Test for cations

Question 1

What are cations?

Answer 1

They are positive metal ions and NH4+

Question 2

Adding aq. NaOH, a little at first and then in excess to NH4+

Answer 2

No ppt seen. NH3 produced on warming.

Question 3

Adding aq. NaOH, a little at first and then in excess to Ca2+

Answer 3

White ppt seen. Insoluble in excess aq. NaOH.

Question 4

Adding aq. NaOH, a little at first and then in excess to Zn2+

Answer 4

White ppt seen. Soluble in excess aq. NaOH to form a colourless solution.

Question 5

Adding aq. NaOH, a little at first and then in excess to Al3+

Answer 5

White ppt seen. Soluble in excess aq. NaOH to form a colourless solution.

Question 6

Adding aq. NaOH, a little at first and then in excess to Pb2+

Answer 6

White ppt seen. Soluble in excess aq. NaOH to form a colourless solution.

Question 7

Adding aq. NaOH, a little at first and then in excess to Fe2+

Answer 7

Dirty green ppt. The ppt formed is insoluble in excess aq. NaOH.

Question 8

Adding aq. NaOH, a little at first and then in excess to Fe3+

Answer 8

Reddish brown ppt. The ppt formed is insoluble in excess aq. NaOH.

Question 9

Adding aq. NaOH, a little at first and then in excess to Cu2+

Answer 9

Light blue ppt. The ppt formed is insoluble in excess aq. NaOH.

Question 10

Adding aq. ammonia, a little at first and then in excess to NH4+

Answer 10

Do not test for NH3 gas when aq. ammonia is added.

Question 11

Adding aq. ammonia, a little at first and then in excess to Ca2+

Answer 11

No ppt seen. If the calcium salt is very concentrated, a little white ppt can be seen.

Question 12

Adding aq. ammonia, a little at first and then in excess to Zn2+

Answer 12

White ppt seen. The ppt is soluble in excess aq. ammonia to form a colourless solution.

Question 13

Adding aq. ammonia, a little at first and then in excess to Al3+

Answer 13

White ppt seen. The ppt remained insoluble in excess aq. ammonia.

Question 14

Adding aq. ammonia, a little at first and then in excess to Pb2+

Answer 14

White ppt seen. The ppt remained insoluble in excess aq. ammonia.

Question 15

Adding aq. ammonia, a little at first and then in excess to Fe2+

Answer 15

Dirty green ppt. The ppt formed is insoluble in excess aq. ammonia.

Question 16

Adding aq. ammonia, a little at first and then in excess to Fe3+

Answer 16

Reddish brown ppt. The ppt formed is insoluble in excess aq. ammonia.

Question 17

Adding aq. ammonia, a little at first and then in excess to Cu2+

Answer 17

Light Blue ppt. The ppt is soluble in excess aq. ammonia to form a deep blue solution.