Chemical Solubility by Rebiaz Studio - Dailymotion

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Solubility is the ability of a solid, liquid, or gaseous chemical substance (referred to as the solute) to dissolve in solvent (usually a liquid) and form a solution. The solubility of a substance fundamentally depends on the solvent used, as well as temperature and pressure.

Transcript

00:00The amount of lead-2-fluoride is dissolved in 250 mL of water until the solution is exactly saturated.

00:08The question is, what is the mass of PbF2, if the solubility product constant of PbF2 is 2.7 x 10-8?

00:19OK, the first step is identification.

00:22The volume of water, V is equal to 0.25 liters.

00:27Ksp of PbF2 is equal to 2.7 x 10-8.

00:34The relative molecular mass of lead-2-fluoride, 207.2 plus 2 x 19.

00:43The result is 245.2 g per mole.

00:49The next step is to analyze the ion equilibrium.

00:56In water, a molecule of lead-2-fluoride ionizes into a Pb2 plus ion and 2 F minus ions.

01:04The Ksp value in saturated and supersaturated solutions is exactly the same.

01:10The following illustration is a supersaturated condition because there is already a precipitate in the solution.

01:17Assume that the number of Pb2 plus ions is S mole.

01:22So the number of F minus ions is 2 S mole.

01:27And the volume of the solution is 1 liter.

01:33So the molarity of Pb2 plus ions is S molar.

01:37And the molarity of F minus ions is 2 S molar.

01:42The next step is to write the chemical equilibrium equation.

01:47A molecule of PbF2 will ionize into a lead ion, 2 fluoride ions.

01:54Now, we can calculate the value of S from the Ksp equation.

01:59Ksp is equal to the concentration of Pb2 plus ions, multiplied by the concentration of F minus ions to the power of 2.

02:09Plugging in the values of ion concentration and Ksp.

02:15For S to the power of 3 is equal to 2.7 times 10 to the power of negative 8.

02:23We can write this equation as S to the power of 3.

02:29Using a calculator, S is about 1.89 times 10 to the power of negative 3.

02:37This value of S is also the value of moles of PbF2 dissolved in 1 liter of water in a perfectly saturated solution.

02:49So, the molarity of PbF2 is 1.89 times 10 to the power of negative 3 molar.

02:58The fifth step is to calculate the mass of PbF2.

03:02Using the concept of molarity, big M equals N over V.

03:08Putting both values in.

03:11N equals 4.75 times 10 to the power of negative 4 moles.

03:17This is the mole value of PbF2 in a 250 milliliter solution.

03:23The mass of PbF2 dissolved is N times the relative molecular mass.

03:28Putting both values in.

03:31The result is equal to 0.115857 grams or 115.9 milligrams.

03:41This is the mass of PbF2 dissolved in 250 milliliters of water so that the solution is exactly saturated.

03:51Yup, hopefully useful.

03:53And, don't forget to follow this channel.

The Mass of PbF2 From Solubility Product Constant

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Chemical Solubility

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