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​Intro image

In this experiment we changed the temperature of the solutions.

We controlled:

We measured the time taken for the cross under the cup to completely disappear (relative to human perception ).

​The purpose of this experiment was to see if the temperature of a reaction could alter the rate of that reaction.

We set up four beakers containing sodium thiosulphate solution and heated them to varying temperatures from left to right, 30oC, 20oC, 11oC and 5oC. Then we poured in dilute phosphoric acid. The acid was added right to left. As the acid is added to the 5o solution and a stopwatch is started. Each time the acid is added to a solution the start time is recorded on the table below. The end time is recorded when the cross under the cup is no longer visible.

​The table to the right shows the different solutions, the time the acid was added, the end time and the total number of seconds it took for the solution to become too cloudy to see the cross.

This graph shows that as the temperature increases the time taken for the reaction to occur decreases. This shows that the rate of reaction increases as the temperature increases.

When the time is large we can say that the rate is low. When the time is small we can say that the rate is high

This makes the rate inversely proportional to the time taken.

This graph shows the rate of the reaction vs the temperature the graph shows a positive correlation between the two. This indicates that a higher temperature will result in a higher rate of reaction.

To see the effect of temperature more clearly we calculate a value of rate by using 1/t. One divided by time.

​The aim of this was to test to see if the concentration of an acid affected the rate of reaction. In this experiment, we used baking soda and different concentrations of limescale remover (phosphoric acid).

On the left, we see the baking soda in the upper row of numbered cups and our phosphoric acid and water in different concentrations in the bottom row of cups. 5.0g of baking soda is measured into each cup.

There are different ratios of water to acid in each of the bottom rows of cups.The numbers shown are the volume in cm3 of each substance.

From left to right there is a 100% acid on the far left followed by 75%, 50% and finally 25%.

measuring mass decrease against time is a simple method for monitoring the rate of a reaction

​In the experiment, we place our cup of baking soda on the scale and zero the scale. Then we start a stopwatch as we pour our acid solution into the cup and taking the first measure on the scale when all the mixture is added in. Every fifteen seconds we take a new reading until sixty seconds have elapsed. This gives us five readings at the end.

When we've done this for each set of cups, we take the final mass value at sixty seconds away from the first mass value at zero to find out the difference in mass ( in g).  Dividing the mass change by the time ( in this case, 60 s) gives us a value for the average rate of reaction in grams per second (g/s).

Baking soda reacts with acids to produce carbon dioxide gas.

On the left are the results of the experiment. The bottom two rows are the average rate of reaction and the percentage concentration. Using this and the graphs below we can see a positive gradient of the concentration to the rate of reaction. This is strong evidence to suggest that the rate of reaction is proportional to the concentration of the acid.

Water is an odourless, colourless liquid. So are many other chemicals .

​Intro image

Water has no obvious smell.  Water has no taste and water is colourless.

Water has a neutral pH value ( pH 7).

Many other chemical substances have similar properties . We therefore need to find a chemiscal test for water.

When water is added to anhydrous (white) copper sulfate the copper sulfate turns blue and gives off heat. This is a reversible reaction meaning that if we heat the blue hydrated copper sulfate water will boil off and the copper sulfate will turn white.

​Intro image

​To test for carbon dioxide. the test is to force the sample that you believe may be carbon dioxide in to a solution of lime water. if the sample does contain carbon dioxide then the solution will turn cloudy, if it does not then the sample cannot contain carbon dioxide.

Oxygen is a  very reactive gas. It makes up approximately 20%  of our atmosphere.

​The standard test for oxygen is to place a glowing splint into a test tube that may contain the gas.

If the splint glows brighter and/or relights into flame then it is a positive result for oxygen.

​Hydrogen is a flammable gas. It burns in air to produce water.

A convenient test for hydrogen is to put a lighted splint in the mouth of a test tube full of the gas . The gas will burn with a characteristic squeaky pop if hydrogen is present.

Hydrogen gas can be used as a fuel.

When hydrogen burns in air it combines with oxygen to form water.

