Sec 2 Science E-Portfolio: Term 2 Reflections on Science Experiences

Term 2: Reflections on Science Experiences

2P1: Indicators for Acids and Alkalis

Objective: To tell whether the solution is acidic, alkaline or neutral.

Venue: HCI Science Laboratory

I have learnt a lot during this lab session. I have learnt that acidic solutions are from pH 1-6. Bromothymol Blue is a better indicator to differentiate between an acid and water. It turns yellow from pH 1-6 and green at pH 7. Hence, it is easy to differentiate between an acid and water. Methyl orange changes from red to yellow at pH 4. It is not able to differentiate between weak acid (pH 4-6) and water (pH 7). Pure acids exist as simple covalent molecules instead of ions. Pure acids do not behave as acids as the properties of acids are due to the presence of hydrogen ions. When acids are mixed with water, ionisation of acids occurs, and hydrogen ions are produced. The presence of mobile ions in the aqueous solutions helps to conduct electricity. I like when we get to play with the acids and experiment with them. Although I know it is dangerous, I still enjoy it.

2P2: Properties of Acids - Part 1

Objective: To investigate the role of water for acid.

Venue: HCI Science Laboratory

I have learnt a lot during this lab session. I have learnt that water is needed to give an acid its acidic properties. Pure acids without water consist of covalent molecules. In the presence of water, the acid ionised to produce hydrogen ions. However, when acids dissolve in ethanol, they remain as covalent molecules. Dilute acids react with reactive metals to produce hydrogen gas and salt. To identify the gas formed during the reaction, insert a lighted splint into a test tube containing the gas. If it is hydrogen, the lighted splint will be extinguished and a 'pop' sound will be heard. I like to hear the pop sound and I find that quite interesting.

2P3: Properties of Acids (continued) and Alkalis

Objective: To investigate the properties of acids (continued) and alkalis.

Venue: HCI Science Laboratory

I have learnt a lot during this lab session. I have learnt that dilute acid reacts with a metal carbonate to produce salt, water and carbon dioxide gas. A white precipitate will be formed in limewater if the gas is carbon dioxide. Acid reacts with alkali to produce salt and water. Acid reacts with ammonium salt to produce a salt, ammonia and water. It is necessary to warm the mixture to evaporate the ammonia gas from the solution. An alkali only shows its alkaline properties in the presence of water. I like the part when we test for the alkali or acid using litmus paper as it is quite interesting to observe the litmus paper changing colour directly in front of your eyes.