What is the difference between FeCl3 and Na2S dropping order?

It should be said that Fe3+ can oxidize S2-, first consider 2Fe3+ +S2- *****==S (precipitation) + 2Fe2+

However, there will also be Fe2S3 precipitation.

Generally speaking, Fe3+ has strong oxidizing properties, while S2- has reducing properties, so when Fe3+ meets S2-, Fe3+ can oxidize S2- to S, and itself is reduced to Fe2+, that is, a reaction occurs:

2fe3++s2-=2fe2++s↓

Fe3+ is more oxidative under acidic conditions than under alkaline conditions When Na2S is added to FeCl3 solution, Fe3+ is excessive, and the solution is acidic Therefore, the above reaction should occur But if Conversely, FeCl3 is added to Na2S solution, Na2S is excessive, and the solution is alkaline, at this time Fe3+ oxidation is weakened Fe3+ and S2- will combine into Fe2S3 precipitate with very little solubility, namely:

2fe3++3s2-=fe2s3↓

In short, which excess also has an effect on the reaction, because FeCl3 is acidic, while Na2S is basic.

1.Add Na2S in FeCl3 solution, Fe3+ excess phenomenon pale yellow precipitate.

That is: 2Fe3++S2-=2Fe2+ +S 2Conversely, there is an excess of Na2S.

The phenomenon is a pale yellow precipitate, and then a black precipitate Fes is generated, i.e., 2Fe3+S2- = 2Fe2 + S Fe2 + S 2- = Fes

When the ferric chloride solution drip ignites Li Feng into the sodium sulfide solution, the sodium sulfide is excessive, and the redox reaction occurs first, followed by the metathesis reaction, and the chemical equation of the reaction is:

The first step reaction: 2FeCl3+Na2S = 2FeCl2 + 2NaCl+S

The second step reaction: FeCl2+Na2S=Fes+S+2NaCl

Total reaction: 2FeCl3 + 3Na2S = 2Fes + 6NaCl + S

Phenomenon: There are both yellow and black precipitates.

When the sodium sulfide solution is dropped into the ferric chloride solution, the ferric chloride is excessive, and only the redox reaction occurs, and the chemical equation of the reaction is:

2fecl3+na2s=2fecl2+2nacl+s↓

Phenomenon: Only yellow precipitate, 7,2FeCl3+3Na2S=Fe2S3+6NaCl has iron sulfide precipitation.

2FeCl3+3Na2S=2Fes+6NaCl+S,1, S2- was added to Fe3+, the solution was acidic, and the redox reaction mainly occurred.

Under acidic conditions, the standard reduction potential of Fe3+ Fe2+ is that there is no H+ in the point pair reaction, and the reaction is almost not affected by pH. There are almost no ferrous ions in the solution, so the electric potential will be higher. The standard reduction potential of the electric pair S H2S (AQ) is , the difference is , so the iron ions can oxidize the negative divalent sulfur.

That is, Fe2+ and S elements are formed first (redox first), and then depending on the pH of the solution (e.g., F...).0,2FeCl3 + Na2S = S (precipitate) + 2FeCl2 + 2NaCl

A yellow precipitate is produced, and the color of the liquid changes from yellow to green, 0,

Dropping into the Na2S solution, the solution is strongly alkaline, at this time Fe3+ can not oxidize S2-, and Fe2S3 has a certain stability (double hydrolysis is slower than Duan Jian), so the cong reaction is 2Fe3+ +3S2- =Fe2S3 Fe3+ +3S2- +3H2O== Left for a few days ==Fe(OH)3+ 3Hs- The two reactions are carried out at the same time, but much faster, so.

When Fe3+ is dropped into S2-, Fe2S3 is a relatively stable substance at this time due to the strong alkalinity of the excess solution of S2-, so the black precipitate is generated, and the reaction formula is 2Fe3+ +3S2-=Fe2S3This substance will slowly undergo a double hydrolysis reaction after a few days, Fe2S3+6H2O=2Fe(OH)3+3H2SFerrric iron is very stable under alkaline conditions, and ferric iron is very unstable (as evidenced by the fact that ferrous hydroxide is easily oxidized by air), so S2- will not be oxidized.

When S2- drops into Fe3+, the solution is acidic, Fe3+ can oxidize S2-, the reduction product Fe2+ will be precipitated, 2Fe3+ +3S2- =S +2Fes, resulting in a mixture of light yellow precipitate and black precipitate. At the same time, because the precipitation rate reaction is faster than the redox reaction and hydrolysis reaction, Fe2S3 will also appear, but it is difficult to distinguish from FeS. However, under this condition, Fe2S3 is unstable and will be double hydrolyzed, that is, 2Fe3+ +3S2-= (fast) = Fe2S3, Fe2S3 + 6H2O = (slow) = 2Fe(OH)3+3H2S, and reddish-brown precipitation will also occur.

Wu Guoqing's "Inorganic Chemistry" has a description of the rotten reaction of these two substances.

