PLEASE HELP!! REALLY CONFUSED WITH ALL OF THESE!! 1. Circle the correct answer.
ID: 813906 • Letter: P
Question
PLEASE HELP!! REALLY CONFUSED WITH ALL OF THESE!!
1. Circle the correct answer.
a. Which solution should be added to 100 mL of 0.100 M KH2PO4 to make buffer with a pH of 7.2? pka?s of H3PO4 are 2.2, 7.2, and 12.1
25 mL of a 0.2 M solution of HCl
25 mL of a 0.2 M solution of NaOH
50 mL of a 0.2 M solution of HCl
50 mL of a 0.2 M solution of NaOH
b. Consider the following titrations
HClO3 + OH- " ClO3- + H2O
HClO3 (pKa = 1.95)
HOCl + OH- " OCl- + H2O
HOCl (pKa =7.52)
Ag+ + Cl- " AgCl(s)
AgCl (Ksp = 1.7x10-10)
Ag+ + l- " Agl(s)
AgI (Ksp =1.3x10-17)
Which one of the following statements is TRUE ?
HClO3 gives a shaper endpoint than HOCl and I- gives a shaper endpoint than Cl-
HClO3 gives a shaper endpoint than HOCl and CI- gives a shaper endpoint than I-
HOCl gives a shaper endpoint than HClO3 and I- gives a shaper endpoint than Cl-
HOCl gives a shaper endpoint than HClO3 and CI- gives a shaper endpoint than I-
c. Which one of the following is FALSE?
A titration reaction should have a very high equilibrium constant
It is not possible to titrate a weak base with a strong acid
Very little dissociation occurs for a weak acid
A titration reaction should be rapid
d. The equivalence point for first derivative curve for a titration curve is indicated by
the maximum in the derivative curve
the point where the derivative curve crosses zero
the steepest point on the derivative curve
the minimum of the derivative curve
e. Which statement is TRUE.
pH is not important in EDTA titrations
An EDTA titration can be done for any metal ion.
A metal ion indicator does NOT change the endpoint in an EDTA titration
EDTA forms 4 bonds to the central metal atom in a complex
f. Select the statement that is TRUE.
The titration of Na2HPO4 with NaOH will have one equivalence point
Fe2+ could probably be titrated at a lower pH than Fe3+
Isoelectric pH is the pH of an amino acid if it is dissolved in pure water
a Zwitterion is an ion with a double positive charge
g. If an acid base indicator has a pKa = 5, then its color change occurs approximately over the pH range of ___ to ___.
h. In this type of titration a known excess of reagent is added to the analyte, and the excess is then titrated with a second standard reagent.
displacement
back
blank
direct
i. Which one of the following is FALSE?
EDTA makes six bonds with the central metal ion
A metal indicator must make a stronger bond to the metal than does EDTA
The formation of the Cu-EDTA complex results in a decrease in entropy
A redox indicator is titrated and affects the endpoint.
j. Which one of the following statement is TRUE?
A redox indicator changes color when it accepts or loses electrons
An acid base indicator cannot have acid base properties
Any compound that is a strong acid in water will be a strong acid in acetic acid
When dissolved in an acidic solution, an amino acid rearranges to a Zwitterion
k. Which of the following is a first intermediate form?
K2HPO4
K2HAsO4
Na2SO4
KH2PO4
l. What is the pH at the second equivalence point in the titration of H3PO4?(the pKa?s are 2.2, 7.2 and 12.2)
4.7
7.2
9.7
12.2
m. For the reaction 2MnO4- + 3SO2 + 4H+ ? 2MnO2(s) + 3SO42- + 2H2O, at the equivalence point
nMnO4-=2nH+
nMnO4-=nSO2
nMnO4-=2/3nSO2
nMnO4-= 3/2nSO2
2. Find the pH of the following solutions. Use the Ka?s from Appendix G
a
0.100 M NaHCO3
b
2.0 M Na2CO3
c
0.1 M K3PO4
d
5.0 M H2CO3
3. Draw the principal forms of serine if it is dissolved in water, in strong acid, and in strong base?
water
acid
base
4. Based on the following fractional composition diagram for the weak acid H3A, answer the following.
a) Give approximate values for Ka1, Ka2, Ka3, Kb1, Kb2 and Kb3
b) What are the principal species in solution at pH?s = 1.5, 4 and 13 Approximately, what is the fraction of each that is present at each pH?
c) What is the chemical reaction that corresponds to Kb2?
d) Which pH?s would be good for buffers for this substance?
_______________________________________________________________________
4 A solution is 0.100 M in EDTA and 0.100 M in Fe3+ and is buffered at pH = 10. The formation constant for FeY- is 1.2x1025. The fraction of EDTA in the form Y4- at pH = 10 is 0.36.
_______________________________________________________________________
5. Assume that you have 1.0 M phosphoric acid and 2.0 M NaOH. How much NaOH has to be added to 100.0 mL of the phosphoric acid to make a pH = 7.50 buffer?
__________________________________________________________________
6. (12) 50.0 mL of 0.100 M Fe2+was added to 0.4137 g of a sample that contains KClO3 and an inert material. The reaction is.
