Study notes, tips, worksheets, exam papers
All the things you need to do well in your studies
The source of biodiesel is from plant parts. During the growth and development of these plants, they absorb carbon dioxide from the environment for photosynthesis. During the combustion of biodiesel, the same amount of carbon dioxide is released to the environment.
The net amount of carbon added to the environment from the burning of biodiesel is considered to be zero, hence “carbon neutral”.
The atoms of Group O elements have a stable electronic configuration, hence these atoms have no tendency to gain or lose electrons to form ions, making them chemically inert.
Pure metals consist of a lattice of positive ions, arranged in regular pattern, surrounded by a sea of delocalised electrons. When a force is applied, the layers of positive ions slide over one another easily, without disrupting the metallic bonding. This makes the pure metal soft and malleable.
An alloy is a mixture of a pure metal with other elements. The atoms of the added element have a different size from those of the pure metal. This breaks up the regular arrangement of atoms in the pure metal. When a force is applied, the atoms of different sizes cannot slide over one another easily. This makes the alloy stronger and harder.
At the start, the gradient of the curve is the steepest. This shows that speed of reaction is the highest at the start. The concentration of the reacting particles is the highest at the start, resulting in highest speed of reaction.
As the reaction progresses, the gradient of the curve decreases. This shows that speed of reaction is slowing down. As the reactants are used up in the reaction, the concentration of reacting particles decreases, resulting in a decrease in speed of reaction.
When the gradient of the curve becomes horizontal, it shows that the reaction has stopped. Either one or all of the reactants have been completely used up, so reaction stopped.
Acid rain speeds up the corrosion of buildings and structures made of limestone or reactive metals, like steel.
Acid rain makes water too acidic, which can be harmful to aquatic organisms.
Acid rain removes essential metal ions needed by plants, such as calcium, potassium, magnesium ions from the soil, affecting the health of plants.
The source of CO comes from incomplete combustion of fuels containing carbon.
Carbon monoxide combines irreversibly with haemoglobin in the red blood cells, reducing the ability of the red blood cells to carry oxygen. This can result in respiratory problems, brain damage or death.
When both substances are added at the same time, they will react to produce a salt, ammonia gas and water.
Slaked lime will be used up in the reaction, hence the acidity of the soil will not be reduced.
Fertilizers will be used up in the reaction. Ammonia gas produced will escape to the surroundings, so nitrogen element, which is needed by the plants for healthy growth, will not be absorbed by the plants.
Advantages:
1. The hydrogen fuel cell produces water as the only waste products. No harmful gases are released to surroundings when it is used.
2. Hydrogen is an abundant resource, if a cost effective method can be used to extract hydrogen from water.
Disadvantages:
1. There is currently no cost effective method of storing the hydrogen gas.
2. There is currently no cost effective method of extracting hydrogen from seawater.
3. The process to obtain hydrogen, either from electrolysis of water, or from cracking of hydrocarbons, produces waste gases and use up large amount of energy.
Each oxygen atom needs to share two electrons to achieve a stable electronic structure of a noble gas.
However, one hydrogen atom can only share one electron to achieve its own stable electronic structure.
Therefore, one oxygen atom will share 2 valence electrons with 2 hydrogen atoms to form the H2O molecule.
Potassium chloride is an ionic compound. The ions in potassium chloride are held together by strong electrostatic force of attraction. A lot of energy is needed to break down these bonds, hence the high melting point.