Chemistry: Chemical Analysis

If the exam says only chemical tests what type of test isn’t allowed?

Flame tests

For the first type of tests what are they and what does it mean?

They are cations and have lost electrons so have a plus sign.

What are the four elements which you use the flame test for?

Lithium: Li⁺

Sodium: Na⁺

Potassium: K⁺

Calcium: Ca²⁺

What colour is Lithium (Li⁺) in the flame test?

Red flame.

What colour is Sodium (Na⁺) in the flame test?

Yellow Flame

What colour is Potassium (K⁺) in the flame test?

Lilac Flame

What colour is Calcium (Ca²⁺) in the flame test?

Orange - Red Flame

For the flame test how do you clean the platinum wire?

By dipping it in hydrochloric acid

What is the method to test for the presence of ammonium gas (NH₄⁺) and what is the positive result?

Method: Add sodium hydroxide and WARM. Test for the gas with damp red litmus paper.

Positive Result: Damp red litmus paper turns blue

What is so special about the Copper (II) Cu²⁺?

You can test for its presence with the flame test AND using chemical testing.

How do you test for copper (II) Cu²⁺ using the flame test and chemical?

Flame test: Blue - green flame

Chemical: Add sodium hydroxide solution ; creates a blue precipitate

What is the test for Iron (II) Fe²⁺?

Add sodium hydroxide solution ; a green precipitate will form

What is the test for Iron (III) Fe³⁺?

Add sodium hydroxide solution ; A red brown precipitate will form.

For the second type of tests what are they and what does it mean?

It means they are anions and have gained electrons.

What does chloride Cl⁻, Bromide Br ⁻ and iodide I⁻ have in common?

They are all HALIDES.

What is the test for chloride?

Add dilute nitric acid, then silver nitrate solution.

White precipitate

What is the test for bromide?

Add dilute nitric acid and then silver nitrate solution.

Cream Precipitate

What is the test for iodide?

Add dilute nitric acid and then silver nitrate solution.

Yellow precipitate

Why is acid used in the process for halides?

The acid will remove impure ions that could interfere with the test and produce a false positive result by creating the wrong precipitate. For examples carbonates.

What is the test for carbonates?

Add dilute hydrochloric acid. Bubble the gas produced through limewater.

Effervescence, the limewater turns milky.

What is the test for sulfates?

Add dilute hydrochloric acid, the barium chloride solution

White precipitate forms.

Test for ammonia gas?

Hold damp red litmus paper over the mouth of a test tube

Red litmus paper turns blue

Test for carbon dioxide?

Bubble gas through limewater.

Limewater turns milky as white precipiate forms.

Test for chlorine?

Hold damp blue litmus paper over mouth of test tube.

Damp blue litmus paper turns red then bleaches white.

Test for hydrogen?

Hold a lighted splint at the mouth of the test tube.

Squeaky pop sound will be heard.

Test for oxygen?

Insert a glowing splint into a tube containing oxygen gas.

The glowing splint will relight if oxygen is present.

Test for water (H20)?

Add to the sample white anhydrous copper(II) sulfate.

The solid changes from white to blue.

EF: This only shows presence of water not that it is pure.

Test for pure water?

Measure its boiling point(100 degrees celcius)