AP Chemistry - Electrochemistry Worksheet #8

 1.   Manganese(II) ion is oxidized to permanganate ion by bismuthate ion, BiO3-, in an acidic solution.  In the reaction, BiO3- is reduced to Bi+.
(a) Write a balanced net ionic equation for the reaction.
(b) How many grams of NaBiO3 are needed to oxidize the manganese in 15.0 g of Mn(NO3)2?
 2. Sodium iodate reacts with sodium sulphite according to the equation

        NaIO3  +  3 Na2SO3  -----> 3 Na2SO4  +  NaI

(a) In this reaction, which substance is the oxidizing agent?
(b) How many grams of NaIO3 are needed to react with 5.00 g of Na2SO3?

 3. A sample of a chromium-containing alloy weighing 3.000 g was dissolved in acid, and all the chromium in the sample was oxidized to CrO42-.  It was then found that 3.09 g of Na2SO3 was required to reduce the CrO42- to Cr(OH)3 in a basic solution, with the SO32- being oxidized to SO42-.
(a) Write a balanced equation for the reaction of CrO42- with SO32-.
(b) How many moles of CrO42- reacted with Na2SO3?
(c) How many grams of Cr were in the alloy sample?
(d) What is the weight percentage of Cr in the alloy?
 4. Solder is an alloy containing the metals tin and lead. A particular sample of this alloy weighing 1.50 g was dissolved in acid.  All the tin was then converted to the +2 oxidation state.  Next, it was found that 0.368 g of Na2Cr2O7 was required to oxidize the Sn2+ to Sn4+ in an acidic solution. In the reaction the chromium was reduced to Cr3+ ion.
(a) Write a balanced net ionic equation for the reaction between the Sn2+ and Cr2O72- in an acidic solution.
(b) Calculate the number of grams of tin that were in the sample of solder.
(c) What was the percentage by weight of tin in the solder?
 5. All the iron in a 2.000 g sample of an iron ore was dissolved in an acidic solution and converted to Fe2+, which was then titrated with 0.1000 M KMnO4 solution.  In the titration the iron was oxidized to Fe3+. The titration required 27.45 mL of the KMnO4 solution.
(a) How many grams of iron were in the sample?
(b) What was the percentage iron in the sample?
(c) If the iron was present in the sample as Fe2O3, what was the percentage by weight of Fe2O3 in the sample?
 6. A sample of a tin ore weighing 0.3000 g was dissolved in an acid solution and all the tin in the sample was changed to tin(II). The solution was titrated with 8.08 mL of 0.0500 M KMnO4 solution, which was oxidized the tin(II) to tin(IV).
(a) What is the balanced equation for the reaction in the titration?
(b) How many grams of tin were in the sample?
(c) What was the percentage by weight of tin in the sample?
(d) If the tin in the sample had been present in the compound SnO2, what would have been the percentage by weight of SnO2 in the sample?
 7. A sample weighing 0.2000 g was known to contain CuSO4.  It was dissolved in water and the copper in the solution was allowed to react with a solution containing excess iodide ion. The I3- that was formed was titrated with 0.01000 M Na2S2O3 solution using starch as an indicator. The titration required 35.65 mL of the thiosulphate solution.  What was the percentage by weight of CuSO4 in the original 0.2000 g sample?
 8. A 1.00 mL sample of household bleach, which contains sodium hypochlorite, NaOCl, was added to a solution containing excess iodide ion.  The hypochlorite reacts with iodide ion as follows.

        2 H+  +  OCl-  + 3 I- -----> I31-  +  Cl-  +  H2O

After the reaction, the I31- was titrated with a 0.0500 M solution of Na2S2O3, using starch as an indicator.  The titration required 28.20 mL of the thiosulphate solution.
(a) How many moles of I31- reacted with the thiosulphate solution in the titration?
(b) How many moles of OCl- reacted to form the I31-?
(c) What was the molar concentration of OCl1- in the laundry bleach?

 9. How many millilitres of Cl2 gas, measured at 25oC and
     98.66 kPa, are needed to react with 10.0 mL of 0.10 M NaI
     if the I1- is oxidized to IO31-and Cl2 is reduced to Cl1-?

