Chem Lab Final

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Given that carbonic acid, H2CO2, has a pKA1 of 6.37 and a pka2 of 10.33, if you wanted to make a pH 7 buffer starting with NaHCO3, would you add .1M HCl or .1M NaOH

.1M HCl

In an experiment you use 8.500g of solvent (FP=78.0C, kf= 5.5C/m) and .6g solute (molecular mass= 188.63g/mol) 1) How many moles of solute have you used? 2)What is the colligative molality of the solution formed 3) What is the predicted freezing point depression of ΔTf? 4) What is the predicted freezing point of the solution formed?

0.00318 mol 0.374 m 2.1 C 75.0 C

Volumes obtained with volumetric flasks, pipettes, and burets are recorded to the nearest _____ mL.

0.01

Burets, pipets, and small volumetric flasks are accurate to about:

0.01mL

The molar absorptivity of FeSCN is 4.41x10^3M^-cm^- at 470nm. Assume the Beer's Law plot has a slop of 4.41x10^3 and a y-intercept of 0.00580. If a solution is a 1cm path length vial has an absorbance of 0.6385, what is the [FeSCN]?

0.6385= (4.41x10^3)[FeSCN] + 0.00580 [FeSCN]= 1.43x10^-4M

How many grams of Cu(NO3)2 must be diluted to 25mL to match a concentration of 0.0706M?

0.706M*25mL= 1.765mmol 1.765mmol * 1mol/1000mmol * 1mol Cu(NO3)2/1molCu^2+ * 187.55g Cu(NO3)2/1mol Cu(NO3)2 = 0.331g

Calculate the requested values when 2.100g CaCl2 is added to 125g of water, given the freezing point depression constant of water is 1.86C/m 1) moles of CaCl2 present 2) Van't hoff factor of CaCl2 3) Colligative molality 4) Predicted change in freezing point 5) Predicted freezing point of water solution

1) 2.10G CaCl2 * (1mol/ 110.98gCaCl2) = 0.01892moles CaCl2 2) CaCl2--> Ca + 2Cl= 3 3) 3 * (0.01982moles/.125kg water)= .4541mol/kg 4)ΔTf= 0.4541m * 1.86C/m = 0.845C 5) Temp pure material freezes at (0.00C) - ΔTf = -0.845C

Similar to part D of the calorimetry lab, 2.116 grams of CaCl2 is dissolved in 50.543g of water. The initial temp of the water is 25.30C and the final temp is 32.69C. The specific heat of water is 4.184J/gC. 1) How many moles of CaCl2 are dissolved 2) What is the value of qwater? 3) What is the value of ΔHsolution for CaCl2 in kJ/mol? 4) Is the ΔHsolution exo/endothermic and why?

1) 2.116gCaCl2 * 1mol/110.99g = 0.01906molCaCl2 2) qwater = (50.543g)(4.184)(32.69-25.30) = 1.56x10^3J 3) -1.56kJ/.01906mol CaCl2 = -81.8 kJ/mol 4) The solution is EXOTHERMIC because it release heat and the temperature of water rises

In solution B, an excess of Cu(IO3)2 is placed in 5.0x10^-3M KIO3. The absorbance this time is measured to be 0.0580. If Cu(NH3)4^2+ is known to have a molar absorptivity of 43.11M^-cm^- 1) What is the [Cu^2+] in solution 2) What is the [IO3] in solution 3) What is the numeric value of Ksp?

1) A= ΣlC .0580= 43.11M^-1cm^-1 * C C= 1.34x10^-3M 2) The [IO3^-] is 7.69x10^-3M because in 5.0x10^-3M KIO3, the [IO3]= 2 * [Cu^2+] + 5.0x10^-3M already in solution 3) Ksp = [Cu^2+][IO3^-]^2 Ksp= 8.09x10^-8

In solution C, an excess of Cu(IO3)2 is placed in deionized water. After centrifugation, the supernatant absorbance is 0.1105 in a cell with a 1cm pathlength at 600nm. If Cu(NH3)4^2+ is known to have a molar absorptivity of 43.11M^-cm^- 1) What is the [Cu^2+] in solution 2) What is the [IO3] in solution 3) What is the numeric value of Ksp?

