Ion Product Quotient Predicting Precipitation The higher the Ksp value the more soluble the compound Important Point from Last Day Solubility Of a substance is the maximum concentration ID: 496030
Download Presentation The PPT/PDF document "Qsp" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Qsp
Ion Product Quotient: Predicting Precipitation Slide2
The higher the Ksp
value, the more soluble the compound
Important Point from Last DaySlide3
Solubility
Of
a substance is the maximum concentration
a substance can have in water to make a
saturated solution.Once the concentration exceeds the solubility, it will accumulate at the bottom of the mixture as a precipitate (supersaturation).Every time we look at a solution in equilibrium, we are dealing with a saturated solution.Most substances, even ‘insoluble’ substance will dissolve to some degree.
Review & RememberSlide4
When two solutions are mixed together the system will try to reach
equilibrium
.
Ksp
is the equilibrium expression used when a solution is saturatedWhen the solution is not saturated, Qsp is usually used to describe the equilibrium You can think of Qsp as a ‘trail Ksp
’
Q has the same form as K, but typically involves non-equilibrium concentrations
When two solutions mix...Slide5
Once the Qsp is calculated, we compare it to the actual
Ksp
for the substance.
Precipitation
can be predicted by comparing Qsp and KspWe will get one of 3 situations:Slide6
A precipitate will form
.
This
means that the solution looks at the trial situation and says that there are too many ions for that specific temperature. It will kick the ions out as
precipitates.Saturated salt will precipitate until Qsp = KspSituation 1: Trail Qsp
>
KspSlide7
A saturated solution
has formed. There is the perfect amount of ions present.
No more salt can dissolve.
Solution is at equilibrium
No precipitate forms.Situation 2: Trail Qsp = KspSlide8
An unsaturated solution has formed.
More salt can dissolve without a precipitate forming
This means that there is
no precipitate
that forms and there is room for more ions.Situation 3: Trail Qsp < KspSlide9
One other necessary discussion is that if I mix two substances together, they dilute
each other
.
This dilution must be considered when deciding on whether a precipitate will form.
Keep in mind... Dilution FactorSlide10
1. Decide if any
possible precipitates
can form from the two substances being mixed using a
solubility table
.Write the net ionic equation for this substance to determine what the trial Qsp expression is.2. Calculate the dilution of both ions that will form the precipitate.Note that the final volume will be the sum of the volumes of both substances.3. Using the concentrations above, calculate the trial
Qsp
4. Compare to the actual Ksp
to determine whether a precipitate will form.
Steps for these questions...Slide11
25.0 mL of 0.00200 M of potassium chromate are mixed with 75.0
mL
of 0.000125 M of lead (II) nitrate. Will a precipitate form if
Ksp
of lead (II) chromate is 1.8 x 10-14?Example: