C126 FINAL
equivalence point
when moles of acid equal the moles of base
how is the order of hypochlorite determined in the chemical kinetics experiment
while still maintaining pseudo-order conditions the concentration of NaOCl is halved and and is plotted as before. any change to the slope reveals the order of the slope
What color ppt does this reaction make Cl^- (aq)+Ag^+ (aq) ↔ AgCl(s)
white
abscissa
x value
b
y intercept
y=mx when
y is equal to zero and x is equal to zero so the line goes through the origin
ordinate
y value
how do you plot two variables that are inversely proportional
y vs 1/x
What color ppt does this reaction make Pb^(2+) (aq)+CrO_4^(2-) (aq) ↔ PbCrO_4 (s)
yellow
What oxidation state of chromium are encountered in a lab and which exists in neutral, basic, and acidic conditions?
+3 and +6 chromium (III) can be oxidized to Chromium (VI) with several oxidizing agents like H2O2 in 6M NaOH. In neutral or basic conditions, Chromium (VI) exists as a bright yellow chromate ion CrO42-. In acidic solutions, the orange chromate Cr2O72-(aq) species is produced. It is easy to distinguish chromium from iron (III) which also forms yellow solutions because iron does not undergo color change upon acidification
What is the value of delta G at equilibrium?
0, but deltaG° is not 0, it is a measure of the driving force for PbCl2 to dissolve in water under standard conditions
boiling point constant for water
0.51°C/m
in the colligative properties experiment what was the value of i for the unknown
1 because the unknown was a nonelectrolyte
freezing point constant for water
1.86°C/m
How much of a face atom lies inside on cubic unit cell?
1/2
1What is the mole-to-mole relationship between KHP and NaOH?
1:1
What is the volume required to reach the half-equivalence point in the titration of a 30.0 mL sample of 0.10 M acetic acid with a 015 M sodium hydroxide solution?
30.0 mL x 0.10 M/0.15 M = 20.0 mL. The volume at the half-equivalence point would be 10.0 mL.
What is a complex ion?
A central atom and one or more ligands (ion or molecule that possesses one or more pairs of unshared electrons) Many are colored and can be used for the determination of metals by visible spectroscopy (depends on the ability of a spectrometer to detect very small differences in the absorption of visible light by a colored substance at a characteristic wavelength. It also depends on the assumption that the amount of absorption relates directly to the concentration of the colored substance)
Why should ions be separated from all other before the identification of that ion?
A false positive could occur when performing the tests if the ions were not separated
Why can't you look for a red solid rather than a red solution as the endpoint of your titration in the free energy lab?
A red solution forms when when the first trace of silver chromate is overlaid on a yellow background. If a red precipitate is present than too much of the silver chromate is present and the titration has been overshot. Therefore the endpoint is determined by the present of a dull red/faint pink solution instead of the formation of a red precipitate
What will happen to the equilibrium position of the solubility reaction when you add strong acid to the saturated solution. What evidence would you use to support this? What would happen if you added strong base next? What evidence would you see to support this?
A strong acid would react with C2O42- creating a hole on the product side. The reaction would shift to make more products and as a result the precipitate will dissolve A strong base would react with the Ca2+ as a result the reaction will shift to make more reactants and a precipitate would form
What happens when you add 6 M NaOH to Mg(OH)2? What happens if you then add 6M HCl?
A white gel like precipitate formed (both were colorless to begin with). After HCl is added, the precipitate dissolved. If more NaOH is added, the precipitate will form again
What happens if you add HCl to AgNO3, then add 15M NH3?
A white precipitate is formed, when NH3 is added it dissolves. If HCl is added, the solution warms, gas forms, and ppt forms.
In our qualitative analysis scheme, what could be used to separate an aqueous solution of Ni2+ from Ag+?
Adding HCl will cause a white precipitate, AgCl, to from. the Ni2+ ion will not precipitate
Which cations dissolved in NH3 in the cation analysis lab
Ag
Which cations precipitate with HCl in the Cation analysis lab?
Ag and Pb
Give an example of an aqueous solution where more than one equilibrium is established
AgCl(s) <--> Ag+ + Cl- NH3(g) +H2O <--> NH4+ +OH- When these two solutions are combined the reaction becomes AgCl+2NH3 <--> Ag(NH3)2+ +Cl- The equilibriums of the two separate reactions influence each other, causing le chatelier effects until all reaction involved are in a state of equilibrium
What happens if you add (NH4)2C2O4 to BaCl, then add water, HCl and NaOH?
An opaque white ppt forms. After the HCl is added, the precipitate, the precipitate will dissolve but will reform when NaOH is added
Why is it not very useful to use HCl as a spot test reagent between Pb2+ and Fe2+?
Because although HCl forms a white precipitate with lead (II), it also forms a white precipitate with other cation so it is not a good indicator for lead. Furthermore, iron (II) does not precipitate with HCl
How could you confirm the presence of Fe with a spot test
Blue black ppt with K4FeCN6 of brown ppt with DMG
For the kinetics experiment, what is absorbing light in during the reaction?
