In case the image is not clear: I only need question 2 and 3 answered. 2. Write

Question

In case the image is not clear: I only need question 2 and 3 answered.

2. Write balanced net ionic equations for the following reactions:

a) Dissolving of Ni(OH)2 in nitric acid.

b) Oxidation of Cr3+ to CrO4^2- by OCl^- in alkaline solution (OCl^- is converted to Cl-)

c) The reaction of Ni^2+ that separates it from Fe^3+

d) The confirmatory test for Fe^3+

3. A solution may contain any of the Group III cations. Treatment of the solution with OCl^- in alkaline medium yields a yellow solution and a colored precipitate. The acidified solution is unaffected by treatment with NH3. The colored precipitate dissolves in nitric acid; addition of excess NH3 to this acid solution produces only a blue solution. On the basis of this information, which Group III cations are present, absent, or still in doubt?

Explanation / Answer

2 a)

Ni(OH)2 (s) + 2 HNO3(aq) --> Ni(NO3)2 (aq) + 2H2O

this is a double displacement type reaction....

b) oxidation

Cr3+ --> Cr6+ + 3e

reduction

Clo- +2e --- > Cl-

multiplying 1st by 2 and second by 3 to get a total of 6 electron exchange and by balancng H and O we have

2 Cr3+ + 3ClO- + 3 H2O --> 2 Cr6+ + 3Cl- +6 OH-

3)

c) The confirming test for Fe3+

Fe3+ (aq) + 6SCN- (aq) --> [Fe(SCN)6]3- (aq)

(blood red)

3)

Group III cations, which include Cr3+, Al3+, Fe3+ and Ni2+

From the information ...following assesment is made

A solution may contain any of the Group III cations is first treated with a mixture of OH- and OCl- solutions. This causes the iron and nickel cations to precipitate out as hydroxide salts, while the chromium and aluminum cations remain in solution:

Fe3+ (aq) + 3 OH- (aq) Fe(OH)3 (s) (precipitate)

Ni2+ (aq) + 2 OH- (aq) Ni(OH)2 (s) (precipitate)

2 Cr3+ (aq) + 3 OCl- (aq) + 10 OH- (aq) 2 CrO42- (aq) + 3 Cl- (aq) + 5 H2O (l)

Al3+ (aq) + 4 OH- (aq) Al(OH)4- (aq)

since we got yellow colour precipitate...since Ni(OH)2 is green colour and  Fe(OH)3 is reddish brown

since the supernatent is of yellow colour..this suggest that Cr3+ is present as CrO42- , which is of yellow colour...and also Al3+ is absent because no change takes place when acidfied solotion is treated with NH3.

the coloured ppt dissolves is HNO3 , and addition of NH3 gives a blue colour solution....this blue colour complex should be Ni(NH3)6 .

hence Ni 2+ and Cr3+ are present.

and Al3+ and Fe3+ are absent

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.