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AMS

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ACJC 2008 H2 PRELIM P1

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Atomic Structure

"All that glitter is not gold"

Act II - Scene VII - Prince of Morocco-William Shake Spear

Diamond is a simply a piece of charcoal that handled stress Exceptionally well

FALSE

Its an allotrope of Carbon where the Carbon atoms are arranged in a variation of the Face-Centred CUBIC crystal

structure called Diamond Lattices

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Chemical Bonding

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n-

4

An ion IF4n−

has a square planar structure as shown below:

What is the value of n?

A 1 B 2 C 3 D 4

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Ice is the crystalline form of water. The diagram below shows part of the structure of ice.

Which of the following statements is not true about ice?

A Ice has a lower density than water at 0 oC due to its open structure.

B The bond angle about oxygen in ice is 109.5o.

C Ice does not conduct electricity.

D Ice has a giant covalent structure.

HCI 2010 P1 H2 CHEM

n−

F F

I

F F

- - - - Hydrogen bond

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Gases

Nobel Gases

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Gases

3 (a) The industrial liquefaction of N2O3 involves its compression.

Suggest why the compression of N2O3 into a region of high pressure is an

exothermic reaction. Why does the application of pressure cause the gas to

liquefy at room temperature?

B (i) N2O3 is unstable above room temperature and decomposes to NO2 and NO. A 2.5 g of

sample N2O3 was allowed to decompose completely in a 0.20 dm3 vessel at 65oC. Calculate the

total pressure in the vessel.

5 The Van der Waal’s equation for a non-ideal gas is

(P + 2

2

V

an )(V - nb) = nRT

The term b is a correction for

A the space occupied by real molecules.

B collisions between real molecules not perfectly elastic.

C the existence of attractive forces between real molecules.

D the existence of repulsive forces between real molecules.

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(ii) The total pressure in the vessel was found to be different from the value in (b)(i). Suggest a reason

for the discrepancy.

(c) The following sketch represents the distribution of molecular speeds of N2O3 at 65°C.

On the same axes, draw the distribution of the molecular speeds of NO.

Explain your answer.

4444444444444444444444444444444444.

4444444444444444444444444444444444.

4444444444444444444444444444444444.

[2]

NJC 2010 P2

Fraction of

molecules

Molecular

speed

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Energetic

Which is energetically more stable of the Carbon allotropesWhich is energetically more stable of the Carbon allotropesWhich is energetically more stable of the Carbon allotropesWhich is energetically more stable of the Carbon allotropes

Graphite or DiamondGraphite or DiamondGraphite or DiamondGraphite or Diamond ????????

Answer: Graphite.

Next, Why Diamond does not decompose to graphite?

(Its just a carbon)

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RJC 2009 P3

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Reaction Kinetic

What happened??

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Chemical Equilibra

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Acid/Base (Ionic)

4 The table below shows the dissociation equations of hydrofluoric acid, methanoic acid and disodium

hydrogen phosphate and the values of their respective dissociation constants. You are to use the

following information to answer (a) and (b).

Dissociation equations Dissociation constants / mol dm−−−−3

HF + H2O F− + H3O+ Ka = 6.8 x 10−

4

HCOOH + H2O HCOO− + H3O+ Ka = 1.8 x 10−

4

HPO42− + H2O H2PO4

− + OH− Kb = 1.6 x 10−7

(a) For the following reaction:

H2PO4− + F− HPO4

2− + HF

(i) identify the one conjugate acid-base pair,

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(ii) predict, with reasons whether the equilibrium constant will be greater than

or less than 1.

(b) Two solutions of pH 4.00 were prepared.

• Solution A contains 0.0113 mol dm−3 methanoic acid and 0.0200 mol dm−3 sodium methanoate

• Solution B contains 0.00113 mol dm−3 methanoic acid and 0.00200 mol dm−3 sodium methanoate

(i) Calculate the change in pH when 0.0500 cm3 of 1.000 mol dm−3 HCl is added to 100.0 cm3 of

each of the two solutions. In this part, give your final answers to 3 siginificant figures.

(ii) Explain the difference in the buffering effect of the two solutions. [5]

H2 Chemistry 9647/02/NYJC J2/10 P2

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The solubility product of some Group II fluorides, at 25oC, are given in the table below:

(a)

(i) Which of the above fluorides is most soluble and what is its solubility, in mol dm-3, at 25 oC?

(ii) Briefly explain how the solubility of the fluoride in (i) would change if it is dissolved in an aqueous KF solution.

(b) A researcher accidentally mixed 50.0 cm3 of 0.200 mol dm-3 CaCl2 solution with 25.0 cm3 of 0.100 mol dm-3 BaCl2 solution in the laboratory. To separate the two metals ions, he added just enough solid KF to precipitate the maximum amount of CaF2 from the mixture.

(i) Calculate the minimum concentration of fluoride ions required to cause

precipitation of BaF2.

(ii) Hence, calculate the concentration of Ca2+ ions in the solution when the first trace of BaF2 appears.

[Total: 6]

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Organic Chemistry

This is a real molecule, which was synthesize via chemical means.

Its purpose is still unknown to date, because the chemist who did it felt that it was cute.

J. Org. Chem., 2003, 68 (23), pp 8750–8766

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.SAJC 2011

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1. Give the IUPAC name of each of the following organic compounds ( And skeletal structure)

(a) CH3CH(CH3)CH2CH2CH3

(b) CH2=CHCH(CH3)C(CH3)3

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