posted by Helen .
4.0g of an unknown potassium halide (KX, where X is the halide) is dissolved in 100g of water. The solution freezes at -1.28 degrees Celsius. What is the identity of the halide?
mass of K is 39
so atomic mass of halide is 77, potassium bromide.
do the math a little more carefully than I did in my head.