4. Chemical Analysis

Question 1

What defines a pure element?

Answer 1

A pure element contains only one substance with no other substances mixed in.

Question 2

How can you assess the purity of a substance?

Answer 2

Purity can be assessed using melting point and boiling point information.

Question 3

Why are measures of purity important?

Answer 3

Measures of purity are important in everyday substances such as foodstuffs and drugs.

Question 4

What is a mixture?

Answer 4

A mixture consists of two or more elements or compounds not chemically combined, retaining their individual properties.

Question 5

How can the substances in a mixture be separated?

Answer 5

Substances in a mixture can be separated by physical methods, including distillation, filtration, and crystallization.

Question 6

What is paper chromatography used for?

Answer 6

Paper chromatography is used to analyze substances present in a solution, such as food colorings and inks/dyes.

Question 7

How do you carry out paper chromatography?

Answer 7

Place a spot of the solution on chromatography paper, dip the paper in solvent, and allow the solvent to rise, separating the components.

Question 8

What is the Rf value in chromatography?

Answer 8

The Rf value is the ratio of the distance moved by the compound to the distance moved by the solvent front.

Question 9

What are the phases in chromatography?

Answer 9

Chromatography involves a stationary phase and a mobile phase, with separation depending on the relative solubility of the components.

Question 10

How can chromatography distinguish pure from impure substances?

Answer 10

Pure substances show one spot, while impure substances show multiple spots.

Question 11

What is the test for hydrogen gas?

Answer 11

A pop is heard when a lighted splint is placed near hydrogen gas.

Question 12

What is the test for oxygen gas?

Answer 12

A glowing splint relights in a test tube of oxygen gas.

Question 13

What is the test for carbon dioxide?

Answer 13

Carbon dioxide turns limewater (calcium hydroxide solution) cloudy white.

Question 14

What are the properties and tests for ammonia gas?

Answer 14

Ammonia has a sharp, choking smell, turns damp red litmus paper blue, and forms white smoke of ammonium chloride with hydrogen chloride gas.

Question 15

What are the properties and tests for chlorine gas?

Answer 15

Chlorine has a sharp, choking smell, turns damp blue litmus paper red, and then bleaches it white.

Question 16

What colors do lithium, sodium, potassium, calcium, and barium produce in flame tests?

Answer 16

Lithium: crimson
Sodium: yellow
Potassium: lilac
Calcium: red
Barium: green.

Question 17

What ions form white precipitates with sodium hydroxide solution, and which one dissolves in excess?

Answer 17

Aluminium, calcium, and magnesium ions form white precipitates; only aluminium hydroxide dissolves in excess sodium hydroxide.

Question 18

What are the colors of the precipitates formed by copper(II), iron(II), and iron(III) ions with sodium hydroxide?

Answer 18

Copper (II): blue
Iron (II): green
Iron (III): brown.

Question 19

How do carbonates react with dilute acids, and how can carbon dioxide be identified?

Answer 19

Carbonates react with dilute acids to form carbon dioxide, which turns limewater cloudy white.

Question 20

What precipitates do halide ions form with silver nitrate solution in the presence of dilute nitric acid?

Answer 20

Silver chloride: white
Silver bromide: cream
Silver iodide: yellow.

Question 21

What is the test for sulfate ions in solution?

Answer 21

Sulfate ions produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid