Chemistry As Level Ocr F321 Standard Answers

Front 1

Standard answers – Module 1A

Back 1

Standard answers – Module 1A

Front 2

1. Isotope

Back 2

Same number of protons and electrons, different number of neutrons.

Front 3

2. Acid

Back 3

Proton Donor

Front 4

3. Base

Back 4

Proton Acceptors

Front 5

4. Strong Acid

Back 5

Dissociates fully in water

Front 6

5. Weak Acid

Back 6

Partially Dissociates in water

Front 7

6. Salt

Back 7

When a H+ ion in an acid is replaced with a metal/ammonium ion

Front 8

7. Alkali

Back 8

Dissociates to give (OH-) hydroxide ions in water

Front 9

8. Acid Reactions
Metal + Acid
Metal Oxide + Acid
Metal Hydroxide + Acid
Metal Carbonate + Acid

Back 9

Metal + acid à Salt + hydrogen

Metal oxide + acid >>> Salt + water

Metal hydroxide + acid >>> Salt + water

Metal carbonate + acid >>>% Salt + water = carbon dioxide

Front 10

9. % Element

Back 10

No of that element x Ar x 100
____________________________________
Mr

Front 11

10. Oxidation

Back 11

Loss of Electrons

Front 12

11. Reduction

Back 12

Gain of Electrons

Front 13

Standard answers – Module 1B

Back 13

Standard answers – Module 1B

Front 14

1) Relative isotopic mass

Back 14

mass of an atom of an isotope compared with 1/12 of the mass of an atom of 12C

Front 15

2) Relative atomic mass, Ar:

Back 15

weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of 12C

Front 16

3) Relative molecular mass, Mr:

Back 16

weighted mean mass of an molecule compared with 1/12 of the mass of an atom of 12C

Front 17

4) Relative formula mass, Mr:

Back 17

weighted mean mass of a formula unit compared with 1/12 of the mass of an atom of 12C

Front 18

5) RAM

Back 18

(% x Ar) + (% x Ar)
________________________
100

Front 19

6) Empirical formula:

Back 19

simplest whole number ratio of atoms of each element in a compound

Front 20

7) Molecular formula:

Back 20

actual whole number ratio of atoms of each element in a compound

Front 21

8) Moles

Back 21

mass (g)
_________
Mr

Conc x Vol
______________
1000

Vol (dm3)
____________
24 (dm3)

Front 22

Standard answers – Module 2A

Back 22

Standard answers – Module 2A

Front 23

1) First ionisation energy:

Back 23

energy required to remove 1 electron from each atom in a mole of gaseous atoms to form 1 mole of gaseous 1+ ions

Front 24

2) Atomic orbital:

Back 24

region in space around the nucleus that can contain 2 electrons with opposite spins

Front 25

Standard answers – Module 2B

Back 25

Standard answers – Module 2B

Front 26

1) Ionic bonding:

Back 26

Electrostatic force of attraction between oppositely charged ions

Front 27

2) Covalent bond:

Back 27

Formed by a pair of shared electrons

Front 28

3) Dative covalent bond:

Back 28

Formed by a pair of shared electrons where both electrons are provided by one atom

Front 29

4) What determines the shape of a molecule:

Back 29

· Pairs of electrons repel as far as possible
· This determines the shape
· Lone pairs repel more than bonding pairs as closer to central atom
· Each lone pair reducing the bond angle by 2.5o as it is closer to the central atom

Front 30

5) How does the addition of H+ ion change shape of ammonia (water)

Back 30

Front 31

Standard answers – Module 2C

Back 31

Standard answers – Module 2C

Front 32

1) Electronegativity:

Back 32

The power of an atom to attract bonding pairs of electrons towards itself

Front 33

2) IMF – VDW:

Back 33

-Between atoms of similar electronegativity
-Uneven distribution of electrons
-Instantaneous dipole
-Induced dipole
-Weak force of attraction

