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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
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  1. Marked by a teacher

    Revision Notes. Substances Manufactured for use in Industries. Chemicals, alloys and polymers.

    5 star(s)

    Burning of these products will oxidise sulphur, S to form sulphur dioxide, SO2. 3. Sulphur dioxide, SO2, is an acidic gas. When it dissolves in rainwater, it forms sulphurous acid, H2SO3, and causes acid rain. 4. Sulphur trioxide, SO3, will also form when sulphur dioxide, SO2, reacts with oxygen, O2, gas in air. 5. When sulphur trioxide, SO3, dissolves in rainwater, sulphuric acid, H2SO4, is also formed causing acid rain. 6. The effects of acid rain on the environment are as follows: (a)

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  2. Marked by a teacher

    Write an essay on electrode potentials.

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    calculation of cell emf ; (b) prediction of reaction feasibility and limitations. ~ Sample Essay ~ An electrode potential is the difference in an potential between an electrode and its surrounding electrolyte. It is always referred to a "zero point" defined by the potential of a reference electrode (e.g. standard hydrogen electrode). Electrode potential is an important measurement in the realm of electrochemistry, and it is particularly useful in the prediction of the energetic feasibility of redox reactions as well as calculation of electromotive force (emf)

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    Write an account of buffer solutions.

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    Buffer solutions could be classified into two types, namely acidic buffer and basic buffer solutions. Acidic buffer solutions An acidic buffer solution is one which has a pH less than 7. They are commonly made from a weak acid and its sodium salt. A mixture of ethanoic acid and sodium ethanoate solutions is a typical example. pH of buffer solutions could be adjusted by changing the ratio f acid and salt, or by choosing a different acid and its salt. Ethanoic acid is a weak acid, and the equilibrium position will be well to the left: CH3COOH + H2O CH3COO- + H3O+ (eqn.

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    Objective To find out the equilibrium constant, Kc, for the reaction below, using acid hydrolysis:

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    Table 1 shows the amount of chemicals added: Reagent bottle's number 1A 1B 2 3 4 Volume of HCl(aq) added /cm3 5.0 5.0 5.0 5.0 5.0 Volume of CH3COOCH2CH3(l) added /cm3 - - 5.0 4.0 2.0 Volume of H2O(l) added /cm3 - - - 1.0 3.0 Total volume of mixture /cm3 5.0 10.0 4.> Record the total mass before and after each addition of chemical into Table 3. 5.> Set them aside for at least 48 hours and shake the bottles occasionally. Procedure -- Titration (48 hours later) 1.> Rinse and fill a burette with standardized NaOH solution. 2.> Pour the contents of bottle 1A into a conical flask and rinse the bottle with deionized water.

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    Heat of Neutralization. Objective: To investigate the enthalpy changes () of various acid-base neutralizations.

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    In this experiment, we were going to determine the enthalpy changes for a specific pair of acid-base neutralization. The experiment was divided into two parts. The determination of the enthalpy change of the neutralization () between an acid and a base by using two methods was involved in the first part. In both methods, the maximum change in temperature of neutralization was measured and (I) the concentration of alkaline solution and (II) the enthalpy change of neutralization could be determined by graphical methods. In the second part of the experiment, the enthalpy changes of neutralization for different combinations of acid and alkali were compared and the experiment data would be collected from our classmates who have carried out the other combinations of acid-base neutralization.

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    Experiment investigating hydrogen bonding in different chemicals.

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    It also plays an important role in the structure of polymers, both synthetic and natural. Breaking or formation of intermolecular hydrogen bonds between molecules in liquids would cause an enthalpy change when the liquids are mixed. In this experiment, we are going to investigate such enthalpy changes and to measure approximate strengths of hydrogen bonds formed between molecules of ethanol and those between molecules of trichloromethane and ethyl ethanoate using simple calorimetric methods. For instance, in parts A and B, ethanol contains -OH group which can form hydrogen bond among its molecules but cyclohexane does not.

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    Stereochemistry of Butenedioic acid

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    For example, an electrophile adds to the double bond, rotation becomes possible. Loss of the electrophile then regenerates the double bond. If rotation occurred in the intermediate, the result is the other isomer. The result of this kind of transformation is an equilibrium mixture of the cis and trans isomers. Frequently, the trans isomer is more stable, so the equilibrium mixture would contain more of the trans isomer. The greater the difference is in the stability of the isomers, the greater the concentration of the trans isomer will be at equilibrium.