This reaction releases energy and it therefore an example of an exothermic reaction

#### Some squeaky pops

Watch the video to see and hear the students using hydrogen to make some squeaky pops.

Are all squeaky pops the same?

Find out and write about three ways to make hydrogen gas. In each case say what the reactants are, what the products are and   write down chemical equations for the reactions.

Some say that hydrogen is a perfect fuel since it is not polluting.

Explain why hydrogen is not pollution when it burns.

Others say that hydrogen is not really a clean fuel. Can you explain why they can make this claim?

The periodic table lists the elements in order of increasing atomic number

​The modern periodic table provides a list of all the known elements categorized in increasing order of increasing atomic number

Each row across the periodic table is known as a period.

Each column is known as a group.

The period number tells us the number of occupied electron shells ion a given atom. The group number shows the number of electrons in the outermost shell of the atom.

The electrons in an atom arrange themselves in shells ( or levels) around the nucleus. The electrons fill the innermost shells first . Each shell can contain a maximum number of electrons. For GCSE and IGCSE we use a simplified model of electron shells.

This model works well for explaining the properties of the first 20 elements in the periodic table  - a more complex model is needed to explain the structure of atoms above atomic number 20.

Electron shells have a maximum number of electrons.

#### Working out  electron configurations

A carbon atom has 6 protons and therefore 6 electronsThe electrons are arranged in two shells; 2 electrons in the first shell and 4 electrons in the second shell. The electron configuration of a carbon atom can be therefore represented as: 2, 4

Carbon atoms have an electron configuration of 2,4

Ruby is a crystalline form of Aluminium Oxide

A crystal or crystalline solid is a solid material whose constituent particles (such as atoms, molecules, or ions) are arranged in a highly ordered structure

How do you know when a substance is crystalline?

Bismuth Crystals.

Metals will form  crystalline structures because their atoms can bond together in a highly organised fashion

​Crystals can form when a molten solid cools and solidifies. They can also form when a saturated solution is cooled. This happens because the solubility of most solid solutes  decreases as the temperature is lowered.

The solute can no longer stay in solution and therefore forms a solid precipitate. The precipitate can be crystalline.

Crystallisation can therefore be used to separate a solid solute from its solvent.

#### Pure crystal

Watch  the video and answer the following:
1. When recrystallising in order to purify a solid, how much solvent is used
2. There is a mistake in the apparatus set up at the beginning of the video. Describe the mistake and explain why it would be dangerous to heat the apparatus as shown.
3. Explain why the filter funnel is heated by a hot water jacket?
4. Why do crystals then form in the filtrate?
5. How are these crystals then separated?

The crystals obtained this way can then be dissolved and recrystallised to improve the purity further.​

#### Crystallisation close up

This video helps you to visualise how molecules ( or atoms) can stick together to form an orderly arrangement and therefore form crystals.

1. What shape is used in the video to represent the sugar molecules ?
2. The four images below show four different ways of "modelling" the arrangement of atoms or molecules forming a crystalline structure. Consider each model in turn. For each model try to say what is good about it and what might be "inaccurate" about it. This could be presented as a table of strengths and weaknesses.
3. It is often said that crystallising something slowly will produce lager and more regular crystals. Can you explain this?
Spheres can be used to model the way atoms and molecules might stack together.

In this video you see how scientist use bubbles in a soap solution to model the behaviour of particles in a crystal.

Fractional distillation in the laboratory

A fractionating column can be added to a simple distillation apparatus. The column is used to achieve a good separation of one liquid from another.

The column is often packed with glass beads which cause repeated condensation and evaporation. This can give a much purer condensate ( product) than when using simple distillation.

By controlling the temperature carefully the different fractions ( components) in the mixture of liquids can be separated from each other.

The most volatile components of the mixture will be the first to be extracted.

Industrial fractional distillation

Fractional distillation is used to separate crude oil into its different fractions. The most volatile fractions rise to the top of the column.

Use the information on this post and the one called "simple distillation" to explain the differences between Simple and Fractional distillation.