Precipitation: Ksp vs Q - Video Tutorials & Practice Problems

Solution Saturation

Now recall that KSP helps to determine how soluble an ionic solid can be in a solvent and equilibrium. Also recall that Q which represents a reaction quotient is a ratio of products to reactants at a particular time. Now, you're going to say comparing KSP to Q will determine if a solid otherwise known as a precipitate is likely to form. Here, we use the idea of solution saturation to determine this idea. Now, solution saturation is just the amount a solu that has been dissolved in a solvent. And we're gonna say the degree of solution saturation can be determined by the relative value of KSP to Q. Now, we know that KSP deals with an ionic solid and we're talking about how it breaks up into its ions. So let's say our hypothetical ionic solid is a B solid. It breaks up into a positive aqueous plus B minus aqueous. Now Q could be less than KSPQ could be greater than KSP or Q could be equal to KSP. Now, if we take a look here at this number line, let's say that this is from negative infinity to positive infinity because we know that KSP can be a number that's very small. Or here we could have a QB a larger number than KSP, something greater than one. Now, before the equivalent point, he was less than KSP. Before the equivalence point, we haven't reached our maximum saturation level or we haven't reached our solu maximum solution saturation. So we are unsaturated. Remember Q will shift to get to KSP. Here, Q will shift in the forward direction to get to KSP. The direction two shifts is the same direction. Our chemical reaction will shift. So it shifts in the forward direction making more ions. So here no precipitate is formed. But let's say that Q is greater than KSP. Well, that'd be after equilibrium, but again, Q will shift to get to KSP, get to equilibrium. So here it will shift in the reverse direction. If it shifts in the reverse direction, my chemical reaction also shifts in the reverse direction and look where we're heading, we're heading towards a solid to precipitate. That's why I precipitate Forbes. And this would represent a super saturated solution. We've gone beyond our maximum solution saturation level. Now, if Q is equal to KSP, then we are at equilibrium and we represent a saturated solution, the maximum amount of solute ha or ionic salt is dissolved within our solvent. And again, no precipitate would fall. So just remember in terms of Q versus KSP, a precipitate can successfully be created when Q is greater than KSP. Because that represents a super saturated solution.

Precipitation: Ksp vs Q Example

Here, it says will barium sulfate precipitate out when 8.2 times 10 to the minus seven molar barium carbonate is mixed with 5.7 times 10 to negative six molar strontium sulfate. Here, the KSP of barium sulfate is given as 1.1 times 10 to the negative 10. All right. So they give us KSP of barium sulfate. So that is our point of interest. That's what we're gonna focus on breaking up into ions. We have barium barium sulfate solid. We see it breaking up into ions, it breaks up into one barium ion plus one salty iron. Now here, if we're dealing with KSP, we're dealing with an ice chart. So initial change equilibrium with a nice chart, we ignore solids and liquids. So this solid will be ignored. Now, this barium sulfate is not breaking up in pure water. It's breaking up in a solution composed of these two compounds. Then mixing together allows the barium ion here and the sulfate ion here to combine together to give us our solid. So we have two common ions involved. We have barium ion. Its concentration is this 8.27 times 10 to the minus seven molar barium ion. And we have this as the concentration of our sulfate ion. This is important because these two ions are common to our ice chart equation. So basically, we have double common ion effect. So this is 8.27 times 10 to the minus seven molar initially. And this 5.7 times 10 to the negative six molar initially, they're both products who are making them, we bring down everything. Now, when you have initial amounts for both of your ions, this helps us to find QE, he was just like KSP people's products here. So it equals be times sulfide. Remember if you have an actual real number, you could ignore the X variables when it comes to KSP and Q. So we plug these numbers in for our two ions and then we're gonna find out what Q is. So when I do that, I find he was 4.674 times 10 to the minus 12. I know what KSP. I know A Q is. So now I can compare them to each other KSP, to the negative 10-Q was to the negative 12, he was smaller. So he was gonna shift in the four direction to get to KSP. If Q moves in the forward direction to get to KSP, then our chemical reaction also moves in the forward direction. Where are we moving? We're moving away from our solid towards our ions are barren sulfate is becoming more soluble. So we're not making any precipitate, we're making more ions. So here you're going to say no barren sulfate will not precipitate out.

Two mixtures are added into one flask at 25 °C, one mixture contains 0.55 mL of 0.75 M BaF₂ and another 0.25 mL of 1.3 M Mg(OH)₂. K_sp of Magnesium Fluoride, MgF₂, is 7.4 x 10⁻⁹. Identify the correct option.

a) MgF₂ solid will form

b) MgF₂ solid forms, along with Mg⁺² and F⁻ ions

c) solution is unsaturated, precipitate does not form

d) solution is saturated, precipitate forms

• A. MgF₂ solid will form
• B. MgF₂ solid forms, along with Mg⁺² and F⁻ ions
• C. solution is unsaturated, precipitate does not form
• D. solution is saturated, precipitate forms