Household bleach is a common chemical used for cleaning and disinfecting. This product is an aqueous solution of sodium hypochlorite (NaOCl) diluted in water. When this liquid is introduced into water, its physical behavior—whether it sinks or floats—is determined by a simple comparison of density.
Standard Household Bleach Always Sinks
The definitive answer to the question of whether bleach sinks or floats is that standard household bleach always sinks in pure water. This behavior is directly related to the concept of density, which is the mass of a substance contained within a specific volume. Standard household bleach typically contains a concentration of sodium hypochlorite between 5% and 8% by weight and has a density ranging from approximately 1.07 to 1.10 grams per milliliter (g/mL).
In contrast, pure water has a density of about 1.0 g/mL. Because the bleach solution’s density is greater than that of water, it displaces the water and moves downward. If poured carefully into a container of water, the denser bleach will stream toward the bottom, forming a temporary, distinct layer beneath the less dense water until the two liquids eventually mix and diffuse. The specific gravity, which is the ratio of the substance’s density to the density of water, is consequently greater than 1.0 for bleach, confirming its tendency to sink.
Understanding Why Bleach is Denser
The reason bleach is denser than pure water lies in its composition as a solution, which is a uniform mixture of a solvent and one or more solutes. Household bleach uses water as the solvent, and the primary solute is sodium hypochlorite, a salt. The addition of this dissolved solid compound and other stabilizing agents, like sodium hydroxide, increases the total mass of the liquid without significantly changing its volume.
Density is calculated by dividing mass by volume. Since the water molecules are holding the heavier sodium and hypochlorite ions in suspension, the same volume of bleach solution contains more mass than the same volume of pure water. This increase in mass per unit of volume is what makes the overall bleach solution heavier than water. The density of a 5% sodium hypochlorite solution is cited to be around 1.07 g/mL, which is a seven percent increase in mass compared to pure water for the same volume.
How Concentration and Temperature Alter Density
The exact density of a bleach solution changes based on two primary factors: concentration and temperature. Concentration refers to the percentage of sodium hypochlorite dissolved in the water, which is the most significant factor affecting density. Industrial-strength bleach, which can contain up to 15% sodium hypochlorite, has a higher density, sometimes reaching 1.21 g/mL.
Conversely, heavily diluted household bleach will have a density that approaches that of pure water. As the concentration of dissolved salts decreases, the solution becomes less dense. Temperature also plays a role, though typically a minor one in household settings. As with most liquids, bleach solution expands slightly when heated, causing its density to decrease. However, as long as the solution contains a measurable amount of dissolved sodium hypochlorite, it will remain denser than pure water and continue to sink.