11TK - Cation, Anion & Gas Tests

Flame Testing

100

What colour flame is copper?

blue-green

200

Identify substance XY:

X - blue-green flame

Y - cream precipitate

CuCl₂

300

Why is nichrome or platinum wire used for flame test?

Chemically inert & won't form a flame colour to interfere with flame test colour.

400

What is the colour of each flame test?

5 elements

Li - red

Na - yellow

K - lilac

Ca - orange-red

Cu - blue-green

500

Describe steps and results for a solid sample of K₂CO₃.

1) Perform flame test using nichrome/platinum wire

2) Flame test for = lilac

3) Add acid to sample.

4) Then, bubble sample through limewater.

5) Positive result = limewater turns cloudy

Cation Testing

100

What colour is the precipitate containing cation Fe³⁺?

orange-brown precipitate

200

Why does testing for ammonium ions need to be conducted in the fumehood?

Ammonia gas is produced which is highly toxic when inhaled.

300

What is the colour of the precipitate of each of the following cations?

Cu²⁺, Fe²⁺, Fe³⁺

copper - blue

iron (II) - green

iron (III) - orange-brown

400

How to test for ammonium ions only in ammonium chloride?

3 points

1) Add NaOH (warm it - optional)

2) Test using damp red litmus paper

3) Litmus paper turns blue (ammonia gas produced)

500

A student is given 2 white solid compounds, and a colourless solution containing the same 2 compounds. Student is told that 1 is a halide & the other is a carbonate.

Give 2 reasons why the compounds cannot be copper(II) carbonate, without doing any tests.

1) copper (II) carbonate is green, not white

2) cannot form solution, not soluble

Anion Testing

100

What is the positive test result for the halogens?

Chlorine - white precipitate

Bromine - cream

Iodine - yellow

200

What is the change in appearance of limewater if hydrocarbon undergoes combustion?

2 points

1) limewater turns milky

1 of 2 from below:

2) CO₂ is formed from combustion

3) CO₂ reacts with limewater to produce CaCO₃ (insoluble product)

300

Why is acid, such as hydrochloric acid, added first if testing for sulfate ions?

To remove any carbonate, to stop from interfering with test results.

400

Describe chemical test for Br_2, and colour if positive test result.

3 points

1) Add nitric acid, HNO₃ [cannot be HCl - halogen]

2) Add AgNO₃

3) cream precipitate = bromine

500

How to test for a sample of MCl versus MSO₄?

6 points

For XCl (chlorine)

1) Add HNO₃, nitric acid, to MCl

2) Add silver nitrate, AgNO₃

3) White precipitate = chloride ions present

For XSO₄ (sulfate)

1) Add nitric acid or HCl [cannot be H₂SO₄]

2) Add BaCl₂/Ba(NO₃)₂

3) White precipitate = sulfate

Gases & Water

100

What is the test for hydrogen?

2 points

lighted split - squeaky pop

200

What is the test for oxygen?

2 points

1) glowing split

2) re-lights

300

What is the difference in testing for:

(i) presence of water

(ii) purity of water [2 points]

(i) anhydrous white copper sulfate turns blue if water is present

(ii) measure its BP - pure water has a boiling point of 100 degrees C

or can do melting point

400

What is the test for chlorine gas? 

***Where must this testing be done and why?

3 points total

1) Use damp litmus paper

2) Chlorine gas is green --> will bleach litmus paper white

or 2) Use damp blue litmus paper --> red --> white

***mandatory to perform in fumehood as it is a toxic gas when inhaled

500

What are the positive test results of:

1) ammonia gas,  NH₃

2) H_{2 + method}

3) O_{2 + method}

1) damp red litmus paper --> blue

2) lighted split - squeaky pop

3) glowing split - re-lights