1) A= ΣlC 0.1105 = 43.11*1cm*C C= 2.56x10^-3M 2) The [IO3^-] = 5.12x10^-3M because in pure water, the [IO3^-] = 2x [Cu^2+] 3) Ksp= [Cu^2+] * [IO3^-]^2 Ksp= 6.73x10^-8

Consider the reaction solution 1, which contains 20ml of .2M KI, 20mL of .1M (NH4)2S2O8 and 10mL of 0.0050M NaS2O3. 1) What is [I^-]? 2) What is [S2O8^2-]? 3) What is the [S2O3^-]?

1) C1V1=C2V2 (0.2M)(20mL)= (50mL)(xM) --> x= .080M 2) C1V1=C2V2 (0.1M)(20mL)= (50mL)(xM) --> x= .040M 3) C1V1=C2V2 (0.005M)(10mL)= (50mL)(xM) --> x= .0010M

There are several hazards associated with the chemicals in the electrochemical cells experiment. Which hazards are for each? 1) 3.0M HCl 2) 3.0M NaOH 3) 0.1M Cu(NO3)2 4) 0.1M AgNO3 5) graphite rods 6) Ascorbic acid (solid)

1) Corrosive and irritating vapors 2) Corrosive 3) Toxic if ingested 4)Causes dark spots if spilled on skin, toxic if ingested 5) none listed 6) none listed

In lab 9 the solubility product of Cu(IO3)2 was determined spectroscopically. The concentration of Cu^2+ is determined by the measuring of absorption of Cu(NH3)4^2+ in solution vs. a calibration plot. Write the dissolution equation for Cu(IO3)2 solid in water. What is the Ksp expression for this dissolution reaction?

1) Cu(IO3)2 <---> Cu^2+ + 2IO3^- 2) Ksp = [Cu^2+][IO3^-]^2

In Lab 8 which chemicals are : 1) Corrosive 2)Toxic 3)Irritant 4) No hazard

1) HCl, NaOH 2) Sodium carbonate 3) potassium hydrogen phthalate, sodium carbonate 4) Methyl orange, phenolphthalein

Anode: Sn2+ (aq) + 2 e− → Sn (s) E°reduction = −0.14 Cathode: Ag+ (aq) + e− → Ag (s) E°reduction = +0.80 1) What is the net redox reaction that takes place in the Galvanic cell? 2) What is the value of E°cell when the concentrations of both cations are 1.0M? 3) How many moles of electrons are transferred?

1) Sn(s) + 2Ag^+ --> 2Ag(s) + Sn^2+ 2) E°cell= E°cat-E°an= 0.80-(-.14V) --> E°cell= 0.94V 3) 2 moles of electrons are transferred

What calculations are used to determine the initial [Fe^3+] and [SCN^-] concentrations in solution 1B when 2.00mL of 2.00x10^-3M Fe^3+, 4ml of 2.00x10^-3M of SCN, and 2ml of water are mixed?

1) [Fe^3+] = C1V1=C2V2 (2.00x10^-3)(2mL)= (xM)(8mL) [Fe^3+]= 5.00x10^-4M 2) [SCN^-] = C1V1=C2V2 (2.00x10^-3)(4mL) = (xM)(8mL) [SCN^-] = 1.00x10^-3M

In part B of the calorimetry lab, a piece of hot metal weighing 50.850G immersed in hot water at 97.65C is placed into the styrofoam calorimeter containing 42.01g of water at 24.55C. The water in the calorimeter rises to 35.45C. The specific heat of water is 4.184J/gC. 1) What is the value of qwater? 2) What is the value of qmetal? 3) What is the specific heat of the metal?

1) qwater= (42.01g)(4.184)(35.45-24.55C) = 2204.4J 2) qmetal= - qwater= -2204.4J 3) (-2204.4J)= (50.850g)(sbar)(35.45-97.65) --> s= 0.6970J/gC

Consider the case where the Cu2+/Cu and Zn2+/Zn half cells are connected in an electrochemical cell: 1) In which half cell with a reduction take place? 2) Which half cell is the anode? 3) Which direction do the electrons go in the external wire? 4) Which direction do the anions in the salt bridge flow? 5)Select the true phenomena at the electrodes 6) What happens if the leads to the copper and since electrodes are switched?

1)Cu^2+/Cu 2) Zn^2+/Zn 3) Toward the copper electrode 4) Toward the zinc cell 5) The copper electrode increases in mass, the zine electrode decreases in mass 6) The direction of current flow through the meter is reserved, and the sign of the voltage reading changes.

