Module 2 – Foundations In Chemistry

Exam Questions

Aluminium will combine directly with fluorine.
Write the equation for the reaction between aluminium and fluorine.

2Al + 3F2 → 2AlF3

Describe what is meant by the term ionic lattice, in terms of the type and arrangement of particles present.

Repeating pattern of oppositely charged ions

Draw a ‘dot-and-cross ’ diagram for aluminium fluoride.

What is meant by the term covalent bond ?

A shared pair of electrons

Draw a ‘dot-and-cross ’ diagram to show the bonding in a boron tribromide molecule.

State whether the following substances conduct electricity when solid or molten, and explain your answers in terms of the particles involved:

• aluminum

• aluminum fluoride

• boron tribromide.

• Aluminum conducts in solid and molten states

• Aluminum has delocalised electrons

• Aluminum fluoride conducts when molten AND because it has mobile ions

• Aluminum fluoride does not conduct when solid AND Solid aluminum fluoride has ions which are fixed in an (ionic) lattice

• Boron tribromide does not conduct in solid and molten states AND Boron tribromide has no mobile electrons

Aluminium has 13 successive ionisation energies.

(i) Write the equation for the third ionisation energy of aluminium.

Al2+(g) → Al3+(g) + e–

State how and explain why the attraction between nuclei and outermost electrons in gaseous atoms varies across Period 3.

The attraction (between nuclei and outermost electrons) increases (across the period) AND The nuclear charge increases

The table shows the boiling points of ammonia, fluorine and bromine. Explain the different boiling points of NH3, F2 and Br2

• NH3 has hydrogen bonding

• F2 AND Br2 have London forces

• the intermolecular force in Br2 is stronger than that of F2 Because bromine has more electrons than fluorine

• The London forces in Br2 are greater than hydrogen bonding in NH3 AND hydrogen bonding in NH3 is stronger than London forces in F2

Complete the diagram below to show hydrogen bonding between the H2O molecule shown and one other H2O molecule.

State and explain two anomalous properties of ice caused by hydrogen bonding.

Ice is less dense than water since the molecules in ice are held apart by hydrogen bonds

Ice has a relatively high melting point because hydrogen bonds are relatively strong

Draw a ‘dot-and-cross’ diagram to show the bonding in CO2.

Silicon dioxide, SiO2, has the same structure and bonding as diamond. State the structure and bonding in SiO2

Giant covalent (lattice)

Describe and explain the electrical conductivity of sodium oxide, Na2O, and sodium in their solid and molten states.

• Sodium conducts in the solid and molten states

• Sodium has delocalised electrons in both states

• Na2O conducts when molten and not when solid

• Molten Na2O has ions which are mobile

• Solid Na2O has ions which are fixed AND in an (ionic) lattice

Phosphine gas, PH3, can be prepared by adding phosphorus, P4, to warm concentrated aqueous sodium hydroxide as shown in the equation below.

P4(s) + 3NaOH(aq) + 3H2O(l) PH3(g) + 3NaH2PO2(aq)

Using oxidation numbers, explain why this is a disproportionation reaction

P in P4 is 0 AND in PH3 is –3 AND in NaH2PO2 is (+)1

Phosphorus has been oxidised (from 0) to +1

Phosphorus has been reduced (from 0) to –3

A chemist reacts 1.86 g of P4 with excess NaOH(aq). Calculate the volume of phosphine gas, in cm3, produced at room temperature and pressure, RTP

Correctly calculates amount of P4 = 1.86/124.0 = 0.015(0) mol  Correctly calculates volume of PH3 = 0.015(0) x 24000 = 360 (cm3)

Phosphine gas burns in air to form an oxide of phosphorus, P4O10, and water. Write the equation for this reaction.

4PH3 + 8O2 → P4O10 + 6H2O

Phosphoric acid, H3PO4, can be made by reacting P4O10 with water.

Sodium phosphate, Na3PO4, is a salt that can be prepared by reacting H3PO4 with sodium hydroxide, NaOH.

