Chemistry 3202Unit 2 Test 2Page 1 of 10
Chemistry 3202
Unit 2 Test 2
2005 - 2006
Part I - Multiple Choice: Using the form on page 5, circle the letter of the best response.
1.What is trueabout anytitrationinvolving a monoprotic acid and a monobasic species?
A.The acid-base indicator changes colour at the equivalence point.
B.The moles of acid equal the moles of base at the equivalence point.
B.The pH at the equivalencepoint is always 7.
D.The volume of titrant equals the volume of the sample.
2.What is the correct buret reading?
A.17.20 mL
B.17.25 mL
C.18.75 mL
D.18.80 mL
3.Consider the titration curve to the right for the titration of HCl with a KOH solution. What volume of KOH(aq) was required to reach the equivalence point?
A.26 mL
B.27 mL
C.28 mL
D.30 mL
4.What is the best way to minimize random error in a titration experiment?
A.Ensure all chemicals are of the highest purity.
B.Ensure all equipment is clean and dry.
C.Have different people perform the experiment.
D.Perform the experiment several times and average the trials.
5. Which best represents the titration of 50.00 mL HCl(aq) with 0.100 mol/L NaOH(aq)?
A.C.
B.D.
6.Hydrofluoric acid is titrated with potassium hydroxide and the pH changes are monitored using a pH meter:
.
What will be the approximate pH at the equivalence point?
A.1
B. 5
C. 7
D.9
7.Which indicator is yellow in an aqueous solution that has a pH of 10.0?
A.methyl red
B.phenol red
Cmethyl violet
D.thymol blue
8.Phenol red and thymolphthalein indicators are added to a 1.0 mol/L solution of HCl(aq). What colour will be visible in this mixture?
A.blue
B.colourless
C.red
D.yellow
Indicator Used / Colour Observedmethyl orange / yellow
phenolphthalein / colourless
phenol red / yellow
methyl red / yellow
9.A solution is tested using the indicators listed. What is the approximate pH of the solution?
A.2.5
B.5.5
C.6.5
D.8.5
10.Which indicator should be used to detect the first equivalence point?
A. indigo carmine
B. methyl orange
C. methyl violet
D. phenolphthalein
11. Which is dibasic?
A.
B.
C.
D.
12.What is the approximate pH of a solution made by mixing 40 mL of 0.0010 MNaOH(aq) with60 mL of 0.0050 MHCl(aq)?
A.3
B.7
C9
D.11
13.Aqueous sulfuric acid is neutralized by the addition of an excess of sodium hydroxide. Whichhas the highest concentrationafter the second equivalence point has been reached?
A.
B.
C.
D.
14.Solid NaOH is a deliquescent solid– it absorbs moisture from the air making it difficult to obtain a precise mass when preparing a solution of NaOH. Which process should be carried out to ensure a known concentration of NaOH is used in a titration experiment?
A.neutralizationof NaOH with hydrochloric acid, HCl
B.neutralization of NaOH with potassium hydrogen sulfite, KHSO3
C. standardization of NaOH with potassium hydrogen phthalate, KHC8H4O4
D.standardization of NaOH with sodium carbonate, Na2CO3
15.In which part of this curve ishighest when phosphoric acid is titrated with sodium hydroxide?
A.I
B.II
C.III
D.IV
16.Which titration pair would have the lowest pH at the equivalence point?
A. HBr with NH3
B. HCl with KOH
C. HNO2 with LiOH
D. HNO3 with NaOH
Chemistry 3202Unit 2 Test 2Page 1 of 10
Name:______School:______
Chemistry 3202 Unit 2 Test 2 Answer Form
Part 1:For each item, circle the letter corresponding to your choice.
1. / A B C D / 7. / A B C D / 13. / A B C D2. / A B C D / 8. / A B C D / 14. / A B C D
3. / A B C D / 9. / A B C D / 15. / A B C D
4. / A B C D / 10. / A B C D / 16. / A B C D
5. / A B C D / 11. / A B C D
6. / A B C D / 12. / A B C D
Part II:Constructed Responses: Complete each item in the space provided. State final answers in sentence form and follow the rules for rounding/significant digits.
17. Bromophenol blue, HBp, is an acid-base indicator with a pH range of 3.0-4.6. As pH increases it changes from yellow to blue.
{1}a) Write an equation for the ionization of bromophenol blue in water and write the appropriate colours below the corresponding forms of the indicator.
{1}b)If a drop of this indicator is added to a 1.0 M HCl solution. What colour should be observed? Explain.
The weak acid form of the indicator is favoured at pH of 3.0 or less. Since the pH of the HCl solution is 0.00 (-log[H3O+]), the weak acid form of the indicator will have a higher concentration and the colour that should be observed is the yellow colour.
{2}c)Describe how to shift the position of the indicator equilibrium to favour the conjugate base form of the indicator. Explain in terms of Le Chatelier’s principle.
Le Chatelier’s principle states that when a system at equilibrium is disturbed, it respons in such a way so as to counteract the effect of the disturbance. The indicator equilibrium is disturbed by the presence of excess hydronium ions in the acid solution. To shift the position of the equilibrium, base has to be added to reduce the hydronium ion concentration. As this occurs, the weak acid form of the indicator is consumed and more hydronium is formed. The conjugate base form of the indicator is formed along with hydronium and eventually, if enough base is added, the conjugate base form will have a higher concentration than the weak acid form and the blue colour will be visible.
18.A student pipettes 10.00 mL of 0.150 mol/L oxalic acid, HOOCCOOH(aq), a diprotic acid, into a 250 mL Erlenmeyer flask. The oxalic acid is titrated to its second equivalence point using an average volume of 22.14 mL of sodium hydroxide, NaOH.
{2}a)Sketch and label a pH curve for the titration.
{2}b)Write a net ionic equation for each step in the curve and write the overall equation.
{3}c)Calculate the molar concentration of the sodium hydroxide solution.
The molar concentration of the sodium hydroxide solution is 0.136 mol/L.
{4}19.By the end of a titration curve experiment, a student had added20.00 mL of 0.0990 M nitric acid, HNO3(aq), to25.00 mL of 0.0510 M potassium hydroxide, KOH(aq). Calculate the final pH of the mixture in the Erlenmeyer flask.
The pH of the mixture is 1.805. Nitric acid was in excess at the end of the titration.