1) What hazards are associated with Copper(II) Sulfate? 2) What actions should you take if you spill this on yourself? 3) What should be done with waste solutions containing copper ion?

1)Irritant and Toxic 2)Flush the affected area with water 3) Dumped in beaker labeled waste copper on bench top during experiment, disposed of in bottle for waste copper ion when work is complete

If the rate law is determined to be rate = k*[I^-]*[S2O3^2-], what is the value and units of k?

1.064x10^-5M/sec = k *[.08][.040] k= 3.32x10^-3 M^-sec^-

In the kinetics lab, which reaction are we trying to find the rate law?

2 I^- + S2O8^2- --> I2 + 2SO4^2-

If you have 15mmol and 23mmol of reactants, how many sig figs will be carried throughout the rest of the reaction table?

2 sig figs

Consider a titration of 20mL of .1M Na2CO3 analyst with .160M HCl titrant. The pka's are shown below: H2CO3 + H2O <--> HCO31- + H3O1+ pKa1 = 6.35 HCO31- + H2O <--> CO32- + H3O1+ pKa2 = 10.33 What is the second equivalence point mL?

2 ways to calculate 1) Double Veq1 2(12.50ml) = 25ml 2) 2(Canalyte*Vanalyate)= Ctitration*Veq2 2(.1)(20)=(.160)(Veq2) Veq2= 25ml

In part B of experiment 2, you will use Copper (II) Sulfate pentahydrade. What is the molar mass of this compound? How much of this compound must be weighed to make 150mL of a .15M solution? How many mL of the 0.15M solution should be diluted to prepare 275.0 mL of a 0.50M solution?

250g/mol 5.6g 92mL

How many moles of Na2HPO4 are in 3 grams of Na2HPO4*7H2O?

3g Na2HPO4 X (1mol Na2HPO4*7H2O / 268.05g Na2HPO4*7H2O) = 0.01119 mol Na2HPO4

During lab 6, there was a reaction of 10 mL of .1M NH4Cl with 5.0mL of 0.1M NaOH. Which of the following describes the solution that was produced?

A buffer A solution containing a conjugate acid/base pair A solution containing a weak and and weak base.

If the reaction with [S2O3^2-]= 0.0075M and a reaction rate of 9.10x10^-6M/sec, how many seconds will it take for the reaction mixture to turn black? Explain.

A reaction rate of 9.10x10^-6M/sec means that I2 is predicted at this rate. In the timer reaction, the S2O3^2- reacts at twice the rate of 1.82x10^-5M/sec. [S2O3^2-]=.0075M* (1sec/1.82x10^-5M) = 412 seconds 4.10x10^2 sec

In the Beer's law equation, A=ΣlC, what do the variables represent with units?

A= Absorbance Σ= Molar Absorptivity (M^-*cm^-) l= pathlength of cell (cm) C= concentration (M)

If the Beer's law equation for absorbance versus [Cu^2+] concentration is y= 3.40x+ 0.0109, what is the concentration of copper ion in an unknown solution if the absorbance is 0.251?

A=ΣlC (0.251)=(3.40)(x)+0.0109 x=0.0706M

What do you do with the wastes created in Lab 8?

All can be flushed down the sink with plenty of water

To decrease the detection limit of copper ions in solution, _________, will be added to form Cu(NH3)4^2+, a complex ion.

Ammonia

Which of the chemicals used in lab 4 are a respiratory hazard with vapors that should not be inhaled?

Ammonia

Which of the chemicals used in Lab 4 are hazardous?

Ammonia Phosphoric acid

At this point all of the CO3^2- has been converted to H2CO3. Therefore, there are 2mmol H2CO3 in 20ml + 25mL solution 2/(45mL) = .044M H2CO3 [H3O^+]=sq(Ka1*Ca) Ka1= 10^-6.35 [H30^+]= 4.467x10^-6 * 0.44M) [H3O^+] = 1.402x10^-4 pH= -log[H3O^+] pH = 3.85*

Why would you expect the percent differences for the absorbance to be similar to the percent differences for the concentration in each part of the experiment?

Because the concentration is calculated from the absorbance, the errors should be the same for both. (Using line equation)

Which of the following are colligative properties?

