Chemistry Recall Flashcards
What are nanoparticles?
Particles of size 1-100nm.
Why is graphite softer than diamond?
Graphite is a giant molecular structure arranged in hexagonal layers with each carbon atom bonded to three other carbon atoms. Between the layers there are weak intermolecular forces of attraction which means that the layers can slide over each other. However, in diamond, each carbon atom is covalently bonded to four other atoms so that they cannot be moved easily.
Why is the start line on chromatography paper not drawn in ink?
Ink would dissolve into the solvent and affect the result.
Give three advantages of instrumental methods compared with chemical tests.
Instrumental methods are more accurate, sensitive
and rapid.
Explain using knowledge of particles how temperature affects rate of reaction.
The particles would have more kinetic energy and so move faster leading to more frequent collisions which are more successful especially as the particles have more energy.
Explain why carbon dioxide has a very low boiling point.
Carbon dioxide is a simple molecular which have intermolecular forces of attraction which are easy to overcome because they are weak. As a result, only a small amount of energy is needed to overcome them.
Explain why cryolite is used as a catalyst in the extraction of aluminium from aluminium oxide using electrolysis.
Cryolite lowers the melting point of the aluminium oxide so less energy and money is needed to melt it.
Graphite conducts electricity, but diamond does not. Explain why.
Graphite has delocalised electrons which can carry the current throughout the structure. This is because each carbon atom is covalently bonded to only three other carbon atoms. On the other hand, diamond does not have any delocalised electrons because diamond each carbon atom covalently bonded to four other atoms.
Give five effects of global climate change.
- melting ice
- agricultural problems
- extremes of weather
- rising sea levels
- loss of habitats
Explain why potassium chloride has a high melting point.
Potassium chloride is a giant lattice, ionically bonded. There are strong bonds/ strong electrostatic forces of attraction and so large amounts of energy is needed to overcome them.
Describe how groundwater and sea water are treated to produce potable water.
Groundwater is filtered to remove any solids. After passing through the filter beds made of sand, the water is sterilised to kill microbes. This can be done by using chlorine or UV light. Sea water is treated by desalination which can be done by distillation or reverse osmosis.
Describe the difference between potable water and pure water.
Potable water differs from pure water as it contains some dissolved substances and may have safe levels of microbes; while pure water has no dissolved solids/ impurities.
Explain why chlorine is more reactive than bromine.
Chlorine is a smaller atom and has the greater attraction to the positively charged nucleus because there are less shieldings. As a result, chlorine can gain an electron (negatively charged particle) more easily.
Using the collision theory, explain why the size of the marble chips affects the rate of the reaction.
Smaller sizes mean an increased surface area therefore an increased change meaning an increased success rate in the collision of the particles (as the reaction takes place on the surfaces of matter).
Give the test and result for chlorine gas.
The presence of chlorine gas makes damp blue litmus paper turn red.
