Qualititative Analysis Flashcards
Why must a test for any ion be unique?
+The results of a unique test lets you determine which specific ion is present, rather than being uncertain about which ion it is.
How many tests are there to identify ions in compounds?
+There are several different tests to test and identify the ions in compounds. +Each test must be unique
What are ionic compounds?
+A chemical compound composed of ions held together by electrostatic forces.
+The compound is neutral overall, but consists of positively charged ions called cations and negatively charged ions called anions
What is a flame test?
A test to identify metal ions
What is the process of a flame test?
1]Clean a nichrome wire loop by dipping it into hydrochloric acid then rinsing in distilled water.
2]Dip the wire loop into a sample of the metal compound and put the loop in the clear blue part of a bunsen flame [roaring flame].
3]Record what colour the flame goes
What colours do different metal ions give in the flame test?
+Lithium ions [Li+] give a crimson red flame
+Sodium ions [Na+] give a yellow flame
+Potassium ions [K+] give a lilac flame
+Calcium ions [Ca2+] give an orange-red flame
+Copper ions [Cu2+] give a blue-green flame
How can you test to identify metal ions using sodium hydroxide solution?
+Add a few drops to sodium hydroxide solution to a solution of mystery compound
+If a hydroxide precipitate forms, you can use its colour to tell which metal ion was in the compound
What colours do different metal ions give in sodium hydroxide solution?
What does adding NaOH to ammonium ions produce?
Ammonia
How can you work out whether a substance contains ammonium ions [NH4+]
- Add some sodium hydroxide solution to a solution of your mystery substance and gently heat it. If ammonia gas is given off, it means that there are ammonium ions in your mystery substance.
- You can test ofr ammonia gas by holding a piece of damp red litmus paper over it. If the mystery gas if ammonia, the litmus paper will turn blue
- Ammonia also has a very distinctive strong smell but it isn’t a good idea to smell it as at high concentrations, ammonia is irritant and toxic.
What do you use to test for carbonates?
Dilute acid
What is the process to test for carbonates?
+1]To test for carbonate ions [CO3 2-] in solution, add some dilute acid
2]If there are carbonate ions present, the mixture will fizz - this is because the carbonate will react with the acid to produce carbon dioxide gas:
3]You can check to see if a gas is carbon dioxide by bubbling it through ilimewater. If it is carbon dioxide, the limewater turns milky.
Colur test
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+ To test for carbonate ions [CO3 2-] in solution, add some dilute acid
What are the tests for anions?
+Test for halide ions [using silver nitrate solution]
+Test for carbonates [using dilute acid]
+Test for sulfate ions [using barium chloride solution]
What do you use to test for halide ions?
Silver Nitrate solution
What is the process to test for halide ions?
To test for the halide ions, add some dilute nitric acid [HNO3] followed by a few drops of silver nitrate solution [AgNO3].
[Nitric acid is added first to get rid of any carbonate ions - they produce a pale precipitate with silver nitrate too, which would confuse the results. You can’t use hyrochloric acid because you’d be adding chloride ions]
What is the process to test for sulphate ions?
1]To test for sulphate ions in solution, first add some dilute hydrochloric acid to test sample - this stops any precipitation reactions not involving sulphate ions from taking place.
2]Then add barium chloride solution. If there are sulphate ions in the solution, a white preciitate of barium sulphate will form:
What is an example of a calibration curve?
