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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)

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  1. Structure and biological significance of lipids.

    As this breaks apart the -COOH group, which is what makes fatty acids acidic, once the condensation reaction has occurred, the fatty acids will no longer have any acidic properties. As the triglyceride is effectively surrounded by hydrocarbons, it is hydrophobic (water-hating) There are two types of fatty acids: saturated and unsaturated. Saturated fatty acids have no double bonds, and so the maximum amount of hydrogen molecules attached. Unsaturated has at least one carbon double bond, and so could potentially have more hydrogen.

    • Word count: 673
  2. Investigate the effect of concentration in the rate of a reaction.

    * We then measured how many cubic centimetres were given off by the reaction every ten seconds over a time span of one hundred seconds. * The three grams of marble chips reacted too fast due to a grater surface area being covered; therefore, we tried 1.5 grams worth of marble chips. * For the 1.5 molar acid experiment we did the same steps as above. Below is a diagram of what we did..... This is a table of a three molar acid, and how long it took for the carbon dioxide to be produced.

    • Word count: 2307
  3. Acid Rain.

    It is also why these rocks are greatly affected by acid rain. The word equation is for this reaction between calcium carbonate and hydrochloric acid is: Calcium carbonate + hydrochloric acid --> calcium chloride + carbon dioxide + water The chemical formulae for this reaction between calcium carbonate and hydrochloric acid is: CaCO? + 2HCL --> CaCL2 + CO2 + H2O The rate of reaction can be calculated by measuring amount of Carbon dioxide gas that is obtained by the syringe.

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  4. Practical on Enthalpy changes between acids and bases.

    But some chemical reactions only occur when energy is put into them from an external source. Reactions which require this sort of input are called endothermic reactions. Enthalpy is the total energy content of the reacting materials. The symbol for enthalpy is ?H. Enthalpy is measured during a reaction. Energy is transferred to and from a reaction system and as a result the enthalpy changes. The equation used to calculate the enthalpy is as follows. ? H = mc ?T (H is the enthalpy change, M is the mass of the reacting solution and C is the specific heat capacity for water.)

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  5. In what ways do human beings modify the composition of the urban atmosphere? How do such atmospheric modifications affect the nature of precipitation in urban areas?

    Carbon monoxide is toxic gas produced by incomplete combustion of fossil fuel like coal and petroleum. Carbon dioxide is the most common gaseous pollutant, which is a very efficient heat absorber and is responsible for a remarkable increase in atmosphere temperature. Improvement in transport leads to heavy traffic for transport of agricultural produce, manufactured goods and raw materials. Innovation of vehicles and increasing capita income cause the mass production of car. Rising car owernship with the use of diesel oil which produce the exhaust fumes which are the great source of CO, SO2, NO, NO2 and compound of lead. In Tokyo, automobile exhaust is estimated to account for 67% of the total amount of nitrogen oxides.

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  6. Determine the unknown concentration of three acid solutions using a standard known concentration of alkali.

    In a 1:1 ratio of acid if there are 0.1 mols of hydrogen ions (H+) present in solution (note H3 O+ in water) then you will need an equal amount of basic OH- ions present to neutralise them (also 0.1mols). H+ + H2O H3O+ H3O+ = OH- = neutral = end point of titration So in simple terms the reaction that takes between the acid and base is always a neutralisations reaction. A base is titrated with an acid until all the acid ions are neutralised by the base. This is called the end-point and the solution is now neutral.

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  7. Organic Molecule – Lysine.

    Due to this lysine is located where part of the side-chain is buried, and only the charged portion is on the outside of the protein. However, this is by no means always the case, as lysine is often positioned on the outside of proteins. Lysine is also frequently involved in salt-bridges, where they pair with a negatively charged amino acids (such as aspartate, shown below) to create stabilizing hydrogen bonds, that can be important for protein stability. Furthermore lysine contains a positively charged amino on its side-chain that is sometimes involved in forming hydrogen bonds with negatively charged non-protein atoms.

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  8. Does the amount of hydrogen gas formed in the below reaction depend on the amount of magnesium used?

    * Type of acid: different kinds of acids are more or less reactive than others so if you use different types of acids you will get different results. * Surface area of magnesium: as the surface area increases it will also become more reactive because there will be a larger area for the acid to collide with. In this particular experiment, my altering factor will be the length of the magnesium strip; this will be measured in cm. Diagram: Plan: Equipment: * 100ml measuring cylinder * Conical flask * 30cm magnesium ribbon * 100cm3 dilute sulphuric acid * Plastic tub

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  9. Thermometric Titration.

