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Important points physics. chemistry and mathematics


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A document on the main points that cause confusion in Physics, Chemistry and Mathematics

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Important points physics. chemistry and mathematics

  1. 1. Important PointsChemistryUnit 1 • Salt preparation: o For example, the reaction between Copper(II)Carbonate(Cu2SO4) and Sulphuric acid • Observations of alkali metals: o Lithium  Gas given off  Fizzing/effervescence  Floats on top of the water o Sodium  Gas given off  Melts into a ball  Floats on water  Fizzing/effervescence o Potassium  Gas given off  Very fast reaction, in comparison to the other 2  Purple/lilac flame given off  Morphs into a ball  Floats on top of the water • When carrying out an enthalpy reaction which involved an exothermic reaction that releases heat, we take a series of temperatures. This is because: o Any fluctuations in temperature smoothed out o Able to allow for cooling effect • Poly(propene) does not have a sharp boiling point because poly could mean different chain lengths.Unit 2 • Indicators o Litmus  Red in Acid  Green in neutral  Blue in Alkali  Range of pH 5 to 8  Link o Phenolphthalein  Pink in Alkali  Colourless in acid or near neutral  Range of pH 8.3 to 10.0  Link
  2. 2. o Methyl Orange  Alkali or neutral is Yellow  Acid begins from Orange and works its way up to red  Range of pH 3.1-4.4  Link o Universal Indicator  It is a combination of many different reagents, which include Methyl Orange and Phenolphthalein. pH Description Colour 0-3 Strong acid Red 3-6 Acid Orange/Yellow 7 Neutral Green 8-11 Base Blue 11-14 Strong Base Purple o From what we can see Litmus is an indicator for determining whether it is an acid or base o Phenolphthalein can be used to judge the strength of an alkali o Methyl orange can be used to see the strength of an acid• Homolytic and Heterolytic bond fission o Homolytic is when a bond is cleaved, and each atom gets an electron o Heterolytic is when a bond is cleaved, and one atom gets on electron and the other does not get any.• Reactions of Halogenoalkanes o Substitution  Happens when KOH/NaOH is dissolved in H2O  Also, dilute KOH and NaOH Both happen o Elimination under reflux.  Happens when KOH/NaOH is dissolved in Alcohol  Also concentrated KOH and NaOH o Reaction with Ammonia  This is a special case, because this happens in a sealed tube, as if it were to happen under reflux, then NH3 would leave the condenser as it simply does not condense.• Frequently asked bond angles o FBF  120o o NHN  107o o HOH  104.5o• Molecules with H-Bonding o Molecules with N-H bonds, such as NH3 o Molecules with O-H bonds, such as H2O and C2H5OH
  3. 3.  But Hydrogen bonding in H2O is stronger than in Ethanol, because the hydrogen bonding is limited by the fact that there is only one hydrogen in each ethanol molecule with sufficient δ+ charge, whereas, in water, there are 2 hydrogen with δ+ charge, thus allowing more bonds to be formed. o Molecules with H-F, such as HF The Maxwell-Boltzmann distribution diagram Fewer molecules will have the activation energy, because there is less kinetic energy due to a lower temperature. 500oC At lower oC, the curve will shift to the right.• Iodine and Sodium Thio-sulphate titrations o The indicator used to find the end point of the titration is Starch.• Balancing Ionic Equations and Overall Equations o When doing this, only certain particles can be added -  Electrons (e )  Water Molecules (H2O) +  Protons, or Hydrogen ions (H ) -  When balancing alkaline reactions, OH ions can be added o You first have to balance the electrons, by multiplying one side by two different integers o Then cancel the H+ ions and H2O on both sides o Then the equations should be balanced• The boiling point of substances o It all depends on the intermolecular forces o In a question, when the only variable is the chain-length, then the longest un- branched chain will have the highest boiling point. o If there is a functional group, such as –OH, then this will be the choice, as normally in organic molecules without special functional groups, there are only London forces. But in alcohols, there are also dipole forces.
