Allotropes (Diamond and Graphite) Revision Pack (C3)

Transcription

1 Allotropes: Allotropes are different forms of the same element in the same physical state; the atoms are bonded differently. Carbon has allotropes: - Diamond - Graphite - Buckminsterfullerene Diamond Properties vs. Graphite Properties: Diamond - Colourless and Transparent - Very Hard - Very High Melting Point - Does NOT conduct electricity - Lustrous with a brilliant shine Graphite - Black and opaque - Soft and Slippery - High Melting Point - Conducts Electricity - Lustrous They are both made of ONLY carbon, yet they have very different properties... Structure of Diamond: Each carbon atom in diamond is held in place by four strong covalent bonds. These bonds require significant amounts of energy to break. This means that they have a high melting point of 3750 o C. Diamond has NO FREE ELECTONS so cannot conduct electricity. Structure of Graphite: The carbon atoms in graphite are arranged in layers; within each layer there are strong covalent bonds this means that it has a high melting point. Between layers there are much weaker forces this means that they are soft and slippery and can slide over each other; this is what allows us to write with a pencil. Between the layers the electrons are delocalised (they can moved freely and gain a charge) meaning that they can conduct electricity. PPQ(1): Page 1 of 70

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8 Batch Process: In a Batch Process, reactants put in one end and product removed at the other end. Advantages of a batch process include: - The product is made on demand and on a small scale; fixed amount - Can be used to make a variety of products as and when they are needed - Can be stored until needed - Easy to change product from one to another Disadvantages of Batch Process include: - They are labour intensive; reactors need to be filled, emptied and cleaned - Due to the fact that it is labour intensive, it will have a high cost per tonne - Time is needed to clean and change production line; time = money Examples of Batch Processes include the making of drugs and the making of bread in family bakeries. Continuous Process: A continuous process is one in which reactants are fed in one end and a constant stream of products exists form the other. Advantages of a Continuous Process include: - It runs 24 hours a day and is only shut down for maintenance of equipment or deep clean - High level of automation so few staff are needed, making it cheaper per tonne of product. - Takes less energy to maintain, as long as the process can be kept running Disadvantages of Continuous Process include: - High set up costs of factories or chemical plants or factories - Is NOT efficient if not used constantly Examples of Continuous Processes include the mass making of daily essentials like bread as well as for well-understood chemical reactions like the Haber process. New Drugs: Page 8 of 70

9 New drugs have often been extracted from plants and other natural products: - The plants are crushed to disrupt the cell walls to release the desired product - Then they are boiled in a suitable solvent to dissolve compounds - Finally, chromatography is used to identify each individual compound Sometimes scientists just change an old drug slightly instead of making new drugs. Chromatography can help check for the presence of other substances, it allows for separation so we can visually see different compounds in the gel. Drug Development: Drug Development is very expensive because: - Research and testing takes a long time - There are a lot of labour costs; experts must be employed to do research - Raw materials are often rare and therefore expensive - Raw materials from plants are very hard to extract - Long-term testing must take place on humans to identify any side effects - Legislative demands; must be shown to be effective and not harmful Sharing Information: Scientists publish findings about new drugs to allow other scientists to test their findings and see if they get the same results. They also publish their results to allow doctors and pharmacists to know about the drug. They may also share their results to show that their drug is safe and to give other scientists a chance to develop it further. PPQ(1): Page 9 of 70

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19 Formulae: E = m x c x T Energy supplied (J) = Mass of water (g) x Specific Heat Capacity of water (4.2J/g/ o C) x Change in Temperature ( o C) Fuel Efficiency (J/g) = Energy Supplied (J) Mass of Fuel Burnt (g) The Test: There is one acceptable test that OCR looks for when asking a question about investigating liquid fuels. (Left) You MUST be able to draw this in an exam and explain how to keep it a fair test. For a fair test: - Same volume of water - Same calorimeter (copper can) - Same heating time For the actual test, measure out a specified volume of water (e.g. 100cm 3 ). You would then burn the fuel under the calorimeter for a specified time (e.g. 5 mins). After this you would record the temperature change. You would repeat the experiment with a variety of fuels to see which supply the most energy for this to work, the same amount of water must be used. PPQ(1): Page 19 of 70

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31 Magnesium Gets Hot Hydrochloric Acid Heat given out; reactant lose energy Energy Level Diagram for Exothermic Reactions: In an exothermic reaction, the reactants start with a lot of energy but lose this during the reaction as heat to the surroundings. The products have a lot less energy than the reactants. Endothermic Reactions: Heat taken in; reactants gain energy Water Gets Cooler 25 o C Ammonium Nitrate 20 o C Energy Level Diagram for Exothermic Reactions: Page 31 of 70

32 The reactants start with a low amount of energy but then gain a lot of energy from the surroundings. The products have more energy than the reactants. POINTS TO NOTE: - In exothermic reactions atom bonds are made - In endothermic reactions atom bonds are broken - For a reaction to be overall exothermic more bonds have to be formed than broken. - For a reaction to be endothermic more bonds have to broken than formed. In an exam NEVER state that more/less bonds are made/broken!!!! USE the following: In an exothermic reaction, more energy is needed to make the bonds than to break the bonds (or vice-versa). PPQ(1): Page 32 of 70

