The set – up below was used during the electrolysis of aqueous magnesium sulphate using inert electrodes
i) Name a suitable pair of electrodes for this experiment ii) Identify the ions and cations in the solution iii) On the diagram label the cathode iv) Write ionic equations for the reactions that took place at the anode. v) Explain the change that occurred to the concentration of magnesium sulphate solution during the experience. vi) During the electolysis a current of 2 amperes was passed through the solution for 4 hours. Calculate the volume of the gas produced at the anode.(1 faraday 96500 coulombs and volume of a gas at room temperature is 24000cm3) vii) One of the uses of electrolysis is electroplating What is meant by electroplating? Give tow reasons why electroplating is necessary.
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The set-up below was used by a student to investigate the products formed when aqueous copper (II) chloride was electrolyzed using carbon electrodes.
(a) (i) Write the equation for the reaction that takes place at the cathode.
(ii) Name and describe a chemical test for the product initially formed at the anode when a highly concentrated solution of copper (II) chloride is electrolysed. (iii) How would the mass of the anode change if the carbon anode was replaced With copper metal? Explain. (b) 0.6 g of metal B were deposited when a current of 0.45A was passed through an electrolyte for 72 minutes. Determine the charge on the ion of metal B. (Relative atomic mass of B = 59, 1 Faraday = 96 500 coulombs) (c) The electrode potentials for cadmium and zinc are given below:
Explain why it is not advisable to store a solution of cadmium nitrate in a container made of zinc
Sodium hydroxide can be prepared by the following methods; I and II.
(a) Name the precaution that needs to be taken in method I.
(b) Give the name of process A. (c) Give one use of sodium hydroxide,
ANSWERS
(a) Small piece of sodium metal (pea size) with a lot of water.
Perform the experiment wearing goggles. (b) Electrolysis. (c) Manufacture of soap.
a) Which one of the following compounds; urea, ammonia, sugar and copper (II) chloride will conduct an electric current when dissolved in water? Give reasons.
b) The diagram below shows an electrochemical cell. Study it and answer the questions that follows.
i) Show on the diagram using an arrow, the direction of flow of electrons
ii) Name two subsrances that are used to fill the part labeled L c) In an experiment to electroplate iron with silver, a current of 0.5 amperes was passed through a solution of silver nitrate for an hour i) Give two reasons why it is necessary to electroplate iron with silver ii) Calculate the mass of silver that was deposited on iron (Ag = 108, 1 Faraday = 96,500 coulombs)
The half equations involved in a cell are:
2H2O(l) + 2e = H2(g) + 2OH-(aq): Eθ = - 0.83V O2(g) + 2H2O(l) + 4e = 4OH-(aq): Eθ = + 0.40V a) Write the overall equation for the electrochemical cell. b) Calculate he e.m.f. generated by a battery consisting of ten cells. c) State one environment advantage of using these cells in spacecrafts.
Use the cell representation below to answer the questions that follow
Complete the table below by writing the product formed at the electrodes during the electrolysis of the electrolytes given in the table.
The set-up below (figure 2) was used to electrolyse a bromide of metal D DBr2
i) Write equation for the reactions at the
I cathode II anode ii) The electrodes used in the experiment were made of carbon and metal D. which of the two electrodes was used as the anode? Give a reason. iii) Give a reason why this experiment is carried out in a fume cupboard. iv) When a current of 0.4A was passed for 90 minutes, 2.31 g of metal D were deposited. I Describe how the amount of metal D deposited was determines. II Calculate the relative atomic mass of metal D. (I Faraday = 96500 coulombs)
The standard reduction potentials of two half –cells are:
Ag+(aq) + e → AG(s) ; E = 0.80V 2H2O (l) + 2e → H2 (g) + 2OH (aq); E1 = 0.83V Draw a labelled diagram of an electro chemical cell that can be constructed using the two half –cells
Hydrogen and oxygen can be obtained by electrolysis of acidified water.
Using equations for the reactions at the electrodes, explain why the volume of hydrogen obtained is twice that of oxygen. Related Chemistry Questions and Answers on Electrochemistry Form 4 Level
When aluminium oxide was electrolysed, 1800kg of aluminium metal were obtained.
a) Write equation for the formation of aluminium metal b) Calculate the quantity of electricity in faradays used (Al=27)
The diagram below represents a set up that can be used to electrolyze aqueous copper (II) sulphate.
