chem - states of matter + mixtures (2)

• The three states of matter are solid, liquid and gas.
• Water used in analysis must be pure because it could react with the substances being analysed.
• Melting and freezing take place at the melting point.
• Boiling and condensing take place at the boiling point.
• Gas particles have the most energy as the particles are the most spread apart (move freely – KE).
• Liquid particles have more energy than those in a solid, but less than those in a gas.
• Solid particles have the least energy – particles are fixed.
• State changes (melting, boiling, freezing and condensing) are physical changes – they involve the forces between the particles of the substances but the particles themselves don’t change.
• Chemical changes are where a new product has been formed.
• Particle theory can help to explain melting, boiling, freezing and condensing.
• The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance.
• The nature of the particles depends on the type of bonding and the structure of the substance.
• The stronger the forces between particles the higher the melting/boiling point of the substance.
• A mixture consists of 2 or more elements or compounds not chemically combined together.
• Chemical properties of each substance in the mixture are unchanged.
• A pure substance is a single element or compound, not mixed with any other substance.
• Pure substances melt and boil at specific/exact temperatures, mixtures do not – This means melting and boiling points data can be used to distinguish pure substances from mixtures (which melt over a range of temperatures due to them consisting of 2 or more elements or compounds).
• Potable water is suitable for drinking and must have low levels of microbes and contaminating substances, but it is not the same as pure water.
• Making waste and ground water potable involves sedimentation, filtration, and chlorination.
• To identify by calculation of Rf values, you can calculate Rf values and then compare them to known values for different substances.
• Impure substances or mixtures will show up with more than one spot on a chromatogram.
• To identify by comparing with known substances, carry out paper chromatography with both the known substance and substance you’re testing on the same paper.
• Crystallisation is a process to separate a soluble salt from a solution by first warming the solution in an open container, allowing the solvent to evaporate, leaving a saturated solution, then allowing the solution to cool, causing the solid to leave the solution and crystals to grow, then collecting and drying the crystals.
• Filtration is a process to separate a precipitate from a solution by filtering the solution, leaving behind the precipitate on the filter paper.
• Fractions can be processed to produce fuels and feedstock for the petrochemical industry.
• If both spots are at the same height up the paper at the end, then you know the tested substance is the same as the known one.
• Making sea water potable using distillation involves filtering the seawater, boiling it, and cooling the water vapour to condense it.
• Pure substances should only have one spot on a chromatogram.
• Paper chromatography is a technique used to separate mixtures of soluble substances by running a solvent (mobile phase) through the mixture on the paper (the paper contains the stationary phase), which causes the substances to move at different rates over the paper.
• Simple distillation is used to separate a pure liquid from a mixture of liquids and works when the liquids have different boiling points.
• Fractional distillation is used to separate a mixture of hydrocarbons into fractions and the oil is heated in the fractionating column.