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35 PPQ(2): PPQ(3): PPQ(4): Mr or Relative Formula Mass: The relative formula mass (Mr) of a compound is the relative atomic masses of all the elements in the compound added together. H2O: Page 35 of 70

36 Therefore, the Mr for water is 16 + (2x1) = 18 How to find the relative atomic mass of an element: 16 8 O STEP 1: Find the element in the Periodic Table STEP 2: Look for the larger of the two numbers STEP 3: Refer to the given formulae and check how many of each element is being asked for; e.g. Carbon Dioxide has two Oxygen atoms so you need 2 x 16 = 32 Conservation of Mass in a Reaction: In any reaction the total mass of products is the same as the total mass of the reactants. Total mass of REACTANTS = Total mass of PRODUCTS A good example would be magnesium oxide and hydrochloric acid reacting: O Mg + H H Cl Cl Cl Mg Cl + H O H Here (on BOTH sides) there are: 1x Magnesium 1x Oxygen Page 36 of 70

37 2x Hydrogen 2x Chlorine This means that the mass will be the same on both sides. Calculating Mass: There are four simple steps to follow when asked to calculate the mass: STEP 1: Identify what the question is asking you, which of the compounds do you need to work out the mass? STEP 2: Put a cross through any compounds that you don t require in your calculation. STEP 3: Work out the Mr of the given compounds (that you NEED) STEP 4: Work out the ratios and apply this to the question Example: What mass of magnesium oxide is produced when 60g of magnesium is burned in air? 2Mg + O2 2MgO 24 Mg 12 PPQ(1): 16 8 O 2Mg = 2 x 24 = 48 2MgO = 2 x ( ) = 80 This means that 48g of 2Mg makes 80g of 2MgO We want 60g of 2Mg so, we do 80/48 = 1.66g x 60 =100g Therefore, 60g of 2Mg makes 100g of 2MgO Page 37 of 70

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41 PPQ2: PPQ(3): Percentage Yield: Percentage yield is a way of comparing amount of product made (actual yield) to amount expected (predicted yield). You want a high percentage yield so that no reactants are wasted. Percentage Yield = Actual Yield x 100 Predicted Yield - 100% Yield means that no product has been lost - 0% Yield means that all of the product has been lost Reasons for not getting expected mass: - Loss when filtering - Loss when transferring liquids - Loss when evaporating - Not all the reactant was made into a product Atom Economy: Page 41 of 70

42 The atom economy of a chemical reaction is a measure of the amount of starting materials that become useful products. Inefficient, wasteful processes have low atom economies; atoms are wasted not made into useful products.. Efficient processes have high atom economies, and are important for sustainable development, as they use fewer natural resources and create less waste. A high atom economy also means that there are less unwanted products made. BASIC SUMMARY: Atom economy is a way of measuring the amount of atoms that are wasted when manufacturing a chemical Atom Economy = Mr of desired product x 100 Sum of Mr of all products - 100% atom economy means that all of the reactant was converted into the desired product - 0% atom economy means that all of the product has been lost PPQ(1): Page 42 of 70

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56 PPQ(7): Rate of Reaction: Concentration: Rate of reaction can be increase by increasing the concentration As the concentration increases the particles become more crowded. This will increase the number of successful collisions between the reacting particles per second More collision per second means more successful collisions This will result in an increased rate of reaction Rate of Reaction: Temperature: Page 56 of 70

57 As the temperature increases the particles gain KINETIC ENERGY (move more) and move around more quickly Therefore particles will collide more frequently with more energy resulting in more collisions per second and therefore more successful collisions resulting in increased rate of reaction Rate of Reaction: Surface Area: As the surface area increases, the particles are more exposed, as such, more collisions are possible This increases the rate of reaction because more particles are available to react increased availability = quicker rate of reaction Rates of Reaction: GAS: You can only increase the pressure if the reactants are gases The reacting particles are squished together. This increases collisions frequency per second which means increased number of successful collisions and therefore increased rate of reaction To Calculate Rate of Reaction: calculate the gradient of a select part of a graph y divided by x A limiting reactant is the reactant not is excess; it is the first reactant be used up and limits the continuation of the chemical reaction. Past Paper Questions: PPQ(1) Page 57 of 70

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67 a) 11 minutes (accept 10minutes 30 seconds to 11 minutes 30seconds) Bi) 15/4 = 3.75 cm 3 per minute Or 15/ 240 = cm 3 per second cii) 7/4 = 1.75 cm 3 per minute Or 7/240 = cm 3 per second The rate during the first four minutes of the reaction are over twice as fast as the second 4 minutes. c) any 6 from the following: temperature: Increasing the temperature raises the kinetic energy of the particles. Increasing the kinetic energy causes the particles to move faster. Moving faster increases the frequency of collisions. Increasing kinetic energy increases the number of collisions with the activation energy. Increasing the number of collisions in a certain time increases the rate of reaction. Concentration Increasing the concentration of the acid increases the number of particles in a given volume. Increasing the number of particles increases the frequency of collisions Increasing the number of collisions in a certain time increases the rate of reaction. Page 67 of 70

68 Surface area Using a powder will increase the surface area. Increasing the surface area increasing the frequency of a favourable collision Increasing the chance of a collision will increase the rate of reaction. PPQ(2): PPQ(3): Page 68 of 70

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