(a) (i) Describe how oxygen gas is produced during the electrolysis
(ii) Explain why copper electrodes are not suitable for this electrolysis (b) Impure copper is purified by an electrolytic process (i) Name one ore from which copper is obtained (ii) Write the equation for the reaction that occur at the cathode during the purification of copper (iii) In an experiment to electroplate a copper spoon with silver, a current of 0.5 A was passed for 18 minutes. Calculate the amount of silver deposited on the spoon (π = 96500 coulombs, Ag = 108) (iv) Give two reasons why some metals are electroplated
(i) Which element is likely to be hydrogen? Give a reason for your answer (ii) What is the Eθ value of the strongest reducing agent? (iii) In the space provided draw a labeled diagram of the electrochemical cell that would be obtained when half – cells of elements B and D are combined (iv) Calculate the Eθ value of the electrochemical cell constructed in (iii) above (b) During the electrolysis of aqueous copper (II) sulphate using copper electrodes, a current of 0.2 amperes was passed through the cell for 5 hours (i) Write an ionic equation for the reaction that took place at the anode (ii) Determine the change in mass of the anode which occurred as a result of the electrolysis process (Cu= 63.5, 1 Faraday = 96,500 coulombs). Aqueous potassium sulphate was electrolysed using platinum electrodes in a cell. a) Name the products formed at the cathode and anode. Anode b) How does the concentration of the electrolyte change during electrolysis. c) Why would it not be advisable to electolyse aqueous potassium sulphate using potassium metal electrodes.
During the electrolysis of aqueous silver nitrate, a current of 5.0a was passed through the electrolysis for 3 hours.
a) Write the equation for reaction which took place at the anode. b) Calculate the mass of silver deposited (Ag = 108; IF=96500C)
a) When brine is electrolyzed using inert electrodes, chlorine gas is liberated at the anode instead of oxygen. Explain this observation.
b) Name the product formed at the cathode.
ANSWERS
(a)Chlorine ions in Brine are high concentration compared to oxide ions in solutions
(b)Hydrogen gas
a) In an experiment to determine the molar heat of reaction when magnesium displaces copper ,0.15g of magnesium powder were added to 25.0cm3 of 2.0M copper (II) chloride solution. The temperature of copper (II) chloride solution was 25°C.While that of the mixture was 43°C.
i) Other than increase in temperature, state and explain the observations which were made during the reaction. ii) Calculate the heat change during the reaction (specific heat capacity of the solution = 4.2jg-1k-1and the density of the solution = 1g/cm3 iii) Determine the molar heat of displacement of copper by magnesium.(Mg=24.0). iv) Write the ionic equation for the reaction. v) Sketch an energy level diagram for the reaction. b) Use the reduction potentials given below to explain why a solution containing copper ions should not be stored in a container made of zinc.
a) What is an electrolyte?
b) State how the following substances conduct electricity. i) Molten calcium chloride ii) Graphite. c) The diagram below shows a set up that was used to electrolyse aqueous magnesium sulphate.
i) On the diagram above, using an arrow, show the direction of flow of electrons.
ii) Identify the syringe in which hydrogen gas would be collected. Explain d) Explain why the concentration of magnesium sulphate was found to have increased at the end of the experiment. e) During the electrolysis, a current of 0.72A was passed through the electrolyte for 15 munities. Calculate the volume of gas produced at the anode.(1 Faraday = 96 500 coulombs; molar gas volume is 24000cm3 at room temperature).
Study the standard reduction potential given and answer the questions that follow.
(The letters are not the actual symbols of the elements).
a) The standard reduction potential for Fe 2+(aq) is -0.44 volts. Select the element which would best protect iron from rusting.
b) Calculate the E ø value for the cell represented as M(s) / M2+ (aq) // P+(aq) /P(s).
The information below relates to element L, Q, R and T. The letters do not represent the actual symbols of the elements. Arrange the elements in
a) Give the formula of an oxide which reacts with both dilute hydrochloric acid and hot concentrated sodium hydroxide. b) Give the formulae of the products formed when the oxide in (a) above reacts with excess hot concentrated sodium hydroxide. |
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