Blue dye
Say you are given 2 solutions one composed of 1.0 mole of an ionic compound that completely dissociates into 3 ions dissolved in 100.0 g of water and a second composed of 1.0 mole of a nonelectrolyte also dissolved in 100.0 g of water. Compare and contrast the change in boiling points of these tow solutions along with a comparison to the solvent. Explain your comparison/contrast.
Both of these solutions would increase the boiling point of water because the particles physically get in the way of water molecules trying to enter the vapor phase. Because of this the vapor pressure is decrease. Since boiling occurs when vapor pressure equals atmospheric pressure, it will require more energy to boil water with these solutes. Furthermore, the ionic compound will increase the boiling point 3 times as much as the nonelectrolyte.
What happens if you add 6M NaOH to Al(OH)3? What if you add water and HCl next?
Both solutions are colorless, when combined a white precipitate will form. When HCl was added, the precipitate disappeared. If more NaOH is added, a precipitate will reform and the solution will become warm
Why is it possible to separate Cu2+ from Mg2+using NH3?
Both the Cu2+ and Mg2+ react with the hydroxide ion that is present in solution producing a blue ppt with the Cu2+ (Cu(OH)2) and a white ppt with the Mg2+ (Mg(OH)2) But with the NH3 present the copper will further react to form Cu(NH3)4+ which dissolves and thus we will have a deep blue solution with the white Mg(OH)2 that can be centrifuged and decanted and thus separated
How is the rate constant for the overall reaction determine in the Kinetics experiment?
By finding the observed rate constant from the slope of the linear relationship and using the bleach concentration and the order to determine the actual rate constant
How is the molarity of NaOH determined in the reversible reactions lab?
By knowing the volume of base needed to neutralize a known weight of KHP. Moles of KHP can be determined using the molar mass At the equivalence point moles of acid=moles of base Use moles of acid and the volume to get molarity Once the molarity is found the percent purity of and unknown KHP sample can be determined by finding the mass of KHP and dividing it by the actual mass.
How was the graph created in the Ka lab
By plotting pH vs volume of base added
Write the equilibrium reaction that occurs when you place enough calcium oxalate, CaC2O4 in water to form a saturated solution
CaC2O4(s)<--> (H2O on top of the arrow) <--> Ca2+ (aq) +C2O42-(aq)
An insoluble salt of a weak acid may frequently be dissolved by the use of a strong acid. Write a balanced equation showing an example of this statement
CaCO3(s) <--> Ca2+(aq) + CO32-(aq) An acid will react with the CO32- and produce HCO3- which will decrease the amount of a product shifting the reaction to the product side and thus dissolve more of the CaCO3
An unknown metal is oxidized spontaneously with Cd2+ being reduced to Cd. The E°cell is measured to be +0.337V. What is the E°red of the unknown metal ion to the elemental metal?
Cd2+ to Cd E°red = -0.403 V Thus 0.337 V = -0.403 V + E°ox and E°ox = 0.74V
Give an example of a reaction that involves a ligand exchange as well as geometrical structural change
Co(H2O)62+(aq)+4Cl-(aq) <--> CoCl42-(aq)+6H2O(l) First complex is pink the second one is a deep blue. Cobalt (II) ion is quite stable, and its aqueous solutions can be can be exposed indefinitely to air without oxidizing to cobalt (III). The aqua complex has a symmetric octahedral arrangement. Cobalt (II) also exhibits a coordination number of 4. This reaction involves a shape change in the geometry of the complex ion from octahedral to tetrahedral. It is an endothermic reaction so at low temp reactants are favorable whereas at high temperature products are favorable
What happens if you add 12 M HCl to Co(NO3)2 and then add DI water?
Co(No3)2 is a light pink solution. When HCl is added, the solution becomes warm, deep blue, and gas forms on top. When water is added the pink color returns and solution is still warm. If the solution is heated it turns blue whereas if it is placed in an ice bath it turns pink
What color is copper in an aqueous solution? Why? What would happen if you add ammonia to this reaction?
Copper exists as a light blue complex, Cu(H2O)42+, with water when no other ligands are present. When ammonia is added, ligand exchange occurs and copper forms a deep blue complex, Cu(NH3)42+, this switch occurs because ammonia acts as a weak base in aqueous solutions. When it is placed in water it reacts to form NH4+ and OH-. However since the forward arrow is shorter, most of the ammonia remains as molecules. When ammonia is added to a copper (II) solution, the copper aqua complex first undergoes exchange with the hydroxo group and a blue precipitate, Cu(OH)2, forms. If more ammonia is added the precipitate dissolves and the copper (II) amine complex is formed. The deep blue color is used to detect very small concentrations of copper (II) ion in solution
What happens if you add 15 M NH3 to CuSO4 and then add HCl?
CuSO4 is a light blue solution to begin with. After NH3 is added, a dark blue/indigo solution forms. When HCl is added, solution turned back to light blue and gas formed
What graph is created in the electrochemistry lab and what values are determined from the graph?
