Year 12 - Tests for ions Flashcards
When a Ca2+ (Calcium) ion is burnt in a flame test, what colour is the flame?
The metal ion when burnt produces a brick red flame.
When an Sr2+ (strontium) ion is burnt in a flame test, what colour is the flame?
The metal ion when burnt produces a red flame.
When a Ba2+ (Barium) ion is burnt in a flame test, what colour is the flame?
The metal ion when burnt produces a pale green flame.
How to you test for ammonia gas (NH3 - NOT AN ION)?
Using a damp piece of red litmus paper, if there is ammonia gas present then the gas will dissolve onto the paper and turn it blue.
How do you test for an ammonium ion (NH4+)?
Add some dilute Sodium Hydroxide (NaOH) to your unknown substance and gently heat the mixture. If ammonia is given off then ammonium ions must be present.
How do you test for the presence of sulfate ions (S04,2-)?
Add a small amount of dilute hydrochloric acid (HCl) followed by Barium chloride solution (BaCl2). If a white precipitate (barium sulfate) forms then the original compound therefore contained a sulfate.
How do you test for the presence of hydroxide ions?
Use a pH indicator to test for alkaline conditions. E.g. you may dip a piece of red litmus paper into the solution and if it turns blue then this shows that OH- ions are present.
How do you test for halide ions (Cl-, Br- and I-)?
Add dilute HNO3 (nitric acid) followed by AgNO3 (silver nitrate solution).
A chloride ion will give you a white precipitate = silver chloride.
A bromide ion will give you a cream precipitate = silver bromide.
An iodide ion will give you a yellow precipitate = silver iodide.
If you aren’t able to tell the difference between the 3 samples then add ammonium solution to be able to tell them apart.
Silver chloride = dissolves in dilute ammonium solution
Silver bromide = only dissolves in concentrated ammonium solution
Silver iodide = won’t dissolve in an ammonium solution
How do you test for the presence of carbonate ions?
You can test for carbonate ions by adding acid. When you add dilute HCl the solution will fizz if it contains carbonate ions due to the carbonate ions reacting with the hydrogen ions to produce C02. You can test for CO2 by using limewater. Bubble the gas through the limewater and If it turns cloudy then CO2 is present.
