# Exercises

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1. Explain or define each of the following terms: (a) Precision (b) Accuracy(c) Determinate error (d) Indeterminate error
2. Normally, we perform only a small number of replicate analyses. Explain!
3. A soil sample was analysed for its magnesium content and the results of the analysis are as tabulated below:
 Experient number Mg Content (mg/g) 1 2 3 4 19.6 20.1 20.4 19.8

Calculate: (a) the mean concentration of magnesium in the soil sample (b) the median of the data set (c) the absolute deviation from the mean of the second data point (d) the standard deviation of the data set (e) the confidence interval for the data set at the 90% confidence interval.

4. If the true value for magnesium content in the soil of question 3 above, is 20.0 mg/g, calculate the relative error of the mean.
5. In an experiment that involved measurement of temperature, mass, volume and pressure of a gas, values were reported with their corresponding absolute errors as follows: mass = 0.3124g ± 0.1mg, temperature = 283 K ± 1K; volume = 150.3 mL ± 0.2 mL; and pressure = 1257.4 Pa ± 0.1 Pa. (a) Which of the above measurements will dominate in determiningthe error in the gas constant, R? (b) Explain your choice.
6. To how many significant figures ought the result of the operation $$\ \dfrac{24\ x\ 6.32}{100.0}$$ be reported and what is the calculated uncertainty?
7. If an analysis is conducted in triplicate and the average obtained in the measurements is 14.35 with a corresponding standard deviation of 0.37,express the uncertainty at the 95% confidence level. The t value at 95% level from a table is 4.303.
8. Label each of the components in the following equations as acids, bases, conjugate acids or conjugate bases: (a) HCl + H2O → H3O+ + Cl- (b) NH3 + H2O → NH4+ + OH-
9. Write equations to show the dissociation of H2SO4, HNO3 and HCl.
10. Determine the base dissociation constant, Kb of a base whose solution of concentration 0.01 mole/L has a pH of 8.63.
11. Calculate the pH of a solution in which the hydronium (H3O+) ion concentration is: (a) 1.0 M, (b) 0.01 M, (c) 1.0 x 10-7 M (d) 3.5 x 10-9
12. Determine the pOH and the hydronium (H3O+) ion concentration of a 0.01M NaOH solution.
13. What is the hydroxide (OH-) ion concentration of a solution if the pH is: (a) 8.00 (b) 5.30, and (c) 4.68
14. Calculate the hydronium ion concentration if the pH is (a) 2.78 (b) 6.95 (c) 8.30
15. Write the equation for the Ka of the monoprotic benzoic acid, C6H5COOH whose sodium salt is C6H5COONa.
16. Periodic acid, HIO4, is a moderately strong acid. In a 0.10 M solution, the [H3O+] = 3.8 x 10-2 M. Calculate the Ka and pKa for periodic acid.
17. Is a solution whose [H3O+] = 4.6 x 10-8 M, acidic, neutral or basic? Explain your answer!
18. Define each of the following terminologies: (a) Standard solution, (b)Primary standard (c) Standardized solution (d) Standardization (e) End point of a titration (f) Equivalence point of titration (g) Titration error (h) Titration curve
19. Calculate the pH of a 0.10 M solution of Ca(OH)2. Hint: Ca(OH)2 is a strong base and dissociates to yield 2 moles of OH- ions (Ca(OH)2 → Ca2+ + 2OH-).
20. Characterize each of the following acids as monoprotic, diprotic, or triprotic and give the corresponding ionization reactions for each hydrogen ion for each acid: (a) CH3COOH (b) H2SO4 (c) H3PO4 (d) C6H4(COOH)2.
21. A 25.0 mL solution of KIO3 was placed in a titration flask. 20.0 mL solution of KI and 10.0 mL of dilute sulfuric acid were added to the flask. Theliberated iodine was titrated using a solution of Na2S2O3 of concentration 0.2mol/L while using starch as the indicator. The end point was reached when 24.0 mL of S2O32- solution was run in.
1. This is an example of a substitution titration (an indirect titration). First the analyte IO3- is reacted with excess I- to produce stoichiometrically equivalent amount of I2.

IO3- + I- ® I2 Not balanced

The librated I is titrated with standard S2O32-

S2O32- + I2 ® S4O62- + 2I Not balanced

Write the two balanced redox reactions responsible for the determination of IO3-

2. What was the concentration of the original IO3- solution?
3. Which indicator is the most suitable to use in this titration?
22. Assign oxidation numbers to each atom in the following species: (a) NO3- (b) CaHAsO4
23. Determine whether the following changes are oxidation, reduction, or neither and show the oxidation number change that proves your point. (a) SO32- to SO42- (b)Cl2 to ClO3- (c)N2O4 to NH3 (d)NO to NO3- (e) PbO to PbCl42-
24. Consider the following unbalanced oxidation/reduction reaction for the next two questions: Hg2+ (aq) + N2O4 (aq) ® 6 NO3- (aq) + Hg22+ (aq)
1. What is being oxidized in the reaction?
2. What is being reduced in the reaction?
25. Find the oxidation number of N in NO3- and Hg in Hg2+.
26. Give the complete balanced equation in acidic media for the reaction in question 24 above.
27. Identify the reducing reagent in the following redox reaction,

Hg2+ (aq)+Cu(s)→Cu2+ (aq)+ Hg(l)

28. Select the spectator ions in the following reaction:

Pb(NO3)2 (aq) + 2NaCl(aq) → PbCl2(s) + 2NaNO3 (aq) (a) Na+ (aq), NO3- (aq) (b) Pb2+ (aq), NO3- (aq) (c) Na+ (aq), Cl- (aq) (d) Pb2+ (aq) ,Cl- (aq), Na+ (aq), NO3- (aq) (e) Pb2+ (aq), Cl- (aq).

29. Permanganate ion is converted to manganese (II) ion by oxalic acid. What is the oxidizing agent? What is the reducing agent? Balance the reaction:

MnO4- (aq) + H2C2O4 (aq) → Mn2+ (aq) + CO2 (g) (in acidic, aqueous solution).

30. Balance the following reaction that occurs in acidic medium using the ion-electron method: Fe2+ + MnO4- → Fe3+ + Mn2+

This page titled Exercises is shared under a CC BY license and was authored, remixed, and/or curated by Paul M. Shiundu (Arican Virtual University) .