Chapter 3 - Elements From The Sea

Question 1

what is the appearance of fluorine at room temperature

Answer 1

yellow gas

Question 2

what is the colour of fluorine gas

Answer 2

yellow

Question 3

what is the appearance of chlorine at room temperature

Answer 3

pale green gas

Question 4

what is the colour of chlorine gas

Answer 4

pale green

Question 5

what is the appearance of bromine at room temperature

Answer 5

red liquid

Question 6

what is the colour of bromine gas

Answer 6

orange

Question 7

what is the colour of bromine in an aqueous solution

Answer 7

brown

Question 8

what is the colour of chlorine in an aqueous solution

Answer 8

pale green

Question 9

what is the appearance of iodine at room temperature

Answer 9

black solid

Question 10

what is the colour of iodine gas

Answer 10

purple

Question 11

what can you do to make it easier to distinguish between the halogens in solution

Answer 11

mix with cyclohexane solution

Question 12

describe the test for halides

Answer 12

precipitation reaction with silver nitrate

Question 13

whats the test for chloride ions

Answer 13

add silver nitrate and a white precipitate forms

add ammonia and ppt dissolves

Question 14

whats the test for bromide ions

Answer 14

add silver nitrate and a cream precipitate forms

add ammonia and ppt partly dissolves

Question 15

whats the test for iodide ions

Answer 15

add silver nitrate and a yellow precipitate forms

add ammonia and ppt doesnt dissolve at all

Question 16

what is the rule for halogen displacement reactions

Answer 16

the halogen nearer the top of group 7 is a stronger oxidising agent and can displace the halogens lower down the table

Question 17

definition of electrolysis

Answer 17

the process of breaking down compounds using an electric current

Question 18

what are the rules at each electrode during electrolysis of aqueous solutions

Answer 18

at the cathode - if the metal is more reactive than hydrogen then H+ accepts electrons and hydrogen gas is given off
at the anode - if no halogen is present then OH- will give up electrons and form oxygen

Question 19

what is the evidence that iodide ions are the strongest reducing agents compared to bromide and chloride

Answer 19

iodide reduces sulfate ions to H2S (from +6 to -2 oxidation state).
bromide only reduces from +6 to +4
chloride doesnt reduce it at all

Question 20

what is dynamic equilibrium

Answer 20

when the forward rate of reaction = the backwards rate of reaction so the concentrations of reactants and products remain constant (only happens in a closed system)

Question 21

what is a closed system

Answer 21

where no more molecules can enter or leave

Question 22

what is the formula for equilibrium constant (Kc)

Answer 22

concentration of products/concentration of reactants

Question 23

what is le chateliers principle

Answer 23

in an equilibrium, if you change the conditions the equilibrium position will shift to oppose the change that was made

Question 24

what are the rules for equilibrium position for concentration, pressure, temperature and using a catalyst

Answer 24

• increasing the concentration of something will cause the equilibrium position to shift to the opposite side to oppose
• increasing overall pressure shifts the equilibrium to the side with fewer molecules
• increasing temperature shifts the equilibrium in the endothermic direction (+enthalpy change)
• using a catalyst doesnt have any effect on equilibrium position as it only speeds up the reaction

Question 25

what is the formula for atom economy

Answer 25

Mr of desired product/total Mr of reactants x100

Question 26

what is atom economy

Answer 26

the percentage of the mass of reactants that is turned into useful products