Temasek Junior College H2 Year One Lecture Test 2 (2009) Answers 1. (a) D is an element with the following successive firstionization energies (IE) in kJmol-1.1st IE of D 1310 3400 5300 7500 11300 13300 20300

(i) State which group of the Periodic Table does the

element D is likely to belong. Explain your answer.

[2]

D is from Group VI. There is a big jump in 7th ionisation energy implying that the 7th electron is from an inner quantum shell or D has 6 valence electrons.

(ii) Write down the formula of the compound formed when [1]D reacts with a Group III element E.

E2D3

(b) Element F after being heated in a non-luminous Bunsenflame has the following electronic configuration 1s22s22p63s23p64s25s15p3.

(i) Identify element F. Write the ground state electronicconfiguration of the element F.

[2]

F has 24 electrons, hence F is chromium 1s22s22p63s23p63d54s1

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(ii)

Draw an energy level diagram for F3+ ion .

[2]

Energy/kJ mol-1

3d 3p 3s 2p 2s

1s [energy level & labelling:1m; electrons arrangement:1m]

2

(a) (i)

By considering the number of lone and bonding pairs [3] of electrons, draw diagrams to illustrate and name the shapes of SCl2, PCl3, ICl4-. [1 mark each]

(ii) PCl3 and AsCl3 are both Group V chlorides. Whichmolecule has a larger bond angle? Explain. [2]

PCl3 has a larger bond angle. P is more electronegative than As. Bond pairs of PCl3 are drawn closer to the P central atom compared to those AsCl3. Thus there is greater electron density around P and bond pairs in PCl3 experience greater repulsion.2

3. )

(a The boiling points of some fluoride compounds are showed [4]below. Compound Formula Boiling point/ C Hydrogen fluoride HF 19 Aluminium fluoride AlF3 1257 Silicon (IV) fluoride SiF4 -95 Phosphorus(V) PF5 -85 fluoride By reference to their structure and types of bonding, explain as fully as you can the differences in the boiling points of the compounds.

Aluminium fluoride has a giant ionic structure. Boiling involves overcoming strong electrostatic forces of attraction (or ionic bonds) between Al3+ and Cl- ions, hence a large amount of energy is required to break the strong bonds, hence it has the highest boiling point of the 4 fluorides. HF, SiF4 and PF5 have simple molecular structures and boiling involves overcoming weak intermolecular forces of attraction. HF has intermolecular hydrogen bonding while SiF4 and PF5 have intermolecular van der Waals forces. Since hydrogen bonding is stronger than van der Waals forces and requires more energy to overcome, hence HF has a higher boiling point than SiF4 and PF5. PF5 has a larger Mr and a larger electron cloud. There is a greater extent of polarisation of electron cloud, resulting in stronger and more extensive van der Waals forces of PF5. More energy is required to overcome the intermolecular forces of PF5 so it has a higher boiling point.3

(b) Explain why hydrogen fluoride is soluble in water [2] but silicon (IV) fluoride is not.

HF is able to form hydrogen bonds with water molecules. This releases sufficient energy to overcome the hydrogen bonds between HF molecules and hydrogen bonds between water molecules. HF and water molecules can intermingle, so HF is soluble in water. HF + H2O H3O+ + FHF ionised partially in water to formed F- and H+ (OR H3O+) ions. Ion-dipole interactions take place between the ions and water. Energy liberated is sufficient to overcome the hydrogen bonds between H2O molecules & those between HF molecules. HF and water molecules can intermingle, so HF is soluble in water. [Bonus]

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In which pair is the bond angle in Species I greater than that in Species II. A B C D Species I BrF3 SF6 XeF4 CO32Species II SF6 XeF4 CO32BrF3

[D]

5

Which of the following particles have more neutrons than protons and more electrons than neutrons? A B C D NO2+ 13 CO3232 2S 14 N2+

[B]4

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Which one of the following has the most unpaired electrons? A B C D the nickel metal the ammonium ion in NH4Cl the manganese ion in MnO2 the nitride ion in AlN

[C]

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A flask L containing an unknown volume of neon gas at pressure of 2 kPa was connected to a flask M containing 3 dm3 of helium gas at 4 kPa. The final pressure in the connected flask was found to be 3.5 kPa. What was the volume of the flask L,assuming that the temperature was constant throughout. [A] A B C D 1.0 dm3 1.5 dm32.0 dm3 2.5 dm3

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Three identical flasks each contain the same mass [D] of gases G, H & J respectively. The temperature and pressure of each flask are indicated below.Gas G Gas H Gas J

Temperature/0C Pressure/Pa

t p

t 2p

2t p

Assume ideal gas behaviour, which of the following is a correct representation of the relative molecular masses of the three gases? A B C D 9 Mr(G) > Mr(J) > Mr(H) Mr(J) > Mr(H) > Mr(G) Mr(G) > Mr(H) > Mr(J) Mr(J) > Mr(G) > Mr(H)

PV/RT

Gas KN2(g) at 298 K K N2(g) at 298 1

P/atm

Which of the following is true of the identity of Gas K? A Nitrogen gas at a higher temperature B Neon gas at 298 K C Carbon dioxide gas at 298 K D hydrogen gas at 298 K

[C]

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