Baking Soda Vs. Washing Soda as an Electrolytic Derusting Electrolyte

Last Revised: 5/6/2010


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Introduction

Here are some facts about the differences between Baking Soda and Washing Soda in general. There is probably more here than most people want to know, but many of the electrolytic derusting articles I have seen either give conflicting or incomplete information on the subject.
So I have run my own comparison test, looked around on the web and extracted some information that sorta tells the story.

Why Choose one over the other?

I ran a test to see if one powder works better than the other.
I define "Works Better" as: "draws more current at a fixed voltage and therefore works faster".
First I cut two identical plates (4" X 4 5/8") out of 1/16" thick mild steel to use as positive (anode) electrodes. I polished them with Scotchbrite so they were shiny on both sides. Then I located two rusty items of identical size and level of rustiness (old drifts from an auction pail) to use as the negative electrode (cathode).
Next I poured 2 gallons of tap water into a 4 gallon plastic pail, filling it to 5 1/2" deep. I added 4 tablespoons of baking soda to the water. I hooked up the electrodes and plugged in my homemade battery charger/power Supply. I set it to 15 volts and took an initial current reading. I took a few readings during the first half hour, then waited one hour and took another reading. I continued taking hourly readings for a total elapsed time of 10 hours. At each reading, I reset the voltage to 15, if needed, so I'd be comparing apples and apples.
Then I cleaned the pail up. I installed the other mild steel plate as the positive electrode and used the other rusty piece as the cathode. So, I had an exact duplicate of the previous test, except that I added 4 tablespoons of washing soda.

Conclusion

Washing Soda causes slightly more current to flow over a 10 hour period than Baking Soda does, but probably not enough more to make it worth a special trip to the store.

If you want to see the details of the test I ran, here's my Excel Spreadsheet:
Derusting Electrolyte Strength Test

Baking Soda VS Washing Soda Result
Here you can see the results of the two tests. Both drifts (the parts that I "Derusted") look about the same after the test.
It's the left end of the drifts that I derusted. The shiny right ends are due to my polishing them slightly to get good electrical contact.
About the only difference I can see between the two tests is that the anode plates themselves rusted very differently. The rust on the "Baking Soda" plate is very fine and tightly attached. But the rust on the "Washing Soda" plate is coarse, thicker and very loose. So loose, in fact that about half of the rusty surface slid off the piece as I was moving it from the pail to the floor for this picture.


Some More Stuff About Baking Soda and Washing Soda

(As long as you have read this far, you might as well learn a little about the chemistry)

What is the difference between Baking Soda and Washing Soda?

Washing soda is not baking soda. Here is an excerpt from http://frugalliving.about.com that explains it better than I would have! ;-)
Washing soda should be in the laundry section of your grocery store. It comes in a yellow box, made by Arm & Hammer, but it's NOT baking soda.
If you're interested, washing soda is Sodium Carbonate (Na2CO3),
baking soda is Sodium Bicarbonate (NaHCO3),
and borax is Sodium Tetraborate Decahydrate (Na2B4O7*10H2O), all different chemical compounds.

One of the main questions that we get asked regarding laundry is about the usage of Baking Soda and/or Washing Soda.

The Baking Soda/Washing Soda question pondered . . .

A definition from Dr. Dan Berger (Faculty- Chemistry/Science dept. at Bluffton College) gives a bit of understanding regarding the primary difference between Washing Soda (Sodium Carbonate) and Baking Soda (Sodium Bicarbonate).

". . . washing soda will consume two equivalents of acid, while baking soda will only consume one equivalent."

Washing Soda is a stronger base than baking soda, and is in fact, CAUSTIC. This is one reason why it isn't used for baking!
Washing Soda is caustic/alkaline with a pH of 11 (with 7 being neutral). Though it does not give off harmful fumes, you do still need to use/wear gloves when handling it directly as a cleansing agent. In reading about safe household cleaners, it always is recommended to save the Washing Soda for the stubborn stains that you are going to tackle by making a paste. For instance, if speaks about petroleum spills on garage floors . . . grease build-up in your oven . . . y'know, truly STUBBORN STAINS!

Baking Soda is only slightly alkaline with a pH around 8.1 (again, 7 being neutral).

...I personally prefer Baking Soda to Washing Soda for my laundry because it is a much milder alkali and yet, still can lift dirt/grease/urine/poopies off my diapers/laundry effectively to dissolve easily in the wash water. Because it is so very water soluable, it dissolves before its soft crystalline molecules can scratch or damage a surface. The same is NOT TRUE of Washing Soda - because of its extra alkaline, it can eat away at elastic and cloth over time and is also used to rough-up fabric for dying. In fact, Washing Soda has just enough alkaline content to fall short of being labeled non-toxic.

Baking Soda and Washing Soda have the power to neutralize odors, instead of just covering them up.
Most unpleasant odors come from either strong acids (like our baby's urine) or strong bases (fish oils - which we find in some of our mainstream diaper rash ointments). The Baking Soda and Washing Soda deodorizes by bringing both acidic and basic odor molecules into a neutral state.

What is pH?

It is a measure of whether a particular substance is alkaline or acidic based. It is compared to water - which has a neutral base of 7.0. If a substance falls below 7.0 it is considered to be acidic. If a substance rises above 7.0, it is considered to be alkaline. Two examples are Blood and Urine. Blood is slighly alkaline (between 7.35 and 7.45) while urine is slightly acidic (with a pH of about 6.4).


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