Boiling point elevation Freezing point depression Vapor pressure lowering Osmotic pressure

How many mL of 0.750M [Cu^2+] stock solution must be diluted to 25mL to match a concentration of 0.0706M?

C1V1=C2V2 (0.750M)(V1)= (0.0706M)(25mL) V1= 2.35mL

What formula is used when 1.50mL of 0.500 CuSO4 stock solution is mixed with 6.50mL of water to determine the final [Cu^2+]?

C1V1=C2V2 (1.5mL)(.5M)=(8mL)(C2) C2= 0.0938M

In this experiment, you used a 1cm path length for all cell measurements. If a 0.1CM PATHLENGTH cell had been used for the measurements, how would that have changed the concentration of the results?

Calculated unknown concentration would be the same

When operating the centrifuge, students should do which of the following?

Centrifuge for apprx. 30 seconds Make sure that the lid is completely shut and the safety knob is turned to engage the safety switch.

According to the introduction of Lab 5, when the reactants are mixed, what is expected to happen to the color?

Changes from colorless to red.

Close estimate is obtained using pH= (pka1 + pka2)/2 = (6.35+ 10.33)2 = 8.34

The videos: "Using an Analytical Balance, Using a Volumetric Flask, and Pipeting techniques", what are the ways to make a solution of a known concentration?

Dilute known volume of stock solution into a known volume of liquid. Dissolve a weighted amount (known mass) of solid into a known volume of liquid.

In lab 5, the wastes in the Determination of an Equilibrium Constant Experiment should be ______________. While working on the experiment, wastes should be __________.

Disposed of in a labeled container. Kept in a labeled beaker at the bench

The waste in the Solubility Product Constant experiment should be ____________. While working on the experiment, wastes should be ________.

Disposed of in the labeled container Kept in a labeled beaker at the bench.

What will the value of Ecell be under these conditions? [Sn^2+] = 0.35M [Ag^+] = 1.21M E°cell = 0.94V

Ecell= E°cell - (0.0592/n)logQ Ecell = .94(0.0592/2)log(.2391) Ecell= 0.96V

When the concentrations of an electrochemical cell are different than standard state (1.0M), the voltage of the cell can be predicted using the formula Ecell = E°cell - (0.0592/n)logQ. What do each of the variables represent with units?

Ecell= the voltage at non-standard state conditions in V E°cell= the voltage at standard state conditions in V n= moles of electrons Q= [products]/[reactants] under non-standard conditions. (Like K but not at equilibrium)

Which terms below are also descriptive of the heat of neutralization to be measured in Part C of the lab 4 experiment?

Enthalpy of reaction

What is heat at constant pressure?

Enthalpy, ΔH

In lab 1, based on the amount of product formed in each of the mixing experiments involving NaOH and HCl, which would you expect to give the same temperature changes?

Exp. 2 and 3 because NaOH is the same limiting reagent in both and the amount of product is the same.

In lab 1, based on the amount of product formed in the mixing experiments involving NaOH and H3PO4, which would you expect to give the same temp changes?

Exp. 5 and 6 Same amount of product formed for each and same amount of limiting reagent. Exp. 4. has a different limiting reagent and amount of product formed.

If any of the solutions in lab 5 are spilled on skin or clothing, what is the first thing to do?

Flush area with water

What should you do if you spill a corrosive chemical on your skin?

Flush the area with water FIRST Should have my lab partner report the incident to the instructor

If any of the solutions in lab 9 are spilled on skin or clothing, what is the first thing to do?

Flush the area with water.

The waste solutions made in Lab 4 should be ________. And the metal samples should be ______________

Flushed down the sink with water. Returned to the containers on the side shelf

If any of the solids in lab 9 come in contact with your skin or clothing, what is the first thing to do?

Gently brush the solid off with a paper towel

What is the pH when 10ml of .1M HCl and 5ml of .1M NaOH are mixed? Draw reaction table

HCl is a strong acid and NaOH is a strong base. They will react so strategy is to use a reaction table to determine which is in excess and determine pH. Equilibrium amounts: HCl= .5mmol NaOH=0mmol 0.50mmol HCl/ 15mL = 0.0333M pH= -log(0.0333M)= 1.48*

What is the pH when 10mL of water and 6mL of .1M HCl are mixed?