 10.  To determine the solubility of copper(II) iodate, Cu(IO3)2, by iodometric titration in an acidic solution at 25oC we start with 20.00 cm3 of a saturated aqueous solution and 30.00 cm3 of a 0.100 molar sodium thiosulphate solution are needed.
a) Write the sequence of a balanced equation for the chemical reaction.
b) Calculate the initial concentration of Cu2+ ions in the solution.
c) Determine the solubility product, Ksp, of copper(II) iodate (including the units). Ignore activity coefficients.

 11. An electrolytic plant produces 50,000 tonnes of aluminum  per year.  If the plant is in operation at all times (even holidays), what current must flow to give this production?

 12. Two electrolytic cells are in series. In one there is a solution of copper(II) sulphate ,CuSO4, and in the other there is a solution of copper(II) chloride in hydrochloric acid ( the complex ion CuCl2- is the predominant species).  How much copper metal will be deposited at the cathode in each cell if a current of 6.00 amperes flows for 2.00 hours?

 13. A sample of pure Fe3O4 weighing 0.4532 g is dissolved in dilute sulphuric acid and then titrated with 0.02430 M KMnO4.  What volume of permanganate solution is required?

 14. If 4 g of Li reacts with excess H2
a) how many moles of electrons are transferred from Li to H?
b) how many electrons?

 15. Excess KI solution was added to 10 mL of a solution containing Cu2+. After reaction had ceased, 5.5 mL of 0.1 M Na2S2O3 solution was required to completely change the brown colour of the solution to colourless.  How much Cu2+ did the original solution contain?

 16. Calculate the weight of copper deposited by the flow of 24,125 coulombs of electricity through a solution of copper(II) sulphate.

17. Calculate the number of coulombs of electricity that pass through a circuit when 5 amperes flow for 2 hours.

18. Calculate the number of coulombs required to liberate 
a) 22.4 L of H2 at STP.
b) 44.8 L of O2 at STP
c) 27.42 g of Fe from an Fe3+ ion solution.

19. A current of 0.4 amps flow for 2.5 hours through a solution of 
a) NiCl2
b) H2SO4
Calculate the weight or volumes at STP of the products formed at the electrodes.

20. An electric current, passing through a solution of CuSO4, liberates 15.9 g of metallic copper.  How many grams of silver will be liberated by the same amount of current?

21 When a solution of ZnSO4 is electrolyzed, the following reaction takes place:

        2 ZnSO4 + 2 H2O ----> 2 Zn + 2 H2SO4 + O2

If 13 g of zinc are plated out, what weight of oxygen gas is liberated simultaneously?  what volume of oxygen, measured at STP is evolved?

22. Two faradays of electricity are passed through a dilute solution of H2SO4.  Calculate the weights of the materials produced at the anode and cathode at STP.

23. How many coulombs of electricity are required to:
a) develop 0.4 amp flow for 2 hours?
b) liberate 11.2 L of H2 at STP?
c) liberate 11.2 L of O2 at STP,
d) liberate 22.4 L of Cl2 at STP,
e) deposit 0.1 g of Ag,
f) deposit 1 g of Fe from (1) Fe2+ solution and (2) Fe3+  solution.

24. A solution of copper(II) sulphate is electrolyzed between inert electrodes.
a) How many minutes must a current of 2.6 amp flow to deposit 6 g of Cu metal?
b) What strength of current must flow for 1.5 hours to deposit 4.8 g of Cu metal?

25. In an electric current, flowing for a certain time, plates out 54 g of silver from a solution of AgNO3, how many grams of lead will the same current deposit during an equal time period from a solution of lead nitrate, Pb(NO3)2.

26. Equal quantities of electricity are passed successively through solutions of
a) aluminum chloride, 
b) dilute sulphuric acid,
c) hydrochloric acid,
d) copper(II) sulphate.

If 11.2 L of chlorine at STP are liberated from the solution:
a) calculate the grams of hydrogen at STP evolved,
b) the volume of hydrogen at STP
c) and the grams of copper plated out from solution.

27. A current of 0.04 amp passed through a solution of silver nitrate deposits 0.16 g of silver.  Calculate the volume of H2 at STP that would be liberated from a aqueous KCl solution by the same quantity of current.

28. What mass of MnO2 is reduced by 45.5 cm3 of 0.30 N oxalic acid,  H2C2O4, in sulphuric acid solution?  The unbalanced equation is

        MnO2 + H+ + H2C2O4 ---->  CO2 + H2O  + Mn2+