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CHEM 1030 Lab Final
Terms in this set (38)
How did we determine the melting point of the unknown solid in Exp 2?
How did we determine the boiling point of the unknown liquid in Exp 2?
What solvents were used to test the solubility of the unknown liquid/solid in Exp 2 and why?
Water (polar) and Cyclohexane (non-polar). To see if the unknown is polar or nonpolar since "like dissolves like".
What are the different IMFs?
1) Dispersion (London / Van der Waals)
-All molecules, created by random movement of electrons
-Between polar molecules
-Strong version of dipole/dipole force, created by bond between H & N, O, or F
-Between ionic and polar molecules, causing ionic compound to dissociate
How did we determine the freezing point of t-Butanol and 2-Pentanol in Exp 3?
How did we find the freezing depression constant for t-Butanol in Exp 3?
ΔT (celcius) = (pure freezing temp) - (mixed freezing temp)
Kf = freezing point derpession
m = molality (moles solute / kg solvent)
How did we find the molar mass of the unknown solute in Exp 3 if we know:
Kf of t-Butanol
kg of t-Butanol
g of unknown solvent used
Solve for moles solute inside molality and divide by grams solute that were measured.
What is the freezing point depression and what affects it?
The amount that a freezing point is lowered due to the concentration of solute particles. (colligative property)
Define colligative properties.
Characteristics defined by ratio of solute particles to solvent particles, disregarding what kind of substance it is.
What are the 4 colligative properties of solutions?
1) Freezing point depression
2) Boiling point elevation
3) Vapor pressure
4) Osmotic pressure
What two substances were mixed in Exp 4 to measure reaction rates?
KMnO4 (Potassium Permanganate) & H2C2O4 (Oxalic Acid)
What two variables were manipulated in Exp 4 in the reaction between KMnO4 & H2C2O4? Why?
1- Concentrations to determine the rate law expression.
2- Temperature to determine the activation energy
How do you determine the rate law of a reaction?
Product of all the reactants taken to their stoichiometric coefficients.
What determined the rate of the reaction for each trial in Exp 4?
[KMnO4] / seconds
How do you find the order of the reactants for a rate law?
Divide rates of different trials that use the same concentration of one substance so it cancels out and you can solve for the order of the other substance.
What do we need in order to find the rate law constant (k) for the reaction rate law expression in Exp 4?
We need to know the rate of the trials, the concentrations of the reactants, and the orders of the reactants.
How did we find the activation energy (Ea) of the reaction between KMnO4 & H2C2O4 in Exp 4?
1) Find the k value using the pre-determined rate law expression and the concentrations of the reactants.
2) Plot the ln(k) versus 1/T (in kelvins)using the data from the part of the experiment where temperature was manipulated but the concentrations remained the same.
3) Add a trend line. It will be given in y=mx+b form and solve for Ea.
m= Ea/R (R=gas constant=8.314 J/k*mol)
b= ln(A) (A=frequency factor)
In Exp 5, what happened when we added HNO3 to a Cu (II) & Ammonia system?
The HNO3 reacted with Ammonia to form NH4+. This removed reactants from the system and caused a left shift.
In Exp 5, what happened when we added HNO3 to a Ca(+2) & C2O4(-2) system?
The HNO3 reacted with the Oxalate Ion to form Oxalic Acid (H2C2O4). This removed reactants and caused a left shift.
In Exp 5, how did we determine if a system was endothermic or exothermic using Le Chatelier's principle?
We split up the sample into 3 test tubes. The first was chilled in an ice bath, the second was kept at room temp, and the third was heated in a water bath.
-If it was Endothermic, heat will act as a reactant so the chilled sample will see a left shift and the heated sample will see a right shift.
-If it was Exothermic, heat will act as a product so the chilled sample will see a right shift and the heated sample will see a left shift.
In Exp 5, how did we determine the Ka/pKa values of Acetic Acid from the measured pH?
Ka = [Products]^n / [Reactants]^m
We need to determine the concentrations of the Products and Reactants at equilibrium.
1-Determine [H+] from pH
2-Set up an ICE table. Subtract [H+] from [Reactants]. Add [H+] to [Products].
3-Using equilibrium concentrations find Ka
4-Using Ka, find pKa
In Exp 5, what happened when we added NaCH3COO to Acetic Acid (CH3COOH)? Why?
This made the pH of the solution increase or become more basic. The NaCH3COO dissociated to form more products (CH3COO-) causing a left shift (formation of Acetic Acid from free H+ and CH3COO-) and a decrease in [H+].
What is Le Chatelier's Principle?
When a chemical system at equilibrium is altered, the system will shift in a direction to counteract the change.
What is a spectator ion?
An ion that does not react with H2O to affect pH of solution. Remains separate.
How does a salt dissolved in water produce an acidic or basic solution?
The salt will dissociate to form anions and cations. The solution will be...
1) Neutral if its an anion from a strong acid or a Group I/II Cation.
2) Basic if its an anion from a weak acid. (will react with H2O to form OH-)
3) Acidic if its a cation from a weak base or a metal. (reacts with H2O to form H+)
What is the theoretical Ka/Kb value of a strong acid or base?
There is no theoretical Ka/Kb value (and if there is it will be very large). The rxn will go to completion so there is no equilibrium to base an equilibrium off of.
If you are given the Ka/Kb value of acid or base, how do you calculate the theoretical pH of that acid or base?
Ka/Kb = x^2 / [conjugate acid/base]
Solve for x and this will be the [H+]/[OH-]. This applies to most acids/bases as long as they are monoprotic. if they produce more than one H+/OH-, the numerator will have to be modified. Set up an ICE table using x to check.
In Exp 7, what did we use to make a buffer solution? What two substances were added to the buffer to test its effectiveness?
NaC2H3O2, HC2H3O2, & H2O
We added HCl and NaOH to test the buffer.
How do we determine the pH of a pure buffer?
pH = pKa + log([base]/[acid])
How do we determine the pH of a buffer after adding an acid/base?
1) Calculate new concentrations of base and acid.
-Subtract or add the moles of acid/base added from the substance that will react with it.
-Add the moles to the substance that it will create.
-Divide by total volume.
2) Use Henderson-Hasselbalch
How do we find the pH of an acid or base?
pH = - log[H+]
pH = 14 + log[OH-]
How is a buffer made? How does a buffer control pH?
A buffer is made with a weak conjugate acid/base pair. It is most effective when the concentrations of both substances are equal. They control pH by...
-The weak acid reacts with OH-
HA + OH- <---> A- + H2O
-The weak base reacts with H+
A- + H+ <---> HA
In Exp 8 what did we titrate with what?
1) HCl with NaOH
2) Unknown weak acid with NaOH
Describe a titration curve and important information we can get from it.
Its a plot of mL titrant vs. pH of sample.
# of equivalence points = proticity of acid/base.
pH at half-way point of each equivalence point = pKa.
At half-way points, moles titrant = moles sample.
In Exp 9, what two substances did we mix to create a precipitate?
CuSO4 + Na2CO3 ---> CuCO3 (s)
How did we calculate the molar solubility of Cu(+2) and CO3 (-2) in Exp 9?
1) Take absorbency reading
2) Use given calibration curve to solve for x (molar solubility), plugging in absorbency reading for y.
3) Since Cu/CO3 are one-to-one ratio, molar solubility will be the same.
How do you calculate solubility product constant (Ksp) from s (molar solubility) of the products?
Ksp = [products]^n = (n * (s of products))^n
where n = # moles = stoichiometric coefficients
What is molar solubility?
molar solubility = s= moles of a substance that can dissolve in a liter of a solution (mol/L)
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