SC2: States of Matter and Mixtures

Describe the arrangement and movement of particles in solids

Tightly packed together in a regular lattice arrangement because of strong forces of attraction. Vibrate in fixed positions.

Describe the arrangement and movement of particles in liquids

Some force of attraction between the particles. Particles are free to move past each other but tend to stick together. Random arrangement.

Describe the arrangement and movement of particles in gases.

No force of attraction; well separated and no regular arrangement.

Compare the relative energies of particles in solids, liquids and gases.

Particles in a solid have the least amount of energy, liquids have more energy, and gases have the most energy.

What does interconversion of state mean?

When matter changes from one state to another due to changes in temperature or pressure.

What are the names for the state changes from a solid to a liquid, and vice versa?

Solid -\> Liquid is Melting. Liquid -\> Solid is freezing.

What are the names for the state changes from a liquid to a gas and vice versa?

Liquid -\> Gas is evaporation. Gas -\> Liquid is condensation.

How does a physical change differ from a chemical change?

A physical change involves changes in the forces between the particles. The particles themselves remain the same and the chemical properties remain the same. A chemical change is different as during chemical reactions, bonds between atom breaks and the atoms change places.

What is the term given for when a solid changes state into a gas?

Sublimation

Describe what happens, in terms of particles, when a solid is heated and turns into a liquid

When heated the particles in a solid absorb thermal energy which is converted into kinetic energy. The kinetic energy allows the particles to vibrate more which causes the solid to expand until the structure of the solid breaks. This forms the liquid.

Describe what happens, in terms of particles, when a liquid is evaporated into a gas?

When heated, particles in a liquid expand and some particles on the surface gain sufficient energy to overcome the intermolecular forces and evaporate. At the boiling point, all of the liquid particles gain enough energy to evaporate.

What is a mixture?

Contains two or more elements or compounds which are not chemically combined. The chemical properties of each substance in the mixture are unchanged.

What is a pure substance?

A single element or compound, not mixed with any other substance

How can you use melting point data to distinguish between a pure substance and a mixture?

Pure substances have sharp exact melting points whereas mixtures melt over a range of temperature since they contain several substances.

When is simple distillation used?

Used to separate a pure liquid from a mixture of liquids. Only works when the liquids have different boiling points.

How can ethanol be separated from water?

Ethanol has a lower boiling point than water so can be separated from water by simple distillation: Distillation apparatus set up -\> Mixture boiled. -\> Ethanol evaporates first -\> Ethanol vapour cools in the condenser, condensing back to a liquid before being collected.

When is fractional distillation used to separate mixtures?

Fractional distilation is used to separate all the elements/compounds in a mixture. These chemicals must have different boiling points to be separated

What is the difference between fractional and simple distillation?

Simple distillation is only able to separate the substance with the lowest boiling point from the mixture. Fractional distillation separates all the substances from the mixture, using different boiling points.

How does fractional distillation work?

Oil is heated until it evaporates into the fractionating column. Vapours rise up the fractionating column and condense at the different fractions, depending on the relative boiling point of each substance.

What sort of mixtures can be separated by filtration?

Filtration is used to separate an insoluble solid from its solution.

Describe how to separate an insoluble substance from a solution

Place filter paper through a funnel. Pour the solution containing the insoluble substance through the funnel into a conical flask. The insoluble substance will collect on the filter paper (residue) and the solution will collect in the conical flask.

When is the process of crystallisation used to separate a mixture?

To separate a soluble solid from a solution if the solid decomposes when heated.

How could you separate a soluble solid from a solution, if the soluble solid decomposes when heated?

Crystallisation: Pour the solution into an evaporating dish and heat gently. When the crystals start to form, remove the dish from the heat and leave to cool. Once cold, filter the crystals out of the solution and leave them to dry in a warm place.

What process can be used to identify soluble substances in a mixture?

Chromatography

How does paper chromatography work to separate a mixture?

The mobile phase (solvent) moves through the stationary phase (paper) so anything dissolved in the mobile phase move with up the paper. Compounds react differently with each phase, so will move different distance through the phase meaning they'll be separated.

How can chromatography show the composition of a mixture?

Different coloured substances in the mixture will separates as they have different solubilities in the solvent and will travel at different rates

Why should pencil be used to draw the line along the bottom of the chromatography paper?

It will not affect the experiment as pencil is insoluble in the solvent.

How many spots would a pure substance produce during paper chromatography?

Pure substances produce one spot. An impure substances contains more than one compound so will produce more spots

What is an Rf value?

The ratio between the distance travelled by the dissolved substance (the solute) & the distance travelled by the solvent

How do you calculate Rf value?

Distance travelled by substance / distance travelled by solvent

When measuring the distance moved by a substance on the chromatography paper, where should you measure between?

Measure from the pencil baseline to the middle of the spot of the substance

How can you use chromatography to see if a certain substance is present in a mixture?

Run a pure sample of this substance alongside the unknown mixture. If the Rf value of the pure substance matches the value of one of the spots from the mixture, it is likely to be present.

What molecules spend more time in the mobile phase than the stationary phase?

Substances with a higher solubility stay dissolved in the mobile phase (solvent) for longer, so they will travel further up the chromatography paper.

How could you separate salt from a mixture of salt and sand

Salt is soluble, sand is not, so you could filter out the sand by adding water and using filtration to filter the solution so that the sand is removed from the mixture. Evaporate the solution so that water is removed and salt crystals are left behind.

What does potable mean?

safe to drink

How can waste and groundwater be made potable?

Sedimentation: Large insoluble particles sink to the bottom after the water is left still for a while. Filtration: Removes small insoluble particles by passing the water through layers of sand and filters. Chlorination: Kills bacteria and microorganisms which are too small to be removed by filtration.

How can seawater be made potable?

Distillation: Filter to remove insoluble particles. Boil. Cool and condense the water vapour.

What issues surround the process of making seawater potable?

Extremely expensive as it requires a lot of energy to boil large volumes of water. Wastewater is toxic due to high concentrations of salt so must be disposed of carefully.

What is deionised water?

Water that has had metallic ions (such as copper or calcium ions) removed.

Why is deionised water used in experimental analysis?

Deionised water is used to prevent the ions in the water interacting with the substances under analysis. If water wasn't deionised, false positives may be produced.