HCl is strong acid. Calculate [H3O^+] after dilution to determine pH. C1V1=C2V2 (.1M)(6mL)= (xM)(16mL) xM+ .0375M. pH= -log[.0375M] pH= 1.43*

What pieces of equipment were used for the freezing point depression lab?

Hot plate Test tube test tube holder beaker Thermistor spatula

Give a brief description of lab 5:

In the Equilibrium experiment, an equilibrium constant is calculated from concentrations determined from a reaction table. The first part of the experiment is preparing Beer's Law Plot relating the concentrations and absorbances of the product. The second part of the experiment involves mixing solutions containing th reactant and using the calibration plot to determine the concentration of the product at equilibrium. Completion of the reaction table provides enough info to determine the equilibrium constant.

Give a brief description of how heat transfer is measured for as system using its surroundings (Lab 4):

In the calorimetry lab, changes for a system (cooling of a hot metal, chemical reaction, dissolution) are measured by the changes in the surroundings (water). In an insulated system, the heat that the system gains or loses should be exactly matched in magnitude, but opposite in sign, from the changes in surroundings.

Which of the following are attributes of a well-prepared graph?

It has labels on the axes, with units It is drawn as large as possible It has numerical labels on the axes. It has a title? It has small dots exactly at the positions of the data points

What should be done with the waste in the kinetics experiment?

It should be flushed down the sink with water

Which of the following are hazardous properties of sodium thiocyanate?

Its an irritant Its toxic

Which of the following are hazardous properties of nitric acid?

Its an oxidant Its corrosive

In lab 9, Solubility product constant experiment, which of the following are hazards of copper nitrate (Cu(NO3)2)?

Its an oxidizer Its corrosive

If [FeSCN] is 1.43x10^-4, calculate the equilibrium constant if [Fe^3+] and [SCN^-] are 3.56x10^-4M and 0.857x10^-3M at equilibrium.

K= (1.43x10^-4)/ (3.56x20^04)(0.857x10^-3) K= 486= 4.7x10^2

The solute in part B of the experiment of the freezing point depression lab is what?

Lauric acid

Which statement about molality is NOT true?

Molality includes the moles of solute and the volume of solvent FALSE bc its Kg of solvent (mass)

When one of the ions produced by a sparingly soluble solid is present in the solution from another source, the common ion effect predicts that the ________________.

Molar solubility

What is the pH when 10mL of .1M NH4Cl and 5mL of .1M NaOH are mixed? Ka of NH4Cl is 5.6x10^-10 Draw reaction table

NH4Cl is a weak acid and NaOH is a strong base. They'll react so strategy is to draw reaction table to determine which is in excess to find pH. Equilibrium amounts: NH4^+ = 0.50 mmol OH^- = 0 mmol NH3 = .50 mmol (product) Use Henderson-Hasselbach equation Need the pka --> log (5.6x10^-10)= 9.25 pH= pka + log(base/acid) pH= 9.25 + log (.5/.5) pH= 9.25*

What is the pH when 10mL of .1M NH4Cl and 6mL of .1M HCl are mixed? Ka of NH4Cl is 5.6x10^-10

NH4Cl is weak acid and HCl is strong acid--> No reaction. The stronger acid determines the pH because it suppresses the weak acid. C1V1=C2V2 (.1M)(6mL)= (xM)(16mL) xM+ .0375M. pH= -log[.0375M] pH= 1.43*

What is the pH when 10.0mL of NaC2H3O2 and 5mL of .1M NaOH are mixed? Ka of HC2H3O2 is 1.8x10^-5.

NaC2H3O2 is a weak base and NaOH is a strong base. There is no reaction between bases. The stronger base determines the pH because the presence of strong base suppresses the weak base. C1V1=C2V2 (.1)(5mL)= (xM)(15mL) C2= .0333M pOH= -log(0.0333M) pH= 14-pOH *pH= 12.52*

What is the pH when 10mL of .1M NaC2H3O2 and 6ml of .1M HCl are mixed? Ka of HC2H3O2 is 1.8x10^-5. Draw reaction table

NaC2H3O2 is weak base, HCl is strong acid --> Reaction Use reaction table to see whats in excess to determine pH Equilibrium amounts: C2H3O2^- = .4mmol H3O^+ = 0mmol HC2H3O2= .6mmol Use Henderson Hasselbach Equation Need pka= -log(1.8x10^-5)= 4.75 pH= pka + log(base/acid) pH= 4.25 + log(.4/.6) pH= 4.57*

What is the pH when 10mL of water and 5mL of .1M NaOH are mixed?