    The precise volumes of acid and alkali solutions will neutralize each other out exactly. In a titration there is always one solution of accurately known solution, containing a known substance with an unknown concentration, is placed in a conical flask. The result from the titration is used to calculate the amount of substance present in the solution in the conical flask. Prediction I predict that as more of the acid is added to the alkali the temperature of the solution will rise because an exothermic reaction is taking place. I also think that at a point the temperature will cease to rise and that will be after neutralization has taken place.

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  10. Determination of isoelectric point of protein (casein).

    If the process was carries out the other way round, the higher concentration of the 1.0 M acid would raise the acidity level of the 0/01 acid. 5. Second, the designated amounts of 1.0 M acetic acid according to table 1 was added to test tubes 3,4,5,6,7 and 8. 6. Third, the designated amount of 1.0 acetic acid according to table 1 was added to test tube 9. 7. Fourth, 1ml of casein 0.5g/1 in 0.1M sodium acetate was pipetted into each test tube.

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  11. Quantitative Analysis of Vitamin C in Food Products.

    We all recognize citrus fruits as a valuable vitamin C source, but few of us realize that many freshly harvested vegetables contain considerably more of this vitamin than do oranges or lime. Unfortunately, storage and processing destroy most of the Vitamin C in vegetables before they reach the consumer. Consumer cooking methods further decrease the amount of vitamin C in vegetables. Vitamin C is water soluble and thus leaches out while cooking or steaming.

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  12. Obtaining pH curves for acid/alkali titrations.

    I will record the values for the pH and the volume of NaOH added. Theoretically, this should give me a pH curve from which to work. In order to obtain a value for Ka, I shall find the equivalence point (at around 25cm3 where the graph goes up vertically) and find the pH at this point, I shall then divide this by two to give me the 1/2 equivalence point. Having obtained this value, I can assume that: [CH3COOH] = [CH3COO-] = [H3+O] And as: Ka = [CH3COO-] [H3+O] [CH3COOH] Therefore: Ka = [H3+O] Or: pKa = pH (at 1/2 equivalence point)

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  13. The Structure and Function of Lipids.

    Lipids link covalently with carbohydrates to form glycolipids and with proteins to form lipoproteins. There are three major classes of lipids: * Neutral lipids * Phospholipids, * and steroids Neutral Lipids Neutral lipids are commonly found in cells as storage fats and oils, are so called because at cellular pH, they bear no charged groups. Generally, they are completely non-polar, with no affinity for water. Almost all neutral lipids are a combination of fatty acids with the alcohol glycerol. Fatty acids are long chains of carbon atoms with attached hydrogens and other groups. A carboxyl (-COOH)

    • Word count: 619
  14. Find if changing the concentration of an acid will increase or decrease the rate of the reaction when marble is dissolved in hydrochloric acid.

    I can measure the speed of the reaction by how much gas is given off. I can measure this in cm3 in a gas syringe. When the experiment takes place, I will take the reading every 10 second to get a good graph for the results. If the reaction goes very quickly, I will take the readings every five seconds. I will use acid of 0.5, 1, 1.5, 2 and 2.5 molar concentrations. To be sure I can rely on my results I will repeat he experiment twice or three times if necessary, because there is chance of inaccurate results for many reasons.

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  15. The ideas involved with viticulture and oenology.

    The resulting mixture from the crushing of the grape berries (minus the stems) is called must- the juice, skins, seeds and the pulps. The acidity of the juice, and also its sugar content need to be determined, as this gives an indication of the strength and volume of the alcohol that will be produced once the juice will have been fermented. Next some sulphur dioxide is added to the juice, which prevents oxidation of the juice and also prevents it from going off because it kills the micro organisms that may cause this.

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  16. Analysis of unknown aqueous solutions.

    ethyl ethanoate is formed. During this reaction, the O-H bond in ethanol is broken. CH3CH2OH + H3C-C-OH H3C-C-OCH2CH3 + H2O EQUIPMENT: 1. 5 solutions (each in a test tube) 2. Concentrated sulphuric acid 3. Ethanol 4. Distilled water 5. 5 beakers 6. Heating equipment (including Bunsen, splints and heatproof mat) METHOD: 1. Heat solutions with ethanol and concentrated sulphuric acid 2. Allow cooling time 3. Pour contents into beakers containing 50cm3 of cold water 4. Cautiously smell vapour. Ethyl Ethanoate smells strongly of pears RISK ASSESSMENTS: 1. Wear eye protection 2. Concentrated ethanoic acid is corrosive so wash away any spills immediately with plenty of water 3.

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  17. The Causes And Forms Of Acid Rain.

