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States of Matter

Edexcel: IGCSE Chemistry, 3rd year
by

Kate Woodhead

on 14 November 2016

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Transcript of States of Matter

Many salts are soluble in water. Salts are ionic solids, such as sodium chloride. Covalent compounds are usually insoluble in water, such as hydrogen.

The solubility of solids increases as temperature increases. When a saturated solution is cooled, some of the solute will crystallise (precipitate) out of the solution, as less solid can be dissolved in the solvent.
States of Matter and Solubility @ IGCSE
Overview of the Topic
Three States of Matter
As Chemists, we are interested in the 3 States of Matter: solid, liquid and gas.

We imagine that all matter is made up of tiny particles, an idea originally suggested by the Ancient Greeks a few thousand years ago.

The way that solids, liquids and gases behave can be explained using the idea of particles.
Melting Points and Boiling Points
The temperature at which a substance melts is called the
melting point
. This is the same as the temperature at which a substance
freezes
.

The temperature at which a substance boils is called the
boiling point
. This is the same as the temperature at which a substance
condenses
.
Solubility
A substance that dissolves in another substance is called a
solute
.

A substance that dissolves another substance is called a
solvent
.

A solute dissolved in a solvent is known as a
solution
.

A
saturated solution
is one in which no more solid will dissolve in the solvent at a particular temperature.

Solubility is usually given in grams of solute per 100g of solvent.
Three States of Matter
Describe how the particles are arranged in solids, liquids and gases.
Describe how the particles move in solids, liquids and gases.
Explain why the particles in solids, liquids and gases are arranged and move like this, based on the energy they have.
Melting Points and Boiling Points
Work out the state of a substance at a specific temperature given its melting point and boiling point.
Know that a pure substance has fixed melting and boiling points, whereas impure substances melt and boil over a range of temperatures.
Recall that impurities lower the melting point and raise the boiling point of a substance.
Changes of State
Recall the names of the changes of state between solids, liquids and gases.
Describe how to make these changes of state happen.
Explain how the arrangement, movement and energy of the particles changes during these changes of state.
Cooling Curves
Conduct an experiment to work out the melting point of wax.
Present the results in the form of a graph.
Interpret the information shown on the graph, identifying what state of matter the substance is in, and the sections where a change of state is taking place.
Dilution
Describe an experiment to show that particles are very small.
Explain how this experiment shows that particles are very small.
Identify a drawback of this experiment.
Diffusion
Describe three experiments that show how particles move, and that they are very small.
Explain how particles move, based on the results of the experiments.
Solubility
Define the words/phrases: soluble, solute, solvent, solution, miscible, immiscible.
Know that ionic substances are usually soluble, and covalent substances are usually insoluble.
Explain what is meant by "dissolving".
Know that some substances react with water to produce acids and alkalis.
Solubility of Solids
Recall that the solubility of a solute in water is usually given in grams of solute per 100g of water.
Explain why the solubility of most solid solutes increases as the temperature increases.
Understand what is meant by a "saturated solution".
Solubility Curves
Outline an experiment to show how the solubility of a solid solute varies with temperature, and present the results on a graph.
Interpret the solubility curve.
Use the solubility curve to explain crystallisation.
Solubility of Gases
Know that many gases are soluble in water.
Know that oxygen, chlorine and carbon dioxide are very useful when dissolved in water.
Explain why the solubility of gases increases as temperature decreases, and as pressure increases.
Explain how carbonated water is produced.
Dilution
Particles are very small - we know this because we cannot see them with the naked eye, or with a light microscope.

But how small are they?

We can use a simple
dilution
experiment to make an estimate of the mass of one particle.
Solubility of Gases
Many gases are soluble in water.

Unlike solid solutes, the solubility of a gas decreases when the temperature of the solution increases.

This is because as the temperature is increased, the gas particles gain more energy and so the gas particles have enough energy to escape from the solution.
Changes of State
A change of state is a
physical
change, which means it is easy to reverse it.

E.g. it is easy to melt an ice cube by heating it up, and it is also easy to re-freeze it by cooling it down again.

Changes of state require either an input of energy (i.e. heating up), or an output of energy.
Cooling Curves
Diffusion
Diffusion is the process where particles in a gas or liquid spread out.

Imagine someone releases a smelly gas in a large room. At room temperature, gas particles can travel at speeds of 600 m/s! So why does it take so long for smells to travel from one end of the room to the other?

The gas particles take a random route, bouncing off air particles on its way. Each gas particle may have traveled 30 km, or more!
Solubility Curves
Solubility curves can be used to work out the mass of solute dissolved in a solution at a particular temperature.

They can also be used to work out the mass of solute that crystallises out of a saturated solution when it is cooled.