    • Word count: 1911
  8. Marked by a teacher

    Electrochemical Cells

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    This is measured by placing it with a standard hydrogen electrode. This is because for the half reaction that turns hydrogen ions into hydrogen gas, the standard electrode potential is 0.00V. If a half-cell has a positive standard electrode potential, then it means that it is more likely to receive than give away electrons, which would make it the reducing agent. The oxidising agent is the negative half-cell. For my investigation, I am using copper sulphate and zinc sulphate. When the solutions are 1mol dm-3, the redox reaction between them is: Zn(s)

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  9. Marked by a teacher

    Revision notes - Test For Gases and Ions

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    The solution turns from colourless to brown (possibly with a black precipitate, iodine). Nitrogen dioxide NO2 Not many tests for this gas. The gas is brown. Sulphur dioxide SO2 Test 1 Bubble gas through a solution of potassium dichromate (VI) dissolved in sulphuric acid. The solution turns from orange to green. Test 2 Bubble gas through a solution of potassium manganate (VII) dissolved in sulphuric acid. The solution turns from purple to colourless. Tests for Ions Ion Formula Test Observations Carbonate CO32- Test 1 Heat the solid in a test tube with a Bunsen burner.

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    Electrochemistry Experiment. Objective: To investigate the effect of change in lead(II) ion concentration on the potential of the Pb2+(aq) ∣Pb(s) electrode

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    electrode Introduction: This experiment investigates the e.m.f. of the cell: Cu(s) |Cu2+(aq) |Pb2+(aq)|Pb(s) Keeping the ion concentration in the copper electrode system constant(1M) and varying the ion concentration in the lead electrode system, the effect of change in lead(II) ion concentration on the potential of electrode as well as the Kc of the above reaction can be found. Chemicals: Copper foil x1, lead foil x1, 1M Cu2+ solution, 0.1M Pb2+ solution, saturated potassium nitrate solution Apparatus: 250 cm3 beakers, 50cm3 beakers multimeter, distilled water bottle, filter papers, electrical wires with electrode holders, forceps, 100ml volumetric flask,10ml pipette x2, dropper Procedure: 1.

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    The history of the atom

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    He also said that all atoms of a given element are the same and atoms of one element are different from those in every other element. This meant that every different element had its own unique type of atoms. (Dalton also developed the first table of atomic masses)

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    Chemical Bonding and CFCs. There are three main types of chemical bonds.

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    The electrostatic attraction of the cations and the 'sea of electrons' hold the atoms together, and this forms the metallic bond. Special types of bonds Dative covalent bond When one of the atoms forming a covalent bond provides both the electrons needed for the sharing, the bond formed is called a dative covalent bond or a coordination bond (e.g., H3N�BF3). Polar covalent bonds Pure covalent bonds are rare, and most of the pure covalent bonds only occur in elements (e.g, Br-Br).

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    Finding out how much acid there is in a solution

    H2SO4 ==> H (+) + SO4 100% as The weakness of an acid doesn't ionize fully (like a strong acid) when it dissolves in water. Ethanoic acid is a typical example of an acid. When this acid reacts with water, it produces hydroxonium ions and ethanoate ions. The reaction which takes place here, can be reversible, and it is more likely for the backward reaction to occur too. The ions react very easily to reform the acid and the water. Once it has reacted with water, approximately 5% of the displaceable Hydrogen in the acid is present in solution as hydrogen ion.

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  14. Peer reviewed

    Ozone chemistry speech. Today, I am here to inform you that an ozone hole has been detected over Antarctica and the concentration of ozone will continue to decrease across the globe if the emission of ODCs, such as CFCs, does not reduce.

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    USA: The CFCs' industry is worth 8 billion dollars per year. I understand. The chemical is ideal for many purposes as it is used as a solvent and cleaning agent in the electronic industry, a non-toxic propellant in aerosol cans, a refrigerant and is a blowing agent in producing Styrofoam and other plastics. However, CFCs account for 80% of ozone depletion so if we don't act soon, our children and grandchildren will have to pay the price. USA: And who's going to pay the price if we abide to this Montreal Protocol you are suggesting?

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    Analysis of Two Brands of Commercial Bleaches

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    Trial 1 2 Final burette reading / cm3 11.90 23.40 35.00 Initial burette reading / cm3 0.20 11.90 23.40 Volume of Na2S2O3 / cm3 11.70 11.50 11.60 Brand 2 Trade Name : LION Price : $6.67per dm3 ($10/1500mL) Trial 1 2 Final burette reading / cm3 14.60 28.70 42.80 Initial burette reading / cm3 0.50 14.60 28.70 Volume of Na2S2O3 / cm3 14.10 14.10 14.10 Questions 1. For each brand, calculate (a) the amount of the active ingredient available in g dm-3.

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    The Development of the Periodic Table of the Elements

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    An advantage of Lavoisier's work is that he distinguished between metals and non-metals but a disadvantage was that he included some compounds and mixtures as elements and substances that were neither, for example light and heat (which he called "caloric"). Nevertheless, this was recognised by the scientific community as a step forward in chemistry - he earned himself the nickname "the father of modern chemistry". Ultimately, his work marked the beginning of categorising the elements, which would prove incredibly useful later on.

