Overview of what you need to know (the foundation)
- How can you tell if a change is a chemical change or just a physical change?
- What reaction will produce gas. What to write an indication of presence of gas? and what test can you use to identify the gas (hydrogen or carbon dioxide)?
- What are ways to identify if a solution is an acid or alkali?
- How does acid rain form?
- Word equations for the standard reactions.
| type of reaction | condition |
| combustion | heat and presence of oxygen |
| thermal decomposition | heat |
| oxidation | presence of oxygen |
| neutralisation | between acid and alkalis |
Chemical Reaction that Produces Hydrogen Gas
metal + acid –> salt + hydrogen
e.g zinc + sulfuric acid –> zinc sulfate + hydrogen
Observation?
Effervescence/Bubbling is observed.
How to identify the gas?
A lighted split will be extinguished with a ‘pop’ sound. This means hydrogen is present.
NOTE: Whenever we want to check if the gas produced is a hydrogen, we will always need to use a lighted splint.
SOME Chemical Reactions that Produces Carbon Dioxide Gas
Method 1: Acid reacts with carbonate
carbonate + acid –> salt + water + carbon dioxide
e.g calcium carbonate + sulfuric acid –> calcium sulfate + water + carbon dioxide
Method 2: Thermal decomposition of carbonate
Method 3: Combustion
How to identify the gas produced?
When the gas is bubbled through limewater, white precipitate is formed. This means Carbon Dioxide gas is present.
Neutralisation
Neutralisation is when acid reacts with alkali.
acid + alkali –> salt + water
e.g nitric acid + calcium hydroxide –> calcium nitrate + water
** This is why we brush our teeth every day. Our food is generally acidic and our body also produces acid to break down the food.
Different ways that we can use to test for acid/alkali?
- Litmus paper. If blue litmus paper turns red, then the solution is an acid.
- pH meter. A substance is considered neutral if it has a pH value of 7. Alkaline substances have pH values more than 7 while acidic substances have pH values of less than 7.
- Universal indicator.
- Data logger with acid/alkali sensor.
Note: Using universal indicator is better than using litmus paper. Universal indicator provides us with the strength of acid/alkali solution whereas litmus paper can only tell us if the solution is acidic or alkaline.
Some important chemical formula that you need to remember (optional for G2 syllabus)
H2SO4 : Sulfuric acid
CO2 : Carbon dioxide
HNO3 : Nitric acid
SO2 : Sulfur dioxide
SO3 : Sulfur trioxide
NO2 : Nitrogen dioxide
Acid rain
Acid rain is formed due to either sulfur trioxide or oxide of nitrogen dissolves in rainwater.
sulfur trioxide dissolves in rainwater –> sulfuric acid
word equation: sulfur trioxide + water –> sulfuric acid
oxide of nitrogen dissolves in rainwater –> nitric acid.
word equation: oxides of nitrogen + water –> nitric acid