Turn baking soda into washing soda by placing a few tablespoons of baking soda on a metal baking sheet and heating it in an oven at 200 degrees Fahrenheit for around an hour. After an hour, allow the washing soda to cool completely before using it.
Converting baking soda to washing soda is so simple because baking soda, known chemically as sodium bicarbonate, is very unstable at high temperatures. When exposed to heat, sodium bicarbonate breaks down, forming water, carbon dioxide and sodium carbonate, also known as washing soda, as products. The water and carbon dioxide are gases at these temperatures, leaving washing soda as the only product on the baking sheet.
Washing soda's primary use is as a water softener for laundry. When dissolved in water, washing soda's carbonate ions bond with metal ions already present in the water. Without washing soda, the metal ions bond with the laundry detergent, decreasing its effectiveness. In areas with very hard water, which has large concentrations of metal ions in the water supply, sodium carbonate also prevents clogs caused by metals accumulating inside of pipes, coffee makers and other household appliances that use water.
Washing soda is a more hazardous chemical than baking soda. While baking soda is alkaline, washing soda is highly alkaline, and very concentrated solutions can irritate and damage skin and eyes.