Solution chemistry Flashcards
What are colligative properties? List them (4)
Properties that depend ONLY on the number of particles in a solution:
- Raoult’s Law (Vapour-pressure lowering)
- Boiling point elevation
- Freezing point depression
- osmotic pressure
Give the formula that can solve for the osmotic pressure of a solution
Π = CRT
R: gas constant
T: degrees K
C: concentration of solute (moles/Litre)
Are highly charge or less charged species more soluble in water?
Less charged species (eg. NaCl - Na+/Cl-) are much more soluble in water than highly charged species (eg. AlPO4 - Al+3/PO4-3) because the higher charged specie ions are more attracted to each other.
List seven ways to express concentration of a solution
Molarity (M): moles solute/L solution
Normality (N): 1 equivalent/L solution ie. (mass g)/(MW compound)/(reacting units)/(L solution) GENERALLY: N = nM
Molality (m): moles solute/kg solvent (not temp dependent)
Density (ρ): mass per unit volume at specific temp (usually g/ml or g/cm^3 at 20 degrees C)
Osmole (Osm): moles/particles contributing to osmotic pressure
Osmolarity: Osm/L solution
Osmolality: Osm/kg solution
What is the Normality (N) for 1.2 M H2SO4?
There are two reactive protons (2 equivalents of protons in each mole), therefore n = 2 eq/mole
N = nM N = (2 eq/mole)(1.2 mole/L) = 2.4 eq/L = 2.4 N
What is the osmolarity of a 0.001 M solution of sodium chloride (NaCl)
Both Na+ and Cl- contribute to osmotic pressure
osmolarity: 0.002 Osm/L (twice the molarity)
What is the osmolality of a 0.01 molal solution of Na2SO4?
0.03 Osm/kg
Na2SO4 dissociates into 3 ions (2 Na+ and 1 SO4-2) that contribute to the osmotic pressure
What is an electrolyte?
Any solute that can dissolve in water to produce ions (which can conduct electricity)
What distinguishes strong electrolytes from weak electrolytes?
Strong electrolytes have extensive dissociation
eg. NaCl = Ca+ and Cl-
eg. salts, strong acids and strong bases
Weak electrolytes have incomplete dissociation
eg. CH3COOH = CH3COO- + H+
eg. weak acids, weak bases, complexes, water, soluble organic compounds, highly charged species
What is the common ion effect?
An excess of one ion over another causes the soluble concentration of the other to be suppressed.
Adding enough of a dissociative molecule to a solution can cause the original ion to precipitate out of solution, as long as the product of the new ion (and the old) exceeds the Ksp
Eg. can precipitate AgCl out of Cl in AgCl solution with excess AgNO3. Product of [Ag+] and [Cl-] must exceed Ksp for Cl to precipitate out
A compound is heated from 20 degrees to 700 degrees. Its mass decreases from 1 to .8 grams. What is the most likely reason for this?
Volatile components are released
An increase in temperature will increase the vapor pressure of volatile components. When the temperature is high enough, they will simply vaporize. This loss of material would be observed as a decrease in mass.
How does the strength of attraction between particles differ with increasing temperature?
The general strength of attraction between molecules would increase, but the non-covalent interactions (like hydrogen bonding) decreases with greater temperature.
A chemist adds 1 L of a 1 M solution of substance X to 1 L of distilled water at 298 degrees kelvin.
What is the molality (m)?
What is the molarity (M)?
Molality: Number of moles of solute added to 1 kg of solvent: 1 M/1 L = 1 m
Molarity: Number of moles of solute per liter of total solution: 1 M/2 L = .5 M
Remember, 1 L of water at room temperature (298 K) is 1 kg.
In a solution containing only Zn2+, the concentration of zinc ions is 5 x 10^-3, what concentration of S^2- is required to just begin the precipitation of zinc sulfide?
Ksp of ZnS is 1.0 x 10^-21
ZnS Zn2+ + S2-
Ksp = [Zn cation][S anion]
[S anion] = Ksp/[Zn cation]
[S2-] = 2 x 10^-19
CuS from a selective precipitation was collected and purified, equal weights of it were placed into each of two beakers. Beaker 1 contained distilled water and beaker 2 contained a .01 M Cu(NO3)2 solution.
Which beaker will the CuS dissolve more readily in and why?
Beaker 1 with distilled water. This is due to the common ion effect, where CuS will dissolve to a lesser extent in the presence of copper (II) ions (or sulfide ions).
