B:
-
2cm3 of ethanol were added to two separate test tubes and were placed them in a beaker of water kept at about 60℃.
-
1 cm3 of 0.1M silver nitrate(V)solution was added to each test tubes.
- Using separate teat pipettes, 5 drops of 1-bromobutane was added to the first test tube, 5 drops of bromobenzene was added to the second.
- The test tubes were shaked and the order in which the precipitates appeared was observed. The precipitate formed in each case was noted.
- Step1~4 was repeated while the test tubes were kept in room temperature.
C:
-
2cm3 of 0.1M silver nitrate(V)solution was added to three test tubes
-
2cm3 of KCl, KBr and KI were added to the three test tubes respectively.
- Half of each test tube was added to another test tube.
-
One set of test tubes were placed under sunlight, while the other set was kept in room and 2 cm3 of ammonium hydroxide was added.
- The precipitate formed in each case was noted.
Result
A:
B:
C:
Without sunlight, ammonium hydroxide was added
With sunlight
Conclusion
- The rate of hydrolysis are as follows:
iodo-alkane > bromo-alkane > chloro-alkane
Discussion
- The equations of the reactions are:
CH2ClCH2CH2CH3 + H2O → CH2OHCH2CH2CH3 + H+ + Cl-
CH2BrCH2CH2CH3 + H2O → CH2OHCH2CH2CH3 + H+ + Br-
CH2ICH2CH2CH3 + H2O → CH2OHCH2CH2CH3 + H+ + I-
-
Ag+ + Cl- → AgCl
Ag+ + Br- → AgBr
Ag+ + I- → AgI
- The reactivity of halo group on the rate of the hydrolysis reaction is:
iodo- > bromo- > chloro-
The reactivity depend on the bond strength of the C-- X bond, the weaker the strength of the C-- X bond, the more reactive the solution is.
- Compare the effect of the phenyl group have on the rate of the hydrolysis reaction, the haloalkane is more reactive than the halobenzene. The steric repulsion of the substituents in the 5-bonds transition state of the carbonium ions raises energy and slows down the reaction effect in the halobenzene
-
The reaction is likely to be faster if ethanol is replaced by NaOH because OH ions in NaOH(aq) has negative charge while H2O has only lone pair, but in fact NaOH will react with AgNO3 and the solution will turn green.
-
AgNO3(aq) acidified with HNO3(aq) plus carbonate because
2Ag+(aq) + CO32-(aq) → Ag2CO3(s)
H+ removes Ag2CO3(s)