Potassium nitrate (KNO3) is a chemical compound that has a variety of applications. Commercially, its most common use is in fertilizer and as an ingredient in black powder. Potassium nitrate is also used as a reagent in many laboratory experiments. The primary reasons for its common use in the laboratory are that it’s easily made and it reacts with many different compounds.
Reactions with Acid
Potassium nitrate reacts readily with acids to produce double exchange reactions. These reactions can be generalized with the following equation: AB + CD -> AD + BC. In this reaction, two compounds exchange one of their ions with each other to form two new compounds.
For example, potassium nitrate reacts with sulfuric acid (H2SO4) to form nitric acid (HNO3) and potassium bisulfate (KHSO4). The following equation shows this reaction: KNO3 + H2SO4 -> HNO3 + KHSO4. Here, the potassium atom is exchanged for one of the hydrogen atoms. The potassium bisulfate drops out of the nitric acid solution as a solid.
Potassium nitrate also has a similar reaction with hydrochloric acid (HCL) to form nitric acid and potassium chloride (HCl) as the following equation illustrates: KNO3 + HCl -> HNO3 + KCl. Again, the salt (potassium chloride will drop out of the acid solution as a solid.
Determine the solubility of potassium nitrate in water. Add potassium nitrate to distilled water while stirring continuously; stop adding potassium nitrate once the chemical becomes saturated and stops dissolving in the water. Filter the solution into an evaporating dish and measure the temperature of the solution. Measure the temperature and carefully heat the solution under low heat. Weigh the potassium nitrate to determine its solubility. You should find that approximately 36 g of potassium nitrate can be dissolved in 100 ml of water at room temperature (25 degrees Celsius).
Make a super-saturated solution of potassium nitrate. Mix a saturated solution of potassium nitrate as before, and heat it gently while continuing to stir. Add additional potassium nitrate until the solution becomes saturated again. Allow the solution to cool and wait for potassium nitrate crystals to appear. Evaporate the water as before and weigh the remaining potassium nitrate crystals. Observe that a modest increase in heat can dramatically increase the solubility of potassium nitrate in water.