Period 3 Elements and their Oxides

Question 1

Sodium reaction with cold water equation and observations

Answer 1

Fizzes around on surface

2Na + 2H2O -> 2NaOH + H2

Question 2

sodium reaction with oxygen observation and equation

Answer 2

yellow flame
produces white solid

4Na + O2 -> 2Na2O(s)

Question 3

Observations of Mg, Al, Si and P when burned in oxygen

Answer 3

burn with White flame
give white solid

Question 4

S burning in oxygen observations

Answer 4

blue flame
choking gas

Question 5

Period 3 oxides

Answer 5

Na2O
MgO
Al2O3
SiO2
P4O10
SO2

Question 6

How to stop sodium and phosphorous from reacting with air

Answer 6

sodium in oil
phosphorous in water

Question 7

Why do metal oxides have high melting points?

Answer 7

ionic giant lattice structures
strong forces of attraction
large electronegativity difference between metal and O

Question 8

Why does Al2O3 show some covalent character?

Answer 8

electronegativity difference is not that large
small Al3+ ion has high charge distorting O2- ion’s electron cloud

Question 9

Highest mp period 3 oxide and why?

Answer 9

macromolecular SiO2
many strong covalent bonds
much energy needed to break them

Question 10

why do P4O10 and SO2 have low mps?

Answer 10

simple molecular
weak vdws
P4O10 has more electrons and is larger so higher bp

Question 11

How to prove p3 oxides have ions?

Answer 11

melt and show they conduct electricity

Question 12

sodium oxide reaction with water and pH

Answer 12

Na2O + H2O -> 2NaOH
pH 13

Question 13

magnesium oxide reaction with water and pH

Answer 13

MgO + H2O -> Mg(OH)2
pH 9

Question 14

Why has Mg(OH)2 got a lower pH than NaOH

Answer 14

stronger lattice
less free OH- produced, lower pH

Question 15

Why do Al2O3 and SiO2 not dissolve in water?

Answer 15

High strength of Al2O3 ionic lattice and SiO2 macromolecular structure so each give a pH of 7.

Question 16

Why is MgO better than NaOH for treating acid in rivers and the stomach?

Answer 16

It is only sparingly soluble and weakly alkaline, so using XS will not make the water excessively alkaline

Question 17

phosphorous oxide reacting with water and pH

Answer 17

P4O10(s) + 6H2O(l) -> 4H3PO4
pH 0 (vigorous exothermic reaction)

Question 18

sulfur dioxide reacts with water and pH

Answer 18

SO2 + H2O -> H2SO3
pH3

Question 19

Sulfur trioxide reacting with water equation and pH

Answer 19

SO3 + H2O -> H2SO4
pH 0

Question 20

Which period 3 oxides form acids when reacting with water and which ones form bases?

Answer 20

metal ionic oxides form acids
non metal simple molecular covalent oxides form bases