Chemistry (Mixtures and Pure Substances, Seperating Techniques, and Polarity) Flashcards
What is a Mixture? What are the types?
Mixtures are combinations of elements and/or compounds.
They can either be Homogenous or Heterogenous.
What are heterogenous mixtures? And an example?
Not uniform in composition (such as concrete which is a non-uniform mixture of gravel, sand, water and cement powder).
What are homogenous mixtures?
Uniform in composition (such as air which is a uniform mixture of nitrogen, oxygen, carbon dioxide and helium gases).
What are pure substances?
A pure substance is a type of matter which exists in its most basic or purest form and cannot be broken down further.
What is an element?
Substances that contain only one type of atom (can be monatomic or polyatomic (atoms, molecules or networks).
What is a compound?
Substances that contain more than one type of atom (polyatomic (molecules, networks or crystals).
What is polarity
Polarity is about where the electrons are placed in a bond. For a molecule to be polar, there must be a dipole moment, which is a separation of the molecule into a more positive area or a more negative area.
What does the polarity of a bond depend on?
- Asymmetric electron distribution: the elements involved in a chemical bond must have a large difference in electronegativity to be polar.
- Asymmetric geometry: the molecule itself must be asymmetrical to be polar.
Can a molecule be non-polar and have polar bonds? If so how? If not why not?
A molecule can contain polar bonds but still be non-polar if the molecule itself is symmetrical. A good example of this is the carbon dioxide molecule. There is a reasonable difference between the electronegativity in the carbon atom and the oxygen atom, which would make the bond polar. However, the carbon dioxide molecule is symmetrical so although there are polar bonds within it, it is non-polar.
Can a polar solvent dissolve a non-polar solute?
A polar substance will not mix with or dissolve in a non-polar substance. Polar solvents dissolve polar solutes. Non-polar solvents dissolve non-polar solutes.
What are methods of separation?
Sieving
Distillation
Gravity Separation
Magnetic Separation
Filtration and Condensation
Describe Sieving Separation? Where is it used?
Separating solid particles through a porous container called a sieve. The smaller particles make it through the sieve and constitute what is termed the ‘negative fraction’. The larger particles remain in the sieve and are termed the ‘positive fraction’. This is a commonly used method in the mining industry to determine the size of the particles in a mineral ore.
Describe Filtration and Evaporation? What is this method usually used for?
Filtration involves separating solid particles from a solution by pouring it through a porous piece of filter paper. Evaporation is drying or heating a solution to separate the solute from the solvent. This is a method that is commonly used to recover salts.
What is distillation and where is it used?
Distillation involves separating components based on their boiling points. A mixture of many solutions can be separated provided they have differing boiling points. Fractional distillation is a form of distillation which is used to take a sample of crude oil and separate it into a number of different useful materials such as liquefied petroleum gas (LPG), paraffin, oils and others.
What is magnetic separation? Where is it used?
Separation of paramagnetic (attracted by magnetic fields) and diamagnetic materials (repelled by magnetic fields). Used in the iron ore industry to separate iron rich material from silica.