Delta G vs. T (Kelvin). -Delta S is the slope delta H is the y-intercept
How is the half equivalence point determined from the graph and what does this tell us about pH?
Divide volume at equivalence point by 2 to get the volume of the half equivalence point Then you look the corresponding pH on the graph At this point pH=pka so you use 10-pka to get Ka
How is a titration different than a reaction?
During a titration, you control the addition of one reactant to the other
The following reaction is pink in cold water and blue in hot water: Is the reaction exothermic or endothermic? Co(H2O)62+ + 4 Cl- <--> CoCl42- + 6H2O (CO(H2O) is pink and CoCl4 is blue).
Endothermic
What kind of blue dye was used in the kinetics lab?
FD&C 1
what type of blue dye was used in the chemical kinetics experiment
FD&C Blue#1 (blue food coloring)
Which type of unit cell has the greatest percent occupied volume?
Face centered (74%)
What happens when you add 0.1 M KSCN to 0.03M FeCl3? What happens if you then add HCl?
FeCl3 is a yellow liquid to begin with while KSCN is colorless. When these two are combined a dark red-brown solution forms. If a lot of HCl is added, the color changes to burnt orange
Explain what happens and describe what you see as you add an aqueous solution of NH3 to an aqueous solution of Cu(NO3)2.
First, this reaction occurs: NH3 (aq) +H2O(l) ↔ NH4+ (aq)+ OH- (aq) Then, Cu2+ from Cu(NO3)2 reacts with the OH- to produce Cu(OH)2. This forms a light blue precipitate. The excess Cu2+ then reacts with NH3 to from Cu(NH3)42+ which results in the formation of a dark blue solution. the aqueous Cu(II) ions interact with the OH- present in the weakly basic solution to form solid copper (ii) hydroxide and then further reacts to form a solution as the complex ion with ammonia
How can you confirm the presence of K+
Flame test. Purple flame confirms K+
If a solution possibly contained Pb, Ag, and Fe, what could you conclude from the fact that no precipitate formed when HCl was added?
HCl foms a white precipitate with Pb and Ag If no precipitate forms, then these two ions are not present in the solution However, Further testing must be done to confirm the presence of Fe
Show a derivation of the relationship between pH and pKa at the half-equivalence point.
Henderson-Hasselbach equation: pH = pKa + log [A-]/[HA] At the half-equivalence point, the [A-] = [HA] thus pH = pKa + log 1 thus pH = pKa + 0 finally pH = pKa at the half-equivalence point.
What are some sources of error in experiment 3 and determining the Kb value and how would it impact the molar mass of ethylene glycol?
If Kb is too large when the molality is calculated there will be a smaller number of moles determined so when the molar mass is calculated it will be too large. Similarly, if the Kb value is too small the number of moles of ethylene glycol will be too large so when the molar mass is calculated it will be smaller than is should be.
Using the indicator chart in your lab manual identify a range of pH values possible if a solution containing methyl red is yellow and a solution containing phenol red is yellow
If Methyl red is yellow then pH > 6, if phenol red is yellow then pH < 6.6. Thus, the pH must be between 6 and 6.6
Describe the function of a salt bridge
In a voltaic cell, the salt bridge allows the spontaneous reaction to continue since we do not have a build up of charge in the compartments. The anions flow through the salt bridge into the anode compartment to counter the build up of positive change and cations flow through the salt bridge into the cathode compartment to counter the build up of negative charge
Explain how an increase in temperature affects the equilibrium of an exothermic reaction and explain the effect on the equilibrium constant
Increasing the temperature causes the reaction to shift to the reactants thus decreasing the K value
In what form (Fe3+ or FeSCN2+) do you think that iron could be determined by visible spectroscopy?
Iron could be determined by visible spectroscopy when it is in the form FeSCN^2+. This is because the FeSCN^2+ is a dark red color with large and complex molecules whereas Fe3+ is light yellow. Because FeSCN^2+ is a darker color it easier to detect using visible spectroscopy
How is chromate ion an indicator in the free energy lab
It causes a red coloration due to formation of Ag2CrO4 once all of the chloride has reacted to form less soluble AgCl
Why is KHP a good acid to use in the standardization of NaOH?
It is a solid so it can be accurately and precisely weight out to 3 or 4 decimal places.
Why is it difficult to completely precipitate aluminum ion as a hydroxide?
It is difficult because aluminum will react with OH- to form insoluble Al(OH)3. However, if additional OH- is present, it will continue to react to form soluble Al(OH)4^-
What is kobserved and how is it obtained?
It is the product of the rate constant (K) and [NaOCL]^n It is the absolute value of the slope of the linear graph
What happens if HCl to K2CrO4 and then add NaOH?
K2CrO4 is a bright yellow. When HCl is added, a bright orange solution forms. When NaOH is added, the bright yellow solution reforms
balanced equation of KHP and NaOH
KHC8H4O4(aq)+NaOH(aq)--> H2O(l)+KNaC8H4O4(aq)
What is the reaction that occurred in the titration of KHP with NaOH?
