PLEASE HELP!! REALLY CONFUSED WITH ALL OF THESE!! 1. Circle the correct answer.

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.

Comment

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)

Explanation / Answer

1. Using H-H equation ,

pH = pKa + log (base/acid)

KH2PO4 + HCl --------------> KCl + H3PO4

so, pKa = 7.2

pH = 7.2

[acid ] = molarity x volume in liters = 0.1M x 0.1L = 0.01moles

So, 7.2 = 7.2 + log (base/0.01)

0 = log (base/0.01)

1 = base / 0.01

base = 0.01moles

in the option, 50mL of 0.2M HCl = 0.2M x 0.05L = 0.01moles

So, Answer:  50mL of 0.2M HCl

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