6 ms·

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-la

by Wistar 6y 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 6y 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 6y ago
  Good catch!
- Dylan16807 6y 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.
      - Dylan16807 6y ago
        It won't matter for "eh somewhere between 55% and 75% is fine", but if you have a good measuring cup you could easily see the difference in volume. I don't know why the chart assumes you're measuring down to thirds of milligrams, though...
azinman2 6y ago
That didn’t answer my question about what kind of water to use.
- deleted 6y ago
  [deleted]
- Gibbon1 6y ago
  Frankly I don't think it matters at all. Consider if you wipe down a surface with 70% IPA it'll dissolve all sorts of crud.
- chiph 6y ago
  Tap water will be fine. The alcohol you're diluting will disinfect it. If you want to be ultra-sure, then use distilled. But be aware it's also bought by people who use it for their CPAP machines, so don't go nuts.
  - aidenn0 6y ago
    It depends on where you are; my tap water has extremely high mineral (>40 gpg) content, and I could definitely see that interfering with its disinfectant properties (not to mention leaving a residue behind).
- Wistar 6y ago
  It repeatedly says "distilled water." "… we find that they would need to add 3.31 ounces of (distilled) water with 8 ounces of 99% IPA …"

by Wistar 6y ago

beervirus 6y 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 6y ago
Good catch!
Dylan16807 6y 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.
    - Dylan16807 6y ago
      It won't matter for "eh somewhere between 55% and 75% is fine", but if you have a good measuring cup you could easily see the difference in volume. I don't know why the chart assumes you're measuring down to thirds of milligrams, though...

azinman2 6y ago

That didn’t answer my question about what kind of water to use.

deleted 6y ago
[deleted]
Gibbon1 6y ago
Frankly I don't think it matters at all. Consider if you wipe down a surface with 70% IPA it'll dissolve all sorts of crud.
chiph 6y ago
Tap water will be fine. The alcohol you're diluting will disinfect it. If you want to be ultra-sure, then use distilled. But be aware it's also bought by people who use it for their CPAP machines, so don't go nuts.
- aidenn0 6y ago
  It depends on where you are; my tap water has extremely high mineral (>40 gpg) content, and I could definitely see that interfering with its disinfectant properties (not to mention leaving a residue behind).
Wistar 6y ago
It repeatedly says "distilled water." "… we find that they would need to add 3.31 ounces of (distilled) water with 8 ounces of 99% IPA …"