AS paper 1 mistakes

Question 1

Describe how the thermal stability of group 2 nitrates can be compared using laboratory equipment.
Include one safety precaution

Answer 1

Same heat applied to both from bunsen burner.
Same amount of nitrate in each tube.
First one to relight a glowing splint or produce brown fumes.
Time and compare
Conduct in fume hood

Question 2

Describe how a flame test is carried out.

Answer 2

Clean platinum or nichrome wire in concentrated HCl.
Dip wet wire into solid ad place in a roaring blue bunsen flame.

Question 3

In the reaction between magnesium and HCl the volume of gas collected wasn’t the same as expected value. Suggest why?

Answer 3

Some gas will have been lost before bung was replaced
Magnesium was coated with oxide so water was formed instead of hydrogen

Question 4

Why is the melting temperature of magnesium oxide greater than that of potassium bromide?

Answer 4

Greater charge on Mg and O ions
Mg smaller ionic radii
More energy required to overcome electrostatic attractions between ions in MgO

Question 5

Suggest why the density of iron is greater than the density of graphite.

Answer 5

Iron atoms have greater mass than carbon atoms
Iron atoms pack closer together than carbon atoms in graphite.

Question 6

Why are there 2 widely different values for the compressive strength of graphite?

Answer 6

Lower value is due to the weak London forces between layers.
Higher value refers to the strong covalent bonds within layers.

Question 7

What is the shape of a ClO3- ion?

Answer 7

Trigonal pyramidal

Question 8

What intermolecular forces are formed between chloroethane and water?

Answer 8

Permanent dipole-dipole interactions and London forces.

Question 9

Why is the density of ice less than the density of water at 0 degrees?

Answer 9

Molecules of water arrange in rings of 6, held together by hydrogen bonds.
Structure creates large areas of space.
When ice melts (to water) the structure is destroyed and average distance between molecules decreased causing an increase in density.

Question 10

Explain why hydrogen bonding causes ice to be less dense than liquid water?

Answer 10

Large spaces between molecules due to 3D lattice
Hydrogen bods are longer than covalent bonds

Question 11

Ionic half Equation for the reduction of chlorine molecules to chloride ions.

Answer 11

Cl2 +2e- = 2Cl-

Question 12

Ionic half equation for the oxidation of chlorine molecule with cold aqueous hydroxide ions. To form chlorate ions.

Answer 12

Cl2 + 4OH- = 2ClO- + 2H2O + 2e-

Question 13

What ion containing chlorine is formed when chlorine molecules react with hot hydroxide ions?

Answer 13

ClO3-

Question 14

What is meant by relative isotopic mass?

Answer 14

The mass of an atom of an isotope relative to 1/12 of the mass of a carbon 12 atom.

Question 15

What do pairs of electrons do to minimise repulsion?

Answer 15

Move apart from each other

Question 16

Why does aluminium fluoride have a greater melting point than Aluminium chloride? Using electronegativity

Answer 16

Greater electronegativity difference between AL and F.
Alcl3 is mostly covalent
AlF3 is mostly ionic so is more polar.
AlCl3 have weaker London forces as it’s molecular
AlF3 is a giant structure

Question 17

3 actions that may be taken to ensure the end point of a titration is accurate?

Answer 17

Add drop by drop so that not too much acid is added
Place white tile underneath conical flask so colour change can be seen more clearly.
Regularly swirl conical flask to ensure acid and alkali react.

Question 18

What colour does methyl orange change to and from when in an alkali solution but and acid is neutralising?

Answer 18

Yellow to orange

Question 19

Why is a small pinch of calcium carbonate added to hydrochloric acid before starting the reaction?

Answer 19

To saturate solution with carbon dioxide

Question 20

State how the relative abundance of two isotopes can be found?

Answer 20

Compare the intensity of signal in a mass spectrometer.

Question 21

Explain why diamond has a much higher melting temperature than iodine.

Answer 21

• iodine is (simple) molecular
  diamond is a giant (covalent / lattice) structure
  (with 4 covalent bonds per carbon atom)
• iodine molecules are held together by weak
  London forces / dispersion forces / van der
  Waal’s forces / instantaneous induced dipole-
  dipole attractions
• carbon atoms in diamond are held together by
  (strong) covalent bonds
• strong covalent bonds require more energy to
  break than intermolecular forces

Question 22

Describe the difference in bond angles between N-H in ammonia and amide ions.

Answer 22

Ammonia = 107* Amide ions = 104.5*
Two lone pairs on amide ions which repel bonding pairs of electrons more than the one lone pair of electrons in ammonia.

Question 23

How to make a standard solution when provided with 10g of a hydrate in a beaker?

Answer 23

• dissolve the solid in distilled / deionised water
  (using a glass rod)
• pour the solution into a volumetric flask (using a
  funnel)
• rinse the beaker and transfer the washings to the
  conical flask (and rinse the funnel and glass rod)
• make up to the mark / line / 250 cm3
• shake / mix / swirl the flask

Question 24

Definition of a covalent bond?

Answer 24

Strong electrostatic forces of attraction between two nuclei and the bonding pair of electrons.

Question 25

Ionic bond?

Answer 25

The electrostatic forces of attraction between positive and negatively charged ions.

Question 26

On descending Group 7, the hydrogen halides become better reducing agents.
Explain how the reactions of potassium chloride, potassium bromide and potassium iodide with concentrated sulfuric acid provide evidence for this statement.

Answer 26

• Sulfur in sulfuric acid is reduced further
  by hydrogen iodide than hydrogen bromide (and
  hydrogen chloride)
• SO2 / S(IV) produced in the reaction with HBr
• more negative oxidation states of sulfur / S / H2S
  / S2‒ are produced in the reaction with HI

Question 27

What happens to the solubility of sulfates as you descend group 2?

Answer 27

Solubility decreases
Barium sulfate is insoluble

Question 28

Explain why phosphorus forms PCl5 but nitrogen does not form NCl5

Answer 28

Phosphorus can accommodate 10 electrons whereas nitrogen can only accommodate 8 electrons in outer shell.