I just looked up prices on Amazon. You can get two 55 oz. boxes of Arm and Hammer washing soda for 18.9 cents per ounce. A 5 lb. bag of Arm and Hammer baking soda is 14.6 cents per ounce, which is about 77% of the washing soda price. I don’t know what the energy cost would be to convert the baking soda to washing soda. You can decide for yourself whether the cost difference is important to you.
2NaHCO3 → Na2CO3 + H2O + CO2
So 168 lbs of Baking Soda will give you 106 lbs of Washing Soda.
Or 1.6 lb of Baking Soda gives 1 lb of Washing Soda
Cost of 4 lb Baking Soda at Walmart = $2.50 (Robot or human?)
or per pound = $0.63
Cost of 3.44 lb Washing Soda at Walmart = $4 (Robot or human?)
or per pound = $1.16
So you will need 1.6lbs of Baking soda worth $1 (0.63 * 1.6 = $1) to make 1 lb of Washing soda which is sold at $1.16 a pound. Sure you will save 16c per pound but I am pretty sure you will spend a lot more on electric/gas costs.
Covid leaves time on my hand, so I calculated the heating costs too.
1 lb of Washing Soda will 500 need BTUs to be formed by heating Baking Soda. (https://www.solvay.us/en/binaries/HeatEffects_of_the_TronaSystem-237230.pdf washing soda is also called soda ash)
A gas oven has around 6% cooking efficiency, (Efficient Cooking - GreenBuildingAdvisor)
So with gas, you’ll need 500/0.06= 8,333 BTUs. Residential price of Natural Gas is about $10/ Million BTU. So for 8333 BTUs, the cost is 0.8c. ($0.008). So 0.8c is added to the cost per pound of washing soda.
Electric ovens are about 14% efficient (Efficient Cooking - GreenBuildingAdvisor). So you will need 500/0.14 = 3,571 BTUs which is approximately 1 kWh. 1 kWh is about 12c.
So @Squink you were right and I was wrong. If you use baking soda from Walmart and use either gas or electricity to convert it to Washing Soda, you will indeed save some money. (considering today’s energy prices).
am77494:
Last time I needed washing soda, the grocery store didn’t have any, and the hardware store wanted like $6 a pound for it. I didn’t need 6.8 pounds of it as Amazon would provide. So making it at home on a cool day was my best option.
If I ever need a lot, say for cleaning walls, the Amazon price might well overcome the baking hassle.
Oh yes, Motogirl, Borax is wonderful stuff if you’ve got hard water. It chelates metals that form insoluble salts with detergents. With 280 ppm Calcium plus counterion in my water, a scoop of borax goes in every load.
I’m fascinated by everyone’s interest in the calculations!
In the winter I MIGHT be willing to convert baking soda to washing soda but right now I don’t want to heat up the house by running the oven.
Regardless, if I am doing the math right, I’d end up paying more to buy baking soda and convert it.
$3.49 for a 64 oz box of baking soda (the biggest size easily available to me), which would become 1.6 lb of washing soda at $0.13 / oz
$0.23/ kWh to run my electric oven ($0.11/kWh for the electricity + $0.12/kWh for the “delivery services”) - if it takes 4 kWh to convert the baking soda to washing soda I’m paying $0.92 for electricity
$3.49 + $0.92 = $4.41 to acquire 25.6 oz of washing soda, or $0.17 / oz
Compared with $5.19 for a 55 oz box of washing soda - $0.0943 / oz
(Borax is infinitesimally cheaper at $0.0904)
Please check my math!
P.S. I’m aware that I could probably get better prices for large boxes of baking soda or washing soda if I could shop around, or by ordering from Amazon, but my ability to shop around locally is quite limited, and I’m not willing to order from Amazon at the moment.