NaOH is a strong base diluted in water. Calculate [OH^-] after dilution and then determine pH. C1V1=C2V2 0.1M*5mL= xM*15mL [OH^-] = 0.033M pOH= -log(0.033M) pOH= 1.48 pH=14-pOH *pH= 12.52*

What is the pH when 10mL of .1M NaOH and 6ml of .1M HCl are mixed? Draw reaction table

NaOH is strong base, and HCl is strong acid--> Reaction occurs Draw reaction table to determine whats in excess. Equilibrium amounts H3O^+ = 0mmol OH^- = .4mmol .4mmol/16mL = .025M pOH= -log(.025M) pH= 14-pOH pH= 12.40

2. The rate-determining step involves a persulfate ion decomposing. If this is true, what would happen to the rate if the concentration of iodide ion is doubled and other concentrations are held constant?

No change in rate

Stearic acid and Lauric acid are ________ but prolonged contact with skin may cause _______.

Nonhazardous Irritation

How would the results have changed if a cell with a DIFFERENT pathlength had been used for measuring the unknown than the calibration standards?

Not enough info to determine how this would change the calculated unknown concentration, but it would NOT be the same.

When draining the pipet:

One allows the liquid to flow with gravity, t hen touches the pipet tip to receiving vessel to remove the last drop.

Only 0.1M Na2CO3 present. Weak base so use [OH^-]= sq(KbCb) pkaBase= 14-pkaAcid= 3.67 Kbase= 10^-3.67 [OH^-] = sq(2.138x10^-4 * .1M) [OH^-]= 4.624x10^-3M pOH= -log[OH^-] pH= 14-pOH pH= 11.67*

Which of the chemicals in lab 4 are corrosive?

Phosphoric acid

When placing test tubes in the centrifuge, what are the best practices?

Place test tubes containing apprx. equal volumes in opposite positions on the rotor Never put stoppers or other items in the centrifuge with your tubes

All wastes from the Freezing Point Depression Experiment should be__________.

Placed in the labeled waste container.

If the concentrations of [Sn^2+] is adjusted to 0.35M and [Ag^+] is adjusted to 1.21M, what is the value of Q for the reaction? Sn(s) + 2Ag^+ --> 2Ag(s) + Sn^2+

Q= [products]/[reactants] (.35M)/(1.21M) Q= 0.2391

When a sparingly soluble solid is in contact with solution, the solution is called _________.

Saturated

Since CO3^-2 can accept two protons, there are 2 midpoints. The first is at 1/2 mmol CO3^2-= mmolHCL 1/2(Canalyate*Vanalyate) = Ctitrant * Vmidpoint 1 (1/2)(.1)(20mL)= .160 * Vmidpoint1. Vmid1= 6.25mL

When working with a volumetric pipet, one adjusts the liquid level:

So the bottom of the meniscus is at the scribed line on the pipet.

This safety issues in the kinetics experiment is: The only hazardous chemical listed in this experiment is _____________. It is listed as ____________, which can _______________. In this experiment, it is present _____________ and can be handled safely with other aqueous solutions.

Sodium persulfate is an oxidizing agent, which can supply its own oxygen and react violently. a dilute solution.

Ksp is the symbol for the ______.

Solubility product constant

In lab 7 which hazards are associated with chemicals, which are listed as hazardous, and what actions should you take if you splash these into your eyes?

Some are corrosive HCl, NaOH, HC2H3O2 Use eyewash immediately, have your lab partner notify the instructor about the accident

Which chemicals in lab 6 are hazardous, and what hazards are they? What actions should you take if you spill these on yourself?

Some are corrosive HCl, NaOH, NH4Cl are corrosive First, flush affected area with water, next have your lab partner notify your instructor about the spill.

What solvent is used for the freezing point depression experiment?

Stearic acid

What is the assumption we are trying to validate in Part A of the calorimetry experiment?

Styrofoam cups isolate the system and surroundings from the environment?

In lab 9, was the original assumption that all of the Cu^2+ would be present as Cu(NH3)4^2+?

