Nigel Baldwin | GCSE Chemistry Testing three unknown substances DXDE9049 @nigelbaldwin3184 | Uploaded April 2022 | Updated October 2024, 1 hour ago.
High School Chemistry
GCSE Chemistry
Testing three unknown white crystalline solids.
The solids were labelled X, Y and Z
If the solids were known to be citric acid, sodium hydrogencarbonate and potassium chloride, which one was which?
Testing for
Solubility in water
pH using Universal Indicator paper
Flame tests
Halide ion test using acidified silver nitrate
Carbonate test
Results
X
dissolved in water quickly
pH 6
a flame test that included lilac, but admittedly there were orange-red colours visible too
a white precipitate with acidified silver nitrate
Y
dissolved in water quickly
pH 2 or 3
no flame colour
no precipitate with acidified silver nitrate
reacted with calcium carbonate to produce bubbles of colourless gas which were presumed to be carbon dioxide
Z
dissolved in water but not as quickly as the others
pH 8
yellow flame colour
orange-red colour was visible on the outside of the flame too
initially produced bubbles of colourless gas and a white precipitate in a first silver nitrate test acidified with 0.1M nitric acid
when acidified with 1M nitric acid in a second silver nitrate test no white precipitate was observed
bubbles of colourless gas were produced on addition of 1M HCl to a solution of Z and when the gas was passed through limewater a white precipitate was produced. Carbon dioxide. Z was a carbonate.
Identifications
X potassium chloride
Y citric acid
Z sodium hydrogencarbonate aka sodium bicarbonate
It would have been nice to have a clearer flame test with X
I did not have any blue glass with which to view the flame colour produced by X although lilac colour was clearly visible
High School Chemistry
GCSE Chemistry
Testing three unknown white crystalline solids.
The solids were labelled X, Y and Z
If the solids were known to be citric acid, sodium hydrogencarbonate and potassium chloride, which one was which?
Testing for
Solubility in water
pH using Universal Indicator paper
Flame tests
Halide ion test using acidified silver nitrate
Carbonate test
Results
X
dissolved in water quickly
pH 6
a flame test that included lilac, but admittedly there were orange-red colours visible too
a white precipitate with acidified silver nitrate
Y
dissolved in water quickly
pH 2 or 3
no flame colour
no precipitate with acidified silver nitrate
reacted with calcium carbonate to produce bubbles of colourless gas which were presumed to be carbon dioxide
Z
dissolved in water but not as quickly as the others
pH 8
yellow flame colour
orange-red colour was visible on the outside of the flame too
initially produced bubbles of colourless gas and a white precipitate in a first silver nitrate test acidified with 0.1M nitric acid
when acidified with 1M nitric acid in a second silver nitrate test no white precipitate was observed
bubbles of colourless gas were produced on addition of 1M HCl to a solution of Z and when the gas was passed through limewater a white precipitate was produced. Carbon dioxide. Z was a carbonate.
Identifications
X potassium chloride
Y citric acid
Z sodium hydrogencarbonate aka sodium bicarbonate
It would have been nice to have a clearer flame test with X
I did not have any blue glass with which to view the flame colour produced by X although lilac colour was clearly visible
