Period 3 Oxides Complete DJWinters

Question 1

Predict a value for the melting point of sulfur(IV)
oxide.
Suggest, in terms of structure and bonding, why the melting point of sulfur(IV) oxide is different from that of phosphorus(V) oxide.

Answer 1

200 (K)
Allow range 10-273 (K)
CE = 0 if temperature >573 K, otherwise mark on
Allow correct answers in °C but units must be given.

SO2 smaller (molecule) (than P4010) (or converse)
also SO, has lower M, / less surface area / less polarisable / fewer electrons
penalise SO3 and P20s for M2 only

vdW forces between molecules are weaker / require less energy to separate molecules
ignore dipole-dipole
If covalent bonds broken lose M2 and M3 but can gain M1

Question 2

(c) Silicon(IV) oxide is insoluble in water.
Explain, using an equation, why silicon(IV) oxide is classified as an acidic oxide

Answer 2

Reacts with / neutralises bases / alkalis
Allow any given base or alkali including OH
Si02 + 2NaOH -+ NazSiO3 + Hz0

Question 3

Explain why sodium oxide forms an alkaline solution when it reacts with water.

Answer 3

Sodium oxide contains 02- ions
These 02- ions react with water forming OH- ions

Question 4

State the structure of, and bonding in, silicon dioxide.
Other than a high melting point, give two physical properties of silicon dioxide that are
characteristic of its structure and bonding.

Answer 4

Macro
Covalent
Hard/brittle/insoluble/nonconductor

Question 5

Give the formula of the species in a sample of solid phosphorus (V) oxide.
State the structure of, and describe fully the bonding in, this oxide.

Answer 5

P4O10
Molecular
Covalent
Vdw b/w mol

Question 6

Write an equation for the reaction between the acidic oxide, phosphorus(V) oxide, and the basic oxide, magnesium oxide.

Answer 6

Question 7

Magnesium oxide, silicon dioxide and phosphorus(V) oxide are white solids but each oxide has a different type of structure and bonding. State the type of bonding in magnesium oxide.
Outline a simple experiment to demonstrate that magnesium oxide has this type of bonding.

Answer 7

Ionic
Melt it - when molten it will conduct electricity

Question 8

By reference to the structure of, and the bonding in, silicon dioxide, suggest why it is insoluble in water.

Answer 8

Macro
Cov bond
Water cannot break the covalent bonds/lattice

Question 9

State how the melting point of phosphorus(V) oxide compares with that of silicon dioxide.
Explain your answer in terms of the structure of, and the bonding in, phosphorus(V) oxide.

Answer 9

Lower
Molecular WITH cov bond
Weak vdw IMF

Question 10

Some Period 3 oxides have basic properties.
State the type of bonding in these basic oxides.
Explain why this type of bonding causes these oxides to have basic properties.

Answer 10

Ionic
Contains O2- ions
These ions form OH-

Question 11

Suggest why silicon dioxide is described as an acidic oxide even though it is insoluble in water.

Answer 11

(e)
SiO, reacts with bases / NaOH / CaO / CaCO3

Question 12

Suggest why white phosphorus is stored under water.

Answer 12

To preventit coming into contact/reacting with oxygen/air

Question 13

Phosphorus(V) oxide is known as phosphorus pentoxide.
Suggest why it is usually represented by P4O10 rather than by P2O5

Answer 13

One molecule contains 4P and 10 O. the molecular formula is P4O10

Question 14

Write an equation for the reaction of P,O, with water to form phosphoric(V) acid.
Give the approximate pH of the final solution.

Answer 14

P4010 + 6H20 - 4H3PO4
0

Question 15

(e) A waste-water tank was contaminated by P401o. The resulting phosphoric(V) acid solution was neutralised using an excess of magnesium oxide. The mixture produced was then disposed of in a lake.

Explain why an excess of magnesium oxide can be used for this neutralisation.

Answer 15

MO is sparingly soluble/insoluble/weakly alkaline
Excess/unreacted MgO can be filtered off/separated

Question 16

Explain why the use of an excess of sodium hydroxide to neutralise the
phosphoric(V) acid solution might lead to environmental problems in the lake.