    The effects on the environment are amplified as a result of the traditional concentration of industry and power production in certain areas. For example, the concentration of power stations along the Trent valley in Britain has resulted in an annual emission of some 600 000 tonnes of S02 from this area alone. Other notorious areas for S02 emissions include the eastern parts of Germany (4 Mt S02 per year), and Poland (4.9 Mt S02 per year). The chemical reactions that lead to acid rain begin as energy from sunlight in the form of photons, which hit ozone molecules (O3)

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  18. Acid-Base Titrations.

    A weak acid-weak base titration would have only a small pH change at the equivalence point. This small change is difficult to detect, and for this reason weak acid-weak base titrations are uncommon. Standards in Acid-Base Titrations One of the substances involved in a titration must be used as a standard for which the amount of substance present is accurately known. The standard can be present either in the form of a pure substance or as a standard solution, which is a solution whose composition is accurately known.

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  19. 'Investigating how changing concentration affects the rate of reaction between Marble chips and hydrochloric acid.

    The temperature can affect how fast the marble chips work and may also give you the wrong results. I predict that the higher the volume of hydrogen (cm3) the quicker the reaction will take place. Scientific knowledge that I think this will happen is that the higher the volume of hydrogen will make the marble chips react quicker than a lower volume of hydrogen. The chemical equation for this investigation is: Marble + Hydrochloric Calcium + Carbon + Water Chips Acid Chloride Dioxide We timed the experiment up to 65 seconds and we used volumes: 1, 1.5, 2.0, and 2.5 of hydrochloric acid.

    • Word count: 747
  20. The purpose of this experiment was to isolate and characterize macromolecules.

    Chromatography was used to characterize the macromolecules. The process is technique that separates mixtures into their individual components. After this process, there is an equation that is to be used. This equation is: Rf = Distance (from origin) travelled by substance (cm) Distance (from origin) travelled by solvent (cm) This equation allows one to calculate how soluble the solvent is in the solution. The resultant figure from this simple calculation allows for the characterization of the macromolecule that is in use. (Department of Biology,2003) Materials and Method: The experimental procedure used for this experiment was outlined in the Biology 130L lab manual under experiments 2 and 3.

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  21. Investigation to find out how concentration affects reaction rate.

    This theory is known as collision theory. I predict that the lines on the graph will rise and then level off. I believe the results with the highest concentration will have the graph with the steepest line, and the one which will level off first. I believe this because the hydrochloric acid will be most concentrated at first so it will react most here. As the hydrochloric acid becomes less concentrated the graph will level off as there less particles colliding.

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  22. I am going to investigate at which concentration of hydrochloric acid, marble breaks down fastest to make hydrogen.

    Two things that cannot be kept exactly the same are the amounts of gas lost before the bung is put in at the start of the experiment and the room temperature. The gas is going to be measured using a gas syringe attached to a stand connected to the conical flask using a bung and tube. The gas syringe will be used to measure the amount of gas been given off during the experiment. We will also use an electronic balance to get make the amounts of marble used, fair.

    • Word count: 633
  23. Structure and Functions of Collagen and Insulin.

    The C-peptide of proinsulin is depicted as open circles. Insulin is derived from proinsulin by cleavage of the C-peptide structure at the dipeptides Arg-Arg and Lys-Arg. Insulin is composed of an A chain of 21 amino acids and a B chain of 30 amino acids, the chains being held together by two disulfide bonds. A third disulfide bond is present within the A chain. Insulin is an anabolic signal. The binding of the hormone to its receptor initiates a series of events within the cells that results in the increased uptake of glucose into the cells, where it is converted into metabolic energy or stored as glycogen and fat.

    • Word count: 620
  24. Levels of protein structure.

    This is called a dipeptide bond. Longer chains are called polypeptides. The shape and the properties of the polypeptides are determined by the order of the 'R' group. The varying of the 'R' group and the arrangements of the other amino acids makes it possible to form an infinite number of different polypeptides. A protein consists of one or more of these polypeptide chains folded into a complex 3D shape. Different proteins have different structures. The first structure is called the primary structure. The primary structure of a protein is a linear sequence of amino acids in its molecule (It is the specific sequence of amino acids in a polypeptide).

    • Word count: 704
  25. Experiment to obtain curves which show how the pH changes during an acid-base titration and;To use these curves to choose suitable indicators for different combinations of acid and alkali.

    or by removing 1 small drop on a thin glass rod and testing with narrow range indicator paper. If which range to use was not known, it is first tested with full range universal indicator paper. However, it is important not to remove more than the minimum acid from the flask. 5. The alkali form the burette were added in steps as shown in result table and the pH at each addition was recorded after thorough mixing. 6. Steps 1~5 were repeated with at least one other combination of acid and alkali, and a copy of result table was completed.

    • Word count: 1310

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