KHC8H4O4(s)+NaOHKNaC84O4(aq)+H2O(l)
What is the salt bridge composed of in the electrochemistry lab and why is it used?
KNO3. It is used to allow electrical neutrality to be maintained. Negative ions flow to the anode and positive ions flow to the cathode.
What is oxidized/reduced in the Pb and Cu voltaic cell?
Lead is oxidized and Cu is reduced
How was the graph created in the free energy lab and what values were calculated from it?
Ln Ksp vs 1/T. the slope was -deltaH°/R the y-intercept was deltaS°/R
Which error would result in too large a calculated value for the molar mass of ethylene glycol in the colligative properties lab?
Loss of measure of ethylene glycol when preparing the ethylene glycol solution
what reactant is standardized in the titration experiment
NaOH
Would your experimental data be of no used if you had used 5 g of lead (II) rather than 2 g in the free energy lab?
No. The lead (II) chloride is dissolved in hot DI water forming a saturated solution. Therefore, if a greater mass is added the same amount will dissolve in the solution and excess precipitate will form. However, since only the solution is transferred with the pipet and the precipitate remains, the formation of excess precipitate should have no effect
What are some sources of error in Determination of Ka lab and how did they effect experimental results?
One error could have resulted from some of the NaOH touching the wall of the beaker which would result in a larger volume oh NaOH used than necessary. Thereby increasing the volume at the equivalence point and half equivalence point which would result in a higher pH at the equivalence point thereby resulting in resulting in a smaller Ka
What are some sources of error in experiment 5 and how did they effect experimental results?
Over titrating the impure sample of KHP result in a too large calculation of the percent purity of the impure KHP sample.
Explain the effect that "over-titrating" the unknown weak acid would have on the calculated Ka value in the determination of Ka lab
Over-titrating the unknown acid would have no effect in this experiment, different indicators were used. Each indicator changed color at a different pH so to reach the equivalence point the solution would need to be titivated beyond the end point. Additionally, in this experiment, the solution was titrated to the point where the pH levelled off. If the solution was over titrated the part of the graph which levelled off would just be longer. Furthermore, the Ka is determined by the half equivalence point which is before the equivalence point so no effect will be observed
which should give better accuracy to the theoretical molar mass, p vs 1/v or p vs. V?
P vs 1/v because it is a linear relationship so you can use the slope which takes into account all the points in the data set which minimizes error. If using P vs V you use just one point and for all we know that point could be an outlier.
Which cations dissolved in HNO3 in the cation analysis lab?
Pb and Fe
Which cations precipitate with NH3 in the cation analysis lab?
Pb and Fe
Determine the reaction that would occur in a voltaic cell between the two reduction half reactions of Sn2+ going to Sn and Pt2+ going to Pt
Pb2+(aq) + 2e- <--> Pb(s) Ered° = -0.126V Sn2+(aq) + 2e- ,<--> Sn(s) Ered° = -0.136V Turn the tin containing reaction around, E°ox = +0.136V and the E°cell = 0.010 V
How can you confirm the presence of nickel?
Pink precipitate when adding DMG or teal precipitate K4[Fe(CN)6]
Identify the particular situation in which you would use a spot test reagent, a precipitating reagent and a precipitate-dissolving reagent
Precipitating reagants and precipitate-dissolving reagents are used to isolate the ions from a mixture. Spot tests are used to confirm the presence of a suspected ion. Use precipitating when more than one ion and spot test when there is only one
Explain how the use of "precipitating reagents" and the use of "spot test" reagents are different
Precipitating reagents are used to separate certain ions by forming a precipitate with them, after a precipitate forms it is centrifuged, decanted, and further precipitating agents may be added to see if any other precipitates form. However, they are not used to confirm or deny the presence of cations because the precipitating agent can precipitate more than one ion. Instead, a spot test reagent is use to confirm/deny the presence of a particular cation. Furthermore, it is used when only one cation is present in the solution.
What are some sources of error in Free energy lab and how did they effect experimental results?
Pulling in solid lead (II) chloride into the pitpet, leaving the solid lead (III) chloride in the pipet that precipitate after pulling up only solution (the calculated value of Ksp would be too big). Transferring any solid lead (II) chloride from the outside of the pipet. One example, pulling undissolved solid into the pipet when retrieving the dissolved PbCl2 at temperature. This causes too much AgNO3 to be used since there is too much Cl- ion present Thus calculating too large a concentration of both Cl- and Pb2+ and a calculated Ksp is too large.
How could you confirm the presence of Ag with a spot test?
Purple brown ppt with K2CrO4 and brown ppt with DMG
correlation coefficient
R^2; gives a numerical value (maximum of one) that helps describe the fit of the data to a linear relationship
Describe, using words and chemical equations, the reaction of an aqueous solution of silver nitrate with aqueous hydrochloric acid and the subsequent reaction with aqueous ammonia
Silver nitrate is a soluble salt with the nitrate ion as a spectator ion, the aqueous hydrochloric acid with form a white precipitate of AgCl Then the addition of ammonia will form the silver complex with the NH3 which dissolves the precipitate and forms an aqueous solution. Ag+(aq) + HCl(aq) <--> AgCl(s) + H+(aq) AgCl(s) + NH3(aq) <--> Ag(NH3)2+ (aq) + Cl-(aq)
In the Colligative properties lab, What are the I values for NaCL and Ethylene Glycol, and what happens if the NaCl solution is overboiled?
