Cations, Anions, and Gas Tests

Flashcards about cation and anion identification, flame tests, gas tests, and salt identification.

What are the limitations of using a flame test to identify the cation in a salt?

It can be difficult to see the color, it might be difficult to tell the difference between some colors; some colors overwhelm and it may not work well in mixtures.

What is the precipitation method for identifying cations in a salt?

Dissolve salt in water, add sodium hydroxide or ammonia to see what precipitate color forms.

What colors are formed in flame tests for the following cations: Li+, Na+, K+, Ca2+, Cu2+?

Li+ is red, Na+ is yellow, K+ is lilac, Ca2+ is orange-red, and Cu2+ is blue-green.

Describe the Practical-Flame test procedure

Dip the end of a damp splint into the solid salt, hold the splint in the non-luminous flame of a Bunsen Burner (roaring blue flame), and observe the flame color.

What reagent is used to test for Cl-, Br- and I-?

Add acidified silver nitrate solution.

What reagent is used to test for SO42-?

Add acidified barium chloride solution.

What reagent is used to test for CO32-?

Add hydrochloric acid and identify the gas evolved.

When testing for anions using the order carbonate test, sulphate test, and Halide test, what steps are involved.

Carbonate test -> add nitric acid -> if it fizzes it is carbonate; Sulphate test ->add nitric acid (if not already done) -> add barium nitrate -> if sulphate, forms a white precipitate; Halide tests -> add nitric acid -> add silver nitrate -> chloride - white precipitate, bromide - cream precipitate, iodide - yellow precipitate.

Test for Hydrogen (H2)

Lit splint brought to mouth of test tube; should make a squeaky pop.

Test for Carbon dioxide (CO2)

Gas bubbled through lime water or lime water added to test tube; should turn milky.

Test for Oxygen (O2)

Glowing splint brought to mount of test tube; glowing splint re-lights.

Test for Chlorine (Cl2)

Damp blue litmus paper above mouth of test tube; turns red then bleaches.

Test for Ammonia (NH3)

Dampened litmus paper brought to mouth of test tube; turns blue.

What is the positive result of the test for the Carbonate anion (CO32-)?

Cloudy lime water

What is the positive result of the test for the Halide Chloride (Cl-)?

White precipitate

What is the positive result of the test for the Halide Bromide (Br-)?

Cream precipitate

What is the positive result of the test for the Halide Iodide (I-)?

Yellow precipitate

What is the positive result of the test for the Sulphate anion?

White precipitate