A student prepared a solution of Na3PO4 by reacting 15.0 cm3 of 0.100 mol dm–3 H3PO4 with 0.200 mol dm–3 NaOH.

(i) Why is Na3PO4 described as a salt of H3PO4?

The hydrogen ions

Calculate the amount, in moles, of H3PO4 in 15.0 cm3 of 0.100 mol dm–3 H3PO4

0\.0015

The equation for the preparation of Na3PO4 from NaOH and H3PO4 is shown below.

3NaOH(aq) + H3PO4(aq) Na3PO4(aq) + 3H2O(l)

Calculate the volume of 0.200 mol dm–3 NaOH that reacts exactly with 15.0 cm3 of 0.100 mol dm–3 H3PO4.

) 22.5

NH3 and PH3 are both simple molecules. The boiling points of NH3 and PH3 are shown in the table below.

hydrogen bonding

Permanent dipole

Suggest why PH3 has a lower boiling point than NH3.

the intermolecular forces are weaker in PH3

What is a dative covalent bond?

Both electrons have been donated by one atom

Draw a ‘dot-and-cross’ diagram to show the bonding in H3NBF3

) The F–B–F bond angle in BF3 is different from the F–B–F bond angle in H3NBF3. Complete the table to predict the F–B–F bond angles in BF3 and in H3NBF3

BF3 = 120(°)

H3NBF3 = 109.5(°)

Explain why the student might expect the H–N–H bond angle to be larger in H3NBF3 than in NH3.

NH3 has three bonding pairs and one lone pair of electrons

H3NBF3 has four bonding pairs (and no lone pairs) of electrons

Lone pair of electrons repels more than bonding pairs

Bleach can be made by reacting chlorine with cold aqueous sodium hydroxide. A solution of bleach contains the chlorate compound NaClO. Write the equation for the reaction taking place

2NaOH + Cl2 → NaClO + NaCl + H2O

Give the systematic name for NaClO3.

Sodium chlorate(V)

When heated, NaClO3 disproportionate as shown in the equation below.

4NaClO3 3NaClO4 + NaCl

Using oxidation numbers, explain why this is a disproportionation reaction.

Cl in NaClO3 is (+)5 AND Cl in NaClO4 is (+)7 AND Cl in NaCl is –1

Chlorine has been both oxidised and reduced

Chlorine has been oxidised from (+)5 to (+)7 AND chlorine has been reduced from (+)5 to –1

State one valid reason that supports the scientists’ case and state one reason why chlorine should be added to drinking water

Chlorine is toxic but it kills bacteria

Draw a ‘dot-and-cross’ diagram to show the bonding in a molecule of CH3Cl.

Name the shape of a molecule of CH3Cl .

Tetrahedral

Describe a simple chemical test that you could carry out to show that brine contains aqueous chloride ions. How would you confirm that no other halide ions are present?

Add silver nitrate

White precipate

Ag+ + Cl– → AgCl

Add dilute NH3 and precipitate (completely) dissolves

Explain, with the aid of a labelled diagram, what is meant by the term metallic bonding

metallic bond as (electrostatic) attraction between the electrons and the positive ions

Write the equation for the reaction of sodium with oxygen to form sodium oxide.

4 Na + O2 → 2 Na2O

State what is meant by the term ionic bond.

(electrostatic) attraction between oppositely charged ions

Draw a ‘dot-and-cross’ diagram to show the bonding in Na2O.

Compare and explain the electrical conductivities of sodium and sodium oxide in the solid and liquid states.

• sodium is a (good) conductor because it has mobile electrons

• sodium oxide does not conduct as a solid

• sodium oxide conducts when it is a liquid

• ions cannot move in a solid

• ions can move OR are mobile when liquid

Explain why there is a difference in the melting points of K, KBr and H2O

• In K, (electrostatic attraction between) positive ions/cations AND e– / electron

• In KBr, (electrostatic attraction between) oppositely OR positively AND negatively charged ions

• K has metallic bonding while KBr has oppositely charged ions

• In H2O hydrogen bonding between molecules

• ionic bonding > metallic bonding > hydrogen bonding

2K(s) + 2H2O(l) 2KOH(aq) + H2(g)

0\.2346 g of potassium is reacted with excess water.