The I value for NaCl is 2 and the I value of ethylene glycol is 1 Overboiling will result in too small a value in calculating the Kb.
Why can you use the pH info at the half-equivalence point in a titration of a weak acid with a strong base to determine the Ka of the weak acid
The amount of weak acid present is equal to the amount of conjugate base produced at the half-equivalence point
How would a determination of the boiling point elevation constant be affected by forgetting to account for the fact that the compound is ionic and breaks up into 3 ions per formula unit?
The boiling point is measured and the concentration in molality is known The kb is calculated from the equation, the true value of kb should be a third of the value of the calculated kb if the value of i is not used
In our qualitative analysis laboratory, what was the important reason for keeping some of the compounds in the hood?
The concentrated acids/bases are kept in the hood to minimize and/or contain spills and odors
As the absorbance value of the reaction mixture decreases throughout the reaction process, what is happening to the concentration of the blue dye? What is happening to the rate law?
The concentration of the blue dye decreases This relationship is illustrated in beer lamberts law, A=bec. Where A is the absorbance, and c is the concentration Since A and c are directly proportional as absorbance decreases the concentration decreases as well. Since the rate law for the kinetics experiment was rate=k[blue][bleach] decreasing the concentration of the blue dye decreases the rate of reaction For example, if the concentration of blue dye decreases by 2 the rate of reaction will decrease by 2.
The boiling point of a solution depends on
The external pressure and the number of dissolved particles in the solution. IT DOES NOT DEPEND ON IMF BETWEEN THE SOLUTE AND SOLVENT
What does coordination number mean?
The number of nearest neighbors is how many atoms touch one atom
In the Kinetics experiment, the rate of disappearance of the color of the blue dye as it reacted with bleach through the use of spectroscopy was observed. How was the order of blue and the order of bleach determined?
The order of bleach: using the ball park concentration a sample of blue dye with excess bleach was placed in a spectrophotometer and the %T was determined The %T was then used to determine the absorbance using A=log(100/%T) then beer lamberts law (A=ebc) was used to determine the concentration of the blue dye Next, 3 graphs were prepared: concentration vs time (zero order), 1/concentration blue vs. time (second order) and ln concentration blue vs time (first order) The graph with a linear relationship determined the order of blue. The order of blue was determined by diluting the bleach by ½ (still in excess) Then using the calculations listed above the concentration of bleach was determined Once the concentration was obtained, the concentration was plotted using the same relationship that resulted in a linear relationship for the order of blue Then the slopes were compared to determine the order of bleach using the following equation where n is the order of bleach. 0.5n/order of blue=2nd slope/first slope.
What is the purpose of sodium chromate in the free energy lab?
The sodium chromate serves two purposes. First, it serves as an indicator and s second the chromate ion bonds with lead, forming a precipitate
The extent to which a salt dissolves in water depends on
The solubility product constant and standard free energy change between products and reactants
What is standardization?
The use of a chemical reaction to determine the concentration of a solution
A graph of ln Pvap vs 1/T is plotted and a linear relationship if found. Which would be the dependent variable?
The vapor pressure
How would the Ka determined be affected if you incorrectly overestimated the volume needed to reach the equivalence point of the titration when visually analyzing the titration curve?
There is probably minimal impact if the volume is only slightly misread. But too large a volume at the equivalence point results in too large of a calculated volume at the half equivalence point and a little higher pH value, resulting in a smaller Ka
What property do Ag+ and Cu2+ ions have in common?
They are both transitional metals that are soluble in NH3 solution?
Outline in 5 or so brief steps, the determination of the Ka of a weak acid using data from a pH titration
Titrate a known volume of a weak acid with a known concentration of a strong base using a pH meter. Graph the titration curve as pH vs volume of strong base added. Identify the volume of the strong base needed to titrate to the equivalence point. Divide this volume in half and determine from the graph the pH at this half-equivalence point. At this point in the titration, the pH is equal to the pKa because there are equal amounts of conjugate pairs present in the solution
Why is it necessary to measure the boiling point of a pure sample of water prior to experimentally determining the Kb of water through measuring the boiling point of a sodium chloride solution in lab 3?
To account for differences in atmospheric pressure from normal boiling point and to cancel out any errors from the thermometer.
A different indicator was added to each of the 3 titrations in the Ka lab, why?
To demonstrate the difference between the endpoint and the equivalence point
What was the goal of the first day of the Cation Analysis Scheme Lab?
To gather observations that will enable us to determine what is present in an unknown
In the electrochemistry lab, why do you need to polish the metal strips being uses as electrodes?
To remove the oxide coating and to make sure we have a good connection to the metal
How do you calibrate a spec-20? After it is calibrated how do you use it?