For example, a saturated solution at 70 deg C has 136g of solute dissolved in it. However the same solution at 50 deg C can only have 84g of solute dissolved in it. If it is cooled from 70 to 50 deg C, then (136 - 84 =) 52g of solute will crystallise out of the solution.
Solubility of Solids
Particles are close together
Particles vibrate about a fixed position
Strong forces between particles
Fixed shape
Cannot be compressed
Solids
Particles are close together
Particles can move freely over each other
There are intermediate strength forces between particles
Take the shape of their container
Difficult to compress
Liquids
Particles are far apart
Particles are in rapid and random motion
Very weak forces between the particles
Fill all available space
Easily compressed
Gases
There are actually more than 3 states of matter, however the others are only accessible at very extreme conditions. They are studied at postgraduate
level.
Iodine is an element that sublimes: it turns directly from a dark grey, shiny solid to a purple vapour when it is heated.
Demo...
1. Collect one tube of pre-melted wax.
2. Place the tube in a beaker of cold water to allow the wax to cool.
3. Take the temperature of the wax every 30 seconds, and record it in a table. DO NOT pull the thermometer out of the wax to take its temperature.
4. Watch the tube carefully and also note down the exact temperature at which the wax solidifies.
Practical...
A to B: the substance is a gas.
B to C: the substance is condensing. The particles get closer together, and energy is given out.
C to D: the substance is a liquid.
D to E: the substance is freezing. The particles can no longer mover freely, and instead vibrate about a fixed point. Energy is released.
E to F: the substance is a solid.
How Much Do You Remember...?
Organise these words and phrases into groups. The groups are up to you...
fixed point
vibrate
random
rapid
far apart
close together
slide
freely
no pattern
strong
weak
high
low
How Much Do You Remember...?
Here are the answers to three questions on States of Matter:

Regular
Sublimation
Gas

You need to write the questions!
Impurities
A pure substance will melt and boil at fixed temperatures.
A substance containing impurities will melt and boil over a range of temperatures.
Impurities cause the melting point to lower, and the boiling point to raise.
Salt is added to water when cooking vegetables and pasta to raise the boiling point of the water. This means that the vegetables or pasta cook faster because they are at a higher temperature.
Demo...
Crushed ice in a funnel has salt sprinkled over it. The ice melts, but what temperature does the thermometer read?
Potassium manganate (VII) gives a deep purple solution when dissolved in water. We assume that we only need one particle of potassium manganate (VII) in the smallest visible drop in order to see the purple colour.
Weigh out 1.0 g potassium manganate (VII).
Measure out 100 cm3 water and add this to the potassium manganate (VII).
Accurately measure out 10 cm3 of the potassium permanganate solution.
Measure out 90 cm3 water and add this to the 10cm3 portion of potassium manganate (VII) solution.
Continue to dilute the potassium manganate (VII) by taking 10cm3 of the solution and adding 90cm3 water to it until the solution appears to be colourless.
Practical...
Dilution Experiment - the Calculation
The dilution experiment shows us that a particle must have a mass smaller than a billionth of a gram (1 x 10^-9g).
In reality, a particle of potassium manganate (VII) actually has a mass of 2.6 x 10^-22g.
Diffusion in Liquids
Diffusion through a still liquid is very slow. It can take days for a strongly coloured solution such as potassium manganate (VII) to spread throughout a beaker of water. This is because there are only small gaps between the liquid particles for other particles to diffuse into.
Demo...
Pieces of cotton wool soaked in concentrated ammonia and hydrochloric acid are placed in the ends of a long glass tube.

A neutralisation reaction takes place, and ammonium chloride is produced. This can be seen as a white ring appearing about a third of the way down the tube from the hydrochloric acid end.

The ammonia particles have traveled faster and therefore further than the hydrochloric acid particles because they are lighter.
Here are three experiments showing diffusion.
Practical...
• Weigh out a specific mass of potassium chlorate.
• Transfer 10cm3 of water to a boiling tube.
• Carefully add the potassium chlorate to the water and dissolve.
• Warm the sample in a water bath stirring carefully with a glass rod.
• Once the solid has dissolved, remove the boiling tube from the water bath and insert the thermometer. Clamp it in a stand.
• Record the temperature at which the potassium chlorate crystals reappear.
Miscible liquids are able to dissolve in each other, for example ethanol and water. They have to be separated by distillation.

Immiscible liquids cannot dissolve in each other, such as oil and water. They can be separated easily by pouring the top layer off.
Miscible and Immiscible Liquids
How much can dissolve?
Remember, solubility is measured in grams of solute dissolved in 100g of solvent.

If 60g of solute can dissolve in 100g of water at room temperature, then 30g of solute will be able to dissolve in 50g of water.
Demo...
Fizzy drinks have carbon dioxide gas dissolved in them to make them fizzy. Carbon dioxide makes the drink acidic.

Watch the demonstration of fizzy water being heated. Some universal indicator has been added.

Initially the indicator is red, showing that the water is acidic. As it is heated, the water bubbles rapidly, and the indicator turns yellow, then green. This means that it is neutral. It no longer has carbon dioxide dissolved in it.
Important Gases
Oxygen - this is essential for all life; it is required for respiration. Dissolved oxygen enables sea plants and creatures to respire. Problems may occur when the temperature of the water increases, as the amount of dissolved oxygen is reduced; this causes problems for sea plants and creatures to respire properly.

Carbon dioxide - this is dissolved under high pressure to produce fizzy or “carbonated” drinks. On a hot day, fizzy drinks become flat more quickly because the solubility of carbon dioxide is reduced and it escapes from the solution.

Chlorine - this is added to water to kill bacteria. When dissolved, it reacts with the water to form a bleach.
Cooling Curve Questions...
Practical...
We started with 1g of potassium manganate (VII) in 100cm3 water.
Each time the solution is diluted, the mass of potassium manganate (VII) in that solution is divided by 10.
We can calculate the mass of potassium manganate (VII) in the final dilution by dividing by ten as many times as the solution has been diluted.
We assume that we need at least one particle of potassium manganate (VII) in each droplet of water to be able to see the pink colour.
The smallest droplet we can see is about one thousandth of 1cm3, so we have to divide the mass of potassium permanganate in the final dilution by 10 000 to find the mass of one particle.
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