Calculate the volume of gas formed.

amount of K = 0.2346 / 39.1 OR = 6.(00) × 10–3 OR 0.006(00) mol amount of H2 = (mol of K) / 2 OR = 3.(00) × 10–3 OR 0.003(00) mol

Volume of gas = (mol of H2) × 24000 OR = 72(.0)

What is meant by the term electronegativity?

The ability of an atom to attract electrons in a covalent bond

Show, using δ+ and δ– symbols, the permanent dipoles on each of the following bonds.

δ+N–F δ- AND δ-N–Br δ+

State the shape of a molecule of SF6.

octahedral

Using outer electron shells only, draw ‘dot-and-cross’ diagrams for molecules of BF3 and NH3.

Use your diagrams to explain why a molecule of BF3 has bond angles of 120° and NH3 has bond angles of 107°.

electron pairs repel

NH3 has one lone pair and three bonding pairs of electrons AND lone pair of electrons repels more than bonding pairs

BF3 has three (bonding) pairs of electrons (which repel equally)

Molecules of BF3 contain polar bonds, but the molecules are non-polar. Suggest an explanation for this difference.

BF3 is symmetrical

The dipoles cancel out

Draw a ‘dot-and-cross ’ diagram to show the bonding in magnesium sulfide. Show outer electron shells only.

Draw a ‘dot-and-cross ’ diagram of a molecule of F2O. Show outer electron shells only

Predict the bond angle in an F2O molecule. Explain your answer.

• Predicted bond angle 104–105O.

• There are 2 bonded pairs and 2 lone pairs

• Lone pairs repel more than bonded pairs

Draw a labelled diagram to show hydrogen bonding between two molecules of liquid ammonia.

Describe and explain one anomalous property of water which results from hydrogen bonding.

H2O has a relatively high boiling point since a lot of energy is needed to overcome hydrogen bonds

Explain, using your ‘dot-and-cross’ diagram, why ammonia has this shape and has a bond angle of 107°.

• pyramidal

• There are 3 bonded pairs and 1 lone pair

• Lone pairs repel more than bonded pairs

Complete the electron configuration of the Cl – ion.

1s2 2s2 2p6 3s2 3p6

State the shape of, and bond angle in, an NH4 + ion.

• tetrahedral

• 109.5º

Draw a ‘dot-and-cross’ diagram to show the bonding in NH4 +

Draw a ‘dot-and-cross’ diagram to show the bonding in NH4
\+.

.

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She noticed that when the ammonium chloride was solid it did not conduct electricity. However, when ammonium chloride was dissolved in water, the resulting solution did conduct electricity. Explain these observations.

ions OR electrons cannot move in a solid but can move in solution

Write a balanced equation to show how ammonium sulfate could be formed by the reaction between aqueous ammonia and sulfuric acid.

2NH3 + H2SO4 → (NH4)2SO4

Explain what is meant by the term salt.

when the H+ in an acid is replaced by a metal ion

Why is ammonia acting as a base in the neutralisation of ammonia and sulfuric acid?

It accepts a protons

What is the relative formula mass of (NH4 ) 2SO4? Give your answer to one decimal place.

132\.1

MnO2(s) + 4HCl(aq) MnCl 2(aq) + 2H2O(l) + Cl 2(g)

Using oxidation numbers, show what has been oxidised and what has been reduced in this reaction.

Cl (has been oxidised) from Cl = –1 to Cl = 0

Mn (has been reduced) from Mn = +4 to Mn = +2

Complete the electron configuration of a manganese atom.

1s2 2s2 2p6 3s2 3p6 3d5 4s2

Chlorine gas can be added to a cold, dilute alkaline solution to form bleach. Write the equation for this reaction.

Cl2 + 2NaOH → NaClO + NaCl + H2O

A student bubbles chlorine gas through aqueous potassium iodide. A reaction takes place. (i) State what the student would observe.