Use left knob to set the meter to 0, then turn the light control knob (right) counterclockwise almost all the way and insert the cuvette with water. Close the top and use the right know to adjust to 100%T
How would you dissolve an insoluble salt of a weak acid?
Using a strong acid
What does the term extrapolate tell us?
We are looking at the area outside our data range
How does the indicator methyl orange work?
Weak organic acid. HMO+ is read whereas MO is yellow. The color of the solution reflects whether MO or HMO+ is present in higher concentration
Io/I
When light passes through solutions of colored compounds some of the light is absorbed. The intensity of the light that comes out of the solution (I) is therefore less than the intensity of the light that is originally incident on the solution (Io), and the ratio of Io/I is larger than 1. This ratio depends upon the amount of the light-absorbing compound in the solution. In other words, the ratio depends upon the concentration of the compound in the solution.
What is the half equivalence point?
When the number of moles of base is ½ the number of moles of acid originally present. at this point the Ka=[H3O+]
How could you confirm the presence of Pb with a spot test?
Yellow ppt with K2CRO4 and K4FeCN6 and white ppt with NH3 and DMG
How would you dissolve solid Mg(OH)2?
You could dissolve solid Mg(OH)2 by adding HCl
How could you remove essentially all of the magnesium ion from a solution?
You could remove all of the magnesium ion from a solution by adding NaOH to the solution causing the magnesium to form a solid precipitate, Mg(OH)2
A solution contains Mg2+ and Al3+ ions. How could you separate them?
You could separate the ions by adding something that would precipitate out one of the above ions but not the other. For example, adding a large amount of NH4OH would form soluble Al(OH)4^- and Mg(OH)2 precipitate. Once Mg(OH)2 is precipitated, it could be easily removed, thus separating the ions
A solution contains Mg2+ and Cu2+ ions. How could you separate them?
You could speracte Mg^2+ and Cu^2+ by adding NH3 to the aqueous solution which would form soluble Cu(NH3)2 (aq). Adding additional NH3 would split water forming NH4+ (aq) and OH-(aq) ions. The OH- ions would bond with the Mg 2+ ions forming an insoluble Mg(OH)2 (s) compound separating the two ions.
What is oxidized/reduced in the Zn/Pb voltaic cell?
Zinc is oxidized and lead is reduced
What is oxidized/reduced in the Zn and Cu voltaic cell?
Zn is oxidized and Cu is reduced
colligative properties
a property that depends on the number of particles dissolved in solution, not on the type of particle; vapor pressure, boiling point freezing point, and osmotic pressure
typically how is a reaction run to determine the order of reactions
a series of reactions is run in which the concentration of one reactant is varied systematically and all other concentrations are held constant. this is done so that any observed changes in rate can only be due to the change in concentration of the species that was varied
1. In each case indicate which reagent, hydrochloric acid or sodium hydroxide, would shift the ionic reaction in the desired direction. a. SnS2(s) + S2- (aq) <--> SnS32- (aq) (left) b) NH3(g) + H2O(l) <--> NH4+ (aq) + OH- (aq) (right) c) 2 Sr2+(aq) + H2O(l) + Cr2O72- (aq) <--> 2SrCrO4(s) + 2 H+(aq) (left) d) H+(aq) + HCO3- (aq) <--> H2O(l) + CO2(g) (right)
a. HCl b. HCl c. HCl d. HCl
How do you know when to stop titrating in the Ka lab?
after the pH meter values change dramatically and then the pH levels off
classification of solids
amorphous (no regular structure) or crystalline (regular repeating arrangement of atoms, ions, or molecules)
In the free energy lab, why does the solution not have to be at the temperature collected when titrating?
because the silver chloride is more insoluble than the lead chloride
in the chemical kinetics experiment what is the reactant in excess
bleach (NaOCl, hypochlorite)
Looking at this equation: Fe2O3(s) + 3 H2(g) <--> 3 H2O(g) + 2 Fe(s) Adding Fe would: ____ Raising the pressure would: ___
both no change
how is the rate constant of the overall reaction determined in the kinetics experiment
by finding the observed rate constant from the slope of the linear relationship and using the bleach concentration and the oder to determine the actual rate constant
how was the order of blue dye determined?
by plotting [blue] vs. time (zero order). 1/[blue] vs. time (second order), and ln[blue] vs. time (first order)..the absolute value of the slope is the pseudo order rate constant Kobserved
end point
characterized by a color change since slight excess of base
nonelectrolyte
compounds such as sugar that do not dissociate into ions in water
How would you drive an exothermic reaction that has a greater number of gaseous products than reactants?
