Baking soda (sodium bicarbonate) is prepared by bubbling carbon dioxide gas through a solution of ammonia and sodium chloride. Ammonium carbonate is first formed which then reacts with the NaCl to form sodium bicarbonate and ammonium chloride. The sodium bicarbonate is less soluble than the other materials, so it will precipitate out of solution.
Solubility is normally expressed in g/L of saturated solution. However, solubility can also be expressed as the moles per liter. Molar solubility is the number of moles of solute in one liter of saturated solution. In other words, the molar solubility of a given compound represents the highest molarity solution that is possible for that compound. The molar mass of a compound is the conversion factor between solubility and molar solubility. Given that the solubility of Zn(OH) 2 is 4.2 × 10 -4 g/L, the molar solubility can be calculated as shown below:
Solubility data can be used to calculate the Ksp for a given compound. The following steps need to be taken.
The solubility of lead(II) fluoride is found experimentally to be 0.533 g/L. Calculate the Ksp for lead(II) fluoride.
Step 1: List the known quantities and plan the problem .
The dissociation equation for PbF 2 and the corresponding Ksp expression
The steps above will be followed to calculate the Ksp for PbF 2 .
Step 2: Solve .
The dissociation equation shows that for every mole of PbF 2 that dissociates, 1 mol of Pb 2+ and 2 mol of F − are produced. Therefore, at equilibrium the concentrations of the ions are:
Substitute into the expression and solve for the .
Step 3: Think about your result .
The solubility product constant is significantly less than 1 for a nearly insoluble compound such as PbF 2 .
Read the material at ChemTeam.info and do the problems at the end.