(The solution would turn) yellow OR orange OR brown

Explain what is meant by the term electronegativity

The ability of an atom to attract electrons in a (covalent) bond

Draw a 3-D diagram of a molecule of CH2Cl 2. Use partial charges to indicate polar bonds.

Explain why a CH2Cl 2 molecule is polar

The dipoles do not cancel out OR Because the molecule is non-symmetrical

Bromine has two isotopes, Br–79 and Br–81. The relative atomic mass of bromine is 79.9. Calculate the percentage of Br–79 atoms in a sample of bromine.

55%

What is meant by the term isotopes?

Atom(s) of an element with different numbers of neutrons

Different isotopes of antimony have the same chemical properties. Explain why.

same number of electrons in outer shell OR same electron configuration OR electron structure

Define the term relative atomic mass.

The (weighted) mean mass of an atom compared with 1/12th (the mass) of (one atom of) carbon-12

Predict the shape of a molecule of SbCl 3. Explain your answer.

(Trigonal) Pyramidal

(Sb has) three bonding pairs AND one lone pair of electrons

Pairs of electrons repel

SbCl 3 molecules are polar. Explain why

There is a difference in electronegativities (between Sb and Cl) OR (Sb-Cl) bonds are polar OR have a dipole OR Dipoles seen on the diagram

The molecule is not symmetrical AND dipoles do not cancel

State and explain the trend in atomic radius from Li to F.

atomic radius decreases AND nuclear charge increases or number of protons increases

electrons are in same shell OR (outer) electrons experience similar or same shielding OR same number of shells

Greater nuclear attraction on (outer) electrons or shells

Complete the electron configuration of a bromide ion.

(1s2) 2s2 2p6 3s2 3p6 3d10 4s2 4p6

A student adds a small volume of aqueous silver nitrate to an aqueous solution of bromide ions in a test-tube. The student then adds a similar volume of dilute aqueous ammonia to the same test-tube. Describe what the student would see in the test-tube after the addition of aqueous ammonia.

Cream AND precipitate

Chlorine reacts with aqueous sodium hydroxide to form bleach. Write the equation and state the conditions for this reaction.

Equation: 2NaOH + Cl2  NaCl + NaClO + H2O

Conditions :cold AND dilute (sodium hydroxide)

A disproportionation reaction takes place as shown below.

3Cl 2(g) + 6NaOH(aq) 5NaCl (aq) + NaCl O3(aq) + 3H2O(

State what is meant by disproportionation and show that disproportionation has taken place in this reaction. Use oxidation numbers in your answer.

• (Disproportionation) is the (simultaneous) oxidation and reduction of the same element (in the same redox reaction)

• Cl in Cl2 is 0 AND Cl in NaCl is -1 AND Cl in NaClO3 is +5

  • Chlorine has been oxidised from 0 to +5 AND Chlorine has been reduced from 0 to –1

Write the formula of cerium(III) sulfate and, explain what has happened to the cerium in this reaction in terms of the number of electrons transferred

Ce2(SO4)3

(Cerium) loses three electrons

How has a salt been formed in this reaction?

A hydrogen ion (of an acid) has been replaced by a metal ion

Europium, atomic number 63, reacts with oxygen at room temperature.

4Eu + 3O2 2Eu2O3

Calculate the volume of oxygen, in cm3, required to fully react with 9.12 g of europium at room temperature and pressure.

Amount of Eu = 9.12/ 152.0 = 0.06(00) mol

Amount of O2 = 0.0600 x 3/4 = 0.045(0) mol and Volume of O2 = 0.0450 x 24000 = 1080 cm

State what is meant by the term empirical formula

The simplest whole number ratio of atoms (of each element) present in a compound

Ytterbium, atomic number 70, is the first element in the Periodic Table to have the first four shells full.

(i) State the number of electrons in the fourth shell of ytterbium.

