alcohol volume, out to four digits. That's not how it works. A mixture of water and alcohol (whether ethanol or isopropyl) gets more compact because the different molecules can pack together better, by up to a few percent.
    - Wistar 6y ago
      Is it inaccurate enough that it cannot be used to safely create disinfectant-grade 70% dilutions from 99% or 91%?
      - beervirus 6y ago
        If you're measuring things by slopping them into a measuring cup instead of weighing them out to the milligram, you'll never know the difference.
simonblack 7y ago
Yes. Just dilute it in the correct ratio to bring it to the required concentration. The purity of the water is not particularly important. (If it's drinkable, it's perfectly OK to use. Go ahead and use tap water if you want.) The formula is simple: 'Concentration Required' divided by 'Concentration Supplied' multiplied by 'Final quantity Required'. That will give you the amount of 91% isopropyl alcohol you need to measure out, then dilute to the 'Final quantity required' with your tap water. (Or better still, use Distilled Water or De-Ionized Water.) So: You want 500 mls of isopropyl alcohol 70% and you have isopropyl alcohol 91% on hand - Concentration required = 70% Concentration Supplied = 91% Final quantity required = 500 mls Amount of isopropyl alcohol 91% needed = 70 / 91 x 500 = 384.6 mls Dilute that 384.6 mls to 500 mls with water and there's your 500 mls of isopropyl alcohol 70%. Of course, you don't need to be quite so finicky when it comes to biological measurements. You'd round off the 384.6 mls to 385 mls (or even 380 mls or 390 mls) without any appreciable loss of effectiveness.

tldmanagement 7y ago

It’s preferable to used sterile distilled water or water that has been boiled according to the WHO. https://www.who.int/gpsc/5may/Guide_to_Local_Production.pdf https://www.who.int/gpsc/5may/Guide_to_Local_Production.pdf

azinman2 7y ago
Thank you!

deleted 7y ago

[deleted]

p1mrx 7y ago

If you mix cheap booze (e.g. 40% vodka) with 91% isopropyl, you can make a larger quantity of 70% sanitizer than you could with pure water. Mixing on a scale can be pretty confusing, though, because the percentages are (I think) by volume, and water and alcohol have different densities.

mdturnerphys 7y ago
It can also be confusing if you check the volumes after mixing, since the water-alcohol interaction decreases the molecular spacing and the total volume. V_(water + alcohol) < V_water + V_alcohol. https://en.wikipedia.org/wiki/Alcohol_by_volume#Volume_change https://en.wikipedia.org/wiki/Alcohol_by_volume#Volume_chang...
hutzlibu 7y ago
Any booze you buy has a huge tax on it, so you would be better of, with cleaning alcohol.
- mokus 7y ago
  Normally, yes. Today, I’m not even able to find isopropyl at many stores. I’m actually thinking about ordering flux cleaner for my soldering, for the first time in my life.
  - ficklepickle 7y ago
    You can get methanol pure and cheap from auto stores (in regions that get cold, anyway). Just try not to get it on your skin or breath the fumes too much. It's quite a bit more toxic. Definitely don't use it to make hand sanitizer.
azinman2 7y ago
But then don’t you lose the qualities that make water important in disinfecting?
- p1mrx 7y ago
  What do you think the other 60% of vodka is?
vikramkr 7y ago
And also ethanol vs isopropanal, might add a bit of complexity

Wistar 7y ago

Diluting Down 99% IPA to the desired concentration: A Lesson in Math & Chemistry https://onsenlabs.com/blogs/blog/isopropyl-alcohol-ipa-aka-iso-shortage-how-labs-dilute-99-ipa-with-water-for-a-more-efficient-conservative-cleaning-experience https://onsenlabs.com/blogs/blog/isopropyl-alcohol-ipa-aka-i... Also includes a dilution table for 91%.

beervirus 7y ago
Their table seems reasonable, but the first example they work through is wrong. >Example 1: >Suppose a scientist has a bottle of 99% IPA (C1) that they want to dilute down to 70% (C2). To end with 50mL of 70% IPA (V2), how much volume of 99% IPA should they use and dilute with distilled water to create the final solution? >99% x V1 = 70% x 50mL = 35.35mL >Thus, adding 35.35mL of distilled water to 14.65mL of 99% IPA creates a 50mL solution of 70% IPA. (They reversed the water and IPA quantities.)
- Wistar 7y ago
  Good catch!
- Dylan16807 7y ago
  The table's garbage. It's showing the total volume as exactly equal to water volume plus alcohol volume, out to four digits. That's not how it works. A mixture of water and alcohol (whether ethanol or isopropyl) gets more compact because the different molecules can pack together better, by up to a few percent.
  - Wistar 6y ago
    Is it inaccurate enough that it cannot be used to safely create disinfectant-grade 70% dilutions from 99% or 91%?
    - beervirus 6y ago
      If you're measuring things by slopping them into a measuring cup instead of weighing them out to the milligram, you'll never know the difference.

simonblack 7y ago

Yes. Just dilute it in the correct ratio to bring it to the required concentration. The purity of the water is not particularly important. (If it's drinkable, it's perfectly OK to use. Go ahead and use tap water if you want.) The formula is simple: 'Concentration Required' divided by 'Concentration Supplied' multiplied by 'Final quantity Required'. That will give you the amount of 91% isopropyl alcohol you need to measure out, then dilute to the 'Final quantity required' with your tap water. (Or better still, use Distilled Water or De-Ionized Water.) So: You want 500 mls of isopropyl alcohol 70% and you have isopropyl alcohol 91% on hand - Concentration required = 70% Concentration Supplied = 91% Final quantity required = 500 mls Amount of isopropyl alcohol 91% needed = 70 / 91 x 500 = 384.6 mls Dilute that 384.6 mls to 500 mls with water and there's your 500 mls of isopropyl alcohol 70%. Of course, you don't need to be quite so finicky when it comes to biological measurements. You'd round off the 384.6 mls to 385 mls (or even 380 mls or 390 mls) without any appreciable loss of effectiveness.