Unit 10- Buffers & Ksp Flashcards
What does the common ion effect state?
The extent of ionization of a weak electrolyte is decreased by the addition of a strong electrolyte that has an ion in common.
What is needed in order to have a buffer?
In order to have a buffer, we need a weak substance and its conjugate.
Define Buffer Capacity
The amount of strong acid or strong base that can be added to a buffer without it undergoing a significant change in pH.
Buffers work best when the _____ is close to pKa.
Target pH
Can the assumption rule be used for buffer problems?
Yes, it can always be used for buffer problems.
What is the Henderson-Hasselbach Equation and when can it be used?
pH= pKa+log(b/a); it can only work for buffer problems.
Describe the idea of Ksp
When you throw a slightly soluble ionic compound into water, a small amount dissolves while the rest remains undissolved at the bottom of the flask. This is a saturated solution and is at dynamic equilibrium. Solid crystals are constantly precipitating at the same rate as solids dissociate into soluble ions. As a result, we can represent this process using a reversible reaction.
Like other equilibrium constants, Ksp is dependent upon _____.
Temperature.
Ksp is the solubility constant, not the solubility. Solubility is the measure of how much of a solute dissolves per amount of solvent generally grams/liter of solution or moles/liter of solution. Solubility will be the _____ in your ICE chart when using the solubility constant.
“x” value
List the factors that effect solubility and explain them.
Addition of a common ion and changes to pH.
If either of the ions that make up the slightly soluble compound is acidic or basic, the solubility of the compound will be impacted by the pH of the solution.
If Q> Ksp, then
Precipitation will occur
If Q< Ksp
Precipitation will not occur.
Define Titration
In general, a titration is an experimental process where we’re trying to figure out the concentration if an unknown substance; we do that by reacting two substances with each other (one is called the titrant which is a solution of known concentration).
Define Titrant
a solution of known concentration
Define Equivalence Point
stoichiometric equivalence where moles of titrant and unknown are equal.
When we’re dealing with acids and bases, the main indicator that we use is _____; it’s colorless at low pH’s and at pH’s above 8 it turns a pinkish-red color
Phenolphtalein
When a strong acid and strong base are reacting, we don’t care about the _____
Conjugate Ions
What are the steps of finding the pH of solution when doing a strong acid and strong base titration?
1) Write an overall reaction without the conjugate ions
2) Make an initial/final table and get the values of each species by multiplying the volume of the substance by its concentration (you should get mmol)
3) Then, find the concentration of the species by dividing the mmmol value by the overall volume
4) From there, use the formula of pH or pOH to get the answer.
What are the steps of finding the pH of solution when doing a weak acid/strong base titration?
1) If you have no amount of strong base, simply write the equation for the base or the acid and use an ICE chart to figure everything out.
2) If you have some amount of strong base, you need to have an initial/final chart with a full reaction. (For acids, you add the acid to OH- and get the conjugate base and water on the other side) (For bases, you add the base to water and get the conjugate acid and OH- on the other side).
3) Now, you find the concentration of the desired species by dividing the mmol by the overall volume.
4) Finally, you use the H-H equation to find the pH value.
When you’re at the equivalence point, the pH will always equal ______ .
pKa.
What do you do when, in the initial/final chart, the only remaining value is ONLY the conjugate of the substance?
You find the concentration of the substance; then, you make an ICE chart by writing the equation. (The equation is literally the reverse of the reaction in the initial/final chart). Finally, you solve for pH.
What do you do when, in the initial/final chart, the remaining values are both bases?
You ALWAYS use the stronger base for solving pH.
You find the concentration of the species and use the pOH and pH equation to find the final value.
For buffer problems, if you have a weak acid and you add a strong acid, what happens?
Hydrogen ion reacts with the conjugate of the weak acid to form the weak acid.
For buffer problems, if you have a weak acid and you add a strong base, what happens?
The weak acid reacts with OH- to produce H2O and its conjugate.
For Ksp problems, what do you need to do to solve Ksp?
1) Write the balanced decomposition reaction of the solid
2) Then, based off of the information in the problem, get the concentration of the species at equilibrium. Finally, calculate Ksp using the values.
For solubility problems, what do you need to do to solve solubility?
1) Write the balanced decomposition reaction of the solid.
2) Then, with the given Ksp value, solve for “x” (x is the solubility)
3) If needed, change the units of solubility through stoichiometry.
For precipitation problems, how do you find out if precipitate forms?
1) Write the balanced decomposition reaction through eliminating the conjugate ions in each of the given substances (the overall solid should consist only of the two of them) and also write the equation for Q.
2) Then, through using M1V1=M2V2, get the value of M2 (The given concentration and volume of each substance should be plugged into M1 and V1 and the V2 value should be the sum of the volume of the first substance and the second substance).
3) Plug the M2 values into the Q equation.
4) If Q is larger than Ksp, then precipitate forms; if not, then it doesn’t form.
