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# AS and A Level: Physical Chemistry

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## The dynamic equilibrium and 'Le Chatelier Principle'

1. 1 Le Chatelier Principle states “If a system that is in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise that change”. Put simply- if you do something, the system will try and reverse what you’ve done!
2. 2 Adding a catalyst does not change the concentration, pressure or temperature of a system. Therefore adding a catalyst has no effect on the position of equilibrium.
3. 3 If you increase the concentration of one side of an equation, the position of equilibrium will shift to the other side (to try and return the concentration back to its original value).
4. 4 If you increase the pressure of the system, the position of equilibrium will shift to the side of the reaction with less moles of gas (to try and reduce the pressure back to its original value).
5. 5 If you increase the temperature the position of equilibrium will shift in the direction of the endothermic reaction (to try and reduce the temperature back to its original value).

## Top equations for acid / base chemistry (A level only)

1. 1 For a strong acid the acid concentration is equal to the H+ concentration. This is because strong acids fully dissociate their H+ ions. [acid] = [H+]
2. 2 For a weak acid, because they only partially dissociate their H+ ions, to find the H+ concentration we must use the following equation: [H+] = √ka[acid]
3. 3 For a buffer, we calculate the value of H+ by using: [H+] = Ka[acid] / [salt] (where Ka is the acid dissociation constant)
4. 4 For a strong base, we calculate the H+ value by using: [H+] = Kw / [base] (where Kw is the ionic product of water = 1 x 10-14)
5. 5 To convert [H+] into pH, we would use the equation: pH = -log[H+]

## Top tips for ionisation energy

1. 1 One of the factors which will affect ionisation energy is electron shielding. This is how many inner shell electrons an atom has. The more electron shielding, the lower the ionisation energy. Electron shielding stays the same across a period and increases down a group.
2. 2 The second factor affecting ionisation energy is the proton number / nuclear charge. The higher the nuclear charge the higher the ionisation energy. Nuclear charge increases across a period and down a group.
3. 3 The third factor affecting ionisation energy is the atomic radius (size of the atom). The higher the atomic radius the lower the ionisation energy. Atomic radius decreases across a period (as the increased number of protons pulls the electron shells closer) and increases down a group.
4. 4 All three of these factors combine to have an effect of increasing the ionisation energy as we go across a period (eg F has a higher ionisation energy than O)
5. 5 All three of these factors combine to have an effect of decreasing ionisation energy as we go down a group (eg K has a lower ionisation energy than Na)

• Marked by Teachers essays 14
• Peer Reviewed essays 19
1. ## The main purpose of this experiment was to determine the equilibrium constants of deprotonation reactions of 2-naphthol using UV-Vis and fluorescence spectroscopy.

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2. ## Experiment to demonstrate the effects of buffers on ph changes.

However, a weak acid is one that does not completely dissociate or ionize, in a solution. ________________ 3.0 Introduction: Introduction: Mainly, the purpose of this lab is to demonstrate the power and importance of buffer sin regulating the pH of solutions, by adding very small amounts of acid or base to different buffer solutions. Students were able to calculate the buffer capacities of those solutions and some general trends with regard to buffer strength with regards to acid/base balance. Furthermore, the buffer capacity ?, is important in evaluating the buffers used in the lab. The buffer capacity is calculated using the equation below: - In this equation ? represent that the buffer capacity, d[b] and d[a]

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3. ## Experiments to examine dynamic equilibrium and Le Chateliers principle

Le Chatelier's principle describes what happens to a system when something momentarily takes it away from equilibrium. There are three changes that will affect the position of equilibrium momentarily. First, changing the concentration of one of the components of the reaction. Second, changing the pressure on the system. Third, changing the temperature at which the reaction is run. Objectives: Observe the effect of an applied stress on chemical system at equilibrium. A reversible reaction is a reaction in which both the conversion of reactants to products and the conversion of products to reactants occur simultaneously.

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4. ## Lab Report. Objectives 1. To determine the enthalpy of neutralization of strong acid and strong base. 2. To determine the quantity and direction of the heat transfer in the dilution of a salt.

Measure the temperature change, The unit of is kJ/mol of acid and base reacted. Mass (g) of solution is the total mass of acid and base in solution. The enthalpy of solution is produced when a salt dissolve in water. Energy is absorbs and releases. KI dissolves in water : The lattice energy (enthalpy) of salt, and hydration energy (enthalpy), will determined whether heat is absorbed or released when 1 mole of salt dissolve in water. The enthalpy of solution and dilution; is total of and . Salt dispersion enthalpy, is determined experimentally with the combination of heat loss from the salt and water whenever both of them are mixed.

