Unit 4- Solutions Equilibria Flashcards
What is solubility Equilibria?
An equilibrium can exist between a solute and a solvent
What is dissociation?
The process through which ionic solids, when dissolved in water, dissociate into the ions they contain.
What is precipitation?
The process through which once ions are free in solution, they can collide with one another, causing them to reform the solid compound they once were. When this happens a precipitate (or solid) will form.
What happens when a solution is at equilibrium?
The rate at which ions dissolve will be equal to the rate at which ions precipitate. At equilibrium the solution is saturated- meaning it contains the maximum amount of solute that can dissolve under certain conditions.. In saturated solutions the concentrations of ions remain constant.
What is special about solubility equilibrium in molecular compounds?
Solubility equilibrium is based on solids dissolving in water to give the basic particles from which they are formed. As such, molecular compounds (Covalently bonded), such as sugar, do not dissociate but rather dissolve to give individual aqueous molecules.
NOTE: Beware of acetate (CH3COO-) and other organic ions. They will dissociate into ions!
Explain how to interpret a solubility curve.
- Each line represents the maximum amount of a solute that can be dissolved in 100g of H2O at a particular temperature. In other words, this is the amount of solute in a saturated solution.
- Below the line, the solution is unsaturated- more solute can dissolve.
- Above the line, the solution is supersaturated- more than the usual amount of solute is dissolved- a precipitate is formed.
What happens for most substances as temperature increases?
For most substances, as temperature increases, solubility increases (not for all).
Define the following:
1. Solute
2. Precipitate
3. Saturated Solution
4. Dissociation
5. Unsaturated Solution
- The minor (lesser) component in a solution.
- Ions in solution combine to form a solid.
- The rate of dissolving is equal to the rate of precipitation.
- Compounds separate into positive and negative ions.
- The rate of dissolving is greater than the rate of precipitation.
Explain Ksp.
- The Ksp is a measure of the solubility of an ionic salt.
- sp stands for “Solubility Product”
- You can only calculate Ksp if the solution is saturated. Only saturated salt solutions are in equilibrium.
- The LARGER the value of Ksp, the GREATER is the solubility of the salt.
Ex) - FeS has a Ksp of 4 x 10^-19 which means that in a saturated solution there would be few Fe2+ or S2- ions.
- PbCl2 has a Ksp of 1.8 x 10^-4 which means a saturated solution of PbCl2 would have many Pb2+ and Cl- ions.
What are spectator ions?
Ions that are present in a reaction but do not participate in it.
Explain double displacement precipitation reactions.
- Sometimes when two aqueous solutions are mixed together, a solid, or precipitate is produced. The solid is said to have low solubility and this reaction is called a precipitation reaction.
- A double displacement reaction is specifically classified as a precipitation reaction when the reaction occurs in aqueous solution and one of the products formed is insoluble.
What is Trial Ion Product (TIP) used for?
- We can predict the products of a double displacement reaction to determine if a precipitate is likely to form. However, this precipitate will only be created if there are enough ions in solution to establish equilibrium.
- As such, we need to do the math to determine if we have enough ions. This is called the TRIAL ION PRODUCT (TIP), this math is basically a trial Ksp/ Keq>
Explain the effect of common ions in solubility.
An example of Le Chatelier’s principle, the common ion effect states that equilibrium in a solution can be shifted by dissolving any compound that contains ions already present, or any compound that reacts with one of the ions present in solution.
What is selective precipitation?
- Separation of ions in an aqueous solution by using a reagent that forms a precipitate with one or a few of the ions.
- Ions can be separated from each other based on their solubility
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