Answer 16

An excess of NaOH would make the lake alkaline/toxic/kill wildlife

Question 17

Write an equation for the acid-base reaction that occurs when Na2O reacts with P4O10 in
the absence of water.

Answer 17

6Na2O + P4010 - 4Na3PO4

Question 18

Suggest one reason why a thin layer of aluminium oxide protects aluminium from corrosion in moist air.

Answer 18

Insoluble

Question 19

Write an ionic equation in each case to show how aluminium oxide reacts with the aqueous NaOH

Answer 19

Question 20

Predict whether the melting point of lithium oxide is higher than, the same as, or lower than the melting point of sodium oxide and explain your prediction.

Answer 20

Higher
Li+ smaller than Na+
Attracts O2- ion more strongly

Question 21

write an ecuation for he reaction heiween aluminum oxide and an excess of
aqueous sodium hydroxide.

Answer 21

Question 22

State and explain the trend in electronegativities across Period 3 from sodium to sulfur.

Answer 22

Question 23

(b)
Explain why the oxides of the Period 3 elements sodium and phosphorus have different melting points. In your answer you should discuss the structure of and bonding in these oxides, and the link between electronegativity and the type of bonding.

Answer 23

Question 24

A chemical company has a waste tank of volume 25 000 dm°. The tank is full of phosphoric acid herO solution formed by adding some unwanted phosphorus oxide to water in
the tank.
A 25.0 cm° sample of this solution required 21.2 cm° of 0.500 mol dm sodium hydroxide solution for complete reaction.
Calculate the mass, in kg, of phosphorus(V) oxide that must have been added to the water in the waste tank.

Answer 24

Question 25

Answer 25

1 - B
2 - E
Low mp/ weak vdw IMF

Question 26

Give a simple chemical test which could be used to show which of the oxides in the table is sodium oxide. State the observation you would make.

Answer 26

Chemical test Add water or flame test
Test pH or flame colour
Observation pH = 13/14 or colour yellow

Question 27

Write an equation for the action of heat on calcium carbonate.

Answer 27

CaCO3 - CaO + CO

Question 28

Despite the additional cost, operators of power stations are encouraged to remove the sulfur dioxide from flue-gases. Explain why this may not be environmentally beneficial.

Answer 28

Disposal of large quantities of CaSO3 (allow CaSO4)
Produces CO2 or uses up CaCO3

Question 29

Equation of Na2O and H3PO4

Answer 29

Question 30

Draw the displayed formula of the undissociated acid formed when sulfur dioxide reacts with water

Answer 30

Question 31

This question is dealing with sodium to phosphorous

The element x forms an oxide that has a low mp this oxide dissolves on water to form an acidic solution

Deduce type bonding in this oxide
Identify element x

Answer 31

Covalent
P (phosphorous)

Question 32

Sulfur(IV) oxide reacts with water to form a solution containing ions
Write an equation for this reaction.

Answer 32

SO2 + H20 -› H+ + HSO3-
Products must be ions
Allow S02 + H20 - 2H+ + SO3^2-

Question 33

Outline an experiment that could be used to show that aluminium oxide contains ions.

Answer 33

Heat until molten
Conducts electricity

Question 34

Suggest why sulfur dioxide forms a weakly acidic solution

Answer 34

Reaction is in equilibrium,/ partially dissociated

Question 35

State how you would collect the hydrogen produces. State the measurements that you would make in order to calculate the number of moles of hydrogen produced. Explain how your results could be used to determine the number of moles of magnesium metal in the sample.

Answer 35

Question 36

Oxide Q is a colourless gas at room temperature. It dissolves in water to give a solution with a low pH.

Identify Q. State the type of bonding present in Q and explain why it is a gas at room temperature. Write an equation for the reaction of & with water

Answer 36

SO2
Covalent
Intermolecular forces weak with vdw
SO2 + H2O -> H2So3

Question 37

Why is Al2O3 insoluble in water

Answer 37

Large lattice energy or strong covalent bonds or enthalpy is very positive or delta G is positive
or sum of hydration energies less than covalent bond energies (1)

Question 38

State the element in Period 3 that has the highest melting point.
Explain your answer.

Answer 38

Silicon / Si
covalent (bonds)
Strong or many of the (covalent) bonds need to be broken / needs a lot of energy to break the (covalent) bonds