6 H+ + ClO3- + 6 Fe2+ ? Cl- + 6 Fe3+ + 3 H2O
When the reaction was complete, the excess Fe2+ was titrated with 11.40 mL of 0.0771 M Sn4+. The titration reaction is
Sn4+ + 2 Fe2+ ? Sn4+ + 2 Fe3+
Calculate the weight percentage of KClO3 in the sample.
25 mL of a 0.2 M solution of HCl
25 mL of a 0.2 M solution of NaOH
50 mL of a 0.2 M solution of HCl
50 mL of a 0.2 M solution of NaOH
PLEASE HELP!! REALLY CONFUSED WITH ALL OF THESE!! 1. Circle the correct answer. a. Which solution should be added to 100 mL of 0.100 M KH2PO4 to make buffer with a pH of 7.2? pka?s of H3PO4 are 2.2, 7.2, and 12.1 b. Consider the following titrations Which one of the following statements is TRUE ? Which one of the following is FALSE? d. The equivalence point for first derivative curve for a titration curve is indicated by e. Which statement is TRUE. f. Select the statement that is TRUE. g. If an acid base indicator has a pKa = 5, then its color change occurs approximately over the pH range of ___ to ___. h. In this type of titration a known excess of reagent is added to the analyte, and the excess is then titrated with a second standard reagent. i. Which one of the following is FALSE? j. Which one of the following statement is TRUE? k. Which of the following is a first intermediate form? l. What is the pH at the second equivalence point in the titration of H3PO4?(the pKa?s are 2.2, 7.2 and 12.2) 2. Find the pH of the following solutions. Use the Ka?s from Appendix G 3. Draw the principal forms of serine if it is dissolved in water, in strong acid, and in strong base? 4. Based on the following fractional composition diagram for the weak acid H3A, answer the following. a) Give approximate values for Ka1, Ka2, Ka3, Kb1, Kb2 and Kb3 b) What are the principal species in solution at pH?s = 1.5, 4 and 13 Approximately, what is the fraction of each that is present at each pH? c) What is the chemical reaction that corresponds to Kb2? d) Which pH?s would be good for buffers for this substance? 4 A solution is 0.100 M in EDTA and 0.100 M in Fe3+ and is buffered at pH = 10. The formation constant for FeY- is 1.2x1025. The fraction of EDTA in the form Y4- at pH = 10 is 0.36. 5. Assume that you have 1.0 M phosphoric acid and 2.0 M NaOH. How much NaOH has to be added to 100.0 mL of the phosphoric acid to make a pH = 7.50 buffer? 6. (12) 50.0 mL of 0.100 M Fe2+was added to 0.4137 g of a sample that contains KClO3 and an inert material. The reaction is. When the reaction was complete, the excess Fe2+ was titrated with 11.40 mL of 0.0771 M Sn4+. The titration reaction is Calculate the weight percentage of KClO3 in the sample.Explanation / Answer
1.a.
25 mL of a 0.2 M solution of NaOH
H2PO4- + NaOH = HPO4-2 + H2O
acid salt
let, x mL of 0.2 M NaOH solution was added.
[salt] = 100*0.1 - 0.2x/100+x
[acid] = 0.2x/100+x
pH = pKa + log[salt]/[acid]
or, 7.2 = 7.2 + log (10-0.2x)/0.2x
or, x= 25 mL
b.
HClO3 gives a shaper endpoint than HOCl and I- gives a shaper endpoint than Cl-
The larger the value of equilibrium constant greater will be the rate of change of EMF (or pH or conductance whatever method is used) at the end point. So strong acids and compounds with smaller values of solubility product give a sharper end point.
c. False statement : It is not possible to titrate a weak base with a strong acid
d. The equivalence point for first derivative curve for a titration curve is indicated by the maximum in the derivative curve
e. True statement: A metal ion indicator does NOT change the endpoint in an EDTA titration
f. True statement: The titration of Na2HPO4 with NaOH will have one equivalence point
g. The color change is not instantaneous at the pKa value, but a pH range exists where a mixture of colors is present. This pH range varies between indicators, but as a rule of thumb, it falls between the pKa value plus or minus one.
pH range = 4-6
h.
Ans : Back titration
Back titration is a titration done in reverse; instead of titrating the original sample, a known excess of standard reagent is added to the solution, and the excess is titrated.
i. False statement: A metal indicator must make a stronger bond to the metal than does EDTA
In fact at the end point EDTA replaces the metal ion indicator from its complex. The colour change occurs due to the formation of free indicator.
j. True: A redox indicator changes color when it accepts or loses electrons
k. KH2PO4 is a first intermediate form. It forms from the dissociation of single hydrogen from H3PO4.
l. ans: 9.7
No calculation is necessary to get the answer. At the second half equivalence point the value of pH = pKa2 = 7.2
At the third half equivalence point the value of pH = pKa3 = 12.2
The value of second equivalence point must be between 7.2 and 12.2
Here you get the answer 9.7
m. At equivalence point no of equivalent of MnO4- and no of equivalent of SO2 will be same
from the reaction we can write , at the equivalence point:
2 MnO4- = 3SO2
or, 2 nMnO4- = 3nSO2
or, nMnO4- = 3/2nSO2
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