Metal Hydroxide Precipitate Testing

Question 1

How do you determine metal hydroxide precipitate colours?

Answer 1

A. Using a dropping pipette, fill test tube to depth of about 2cm with 1 of 5 known solutions.
B. Using a different pipette add few drops of sodium hydroxide solution to tube. Hold test tube near top and shake the bottom gently from side to side to mix contents.
C. Observe and record colour of the precipitate produced.
D. If a white precipitate is obtained in step C add more sodium hydroxide until the tube is about half full. Observe and record whether precipitate disappears to leave colourless solution.
E. Repeat steps A-D with other known solutions. Do not contaminate one solution with another.

Question 2

What is the precipitate colour and effect of adding excess sodium hydroxide to aluminium AI3(superscript)

Answer 2

Colour white, effect turns colourless

Question 3

What is the precipitate colour and effect of adding excess sodium hydroxide to calcium Ca2(superscript)

Answer 3

Colour white, effect stays white

Question 4

What is the precipitate colour and effect of adding excess sodium hydroxide to copper Cu2(superscript)

Answer 4

Colour blue, effect?

Question 5

What is the precipitate colour and effect of adding excess sodium hydroxide to iron Fe2(superscript)

Answer 5

Colour green, effect…

Question 6

What is the precipitate colour and effect of adding excess sodium hydroxide to iron Fe3(superscript)

Answer 6

Colour brown, effect…

Question 7

What is the precipitate colour and effect of adding excess sodium hydroxide to ammonia NH

Answer 7

Turns red litmus blue
Smells chemically

Question 8

How do you test for NH4(subscript) - ammonium ions?

Answer 8

1. Add sodium hydroxide
2. Warm gently
3. Observe the sharp smell of ammonia (NH3(subscript))
4. Confirm with moist red litmus paper - turns blue