When the ferric chloride solution is dropped into the sodium sulfide solution, the sodium sulfide is excessive, and the redox reaction occurs first, followed by the metathesis reaction, and the chemical equation of the reaction is:

The first step reaction: 2FeCl3 + Na2S = 2FeCl2 + 2NaCl + s The second step reaction: FeCl2 + Na2S = Fes + S + 2NaCl total reaction:

2FeCl3+3Na2S=2Fes +6NaCl+S Phenomenon: There are both yellow and black precipitates.

When the sodium sulfide solution is dropped into the ferric chloride solution, the ferric chloride is excessive, and only the redox reaction occurs, and the chemical equation of the reaction is:

2FeCl3+Na2S=2FeCl2+2NaCl+S Phenomenon: Only yellow precipitate.

(1) The addition of two substances increases the concentration of reactants in the reaction, resulting in the chemical equilibrium moving to the right and the color deepening; The addition of NH4SCN increases the concentration of reactants in the reaction and increases the concentration of Fe(SCN)2+, so the color is darker, so the answer is:

Both substances promoted the positive movement of the reaction, Fe3+ had a greater influence on the reaction, and NH4SCN not only promoted the positive movement of the reaction, but also directly promoted the positive movement of the reaction, resulting in the formation of more crimson substances.

2) Since Fe2+ is reducible, it can be oxidized by oxidizing H2O2 to Fe3+, and H2O2 is reduced to H2O, according to the reactants and products, the ion equation is written: H2O2+2H++2Fe2+=2Fe3++2H2O; Continue to add H2O2 dropwise to produce a large amount of gas that can make the clarified lime water turbid, and the gas is judged to be CO2; Add BaCl2 solution dropwise to the solution after the reaction, there is a white precipitate insoluble in dilute hydrochloric acid to form, the precipitate is Baso4, there is SO42- generation in the reaction, combined with the generated N2, write the ion equation: 2SCN-+11H2O2=2SO42-+2CO2 +N2 +10H2O+2H++, so the answer is: H2O2+2H++2Fe2+=2Fe3++2H2O, 2SCN-+11H2O2=2SO42-+2CO2+n2 +10h2o+2h+

3) Due to Ksp(AgsCN) Ksp(Ag Cl), some AGCL precipitates will be converted into AGScn with the added NH4SCN standard solution, and if the consumption of NH4SCN standard solution is high, the remaining AGno3 solution in the calculation results is high, and the amount of AgNO3 solution with Cl- is low, so the amount of Cl- is low, so the determination result is judged to be low;

Trivalent iron and SCN- can form a red complex.

Analysis: Fe(scn)3 is a dynamic equilibrium in solution, and it has a reaction equilibrium:

Fe(scn)3 Fe)3+ +3(scn)- (denotes reversible sign).

According to the principle of Le Châteatle, if you add FeCl3 solution or KSCN solution, the concentration of (Fe)3+ or (SCN)- increases, then the equilibrium will move in the direction of decreasing the concentration of (Fe)3+ or (SCN)-, then the amount of Fe(SCN)3 will increase, so the color will be darker.

Since FeCl3 is a salt formed by strong acid and weak alkali, it can be hydrolyzed to form insoluble Fe(OH)3Fe3+ +3H2O Fe(OH)3 + 3H+ to make the solution turbid, so if a certain amount of hydrochloric acid is added in the preparation of FeCl3, the balance can move in the direction of the anti-trembling orange stool and inhibit hydrolysis.

The reason is that hydrochloric acid provides H+, which can inhibit hydrolysis.

FeCl3 drops into Na2S, the solution is very alkaline, Fe2S3 is relatively stable, so there will be a mixture of black Fe2S3 precipitation and reddish-brown Fe(OH)3 precipitation. After 1-2 days, the black pellet gradually turns reddish-brown and slowly emits bubbles.

Na2S drops into FeCl3, the solution is more acidic, Fe3+ can oxidize S2-, so there are light yellow S elemental and reddish-brown Fe(OH)3* (Fe2S3 is no longer stable, but directly double hydrolyzed) at the same time, and bubbles emerge.

This phenomenon can be found in the second volume of Mr. Wu Guoqing's book "Inorganic Chemistry".

FeCl3 is a strong acid and weak alkali salt, which is acidic.

Na2S is a strong alkali and weak salt, and it is alkaline.

When Na2S is added to FeCl3 dropwise, Fe3+ is oxidizing under acidic conditions, and 2FeCl3+Na2S = 2FeCl2+2NaCl+S

A yellowish precipitate begins to form.

When FeCl3 is added dropwise to Na2S, the solution is alkaline, 2FeCl3+3Na2S = 2Fe(OH)3+6NaCl+3H2S, and a reddish-brown precipitate is generated, and a small amount of H2S gas is generated.

FeCl3 was added dropwise to Na2S, and a white precipitate and a pale yellow precipitate (at the same time) appeared

Na2S was added dropwise to FeCl3, and a pale yellow precipitate appeared first, and a white precipitate appeared after a period of time.