(ii) How many orbitals are there in the third shell of ytterbium?

i) 32

ii) 9

(i) Mol of H2SO4 = 0.100 x 18.00/1000 = 1.80 x 10–3 mol

(ii) Mol of NaOH in = 1.80 x 10–3 x 2 x 1000/25.0 = 0.144 mol dm–3

Explain what is meant by the terms base and alkali.

Base: A substance which readily accepts H+ ions (from an acid) Alkali: releases OH– ions into (aqueous) solution

) A student prepared some calcium hydroxide by adding a small piece of calcium to a large excess of water. Describe what the student would observe and write the equation for the reaction.

Fizzing and the metal would dissolve

Ca + 2H2O → Ca(OH)2 + H2

A student prepares a solution of calcium nitrate from calcium carbonate. What reagent would the student need to use? Write the equation for the reaction.

Nitric acid OR HNO3

CaCO3 + 2HNO3 → Ca(NO3)2 + H2O + CO2

A compound used as a fertiliser has the following composition by mass: C, 20.00%; H, 6.67%; N, 46.67%; O, 26.66%. Calculate the empirical formula of this compound.

CH4N2O

A salt used as a fertiliser has the empirical formula H4N2O3. Suggest the formulae of the ions present in this salt.

NH4+

NO3

Calcium phosphate(V), Ca3(PO4) 2, is another salt used in fertilisers. Calcium phosphate(V) can be prepared by reacting together an acid and a base.

(i) Suggest the formula of the acid used to prepare Ca3(PO4) 2.

(ii) Name a base which could be used to prepare Ca3(PO4) 2.

H3PO4

Calcium oxide OR calcium hydroxide OR calcium carbonate

) Silicon reacts with chlorine to form molecules of silicon tetrachloride, SiCl 4. How many molecules are present in 8.505 g of SiCl 4?

170\.1  (ALLOW in working shown as 28.1 + 35.5 x 4) Correctly calculates amount of molecules 8.505 / 170.1 = 0.05(00) mol  Correctly calculates number of molecules 0.05 x 6.02 x 1023 = 3.01 x 1022 

Ions of two isotopes of iron are

53Fe2+ 56Fe2+

Which statement is correct?

A The ions of both the isotopes have the electronic configuration 1s22s22p63s23p64s23d6

B The ions of both the isotopes contains 26 neutrons

C 53Fe2+ has fewer protons than 56Fe2+

D After acceleration to the same kinetic energy 56Fe2+ will move more slowly than 53Fe2

D After acceleration to the same kinetic energy 56Fe2+ will move more slowly than 53Fe2

Deduce the formula of the compound that contains 2+ ions and 3− ions that both have the same electron configuration as argon.

Ca3P2

Deduce the formula of the ion that has a charge of 2+ with the same electron configuration as krypton.

Sr2+

State and explain the general trend in first ionisation energy across Period 3.

• General increase

• Greater nuclear charge / more protons

• Same shielding / electrons added to same shell

• Stronger attraction (from nucleus) for outer electron(s)

Give one example of an element which deviates from the general trend in first ionisation energy across Period 3. Explain why this deviation occurs

• Aluminium / Al (lower than Mg) CE if not Al or S

  • (Outer) electron in (3)p orbital / sub-shell (level)

  • (3p) higher in energy

• Sulfur / S (lower than P) (Outer) electrons in (3)p orbital begin to pair Repel

Identify the Period 3 element that has the highest melting point. Explain your answer by reference to structure and bonding

* Silicon
* Giant covalent structure / macromolecule
* Covalent (bonds) Giant covalent scores
* Many / strong (covalent bonds) or (covalent bonds) need lots of energy to break

Use the Periodic Table to deduce the full electron configuration of calcium.

1s2 2s2 2p6 3s2 3p6 4s2

Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of water.

Ca(s)+ 2H2O(l) → Ca2+(aq) + 2OH– (aq) + H2(g)

State the role of water in the reaction with calcium.

Oxidising agent

Write an equation to show the process that occurs when the first ionisation energy of calcium is measured.

Ca(g) → Ca+ (g) + e–