Front 34

3) IMF – Permanent dipole – dipole forces of attraction:

Back 34

Front 35

4) IMF – Hydrogen bonding:

Back 35

Front 36

5) Anomalous properties of water:

Back 36

· Unusually high melting / boiling point – H bonding is strongest IMF, more energy needed to overcome
· Ice less dense than water – H bonds are longer than covalent bonds
· Surface tension – extensive H bonds across the surface of water

Front 37

6) Metallic bonding:

Back 37

Front 38

7) Conductivity of metals:

Back 38

Electrons are free to move

Front 39

8) Conductivity of ionic compounds:

Back 39

· Solid – does not conduct as ions in a fixed position
· Molten / dissolved – does conduct electricity as ions are free to move

Front 40

Standard answers – Module 3A

Back 40

Standard answers – Module 3A

Front 41

1) Explain the trend in boiling point of Gp 1 – 3 metals:

Back 41

· As you go across Period, metal ions have a larger charge
· Also has more delocalised electrons
· Attraction is greater between larger ionic charge and more delocalised electrons

Front 42

2) State and explain the trend in atomic radii across a Period:

Back 42

· Across period nuclear charge increases
· Electrons in same shell, shielding remains the same
· Greater attraction
· Atomic radius decreases

Front 43

3) State and explain the trend in first ionisation energies across a Period:

Back 43

· Across period nuclear charge increases
· Electrons in same shell, shielding remains the same
· Greater attraction
· Atomic radius decreases
· Electrons more difficult to remove

Front 44

4) State and explain the trend in Atomic radii down a Group:

Back 44

· More electron shells
· Atomic radii increases

Front 45

5) State and explain the trend in ionisation energies down a Group:

Back 45

· More electron shells
· More shielding
· Atomic radii increases
· Attraction decreases despite an increase in the nuclear charge

Front 46

6) State and explain the trend in melting / boiling points across a period:
Gp 1-3:
Gp 4:
Gp 5-7:
Gp 0:

Back 46

Gp 1-3:
· Increases
· Metal ions have a larger charge
· Also has more delocalised electrons
· Attraction is greater between larger ionic charge and more delocalised electrons
Gp 4:
· Highest
· Giant covalent structure, extensive strong covalent bonds
· Lots of energy required to break covalent bonds
Gp 5-7:
· Low
· Simple molecular – weak IMF – VDW
· Little energy required
Gp 0:
· Lowest
· Atomic – weak IMF – VDW
· Little energy required

Front 47

Standard answers – Module 3B

Back 47

Standard answers – Module 3B

Front 48

1) State and explain the reactivity as you go down Gp 2:

Back 48

· Reactivity increases down group
· Atomic radius increases due to more shells
· More inner shells, shielding
· Overall attraction decreases
· Easier to remove outer electrons

Front 49

2) State and explain the alkalinity / solubility of Gp 2 hydroxides:

Back 49

· Solubility increases down the group
· More hydroxide ions released
· M(OH)2(s) + aq à M2+(aq) + 2OH-(aq)
· More hydroxides = more alkaline

Front 50

3) State the ease of the decomposition of Gp 2 carbonates:

Back 50

· Ease of decomposition decreases down the group

Front 51

Standard answers – Module 3C

Back 51

Standard answers – Module 3C

Front 52

1) State and explain the trend in the boiling points down Gp7:

Back 52

· Increases as you down the group
· Due to greater number of electrons
· Causing stronger VDW forces of attraction

Front 53

2) Colours of the halogens

Back 53

Front 54

3) Precipitation reactions of the halides

Back 54

Front 55

4) State and explain the reactivity as you go down Gp 7:

Back 55

· Reactivity decreases down group
· Atomic radius increases due to more shells
· More inner shells, shielding
· Overall attraction decreases
· Harder to capture an electron

Front 56

4) Disproportionation:

Back 56

Has been both oxidised and reduced