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5. ## Assignment 2 M3 Specialist and Non specialist lab

The science lab will have a first aid kit and eye wash stations. The lab will also have other safety equipment such as fire extinguisher, fire blanket and a sand bucket. This kind of lab would be used by secondary school students to carry out general practicals such as animal dissections, titrations of a chemical and testing electric circuit for voltage and current change. My non-specialist lab has the following equipment: * New fast and efficient computers to be able to do research and type up work * New student benches with integrated gas taps and plug sockets so that they are easily accessible during a practical.

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6. ## Rates of reaction experiment HCl and Sodium Thiosulphate

Another one could be a catalyst because this is a lower activation energy required by particles to start a reaction and provides another route for the reaction to occur, thus speeding up the reaction. In the reaction what I will carry out the equation is: Hydrochloric acid + sodium thiosulfate sodium chloride + sulphur dioxide + Sulphur + water 2HCl (aq) + Na2s2o3 (aq) 2Nacl (aq) + SO2 (g) + S (s) + H2O (l) On this experiment we will be changing the concentration of the hydrochloric acid.

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7. ## Using Catalysts to Manufacture Margarine

Factors like the temperature or the amount of time it takes for the hydrogen to go through the oil should be carefully controlled. This is so that most of the carbon-carbon double bonds are hydrogenated. What are the properties and uses of nickel? Nickel is a good conductor of heat and electricity, it can be beaten and turned in a thin sheet. It has also a great resistance to rusting and corrosion which means that it does not react with oxygen in the air to form any kind of metal oxide.

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8. ## Investigation (reaction of transition metal ions)

and see how it changes * We noted the results of what we observed in a table like the one below * We Repeated the same process with other chemical ions (chromium and copper) Results Hexaqua ions Ph. HCL Ammonia Sodium Hydroxide Sodium carbonate Cobalt (red) Ph3 Blue. Produced heat, and smoke Went cloudy, produced a blue precipitate Light blue cloudy and dark Light pink Precipitate, cloudy liquid Copper (bleu)

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9. ## Comparing the commercial production process of iron and aluminium in relation to their properties

The manufacture of aluminium can be done through both processes depending on the rise of its demands in the market and industry where it is mostly used. Continuous process In the continuous process, the production is always running 27/7 and it never stops. The continuous production process is mostly used to manufacture large quantity of chemicals needed. An example of a continuous production process is the Haber process. This production process is used to manufacture Ammonia. The rate of production in the continuous process is much more higher compared to the rate of production in the batch process simply because the production here is continuous.

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10. ## Purification of aluminium from Bauxite

Sometimes other metals are added to it while it is molten in order to make alloys with useful properties. Overall process Mine bauxite ? mix with cryolite ? met by electrolysis- lower anodes into electrolysis ? pass large electric current- tap off molten aluminium ? replace carbon anodes http://www.elmhurst.edu/~chm/onlcourse/chm110/outlines/images/elecaluminum.GIF http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/electrolysis/electrolysisrev3.shtml The final product (aluminium) is used in many industrials sectors. Some of them are transport, construction or even in the electrical sector. Aluminium can be used to make car engines, trucks and buses and also. But the uses don?t stop there; aluminium can also be used to make alloy sheets to wrap up food.

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11. ## AQA As Applied Science Unit 3. Colorimetry experiment on Ribena juices

What is colorimetry used for? Colorimetry is used in most industries such as: * Food * Paint manufacturing * Colour printing * Textile manufacturing * Chemistry ASDA Equipment: * Ribena * Distilled water * Curette * Graduated flask * Graph paper * Pipette * Colorimetric * Glass Beakers * Pipette filler Method: 1. Set up all the Colorimetry equipment 2. Get a Pipette filler and a Pipette and measure 20ml of the Ribena 3. Put 20ml in to a graduated flask 4. Put water in until it reaches the mark 5.

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12. ## Chemistry Revision Notes - Semiconductors, Superconductors & Oxidation States

The exceptions include the hydrides (the oxidation state is -1) and the peroxides (the oxidation state for oxygen is -1). In the compounds, halides usually have the oxidation number -1. The sum of all the oxidation numbers in a compound have to be equal to zero. The sum of all the oxidation states in a complex ion is the same as the charge on the ion. Semiconductors A covalent element such as silicon or germanium which has a higher conductivity than that of a typical non-metal but a much lower conductivity than that of a metal is described as a semiconductor.