cool it down and decrease the pressure
examples of varying arrangement of particles
cubic (all sides the same length and angles of 90°) and triclinic (all sides are different lengths and all angle are different and other than 90°)
when you pour liquid off of a precipitate it is called ___
decanting
nonvolatile solute
do not evaporate easily
the boiling point of solution depends upon a. intermolecular forces present between solute and solvent b. the external pressure c. the number of dissolved particles in the solution d. a and b e. b and c
e
volatile solute
evaporate easily
how is the oder of the reactants determined
experimentally
an experiment is run in a laboratory. the ext P is varied and the boiling point of a sample of water is measured at different pressures what is the independent variable
ext pressure
extrapolate
extending a "curve" outside of the experimental data range, looking for data outside of the experimental data range
What was the indication that your titration was completed in the titration of lead (II) chloride with silver nitrate
formation of a tiny amount of red silver chromate
How would you drive an endothermic reaction that has a greater number of gaseous reactants than products?
heat it up and decrease the pressure
how is titration different from a reaction
in a titration we are controlling the addition of one reactant to the other reactant
how does the addition of a nonvolatile solute affect the properties of a solvent
interferes with the ability of the solvent particles to leave the liquid and enter vapor phase (lowers vapor pressure) which means that a large amount of energy must be supplied to the solution in order for the vapor pressure to equal atmospheric pressure as a result the solution has a higher boiling point
if the reaction order of A is 2 what happens to the rate of the reaction when the concentration of A is doubled
it changes by a factor of 4
why is KHP a good standardizing agent
it is a solid acid so it can be accurately weighed out
What is special about aluminum hydroxide
it is amphoteric (dissolves in both acid and base)
why do we want a linear relationship when graphing
it is easiest to work with
what is parallax and why do you want to avoid it in the colligative properties experiment?
it is the displacement of an object viewed along two different lines of sight. parallax can give you inaccurate readings of the thermometer
Why couldn't you pour the titration waste down the sink in the Ka lab?
it was way to basic
What happens when you cool an endothermic reaction?
it will make more reactants
How would the incomplete dissolution of KHP affect the calculated molarity of the NaOH solution?
it would decrease the molarity
What was the slope of the linear graph in the chemical kinetics lab
kobserved
body centered cubic unit cell
lattice sites are at the corner of the unit cell and one lattice sit is in the middle of the cube 1/8 of each corner atom lies within the unit cell while all of the atom in the middle (body atom) lies within the unit cell 4r=sqrt3*l 68% occupied volume coordination number=8 stoms do not tough along the side nor along the face diagonal instead they tough along the body diagonal (4r)
face centered cubic unit cell
lattice sites are at the corners of the cube and in each face of the cubic unit cell 1/8 of the corner atom and 1/2 of each face atom lie within the unit cell which gives a total of 4 atoms within the unit cell 4r=sq rt 2 times l 74% occupied volume coordination number=12
primitive cubic unit cell
lattice sites are at the corners of the cube only center of the atom (or molecule) lies ar the corner of the cube. corner atom is cut in half by 3 planes of the cube the intersect the corner leaving 1/8 of the atom inside the unit cell 2r=l atoms touch along the side of the unit cell 52% occupied volume coordination number=6
What reaction occurs at the cathode in the reaction in the electrochemistry lab
lead and the unknown metal
Which side of the following equation would heat be on? Co(H2O)6^2+(aq) + 4 Cl-(aq) + <--> CoCl4^2-(aq) + 6H2O(l)
left
How is the Spect 20 set up
left knob (power control knob) to set it to zero when nothing is in the compartment and then you use the right knob (light control knob) to set it to 100 when the bank (water) is in the compartment.
Looking at this equation: 2 SO2(g) + O2(g) <--> 2 SO3(g) + heat Lowering the pressure would cause the reaction to shift ___ Raising the temperature would shift the reaction to the ___
left left
Looking at this equation: 2 Cl2(g) + 2 H2O(g) + heat <--> 4 HCl(g) + O2(g) Raising the pressure would shift the reaction to the ____ Raising the temperature would shift the reaction to the ___
left right
What graph was created in the free energy lab?
lnKsp vs. 1/T
interpolate
looking within the experimental data range for relationships
which of the following errors would result in too large of a calculated value for the molar mass of ethylene glycol in the colligative properties experiment?
loss of measured ethylene glycol
proportionality constant
m, the slope, change in y over change in x
what concentration should be used as the actual concentration of the standardized base
mean concentration
osmosis
movement of solvent particles across a semipermeable membrane
The accuracy of a single measurement can be determined by comparison to a "known value." What additional information, if any, is needed in order to state the precision of the measurement?
multiple data points
Looking at this equation: CO(g) + H2O(g) <--> CO2(g) + H2(g) + heat Raising the pressure would cause ____ ___ Lowering the temperature would shift the reaction to the ___
no change right
does the %T data need to be taken at exactly one minute intervals
no, but you have to know exactly the time changes i.e. if you start at 10:36:18 then 10:48:26 becomes t=12 min 8 sec
What are some sources of error in the chemical kinetics lab and how did they effect experimental results?
not calibrating the spectrophotometer properly and touching the cuvette with bare hands which would lead to erroneous percent transmittance values
What would happen when HCl is added to an aqueous solution of Pb2+?
