Laundry pH with Borax

[svenpup]

Now that I have been indoctrinated into BBB and have Borax around the house, I have started using it for it's intended purpose: a laundry booster. I seems to make towels fluffier and help remove odors.

My question is; how high does the pH get when I use Borax? I have an HE washer so there is only about a gallon of water. The directions say to use 1/2 cup. It seems like this would be a huge pH increase in such a small volume of water based on how much you need to add to, say a 20,000 gallon pool to raise pH.

 

[benavidescj]

Well, assuming you start with a pH of around 7.5, the pool calculator says the pH should end up at 14.7 for 1/2 cup in one gallon of water. Since the pH scale ends at 14 I don't think that is correct.

 

[Circle-D]

I did not do the math on the PH levels, but I think most HE washer use 10-20 Gallons per wash. Not sure when it releases the Borax and how much water that is mixed with though.

Chris

 

[chem geek]

1/2 cup of Borax in 1 gallon of water would raise the pH from 7.5 to 9.05. Interestingly, in 10 gallons, it would raise the pH to around 9.12. Borax is a weak base, not a strong one like lye, so the pH will be self-limiting towards it's pKa value since what is added is effectively equal parts of boric acid and borate ion salt (adjusted for ionic strength which is why the pH is higher at a somewhat lower concentration). The Pool Calculator has an approximate pH calculation so does not take into account such subtleties.

[WARNING: Technical description follows]

20 Mule Team Borax is sodium tetraborate decahydrate so the reaction when added in large quantities is the following:

Na₂B₄O₇•10H₂O ---> 2Na⁺ + 4B(OH)₃ + 2OH^- + 3H₂O
Sodium tetraborate decahydrate ---> Sodium ion + Boric acid + Hydroxyl ion + Water

4B(OH)₃ + 2OH^- ---> 2B(OH)₃ + 2B(OH)₄^-
Boric acid + Hydroxyl ion ---> Boric acid + Borate ion

You can see that the net effect of adding 20 Mule Team Borax is to add equal parts of boric acid and its salt of borate ion. These two are equally balanced in quantity at a pH that is equal to the acid equilibrium constant (pKa).

Richard

 

[Beez]

1/2 cup of Borax in 1 gallon of water would raise the pH from 7.5 to 9.05. Interestingly, in 10 gallons, it would raise the pH to around 9.12. Borax is a weak base, not a strong one like lye, so the pH will be self-limiting towards it's pKa value since what is added is effectively equal parts of boric acid and borate ion salt (adjusted for ionic strength which is why the pH is higher at a somewhat lower concentration). The Pool Calculator has an approximate pH calculation so does not take into account such subtleties.

[WARNING: Technical description follows]

20 Mule Team Borax is sodium tetraborate decahydrate so the reaction when added in large quantities is the following:

Na₂B₄O₇•10H₂O ---> 2Na⁺ + 4B(OH)₃ + 2OH^- + 3H₂O
Sodium tetraborate decahydrate ---> Sodium ion + Boric acid + Hydroxyl ion + Water

4B(OH)₃ + 2OH^- ---> 2B(OH)₃ + 2B(OH)₄^-
Boric acid + Hydroxyl ion ---> Boric acid + Borate ion

You can see that the net effect of adding 20 Mule Team Borax is to add equal parts of boric acid and its salt of borate ion. These two are equally balanced in quantity at a pH that is equal to the acid equilibrium constant (pKa).

Richard

Uh, OK, but I have a dumb question...how does that affect the laundry in question? In other words, why worry about the pH?

Also, svenpup, I'd be careful adding that much Borax in a front loading washer. Front loaders usually call for very small amounts of detergent compared to top loaders. Course I'm sure you already knew that...

 

[chem geek]

how does that affect the laundry in question? In other words, why worry about the pH?

You don't need to worry about the pH since it doesn't get that high. Borax helps laundry detergent by maintaining a stable higher pH where the detergents operate more effectively. Borax also helps with hard water since borax is a mild metal sequestrant (see this link for more technical details).

 

[svenpup]

Beez...

I'd be careful adding that much Borax in a front loading washer. Front loaders usually call for very small amounts of detergent compared to top loaders.

The instructions on the Borax calls for 1/2 cup for both front and top loaders.

Richard - Thanks for the info. I knew you would know!