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13. ## Comparing High Pressure Liquid Chromatography and Gas Chromatography

This is because compounds that react very slowly due to their complex structure are being separated within the column. A vacuum degasser is also present in HPLC and it removes the air bubbles that are in the mobile phase; otherwise these air bubbles will give false peaks in the chromatogram. On the other hand, Gas Chromatography, highly volatile substances such as alcohols are being separated in a mixture, therefore a very high pressure is not necessary because in GC the components are volatile and they do not have to be forced to interact with the mobile phase and the stationary phase because the components themselves are reactive; instead components travel through the stationary phase with capillary action.

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14. ## High Pressure Liquid Chromatography procedure steps

Each of these standard solutions- including the mixture itself- could either be manually loaded into the injection port one after the other by using a hypodermic syringe or by using an auto-sampler. The hypodermic syringe allows inserting sample volumes which could be from 5 to 20 microlitres; this indicates how only very small quantities are required for the process. The auto-sampler will load each standard solution with the appropriate volume that is set, into the injection port without human intervention.

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15. ## Column chromatography is a larger scale of thin layer chromatography.

The hydrogen bonds form between the ?highly electronegative oxygen atoms in Alumina? and the hydrogen atoms in the compounds. Whereas, the less polar compound will dissolve more in the water-ethanol mixture; and form less hydrogen bonds with the alumina compared to the number of Van der Waals forces that will also form. The compound which is adsorbed more will not travel as further as the compound with lower polarity. The compound with lower polarity will travel in the mobile phase, further down the column as it spends most of its time dissolved in the water-ethanol mixture than in being adsorbed by the alumina stationary phase.

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16. ## Primary and Secondary Standard solutions in chemistry (titration & colorimetry)

than the secondary standard, sodium hydroxide (40 RMM) for e.g. Primary standards? reactivity with the surrounding is low in oppose to secondary standards where it is high and react with the water molecules in the atmosphere. The function of the both standards is to provide as a reference to be used when standardising a solution. Initially, a primary standard is used to standardise a secondary standard. Titration is the quantitative technique used to identify the concentration of an unknown solution by using a solution of which its concentration is known.

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17. ## Titration - Preparation,Neutralisation and Applications in Industry

We then poured 10ml of Hydrochloric Acid into the Burette. We then placed our Sodium Hydroxide solution underneath the Burette in a conical flask and added 2 drops of universal indicator turning the solution purple (alkali). Results: First try Second Try Third Try Average 3.3ml 3.1ml 2.9ml 3.1ml 2.5 x 10 - 3 / 3.1 x 10 - 3 = 0.81molar (out by 0.19 moles) Evaluation: Our result was out by 19% we could have improved this by measuring the sodium hydroxide solution and hydrochloric acid more accurately. Also whilst mixing the solution we should have used a magnetic stirrer.

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18. ## Compare the techniques and methods I used to measure the purity of a sample of aspirin.

Another downside to this technique is that to carry it out safely, a fume cupboard is necessary to get rid of the harmful gases. Titration The titration technique for estimating the purity of aspirin also had its good points and bad points. The good points were that this technique provided accurate results to decimal places. Also by this technique you can find out how much sodium hydroxide it would take to neutralise a sample of aspirin; this is also a good point.

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19. ## Producing Aspirin By Vacuum Filtration

Release the tap so water allows the filtration to process quickly. Then collect the solids which have been separated in the vacuum filtration * Re-crystallise by transferring the crude product to 100cm3 flask and add in 15cm3 of ethanol, alongside 45cm3 of distilled water. Then fit the air condenser and place the conical flask into the water bath until the crude has dissolved * Allow the solution to cool and then collect the product by vacuum filtration. * Finally dry the product at room temperature.

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20. ## Outline different methods of separating substances.

from the salty water, it is where the solution is heated up and the water evaporates from the solution, and goes in to a different container where it is firstly cooled and condensed, the salt from the solution cannot be carried so it is left behind, so to sum it up it is the process of ?purifying? a substance by the process of heating and cooling. Precipitation- it is when a transition metal compound is mixed with a sodium hydroxide solution which leads to a displacement reaction, since sodium is more reactive then transitional metals so it takes over the

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