4 - inorganic chemistry & periodic table

Question 1

does atomic radius increase or decrease down the group, and why?

Answer 1

increases - the atoms have more shells of electrons

Question 2

group 2

does melting point increase or decrease down a group, and why?

Answer 2

decrease - the metallic bonding weakens as the atomic size increases

Question 3

test and colour

Ba²⁺

Answer 3

. flame test
. apple green to a bunsen burner

Ba²⁺ + 2e⁻ → Ba

Question 4

test and colour

Cu²⁺

Answer 4

. add a few drops of NaOH
. light blue ppt is formed
. flame test - blue/green

Cu²⁺ + 2e⁻ → Cu

Question 5

test and colour

Fe²⁺

Answer 5

. add a few drops of NaOH
. green ppt formed

Fe²⁺ + 2e⁻ → Fe

Question 6

test and colour

Fe³⁺

Answer 6

. add potassium thiocyanate
. rust brown colour is produced

Fe³⁺ + 3e⁻ → Fe

Question 7

test and colour

Mg²⁺

Answer 7

. add NaOH
. white ppt that doesnt dissolve in excess NaOH
. flame test - no colour

Mg²⁺ + 2e⁻ → Mg

Question 8

test and colour

Ca²⁺

Answer 8

. flame test
. brick red to a bunsen

Ca²⁺ + 2e⁻ → Ca

Question 9

test and colour

NH₄⁺

Answer 9

. add a few drops of dilute NaOH, warm gently until ammonium gas is produced, use damp litmus paper to test
. turns blue

NH₄⁺ + e⁻ → NH₃

Question 10

test and colour

Na⁺

Answer 10

. flame test
. yellow colour

Na⁺ + e⁻ → Na

Question 11

test and color

K⁺

Answer 11

. flame test
. lilac colour

K⁺ + e⁻ → K

Question 12

test and colour

Li⁺

Answer 12

. flame test
. red colour

Li⁺ + e⁻ → Li

Question 13

test and colour

Cl⁻

Answer 13

. add small volume of nitric acid
. add a few drops of silver ntirate
. white ppt will form

2Cl⁻ → Cl₂ + 2e⁻

Question 14

test and colour

Br⁻

Answer 14

. add a small volume of nitric acid
. add a few drops of silver nitrate
. creamy ppt will form

2Br⁻ → Br₂ + 2e⁻

Question 15

test and colour

I⁻

Answer 15

. add a small volume of nitric acid
. add a few drops of silver nitrate
. yellow ppt will form

2I⁻ → I₂ + 2e⁻

Question 16

test and colour

SO₄²⁻

Answer 16

. add dilute HCl, add a few drops of barium chloride
. white ppt forms

SO₄²⁻ → SO₄ + 2e⁻

Question 17

test and what happens

CO₃²⁻

Answer 17

. add a dilute acid and bubbling will occur (CO₂ is released)
. confirm its CO₂ by bubbling through limewater

CO₃²⁻ → CO₃ + 2e⁻

Question 18

test and colour

OH⁻

Answer 18

. red litmus paper turns blue

H⁺ + OH⁻ → H₂O

Question 19

group 2

reactions with oxygen

Answer 19

they burnnnn

eg. 2Mg + O₂ → 2MgO

Question 20

(4)

reactivity of group 2

Answer 20

• increases ↓ the group
• atomic radii increase (more shielding)
• nuclear attraction ↓ (easier for cations to form)
• w water: fizzing increases, metal dissolves faster going ↓

Question 21

group 2

hydroxide solubility

Answer 21

more soluble down the group
if not, white ppt forms

Question 22

group 2

sulphate solubility

Answer 22

less soluble down the group
BaSO₄ is the least soluble

Question 23

cations, thermal stability, g1 decomposition

group 2 carbonates

Answer 23

• cations get bigger, have less of a polarising effect
• more thermally stable as you ↓
• group 1 carbonates dont decompose

Question 24

salt, decomposition, smallest ion

group 2 nitrates

Answer 24

• g1 nitrates decompose to give nitrate (III) salt + O₂
• magnesium nitrate decomposes the easiest → ion is the smallest, ↑ charge density

Question 25

# (3) flame test explanation

Answer 25

- the heat causes the electron to move to a higher energy level - electron is unstable at that level so it drops back down - as it drops down the energy is emitted in the form of visible light

Question 26

# (3) flame test method

Answer 26

- use a nicrome wire - clean the wire by dipping in conc HCl acid - dip in solid then put in flame