nothing
unit cell
one cube, repeating unit of a lattice
a molecular compound that exists as a single entity in solution supplies _______ particle(s) per molecule. an ionic compound that dissociates into ions tin solution will supply ____
one; more than one particle per "molecule" (the number of particles depends on the number of ions into which the ionic compound dissociates)
How was each order graph plotted in the chemical kinetics lab and which one had a linear relationship?
order of 1: ln concentration vs time (linear) order of 2: 1/concentration vs time order of 0: concentration vs time
What is the Ka of a weak acid whose pH at the half-equivalence point is 6.3?
pH = pKa = 6.3 thus Ka = 10-6.3 = 5.0 x 10-7
What was plotted to make the titration graphs in the reversible reactions lab?
pH vs. mL NaOH added
what indicator is used in the titration lab
phenolphthalein
how does addition of a solute affect osmotic pressure
physically get in the way of the process of osmosis occurring which increases the osmotic pressure
what is KHP
potassium hydrogen phthalate, KHC8H4O4
the temperature dependence of the rate of the reaction lies within the value of the
rate constant
the rate law is always written in the form
rate=k[A]^m[B]^n
Looking at this equation: 2 NH3(g) + heat <--> N2(g) + 3 H2(g) lowering the pressure would shift the reaction to the ____ Raising the temperature would shift the reaction to the ___
right right
For an ideal gas when the pressure is plotted vs 1/volume what would the slope of the line be equal to?
slope = nRT
the constants Kf or Kb are characteristics of the particular ____ being used and have units of ______
solvent, °C/m where m is molality (mol solute/kg of solvent)
In the free energy lab you are using AgNO3 to determine the amount of an ion present in solution what ion are you directly determining?
the amount of chloride ion present
what was absorbing light in the kinetics experiment
the blue dye
the rates of chemical reactions are dependent upon
the concentration of the reactants and the temperature of the reaction mixture
what happens to the concentration of a solution if it is over-boiled?
the concentration would increase
the rate of a chemical reaction depends upon
the concentrations of the reactants present and the temperature at which the reaction is occurring
An experiment is run in a laboratory. The external pressure is varied and the boiling point of a sample of water is measured at the different pressures. What variable is the independent variable.
the external pressure
What is the point called in an acid-base titration where the conjugate pairs have equal concentrations?
the half-equivalence point
how does the kb value calculated vary when dissolving NaCl in water vs dissolving ethylene glycol in water
the kb value is unchanged between the two solutes
what happens when a substance freezes
the molecules arrange themselves into a more ordered system. in a solution solute particles interfere with this thus more energy must be REMOVED from the solution to cause it to freeze
when comparing equal concentrations of of ionic compound, the compound that dissociations into ______ ______ particles will affect the colligative property to the greatest extent
the most; a strong electrolyte (strong acid, strong base, soluble salts) will have a greater effect than a weak electrolyte of the same concentration
coordination number
the number of atoms that touch completely surrounded atom
in the chemical kinetics experiment the slope of the graph changed by a factor when the concentration of NaOCl was halved. this indicates
the order of the reactant held in excess...if the slope is unchanged, the reaction order is zero, if it changes by the same factor is is first order, if it changed by the square of the factor then is is second order
what causes the change in the colligative property
the physical presence of the solute particles. it doesn't matter what kind of nonvolatile particles are present rather how many particles are present
What would happen when NH3 is added to precipitate AgCl?
the precipitate would dissolve
What is the primary reaction in the Free energy lab?
the precipitation of chloride with the silver ion
titration
the process used to control the progress of the reaction and to determine when it is complete. its the controlled addition of one reactant to another
what is K observed in the chemical kinetics experiment
the product of the rate constant K and [NaOCl]^n
neutralization
the reaction of acids and bases. it is a fast reaction that occurs almost instantaneously as the acid and base are mixed. proceeds to completion until the limiting reagent is completely consumed key feature is combination of hydronium ions and hydroxide ions to produce water produces a salt and water
In the chemical kinetics experiment, the reaction was observed qualitatively and performed quantitatively. Explain how this was done
the reaction was observed qualitatively when the FD&C Blue #1 and bleach was varied to determine the ballpark concentration that will give a reasonable reaction rate. Then the reaction was performed quantitatively to determined the values of m and n and the value of the rate constant for the reaction at room temperature
standardization
the use of a chemical reaction to determine the concentration of a solution
why are neutralization reactions good for standardization
there are typically fast and complete
why did you boil pure water in the colligative properties lab
to take into account for atmospheric pressure differences from the normal boiling point and to cancel out any small errors due to the thermometer that is being used
what balance did you use in the colligative properties experiment
top-loading
true or false. the end point is very close to the equivalence point
true
in cases where the rate of the reaction actually depends on the concentrations of more than one reactant how is the order determined
using "pseudo-order conditions" which means the reaction is run in a large excess of all of the reactants except one which ensures that the concentration of all the reactance in excess will be constant throughout the duration of the experiment
independent variable
value that is being controlled and causes changein another variable.
dependent variable
value that is being measured, changes as another variable is controlled.
weak electrolyte
weak acid or a weak base
