Period 3 elements and oxides

Question 1

Why is sodium more reactive than magnesium? [2]

Answer 1

• sodium forms a 1+ ion as opposed to a 2+ion

- requires less energy to one electron than two.

Question 2

Why is the reaction of water with magnesium slow, and predict a value for the pH? [3]

Answer 2

• reaction produces magnesium hydroxide (insoluble)
• hydroxide coats surface of metal, blocking water
• (weak alkali) pH in range of (8-9)

Question 3

‘Magnesium reacts with steam’

Write an equation, and describe what you would observe with the reaction? [3]

Answer 3

Equation: Mg + H2O → MgO + H2

White solid / powder / ash / smoke
ignore precipitate
ignore fumes 1

(Bright) white light / flame
allow glow
penalise effervescence under list principle 1

Question 4

Write an equation for the reaction that occurs when sodium is heated in oxygen, and describe what you would observe when this reaction occurs? [3]

Answer 4

Equation: 2Na + O2 → Na2O2

white / yellow solid / ash / smoke
ignore precipitate
ignore fumes 1

orange / yellow flame 1

Question 5

Explain why the atomic radii of elements decreases across period 3? [2]

Answer 5

number of protons in nucleus increases 1

so there is a stronger attraction between the nucleus and electrons 1

Question 6

Explain why the melting point of sulfur is greater than that of phosphorous? [2]

Answer 6

(S) greater as it has more atoms / is a larger molecule 1

so it has stronger van der waal forces to overcome 1

Question 7

Explain why sodium oxide forms an alkaline solution when it reacts with water? [2]

Answer 7

it contains oxide ions/ (O2-) that accept a proton from the water 1
this produces OH- ions 1

Question 8

Write an ionic equation for the reaction of phosphorous oxide with excess sodium hydroxide? [1]

Answer 8

P4O10 + 12OH- —–> 4PO4[3-] + 6H2O 1

Question 9

Describe what you would observe when sulfur burns in oxygen, and write an equation for reaction? [3]

Answer 9

blue flame 1
colourless choking/ smelly gas 1

Equation: S + O2 ——> SO2

Question 10

Outline an experiment that you could use to show aluminium oxide contains ions? [2]

Answer 10

heat metal until molten state 1
use electrolysis / electrolytes 1
or accept ( pass electrical current through solution)

Question 11

Suggest one reason why a layer of aluminium oxide protect aluminium from corrosion in moist air? [1]

Answer 11

the oxide is insoluble in water? 1

Question 12

Write an equation or the reaction of aluminium oxide with the following:

i) [HCl]
ii) [NaOH]

Answer 12

i) Al2O3 + 6H+ ——-> 2Al[3+] + 3H2O 1
ii) Al2O3 + 2OH- ——–> 2Al(OH)4- + 3H2O 1

Question 13

State the type of bonding present in basic oxides

Explain why this causes the oxide to have basic properties? [3}

Answer 13

ionic bonding 1
contain oxide ions, which are able to accept protons 1
produces OH- ions 1

Question 14

When reacted with water sulfur dioxide produces a weakly acidic solution
Write the equation for this reaction? [1]

Answer 14

SO2 + H2O ——–> H2SO3 / 2H+ + SO3[2-]

Question 15

Suggest why sulfur dioxide forms a weakly acidic solution? [1]

Answer 15

the sulphurous acid produced is an acid, so will dissociate H+ ions 1

Question 16

in terms of structure and bonding, explain why P4O10 can be vaporised by gentle heat but SiO2 cannot? [4]

Answer 16

(P4O10) has a simple covalent / molecular structure 1
it has weak van der Waals forces between molecules 1

SiO2 has a giant covalent structure    1 
it has (strong) covalent bonds to overcome    1

Question 17

Phosphorous (V) oxide is classified as an acidic oxide

write an equation for its reaction with NaOH ? [1]

Answer 17

P4O10 + 12NaOH ——–> 4Na3 PO4 + 6H2O

Question 18

Explain why the use of excess sodium hydroxide to neutralised phosphoric acid may cause environmental issues in the lake? [1]

Answer 18

would make the water strongly alkaline, so will make the water (toxic) 1

Question 19

Explain why magnesium will have a higher melting point than sodium? [2]

Answer 19

(Mg) forms a 2+ ion so has greater (charge density) 1

so it will have stronger attractions in ionic lattice 1

Question 20

Describe and explain the trend in electronegativity across Period 3? [3]

Answer 20

increases 1
the nuclear charge increases 1
so the ability to attract electrons increases 1

Question 21

Describe and explain the general trend in 1st ionisation energy across Period 3? [3]

Answer 21

increases 1
number of protons / nuclear charge increases 1
shielding (stays same) as outer electron is in the same energy level 1

Question 22

The 1st ionisation energy drops slightly at both Aluminium and sulfur? [3]

Answer 22

(Al) outer electron being removed from ‘3p’ orbital, that has more energy 1

(S) outer electron is removed from a ‘paired’ orbital 1
causes repulsion between electrons 1

Question 23

Describe and explain the trend in electrical conductivity across Period 3 from ( Mg —> Ar )? [3]

Answer 23

from (Na —> Al) increases, due to metallic structure 1
delocalised electrons able to move through structure and carry a current 1

after (Al) decreases, as NO metallic structure 1