The assumption was very good as the [Cu^2+] is so small as to be negligible.

Give a brief description of lab experiment 3:

The colligative properties lab was designed to determine the offed on the freezing point of steric acid when small amounts of lauric acid are added. Each addition lowered the freezing point

Select the statements with respect to waste disposal in the Electrochemical Cells Experiment:

The contents of the HALF CELL module should be disposed of in the waste container in the hood. Metal and graphite electrodes should be rinsed with water, dried, and returned to their positions on the lab bench. Dilute Copper and ascorbic acid solutions should be disposed of in the waste container in the hood

The first occurs when mmolCo3^2- = mmolHCl Canalyate*Vanalyte = Ctitrant*Veq1 (.1)(20ml) = (.16)(Veq1) Veq1= 12.50mL

Which of the following are benefits of a pH titration that is monitored using a pH electrode?

The identity of the analyze can usually be determined from the pH at the midpoint. An accurate visual indicator is not necessary. The titration does not have to be stopped exactly at the equivalence point.

Select those that are TRUE for a titration of .2M KHP with a .20M HCl as the titrant compared to a titration with .20M NaOH as the titrant in the lab.

The initial pH would be the same The equivalence volume would be the same

When pouring two liquids together in the styrofoam cup calorimeters, why should care be taken to avoid splashing or spilling the liquid?

The mass of the liquids are part of the calculations, loss of mass affects accuracy

Please describe the rules for handling significant figures for Lab 1 Data Table A

The mmol, volume, and concentration all have 2 sig figs The temperature is to the .01C

The pH will be equal to pKa1 at the second midpoint or 6.35

The pH will be equal to pka2 at the first midpoint or 10.33

In lab 11, if the reaction of .001M S2O3^2- goes from colorless to dark in 47 seconds, what is the reaction rate? How is this calculated?

The rate of consumption of S2O3^2- is 0.001M/47seconds --> 2.1x10^-5M/sec Because of the 1:2 stoichiometry of 12 to S2O3^2- in the timer reaction, the rate of I2 disappearance is 2.128x10^-5M/S * 1M I2/ 2M S2O3^2- --> 1.064x10^-5M I2/sec. Since this has a coefficient of 1, it represents the reaction rate. SO the reaction rate is 1.064x10^-5M/sec

2. The rate-determining step involves a persulfate ion decomposing. If this is true, what should happen to the rate if the concentration of per sulfate ion is doubled and other concentrations are held constant?

The rate will double

The rate-determining step has two iodide ions coming together. If this is true, what would happen to the rate if the concentration of iodide ion is doubled and other concentrations are held constant?

The rate will increase by a factor of 4

The rate-determining step has two iodide ions coming together. If this is true, what would happen to the rate if the concentration of per sulfate ion is doubled and other concentrations are held constant?

The rate will not change

If the spectrophotometer had been set to a DIFFERENT wavelength to measure absorbances, how would this have changed the results?

The results would have been the same

Based on the result for the equilibrium constant of the reactions in Lab 5, which of the following statements are correct about the reaction?

The sign on ΔHnot cannot be determined from K ΔGnot is less than zero The reaction favors PRODUCTS.

What happens to the temperature change when the amount of limiting reactant is doubled?

The temperature change will double

What happens to the temperature change when the amount of NON-limiting reactant is doubled?

The temperature change will remain the same

In your lab write-up, three possibilities for the mechanism of the rate determining step were listed. 1. The rate-determining step has two iodide ions coming together. 2. The rate-determining step involves a persulfate ion decomposing. 3. The rate-determining step has an iodide ion and a persulfate ion coming together. Which mechanism did your experiment confirm?

The third

When working with a buret, one should take care that:

The tube below the stopcock is completely filled The buret is conditioned by rinsing it with the titrant before use The last drop of liquid on the tip is flushed into the analyte

A calibration curve should have which of the following graph attributes?

The x- and y- axis should be labeled with units as well as quantities. The command for getting and equation is "Add Trendline" in Microsoft excel Absorbance is on the y-axis Concentration is on the x-axis

Given the concentrations and volumes of Fe^3+ and SCN^- to be used in Parts A and B of Lab 5, which of the following statements is true?

There is a large excess of Fe^3+ for the calibration curve, but roughly equal amounts of the two ions for determining the equilibrium constant.