  4. 4. o A typical example:The correct answer is D. Because it has –OH and also, the alcohol is primary. In secondary alcohols,the –OH is cluttered by hydrogen atoms, thus the intermolecular bonding is less effect than in D.Unit 3 • Enthalpy Change reactions (EDEXCEL_JUN_09_3B_2) o If, in a reaction, a metal is involved, often the mass of the metal is not taken into consideration when measuring the enthalpy change, because the specific heat capacity of the metal is negligible. o The reason why the experiment is continuously stirred is to spread out the temperature more uniformly, also to make sure that all the reactants have reacted. o The greater the enthalpy change, the greater the difference in reactivity between the reactants(c). • The way to distinguish halides using sulphuric acid o A chloride, such as Lithium Chloride would give out white/steamy fumes. o A bromide, such as Sodium Bromide would give out brown/orange vapour or liquid. o An Iodide, such as Potassium Iodide would give a purple vapour / dark solid or liquid or residue.
  5. 5. PhysicsUnit 1 • The point beyond the elastic limit is called the yield point, here there is a large increase in strain for a small increase in stress, meaning that for a small force there is a large extension. Adobe Acrobat Figure 1: Properties of Materials Stress-Strain graph Document • Streamlined flow or laminar flow is flow that has no abrupt change in direction or speed of low, usually this occurs at low speeds. Streamlines do not mix. • Turbulent flow is flow in which there is abrupt change in speed and direction and thus causes the formation of eddies. Comment [R1]: In fluid dynamics, an eddy is t swirling of a fluid and the reverse current created when the fluid flows past an obstacle.
  6. 6. • The major difference between ductile and malleable is that the forces of attraction in malleable materials are weak and thus they can be moulded into shape. But, in ductile materials, the material has empty spaces between the particles in the materials. So ductile materials can be stretched into lines. • Tough materials are those that absorb a lot of energy before breaking. But hard materials cannot, they cannot absorb energy much, but they can withstand large impact forces, i.e. they are hard to scratch or indent. • A strong material is a material that requires a large stress to break it. • A hard material is a material with high breaking stress, ������������������������������������������������ ������������ ������������������������������ℎ meaning that a lot of energy is required to break it. ������������������������������������������������ ������������������������������ℎ • Compressive strain: ������������������������������������������������������������������ ������������������������������ ������������������������ ������������ ������������������������������−������������������������������������������ • Compressive Stress: Adobe Acrobat Document Figure 2: PH01_0906_14-15_Worked • Often, a data logger is used, because it can accurately record large amounts of data in real time, so it is easier to process, and reduces the chances of human error.Unit 2 • A source of light emits a train of waves lasting 0.04 μs. The light has a wavelength of 600 nm and the speed of light is 3×108 ms-1. How many complete waves are sent out? A. 2.0 × 107 B. 4.5 × 107 C. 2.0 × 1010 We need to keep in mind the values of ������ and n, ������=10-6 and n=10-9 D. 4.5 × 1010 The total length for the ray of light is 0.04 × 10−6 × 3 × 108 = 12������ o ∴ ������������������ℎ ������������������������ ������������������������������ 600 × 10−9 ∴ 12 ÷ 600 × 10−9 = 2.0 × 107 o o
  7. 7. o The single resistor will have 2X the current. o Therefore, as P=I2R, current will be made four times, and therefore quadrupled. o This is in comparison to one of the two resistors, not both of them. o Thus, the first will have 4 times than one at the bottom as 2 is squared.How much electrical energy is required to move 4.00 mC of charge through a potentialdifference of 36.0 V? A. 1.11 × 10-4 J B. 0.144 J C. 144 J D. 9000 J Remember that ������ = ������������������������������������(������������������������������������,������) ������ℎ������������������������(������������������������������������������������,������) • • NTC resistors decrease their resistance as the temperature increases • As the voltage increases, so does the temperature of the NTC resistor • As we can see that the curve becomes steeper, so for a larger value of V, there is a greater Thus, the answer is B. Because ������ = ������ increase In I than R, which is the gradient ������ • • Another interesting question is Question 8_SAM_GCE_UNIT2
  8. 8. , ������������ 1�8 ������ℎ, ������������ ������ ������������������������������������������������ ������������������������ ℎ������������ ������ ������ℎ������������������ ������������ 2������ ������ 4 So, 0.5 × 8 = 4, ������������ ������ℎ������ ������������������������������������������������������ℎ• This as ������ = ������������, ������ = 10 × 4 = 40 ������������ −1••• The rate at which electrons are liberated due to the photoelectric effect, from a metal surface is depends on the distance between the source of light and the metal surface. Thus, the number of photoelectrons emitted only depends on the intensity, not the frequency.• UV light only transfers energy to the metal surface, not electrons, so on a positively charged metal surface, on an electroscope, it would have no effect.•• The difference between sound waves and radio waves: Radio Waves Sound waves1. Transverse 1. Longitudinal2. Travels through Vacuum 2. Travels through medium3. Much faster than sound 3. Much slower than radio4. Infinite range of frequencies 4. Frequencies between 20Hz-20KHz
  9. 9. This question is taken from Edexcel June 2009 Physics paper2. Section A question 2. have a speed of 3 × 108 .• The higher the frequency, the lower the wavelength, because all electromagnetic waves• As ������ = ������������, i.e. ������������������������������������������������ = ������������������������������������������������������ × ������������������������ − ������������������������������ℎ
  10. 10. Unit 3 This Value is the mode, and the other value, thus has a chance of being an error.The equipment used is not has errors. The piece of equipment most probably used is a micrometerwhich has a percentage error. The actual reading is too far away from the ones obtained, so not C. Dis also not the answer because the actual reading is to one decimal place as well. It is not A, becausethe students recordings are very close to each other, and therefore we may presume that he/she hasmade very few mistakes. Thus leaving B, as the most logical conclusion.
