Chemistry Unit 1

    Cards (123)

    • Solid:
      Arrangement: Particles are close together and regularly packed.
      Movement: Particles vibrate around a fixed point.
      Energy: Particles have less kinetic energy than both liquids and gasses.
    • Liquid:
      • Arrangement: Particles are close together but irregular.
      • Movement: Particles are free to move.
      • Energy: Particles have less kinetic energy than gasses but more than solids.
    • Gas:
      Arrangement: Particles are far apart and there are no forces between them.
      Movement: Particles are free to move.
      Energy: Particles have more kinetic energy than liquids and solids.
    • Melting: When a solid is heated, the energy makes the particles vibrate fast enough so that the forces of attraction between the particles break. For example   H2O(s) –> H2O(l)
    • Freezing: When a liquid is cooled, the particles move slow enough so that the forces of attraction between them will hold them into a solid. For example   H2O(l) –> H2O(s)
    • Boiling: When a liquid is heated strongly, the energy makes the particles move fast enough so that all forces of attraction are broken. For example   H2O(l) –> H2O(g)
    • Condensing: When a gas is cooled, the particles move slow enough so that the forces of attraction between them will hold them as a liquid. For example   H2O(g) –> H2O(l)
    • Sublimation: A small number of substances have the ability to change directly from a solid to a gas when heated. For example   CO2(s) –> CO2(g)
    • Diffusion is the spreading out of particles in a gas or liquid. There is a net movement of particles from areas of high concentration to areas of low concentration until a uniform concentration is achieved.
    • Dissolving potassium manganate(VII) in water demonstrates that the diffusion in liquids is very slow because there are only small gaps between the liquid particles into which other particles diffuse.
      The random motion of particles cause the purple colour to eventually be evenly spread out throughout the water. Adding more water to the solution causes the potassium manganate(VII) particles to spread out further apart therefore the solutions become less purple. This is called dilution.
    • When ammonia gas and hydrogen chloride gas mix, they react together to form a white solid called ammonium chloride.
      ammonia                  +              hydrogen chloride                 –>            ammonium chloride
      NH3(g)                     +              HCl(g)                                     –>            NH4Cl(s)
    • A cotton wool pad was soaked in ammonia solution and another was soaked in hydrogen chloride solution. The two pads were then put into opposite ends of a dry glass tube at the same time.
      The white ring of ammonium chloride forms closer to the hydrochloric acid end because ammonia particles are lighter than hydrogen chloride particles and therefore travel faster. Even though these particles travel at several hundred metres per second, it takes about 5 min for the ring to form. This is because the particles move in random directions and will collide with air particles in the tube.
    • The substance that dissolves is called the solute.
    • The liquid in which it dissolves is called the solvent.
    • The liquid formed is a solution.
    • A saturated solution is a solution into which no more solute can be dissolved.
    • Solubility is defined in terms of the maximum mass of a solute that dissolves in 100g of solvent. The mass depends on the temperature.
      For example, the solubility of sodium chloride (NaCl) in water at 25⁰C is about 36g per 100g of water.
    • Practical: investigate the solubility of a solid in water at a specific temperature.
    • At a chosen temperature, a saturated solution is created of potassium nitrate (KNO₃) for example.
    • Some of this solution (not any residual solid) is poured off and weighed.
    • The water is then evaporated from this solution to leave a residue of potassium nitrate which is then weighed.
    • The difference between the two measured masses is the mass of evaporated water.
    • The solubility, in grams per 100g of water, is equal to 100 times the mass of potassium nitrate residue divided by the mass of evaporated water.
    • Element: The simplest type of substances made up of only one type of atom.
    • Compound: A substance that contains two or more elements chemically joined together in fixed proportions.
    • Mixture: Different substances in the same space, but not chemically combined. Note: elements such as oxygen (O2) are described as diatomic because they contain two atoms.
    • The full list of elements that are diatomic is:
      • Hydrogen (H2)
      • Nitrogen (N2)
      • Fluorine (F2)
      • Oxygen (O2)
      • Iodine (I2)
      • Chlorine (Cl2)
      • Bromine (Br2)
    • Pure substances, such as an element or a compound, melt and boil at fixed temperatures.
      However, mixtures melt and boil over a range of temperatures.
      Example: although pure water boils at 100⁰C, the addition of 10g of sodium chloride (NaCl) to 1000cm³ of water will raise the boiling point to 100.2⁰C.
      Example: although pure water melts at 0⁰C, the addition of 10g of sodium chloride (NaCl) to 1000cm³ of water will lower the melting point to -0.6⁰C.
    • Simple distillation
      • This method is used to separate a liquid from a solution. For example: separating water from salt water.
      • The salt water is boiled. The water vapour condenses back into a liquid when passed through the condenser. The salt is left behind in the flask.
      • Note: cold water is passed into the bottom of the condenser and out through the top so that the condenser completely fills up with water.
    • Fractional distillation
      • This method is used to separate a mixture of different liquids that have different boiling points. For example, separating alcohol from a mixture of alcohol and water.
      • Water boils at 100oC and alcohol boils at 78oC. By using the thermometer to carefully control of temperature of the column, keeping it at 78oC, only the alcohol remains as vapour all the way up to the top of the column and passes into the condenser.
      The alcohol vapours then condense back into a liquid.
    • Filtration
      This method is used to separate an insoluble solid from a liquid. For example: separating sand from a mixture of sand and water.
      The mixture is poured into the filter paper. The sand does not pass through and is left behind (residue) but the water passes through the filter paper and is collected in the conical flask (filtrate).
    • Crystallisation is a method used to obtain a salt which contains water of crystallisation from a salt solution.
    • An example of crystallisation is hydrated copper sulfate crystals (CuSO4.5H2O(s)) from copper sulfate solution (CuSO4(aq)).
    • To perform crystallisation, gently heat the solution in an evaporating basin to evaporate some of the water until crystals form on a glass rod, indicating a hot saturated solution has formed.
    • Leave the hot saturated solution to cool and crystallise.
    • Filter to remove the crystals.
    • Dry the crystals by leaving them in a warm place.
    • If the solution is heated until all the water evaporates, you would produce a powder of anhydrous copper sulfate (CuSO4(s)).
    • Paper chromatography is a method used to separate the parts of a mixture into their components.
    • The different dyes in ink can all be separated and identified using paper chromatography.