Analytical Chem

Question 1

How can you test if a substance is pure?

Answer 1

By measuring its melting or boiling point. A pure substance will have a sharp, specific melting/boiling point, while a mixture melts/boils over a range of temperatures.

Question 2

What color flame does lithium produce in a flame test?

Answer 2

Crimson red.

Question 3

What color flame does sodium produce?

Answer 3

Yellow.

Question 4

What color flame does potassium produce?

Answer 4

Lilac.

Question 5

What color flame does calcium produce?

Answer 5

Orange-red.

Question 6

What color flame does copper produce?

Answer 6

Green.

Question 7

What happens when sodium hydroxide (NaOH) is added to a solution containing aluminum ions (Al³⁺)?

Answer 7

A white precipitate forms, which dissolves in excess NaOH.

Question 8

What happens with calcium ions (Ca²⁺) or magnesium ions (Mg²⁺) when NaOH is added?

Answer 8

A white precipitate forms, but it does not dissolve in excess NaOH.

Question 9

What happens with copper(II) ions (Cu²⁺) when NaOH is added?

Answer 9

A blue precipitate forms.

Question 10

What happens with iron(II) ions (Fe²⁺) when NaOH is added?

Answer 10

A green precipitate forms.

Question 11

What happens with iron(III) ions (Fe³⁺) when NaOH is added?

Answer 11

A brown precipitate forms.

Question 12

How do you test for carbonate ions?

Answer 12

Add a dilute acid (e.g., HCl). If carbonate ions are present, carbon dioxide gas is produced, which turns limewater cloudy.

Question 13

How do you test for halide ions?

Answer 13

Add dilute nitric acid to remove carbonate impurities, then add silver nitrate solution. The color of the precipitate indicates the halide ion present.

Question 14

What precipitate forms if chloride ions (Cl⁻) are present in the halide test?

Answer 14

A white precipitate of silver chloride forms.

Question 15

What precipitate forms if bromide ions (Br⁻) are present in the halide test?

Answer 15

A cream precipitate of silver bromide forms.

Question 16

What precipitate forms if iodide ions (I⁻) are present in the halide test?

Answer 16

A yellow precipitate of silver iodide forms.

Question 17

How do you test for sulfate ions (SO₄²⁻)?

Answer 17

Add dilute hydrochloric acid, followed by barium chloride solution. A white precipitate of barium sulfate forms if sulfate ions are present.

Question 18

How do you test for ammonia gas (NH₃)?

Answer 18

Expose damp red litmus paper to the gas. If ammonia is present, the paper turns blue.

Question 19

How do you test for hydrogen gas?

Answer 19

Place a lit splint near the gas. A squeaky pop indicates hydrogen.

Question 20

How do you test for oxygen gas?

Answer 20

Insert a glowing splint. It will relight in oxygen.

Question 21

How do you test for carbon dioxide gas?

Answer 21

Bubble the gas through limewater. It will turn cloudy if CO₂ is present.

Question 22

How do you test for chlorine gas?

Answer 22

Damp litmus paper is bleached white in chlorine gas.

Question 23

What are the advantages of instrumental methods over chemical tests?

Answer 23

Instrumental methods are faster, more sensitive, and more accurate.

Question 24

How does flame emission spectroscopy work?

Answer 24

A sample is heated in a flame, and the light emitted is analyzed with a spectrometer. The wavelength of light identifies the metal ion, and the intensity indicates the concentration.