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    Acid-Base titration by double indicator method

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    At the end point ,the yellow colour of the methyl orange changed to orange. 10. The reading of that further quantity of acid (y) was recorded. 11. The steps above were repeated 3 times. Results: Volume of piptte used: 25 cm3 The concentration of the hydrochloric acid used: 0.098M x Trial 1 2 3 Final burette reading / cm3 12.40 31.80 29.40 12.70 Initial burette reading / cm3 0.10 19.50 17.20 0.30 Volume of acid used(x)

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    Redox titration

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    + 5Fe 2+ (aq) +8H+(aq) --> Mn2+(aq) +5Fe3+(aq)+4H2O(l) Between the titration of potassium manganate (VII) solution and ammonium iron (II) sulphate solution, The molarity of ammonium iron (II) Apparatus: Safety spectacles 25cm3 pipette Pipette filler 4 conical flasks 50cm3 burette Small funnel White tile Wash-bottle of distilled water Materials Solution A: ammonium Iron(II) sulphate solution 1M dilute sulphuric acid Solution B: potassium manganate (VII) Procedures: 1. The burette was filled with potassium manganate (VII) solution B 2. 25 cm3of the ammonium iron (II)

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    Enthalpy of formation of calcium carbonate

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    and at temperature of 25 oC (298 K).Moreover, the solution should have unit activity(1mol dm-3 ). 3. Write the equation for the formation of calcium carbonate under standard conditions. (Call this Equation 1) Ca(s) + C(s) + 3/2 O2(g) --> CaCO3(s) 4. Write an ionic equation for the reaction taken place. (Call this Equation 2) Ca(s) + 2H+(aq.) ? Ca2+(aq.) + H2(g) 5. Assuming (a) the solution in the plastic beaker has the same specific heat capacity as water, i.e., 4.2 kJg-1K-1 and (b)

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  20. Peer reviewed

    dDetermination of the partition coefficient of ethanoic acid between water and butan-2-ol.

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    For each experiment, the ratio of the concentration of ethanoic acid in the aqueous layer to that in the butan-2-ol layer was calculated. Result Room temperature: 29? Volume of butan-2-ol: 15 cm3 Volume of 0.2M ethanoic acid / cm3 Volume of 0.1M NaOH titre for aqueous layer / cm3 Volume of 0.1M NaOH titre for alcohol layer / cm3 Partition coefficient K= 15 10.00 12.55 0.796 25 12.10 15.60 0.776 Conclusion The partition coefficient of ethanoic acid between water and butan-2-ol is : = =0.786 Discussion 1.

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  21. Peer reviewed

    Nuclear Fusion as energy provider

    4 star(s)

    Radioactive decay is a passive action, while fission is active. For radioactive decay, the atom is unstable; while the nuclei in the process of fission absorb a neutron, then oscillate to become unstable. Moreover, the product of radioactive decay is only an atom of other element; while the products of fission are 3 neutrons and 2 different elements. Hydrogen and helium are by far the most abundant element, which is 89% and 11% respectively [1]. The process of making the simple elements (like lithium, etc.) is called nucleogenesis. Hydrogen acts as a producer, which is the start of the nucleogenesis.

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    Titration Lab Report

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    On each of the four printed graphs, draw a horizontal line from a pH value of 9 on the vertical axis to its intersection with the titration curve. In which trial(s) does this line intersect the nearly vertical region of the curve? In which trial(s) does this line miss the nearly vertical region of the curve? For Trials 1 and 3, the horizontal line from pH 9 intersects the S curve. For Trials 2 and 4, because the equivalence point is lower than pH9, they nearly miss the vertical region of the curve.

    • Word count: 1095
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    History of table of Elements

    4 star(s)

    Astonishingly his predictions were later found true. Before Dmitri Mendeleev, a French noble prominent named Antoine-Laurent de Lavoisier had made a similar type of table. In 1789 he had grouped 33 elements into gases, metals, non-metals, and earths. Although this was a great leap in chemistry it wasn't the best. Over the years chemists looked for more precise methods of classifications. In 1829, Johann Wolfgang Dobereiner discovered that most of the elements could be grouped in triads. He had observed that when being arranged by atomic number the second element was the average of the first and third.

    • Word count: 894
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    risks of electricity

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    LEGAL DUTIES AND OBLIGATIONS AROUND ELECTRICITY As well as a moral duty on employers to protect employees and members of the public, General Health and Safety Legislation covers all employers and workplaces. In addition, specific duties and obligations are laid out in the following regulations: These regulations apply to all aspects of the use of electricity within the workplace from electrical supplies to the use of electrical equipment. They place a duty on employers, employees and the self-employed to: * have the electrical systems constructed in a way that prevents danger * maintain their electrical systems as necessary to prevent danger * have work on, use of, or closure of, electrical systems carried out in a way that prevents danger.

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    Scientists and Theories of Atomic Structure

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    He also said that these indivisible pieces (atoms) were infinite ? always moving and capable of moving together. However his theory was not widely accepted and forgotten about for over the next 2000 years. Later in the early 1800s an English chemist named John Dalton performed experiments which led to the acceptance of the ideas of atoms. Dalton?s theory consisted of 5 main points, he deduced that: 1. All Elements are composed of extremely small particles called atoms. 2. Atoms are indivisible and indestructible particles, which was along the lines of what Democritus had said but it was developed further.

    • Word count: 1463

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