What should be done with the wastes generated in Lab 6?

They can all be flushed down the sink with water

What should be done with the wastes generated in lab 7?

They can all be flushed down the sink with water

In lab 9, Solubility product constant experiment, which of the following are hazards of potassium iodate (KIO3), and copper iodate (Cu(IO3)2)?

They're strong oxidizing agents

Volumetric flasks are built to __________ a known volume of liquid to an accuracy of about _____% of the flask's capacity.

To contain 0.1%

A buret should be conditioned, then filled:

To slightly below the top scribe mark (0.00mL).

Two ways to calculate 1) Add Veq1 and Vmid1 = (12.50mL + 6.25mL) = 18.75mL 2) 3/2(Canalyate*Vanalyate) = Ctitrant*Vmid2 (3/2)(.1)(20ml)= (.160)(Vmid2) Vmid2= 18.75mL

To prepare a pH = 7.50 buffer with Na2HPO4*7H2O, what other material is needed and why? H3PO4 + H2O <--> H2PO41- + H3O1+ pka1= 2.12 H2PO41- + H2O <--> HPO42- + H3O1+ pka2= 7.21 HPO42- + H2O <--> PO43- + H3O1+ pka3= 12.32

Use NaH2PO4*H2O A pH of 7.50 is closest to the pka of this (7.21)

In the laboratory safety video, they demonstrated the following:

Use of emergency drench hose Use of safety shower Proper lab attire Use of the emergency eye wash

When the centrifuge process is complete, students should do which of the following?

Using an eyehole on top, monitor the spinning rate and open the lid only after the rotor has slowed significantly. Wait for the rotor to come to a complete stop before attempting to remove your test tubes

What formula is used to determine the mmol of acid and base in the reaction table?

Volume (mL) X concentration (M)

If either stearic acid or lauric acid is spilled on the skin, it should be __________.

Washed with soap and water

If you measured a shift in the copper/ascorbic acid cell potential when the pH was changed, what was the origin of the shift? (Which half cell potential was changing?)

When pH changes, the value of Q changes. The reaction quotient contains a term for [H^+] The ascorbic acid hal-reaction contains two H^+ ions The Cu^2+/Cu half cell did not have a role in potential change** The potential change was due to the pH change in the ascorbic acid half cell**

Which of the following is not a colligative property?

density enhancement

Consider the following elementary reaction: Cl2 + 2 Br− → 2 Cl− + Br2 1) If 100 Cl2 molecules react in a second, how many Br− ions react in a second? 2) Compared to the rate at which Br^- ions react, the rate at which Cl2 molecules react is which of the following?

half as large.

Molar solubility has units of _________.

mol/L

How many grams of H2PO4^1- are required to prepare 100ml of a pH= 7.50 buffer with 0.01119 mol Na2HPO4? (pka= 7.21)

pH= pka + log(base/acid) 7.50= 7.21 + log(0.01119mol/mol acid) mol acid= 0.005739 0.005739mol NaH2PO4 * (137.99g/1mol) = 0.792grams

What is the proper attire for lab?

pants that extend to the ankles shoes that over the heels and toes a shirt and pants that overlap about 6" in the middle to cover the torso A shirt that covers the shoulders and extends about 6" below the waist

The formula measuring changes in heat is q=msΔt, what does each of the variables represent with units?

q= the heat of change, in J or kJ m= mass of material in grams s= specific heat (J/gC) ΔT= change in temperature in C

Which of the following would indicate that the styrofoam cup is able to isolate the reaction mixture from the rest of the universe?

qcold = -qwarm

It is good practice to "condition" a pipet before using it by:

rinsing it with a few milliliters of the solution that will be pipetted.

Most pipettes are built to _______ a known volume of liquid.

to deliver

In a Beer's law plot, what is the x-axis, y-axis, slope, and intercept represent?

x-axis is Concentration y-axis is Absorbance Slope is Molar absorptivity*Pathlength Y-intercept is the absorbance of the blank

The formula for predicting freezing point depression is ΔTf= mc(kf), what do each of the variables represent with units?

ΔTf= amount freezing point is lowered in Celsuis mc= colligative molality (number of particles the material forms when it dissolves (van't hoff factor) multiplied by the concentration in mol solute/kg solvent kf= freezing point depression constant in units of Celsius/m

Chem Lab Final

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