Understanding the solubility of chemical compounds is essential for laboratory work, industrial processes, and academic research. Potassium Bromide (KBr) is a widely used salt in infrared spectroscopy and photography. One of the most common questions in general chemistry involves determining its solubility at specific temperatures, such as 23°C.
KBr Solubility Calculator
Enter the temperature to find the solubility of Potassium Bromide in water (g per 100g of H₂O).
What is Potassium Bromide?
Potassium bromide (KBr) is a chemical compound consisting of potassium and bromine. Historically used as a sedative and anticonvulsant in the 19th and early 20th centuries, it remains a staple in modern science. It is highly soluble in water and forms clear, colorless crystals that are transparent to infrared light, which is why it is often used to create "KBr pellets" for IR spectroscopy samples.
The Relationship Between Temperature and Solubility
For most solid solutes like KBr, solubility increases as the temperature of the solvent increases. This is because the addition of heat provides the energy required to break the crystalline lattice of the salt. To calculate the solubility at a specific point like 23°C, we look at the standard solubility curve for KBr in water.
Standard Reference Data for KBr
- 0°C: 53.5 g/100g H₂O
- 20°C: 65.2 g/100g H₂O
- 40°C: 75.5 g/100g H₂O
- 60°C: 85.5 g/100g H₂O
- 80°C: 95.0 g/100g H₂O
Calculating Solubility at 23°C
Since 23°C falls between the known data points of 20°C and 40°C, we can use linear interpolation to find a highly accurate estimate.
The Interpolation Formula
The formula for linear interpolation is:
y = y1 + ((x - x1) / (x2 - x1)) * (y2 - y1)
Where:
- x is the target temperature (23°C)
- x1, y1 is the lower point (20°C, 65.2g)
- x2, y2 is the upper point (40°C, 75.5g)
Plugging in the numbers:
Solubility = 65.2 + ((23 - 20) / (40 - 20)) * (75.5 - 65.2)
Solubility = 65.2 + (3 / 20) * 10.3
Solubility = 65.2 + 1.545 = 66.745 g/100g H₂O.
Factors Affecting Solubility
While temperature is the primary driver for KBr solubility in water, other factors can influence the results in a real-world environment:
- Purity of the Solvent: Dissolved minerals in tap water can slightly decrease the capacity for KBr to dissolve compared to distilled water.
- Pressure: For solids in liquids, pressure changes have a negligible effect on solubility.
- Agitation: Stirring does not change the amount that can dissolve (the saturation point), but it significantly increases the rate at which the salt reaches that point.
Laboratory Applications
When preparing a saturated solution of potassium bromide at room temperature (which is often cited as 23°C in many controlled labs), it is best to add roughly 70 grams of KBr to 100mL of water, stir thoroughly, and allow the excess to settle. This ensures the solution is fully saturated at that specific thermal equilibrium.