Calcium chloride (\(\text{CaCl}_2\)) is a common inorganic salt used for de-icing roads, controlling dust, and serving as a refrigerant brine in industrial cooling systems. When dissolved in water, the resulting liquid is a brine solution. The weight of a gallon is not fixed; it depends entirely on the concentration of the dissolved calcium chloride, which dictates the final density.
Understanding Density and Concentration
Density defines the weight of any liquid per unit volume. When calcium chloride is mixed with water, the salt particles dissolve and occupy spaces between the water molecules. This process adds significant mass to the total volume without causing a proportional increase in the volume itself.
This increase in mass relative to volume makes a gallon of \(\text{CaCl}_2\) brine weigh more than a gallon of plain water. For example, a \(30\%\) \(\text{CaCl}_2\) solution will be substantially heavier than a \(10\%\) solution. The higher the concentration of the dissolved salt, the denser the brine becomes.
To standardize this measurement, specific gravity (\(\text{SG}\)) is often used. Specific gravity is a unitless ratio comparing the density of the brine to the density of pure water. Increasing the concentration of \(\text{CaCl}_2\) directly increases the solution’s specific gravity, which determines the final weight per gallon.
Calculating Weight Using Specific Gravity
Specific gravity provides the necessary factor to calculate the weight of any given volume of \(\text{CaCl}_2\) brine. Since one US gallon of water weighs approximately \(8.34\) pounds, the specific gravity acts as a multiplier against this baseline value. The formula for determining the weight of a gallon of brine is: Weight per Gallon equals Specific Gravity multiplied by \(8.34\) pounds.
To use this calculation, the specific gravity value for the exact concentration of the brine must be known. Manufacturers provide detailed concentration tables that correlate the percentage of \(\text{CaCl}_2\) by weight to its corresponding specific gravity. For instance, a \(29\%\) calcium chloride solution may have a specific gravity of \(1.28\), meaning it is \(1.28\) times heavier than water. Calculating the weight of a gallon of this \(29\%\) solution involves multiplying \(1.28\) by \(8.34\) pounds.
How Temperature Affects Volume and Weight
While concentration is the major factor, temperature acts as a secondary influence on the weight of a gallon of brine. Like most liquids, \(\text{CaCl}_2\) solutions are subject to thermal expansion and contraction. When the liquid is heated, its volume expands slightly.
Conversely, when the solution is cooled, its volume contracts. Since the mass of the salt and water remains constant, this change in volume means that a measured gallon will weigh differently at various temperatures. For precise applications, the temperature must be factored into the final density calculation.
The effect is generally minor compared to concentration, but it is measurable in industrial settings. For instance, a \(32\%\) \(\text{CaCl}_2\) brine may weigh \(11.20\) pounds per gallon at \(0\) degrees Fahrenheit, but only \(11.15\) pounds per gallon at \(20\) degrees Fahrenheit. Specific gravity tables often include temperature specifications for accurate measurement.
Typical Weights in Practical Applications
Common applications for \(\text{CaCl}_2\) brines involve specific, pre-determined concentrations, allowing for the use of established weight values. A low-concentration brine, such as a \(15\%\) solution used in swimming pool maintenance or industrial cooling systems, weighs approximately \(10.09\) pounds per gallon at \(0\) degrees Fahrenheit. This represents an increase of nearly two pounds compared to a gallon of plain water.
For dust control on unpaved roads, a medium-to-high concentration is typically required, such as a \(29\%\) solution. This concentration often results in a weight of around \(10.7\) pounds per gallon. The highest concentrations are frequently used for de-icing highways and creating low-temperature refrigeration brines.
A \(32\%\) \(\text{CaCl}_2\) solution, common for liquid de-icers, is one of the heaviest practical brines. This solution exhibits a specific gravity of around \(1.30\) and weighs approximately \(10.89\) to \(11.20\) pounds per gallon, depending on the exact temperature. These established weight values are fundamental for accurate dosing and application of the brine.