Chemistry SPM Trial SBP 2011

Paper 1; Answer Paper 1

Paper 2; Answer Paper 2

Paper 3; Answer Paper 3

Rate of Reaction and Collision Theory

Collision theory from sweemoi khor

Coagulation of Latex

Latex coagulates when acid is added.

Latex coagulates when ethanoic acid is added to it. Explain.

1. Latex is a mixture of rubber particles and water. Rubber particle is made up of  a protein membrane that surrounds many rubber molecules.
2. The negatively charged protein membrane prevent repel each other. Latex does not coagulate.
3. Acid which consists of H⁺ ion is added into the latex.
4. The H⁺ ion from acids neutralize the negatively charged protein membrane.
5. The rubber particles collide with each other.
6. Protein membrane of the rubber particle breaks. 
7. Rubber molecules clump together. Latex coagulates.

When latex is exposed to the air for some time, it still coagulates. Why?

1. Bacteria from the air enter the latex.
2. The growth of bacteria produces lactic acid.
3. Lactic acid causes coagulation of latex. But this process occurs slowly. Why?
4. Slow bacteria action.

How to prevent coagulation of latex? Explain.

1. By adding ammonia solution.
2. Ammonia solution consists of OH- ion that neutralize the acid produced by the bacteria.
3. The rubber particles remain negatively charged.
4. Coagulation of latex is prevented.

5H students are studying coagulation of latex by adding ethanoic acid

Ethanoic acid is added drop by drop into latex in the beaker. The latex is stirred by using glass rod.

Different type of Voltaic Cells

Voltaic cells from sweemoi khor

Please find more details about the chemicals used for negative terminal, positive terminal & electrolyte and its advantages/disadvantages.

Simple Voltaic Cell

Explain the production of electricity in the simple voltaic cell.

1. Magnesium is more electropositive than copper.  Magnesium is the negative terminal.
2. Each magnesium atom donates two electrons to form a magnesium ion.  Mg --> Mg²⁺ + 2e^-
3. The flow of electrons from the magnesium ribbon to the copper through the external circuit results in the production of electricity.
4. The hydrogen ions from the electrolyte(sodium chloride solution) are discharged at the copper plate by accepting electrons to form hydrogen gas.  2H⁺  + 2e^- --> H₂

What is the observation at each of the terminal? 

Please respond by leaving your answer in the comment box.

Heat of Precipitation

Heat of precipitation from sweemoi khor

Heat of Displacement

Heat of displacement from sweemoi khor

Heat of Neutralization and the Strength of Acids and Alkalis

1. Heat of neutralization between a strong acid and a strong alkali is always -57.3 kJ mol^-1.  Why?

Heat of neutralisation is the sum of of energy absorbed during bond breaking in the acid and alkali and energy released during bond formation of water molecule from H⁺ ion and OH^- ion.  All the reactions form 1 mole of water. 


2.  Heat of neutralization for neutralization involving weak acid or weak alkali is less than -57.3 kJ mol^-1.  Why?
Weak acid/akali does not ionises completely in water. Some energy released during formation of water is used to ionises the weak alkali/acid.

Heat of Neutralisation

Definition :

Energy change when one mole of water is formed from the neutralization between one mole of hydrogen ion from an acid and one mole of hydroxide ions from an alkali.
  

5H students are carrying out experiment to determine heat of neutralisation between an acid with an alkali.