Chemical properties of nickel

4.1. Place 3-4 drops of 0,5N nickel (ІІ) sulfate solution into each of three test tubes and add by drops 2 M sodium hydroxide solution until precipitate forms. After that add by drops 1 M hydrochloric acid solution into the first test tube, stir the precipitate into the second test tube with glass rod and leave it in the stand for some time, add 3-4 drops of ammonia solution into the third test tube. What can you observe? Give the equations of the relevant reactions.

4.2. Put the droplet of 0,5N nickel (ІІ) sulfate solution into a test tube, add 3-6 drops of ammonia solution and 2-3 drops of dimethylglioxyme alcohol solution. What can you observe?

4.3. Put 3-4 drops of 0,5N nickel (ІІ) sulfate solution into a test tube, add 1-2 mls of bromine water and 5-6 drops of 0,5N sodium hydroxide solution. What colour has a precipitate, which is formed?

Place as much as possible liquid off from the obtained precipitate, add to the precipitate the excess amount of concentrated hydrochloric acid and heat up the test tube. What can you observe? Give the equations of the relevant reactions.

4.4. Put 5-6 drops of 0,5N solutions into each of two test tubes: of iron (ІІ) sulfate into the first, nickel (ІІ) sulfate into the second and add 3-4 drops of diluted ammonia solution. What can you observe? Then add the excess amount of diluted ammonia solution to both test tubes. Explain the difference, which is observed. Give the equations of the relevant reactions.

Let us consider the processes occurring in the operation of a cad­mium-nickel accumulator. In the discharge of the accumulator, the cadmium becomes oxidized:

Cd + 20H^-= Cd(OH)₂ +2e^-

and the NiOOH is reduced:

2NiOOH + 2H₂O + 2e^- = 2Ni(OH)₂ + 2OH^-

The electrons are carried through the external circuit from the cadmium electrode to the nickel one. The cadmium electrode is the anode and is charged negatively, while the nickel electrode is the cathode and is charged positively.

The net reaction proceeding in a cadmium-nickel accumulator during its operation can be shown by the equation obtained upon summation of the last two electrochemical equations:

2NiOOH + 2H₂O + Cd = 2Ni(OH)₂ + Cd(OH)₂

The e.m.f. of a charged cadmium-nickel accumulator is about 1.4 V. In operation of the accumulator (discharge), the voltage across its terminals drops. When it falls to below one volt, the accumulator is charged.

In charging, the electrochemical processes on the accumulator electrodes are reversed. On the cadmium electrode, the metal is reduced:

Cd(OH)₂+ 2e^- = Cd + 2OH^-

and on the nickel electrode, the nickel(II) hydroxide is oxidized:

2Ni(OH)₂+2OH^-= 2NiOOH + 2H₂O + 2e^-

The net reaction in charging is the opposite of the reaction in discharging:

2Ni(OH)₂ +Cd(OH)₂ = 2NiOOH + 2H₂O + Cd.

[1] It should be noted that the magnetic properties of iron (as well as any other property) are very dependent on purity of iron and the presence of any impurity.

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