Student A has conducted several tests on FA1. Here are the test results.
Test (i) with NaOH(aq) dropwise, then in excess:
- White ppt formed, soluble in excess.
Test (ii) with NH3(aq) dropwise, then in excess:
- White ppt formed, insoluble in excess.
Comment on the student's observation, amending them if necessary.
The cation in FA1 is
Suggest another test student A can conduct to confirm the identity of the cation in FA1.
State the expected observation(s).
(To confirm identity of compounds/ions in general, ensure positive test result is obtained)
Student A tested FA2 with Na2CO3.
Observations recorded by Student A:
- effervescence was produced and a green precipitate was formed.
Comment on the student's observation, amending them if necessary.
The cation in FA2 is
FA3 contains two cations, iron(II) ion and copper(II) ion.
The identities of the cations are unknown to Student A. However, Student A is aware of the presence of two cations.
Suggest a series of tests for Student A to conduct such that Student A is able to deduce the identities of the two cations.
FA4 contains two cations, zinc ion and chromium(III) ion.
The identities of the cations are unknown to Student A. However, Student A is aware of the presence of two cations.
Student A was told to conduct a series of tests below:
1. To 1 cm depth of the test solution, add NH3(aq) dropwise until no further change is seen.
2. Filter the mixture.
3. To the filtrate, add dilute nitric acid dropwise until in excess.
Student A recorded the observations as follow:
1. Pale green ppt formed, insoluble in excess.
2. Grey-green residue.
3. White ppt reformed, soluble in excess.
For the following questions, select the correct option to amend the observations above.
1. Pale green ppt formed, insoluble in excess.
2. Grey-green residue.
3. White ppt reformed, soluble in excess.
After deducing the two ions to be zinc ion and chromium(III) ion, Student B suggested that the identities of the two ions could be determined by replacing NH3(aq) with NaOH(aq).
Do you agree?
Instead of adding NH3(aq), Student C accidentally added Na2CO3(aq) to FA4.
State the expected observations and the identities of any gases or ppt produced.