Issues in teaching and Learning Science (Term 2)

In Term 2, we learnt about Acids and Bases, Chemistry and Optics(Reflection and Reflection), Physics.

Acids and Bases

Acids

- An acid is a substance which produces hydrogen ions as the only positive ions when it is dissolved in water.
- The strength of an acid depends on its degree of dissociation/ionization in water to form hydrogen ions.
- A strong acid is one that ionizes/dissociates in water to produce hydrogen ions. There are no molecules left. The solution contains a high concentration of ions, which cause it to be a good conductor of electricity.
- A weak acid is one that ionizes/dissociates incompletely in water to produce few hydrogen ions. Most of the acids molecules remain as molecules. The solution contains a low concentration of ions, causing it to be a poor conductor of electricity.
- Acids have a sour taste
- contains hydrogen ions
- react with metal, carbonates and base

Reactions of Acids

1. Acid + Metal----> Salt + Hydrogen
2. Acid + Carbonate----> Salt + Carbon Dioxide + Water
3. Acid + Base----> Salt + Water

Bases and Alkalies

- Bases are the oxides or hydroxides of metals that reacts with an acid to form a salt and water only.
- An alkali is a metal hydroxides which is soluble in water and produces hydroxide ions in water
- All alkalies are bases but not all bases are alkalies
- The strength of an alkali depends on its degree of dissociation/ionization in water to form hydroxide ions. The properties of alkalies are due to the hydroxides ions.
- A strong alkali is one that ionizes/dissociates in water to produce hydroxide ions. There are no molecules left. The common strong alkalies are sodium hydroxide and potassium hydroxides.
- A weak alkali is one that ionizes/dissociates incompletely in water to produce few hydroxide ions. Most of the acids molecules remain as molecules.
- Alkalies have a soapy feel and a bitter taste
- Bases react with acids to for salt and water.

Reflection

- When light hits a mirror at a certain angle, that angle is known as the angle of incidence
- When light is reflected at a certain angle, it is known as the angle of reflection

Refraction

- Occurs when light travels through the medium
- Light is bend towards the normal, when it travels out of the medium, it will go back to its original angle
- The denser the medium, the more the light ray bend


MY REFLECTION FOR TERM 2

This topic was quite easy to understand. The only difficulty I faced was on Refraction. This topic requires lots of memorizing especially on the Acid and Bases parts. The worst was drawing as it required a lot of time and every ray must be accurate.