CAns Chap 1-5B

60.0g of ethanoic acid contains 2 mol of ions true/false?

1. 60.0g of ethanoic acid contains 2 mol of ions WRONG 

• Ethanoic acid is weak acid -> [H+] will be less than 1 mol -> number of moles of ions less than 2!

Determine which reagent is in excess answering

State OS of C2

OS C2: -1

Draw Disulfide ion

Disulfide ion = S2^2-

• Heating a mixture of MnO2 and KOH with oxygen from the air produces a green compound, E. 

• On treatment with dilute acid, a sample of compound E reforms 0.174 g of MnO2 and a purple solution of KMnO4

• Purple KMnO4 is decolourised by the addition of 20.00 cm3 of 1.00 mol dm–3 iron(II) sulfate

• Calculate the oxidation number of manganese in compound E

1. Shielding effect = inner shell electrons only! 

• Eg. Explain why the atomic radius of magnesium and sulfur are different.

• S: 1s22s22p63s23p4, Mg: 1s22s22p63s2

1. Shielding effect = inner shell electrons only! 

• Eg. Explain why the atomic radius of magnesium and sulfur are different.

• S: 1s22s22p63s23p4, Mg: 1s22s22p63s2

• S has the same number of inner shell electrons as Mg = same shielding effect

• S has higher nuclear charge -> greater effective nuclear charge -> S has a smaller atomic radius than Mg

Compare Se electronegativity with O 

1. Compare Se electronegativity with O 

• Se has larger atomic radius than O -> distance between shared pair of electrons in the covalent bond and nucleus in Se is greater -> weaker electrostatic force of attraction -> harder to draw electrons to itself -> electronegativity of Se less than O

1. Ion-dipole interactions > hydrogen bonding > pd-pd > dipole induced dipole 

2. Deflection of liquid towards electrostatically charged rod = POLAR molecules 

3. sp2 hybridised: 3 sigma, 1 pi bond 

Explain, in terms of structure and bonding, the differences in boiling points (CO, NO, BrF)

1. Explain, in terms of structure and bonding, the differences in boiling points 

• CO, NO and BrF are covalent compounds with simple molecular structures consisting of discrete molecules held together by id-id and pd-pd interactions (NOT IMFs) 

Explain why N does not form NOCI3 with similar structure as POCI3 

2. Explain why N does not form NOCI3 with similar structure as POCI3 

• Nitrogen is in Period 2

• Nitrogen does not have energetically accessible vacant d orbitals to expand its octet structure 

Predict the nature of bonding in Ba (barium) and B (boron) compounds using IE 

1. Predict the nature of bonding in Ba (barium) and B (boron) compounds using IE 

• To form B3+: I.E. = 799 + 2420 + 3660 = 6879 kJ mol-1

• To form Ba: I.E. = 502 + 966 = 1468 kJ mol-1.

• B tends to form covalent compounds as IE is very high compared to Ba which tends to form ionic compounds since IE is much lower

Suggest reasons why MgF does not react with F2 to give MgF

2. Suggest reasons why MgF does not react with F2 to give MgF

• Too much IE is required to form Mg4+ and it is unlikely to form 4 covalent bonds with only two valence electrons in Mg

State effect of IMF on vapour pressure

• Vapour pressure: pressure exerted by vapour molecules

• Stronger IMFs → less molecules escape → lower vapour pressure

Draw Ion-dipole interactions

Give 2 reasons why the decomposition of ammonium nitrate is explosive

1. Give 2 reasons why the decomposition of ammonium nitrate is explosive

• Enthalpy change of decomposition is highly exothermic -> lot of heat given out

• The products are gaseous -> great expansion of volume

1. RMR clockwise, anticlockwise (not direction of arrow pls) 

2. When using formula, STATE formula! 

Explain why the decomposition of methanoic acid vapour is likely reversible

1. Explain why the decomposition of methanoic acid vapour is likely reversible

• Ea of both the forward and backward reactions do not differ very much

1. When the pack is squeezed, ammonium nitrate dissolves in the water -> G is -ve! (IK H and S are +ve but read pls)

2. If question never say temperature, use G standard condition (25C, 298K)