Sodium bicarbonate, with the chemical formula NaHCO3, is the white powder widely known as baking soda. A similar compound is sodium carbonate (Na2CO3), used as a cleaning agent or an additive during clothes washing. The basic test for the presence of carbonate salts is a reaction with a diluted acid solution that leads to release of bubbles of the gas carbon dioxide and follows the reaction: NaHCO3 + HCl = NaCl + H2O + CO2. An additional test is required to distinguish between sodium bicarbonate and sodium carbonate.
- Two beakers, 15 ml
- Hydrion pH paper
- Solution of hydrochloric acid (HCl), 0.1 molar
- Distilled water
- Plastic pipette
Weigh approximately 2 g of the sample and put the substance in the beaker.
Pour approximately 10 ml of the distilled water into the beaker. Mix the solution with the spoon until the salt dissolves completely.
Pour the half of the solution into the second beaker.
Using a plastic pipette, add about 2 ml of the hydrochloric acid solution into the first beaker. If bubbles of the gas (carbon dioxide) intensely evolve during the reaction, then the sample is a carbonate salt (NaHCO3 or Na2CO3); proceed to the next step.
Cut a piece of the hydrion pH paper about 1.5 inches long.
Holding one end of the paper strip, dip the other end into the solution in the second beaker for 1 to 2 seconds, and then take it out. The part of the paper that has been in the solution will change color.
Compare the color of the pH paper with the pH scale typically printed on the pH paper pack and assign pH of the solution accordingly. If pH is around 8, the sample is sodium bicarbonate. If pH is in the range 9.5 to 10, it is sodium carbonate.
Things You'll Need
- Chemistry; K.W. Whitten, R.E. Davis, L. Peck and G.G. Stanley; Brooks Cole; February 2009.