  11. 11. Business StudiesTechnique • Whenever reading through a case study, try to understand the motives of the business, and evaluate the position from their point of view. • When answering a context in Edexcel, these are the guidelines that you have to follow: o Knowledge, most of the time, this is a definition o Application o Analysis, this is where you analyse the data o For higher marked questions, there will be an evaluation. • This is an example of the shorter questions: • Examine one way in which Innocent Drinks achieved a competitive advantage.SAM 9(b) [6] • Competitive advantage is any feature of a business that allows it to compete effectively. In Comment [R2]: Knowledge. Here we have defined what Competitive advantage means. this case, the endorsement by Coffee Republic, by stocking their goods. As Coffee Republic is Comment [R3]: Application of your knowledge an established brand, having many stores, this would mean that more people will have a chance to try out the product, so it would raise consumer awareness. Furthermore, as a Comment [R4]: Analysis1, the advantages of having Coffee Republic help you out. brand has endorsed ID, that in itself is an as now a brand image is attached to their name. Comment [R5]: Analysis2Answering MCQs in both Unit 1 and Unit 2From Edexcel Business Studies June 2009 Unit 26. Chocolate maker Green & Black’s objective is to increase profit. Comment [R6]: Key term(a)Which one of the following is most likely to be the best tactic? [1] Comment [R7]: Key term(b)Explain why your answer is correct? [3] • The first mark would be a mark for knowledge, so the definition of either tactic or profit would be acceptable, as they are key terms in the question. So, thus would be the knowledge mark • The second mark would be an explanation as to why you chose D, thus showing your understanding, a third mark could also be scored out of this • However, easier way of getting a mark is to explain why the other options are wrong, so for example why would ceasing advertising be the wrong thing to do. • But, there is a fundamental mark for why you chose your option. The other two marks are optional marks, they can be gained from further explaining your choice or the application of your knowledge
  12. 12. Unit 1 • Competitive advantage: Any feature of the business that enables it to compete effectively. It may be based on price, quality, service, reputation for innovation of the product. • Also, in Dave Hall defined as an advantage which allows the business to perform better than its rivals. • The difference between Unique Selling Point and Competitive advantage is that a unique selling point may provide a competitive advantage, meaning that it is a feature that may give the business a competitive advantage. So, it is a PART of competitive advantage. Or, a feature of the business that may provide a competitive advantage. • Usually the term USP is referred to niche markets and Competitive advantage to mass markets.
  13. 13. S1 Coding • Mean o Affected by all, to calculate the actual mean, just equate it back through the coding • Standard Deviation o Just affected by division and multiplication o Just multiply it by the factor you divided by, and vice versa • Product moment correlation ������ = ������ + ������������ o Not affected • o This is affected by all, just equate a and b back through the equation • Variance o Affected by what you have multiplied it by, and nothing else. o If Var(a+bx) o Then the answer would be bM1 Vectors • When something is due south or due north of a point. Adobe Acrobat Document • Whenever calculating the acceleration in Chapter 3 question, always calculate them for the entire body at all times.C3 Trigonometric Identities