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AS Chemistry Revision Module 1 ( Module F331 – “ Chemistry of Life ” ) Practice Questions and worked answers on particular skills Name: _______________________ 1] Ar, Mr, Moles and Avogadro Ar = Atomic mass (also known as Relative Atomic Mass/ RAM ) Remember: this is the mass of an atom of a particular element compared with / relative to the mass of an atom of carbon-12. This number is different for each element and you get it straight from the periodic table box (it’s the bigger of the 2 numbers). No units of measurement. Mr = Molecular mass (aka .. “Relative Molecular Mass/ RMM / Relative Formula Mass) Remember: this is the sum of the Ar’s of all the elements in a compound. No units of measurement. Mole = amount of a substance with 6.02 x 10 23 (Avogadro’s number) particles in it. 23 eg/ 1 mole of fluffy pillows = 6.02 x 10 fluffy pillows. The mass of 1 mole of a substance is the same as its Mr (in grams). u Calculating number of moles of substance in a give mass You can just use the equation above without any rearrangement. This type of question is only worth 1 mark on module 1 exams, and is nearly always part of a larger question. Questions to try - on calculating number of moles of substance in given mass: 1] How many moles in each of the following: a) b) c) d) e) 4.5g of water (H2O) ? 0.9g of glucose (C6H12O6) ? 3.2g of copper sulphate (CuSO4) ? 0.135g of water ? 25g of Calcium carbonate (CaCO3) ? 2 u Calculating mass when you know the number of moles: Re-arrange the equation to give you the unknown on its own: Questions to try - on calculating mass given the number of moles: 2] What is the mass of : a) 0.1moles of sulphuric acid (H2SO4) ? b) 0.3moles of copper nitrate ( Cu(NO3)2 ) ? c) 1.5 moles of ethanoic acid ( CH3COOH ) ? d) 0.01moles of glucose ( C6H12O6 ) ? u Balancing & Writing Equations: Questions to try - on balancing equations: 3] Balance the following: a) b) c) d) e) Al + Cr2O3 g Al2O3 + Cr Fe2O3 + CO g Fe + CO2 Mg + N2 g Mg3N2 Fe + H2O g Fe3O4 + H2 C6H14 + O2 g CO2 + H2O 4] Write balanced symbol equations for the following: a) Hydrogen + Copper oxide g Copper + Water b) Propane + Oxygen g Carbon dioxide + Water c) Magnesium + Sulphuric acid g Magnesium sulphate + Hydrogen 3 u Reacting Masses: You can predict how much of a substance will be made by a chemical reaction with very little information. As long as you know the mass of one of the reactants and the balanced equation, you’re away………. Worked example: CaCO3 + 2HCl g CaCl2 + H2O + CO2 Calculate the mass of carbon dioxide that would be formed if 2.5g of calcium carbonate reacted completely with hydrochloric acid ? Questions to try - on reacting masses: 5] CH4 + 2O2 g CO2 + 2H2O a) From the equation, how many moles of CO2 are produced when 1 mole of methane is combusted ? b) What is the mass of 1 mole of methane ? c) How many moles of methane are there in 1.0g of methane ? d) What mass of carbon dioxide would be produced if 1.0g of methane were burnt ? e) What mass of water would be formed if 2.0g of methane were combusted ? f) What mass of methane would have to be burnt to produce 10.0g of carbon dioxide? 4 6] Sodium hydroxide neutralises hydrochloric acid : NaOH (aq) + HCl (aq) g NaCl (aq) + H2O (aq) a) It takes 4g of NaOH to neutralise all the HCl. How many moles of NaOH are there in 4g of it ? b) How many moles of NaOH does it take to neutralise 1 mole of HCl ? (from the equation) c) What mass of HCl was neutralised by 4g of NaOH ? 7] Chlorine reacts with Sodium Bromide, displacing it. Cl2 (aq) + 2NaBr (aq) g 2NaCl (aq) + Br2 (aq) What mass of Br2 is formed when 14.2g of Cl2 reacts ? 8] Nitroglycerine is used as an explosive. The very quick production of gases in a confined space is the cause of an explosion. This equation shows how it reacts : 4C3H5(NO3)3 (l) g 12CO2 (g) + 10H2O (l) + 6N2 (g) + O2 (g) a) What mass of Nitrogen would be produced if 100g of nitroglycerine breaksdown ? b) What mass of Water would be produced if 50g of nitroglycerine broke down ? 9] Aspirin, C9H8O4 , is made by the reaction: Salicylic acid + Ethanoic anhydride g Aspirin + Ethanoic acid C7H6O3 + C4H6O3 g C9H8O4 + C2H4O2 How many grams of salicylic acid are needed to make one aspirin tablet, which contains 0.33g of aspirin ? 10] Nitrogen Monoxide (NO) is a pollutant gas which comes out of vehicle exhausts. One technique for reducing the quantity of nitrogen monoxide in exhaust fumes is to inject a stream of ammonia (NH3). This converts NO to harmless products – nitrogen and water. 4NH3 (g) + 6NO (g) g 5N2 (g) + 6H2O (l) An average vehicle emits 5g of nitrogen monoxide per mile. Assuming a mileage of 10,000 miles per year, what mass of ammonia would be needed to clean up the exhaust fumes (in kilograms per year) ? 5 u Different types of formulae: There are a number of different ways of showing the formula of a compound. Questions to try - on formulae: 11] Give the structural and skeletal formulae of the following: a) Propane (C3H8) ? b) Pentanol (C5H11OH) ? c) But-2-ene (C4H8) ? d) CH3(CH2)3CH2OCH2CH3 ? What homologous series is this part of ? e) CH3 CH2 CH2 CH2 CHOHCH2CH3 ? Name this. f) CH3 CH(CH3) CH2 CH2 CH3 ? g) Heptan-2,2,3-triol ? 6 u Working out the EMPIRICAL formula of a compound from experimental results: You can work out the empirical formula of a compound if you know the relative amounts of each element in it. These element figures are usually found out by experiment – where the compound is blasted apart ! Worked example: What is the empirical formula of a compound, given that it contains 77.7% Fe and 22.3% O ? Questions to try - on empirical formula: 12] Calculate the empirical formula of the following: a) A compound contains: C (54.5%), H (9.10%) and O (36.4%) ? b) A compound contains: Ni (37.9%), S (20.7%) and O (41.4%) ? c) A compound contains: C (18.24%), H (0.76%) and Cl (81.00%) ? 7 u Isotopes & their Average Mass Isotope = Same number of protons, different number of neutrons. Questions to try - on isotopes: 13] a) Calculate the average atomic mass of the following elements: (i) Gallium has common isotopes: Ga-69 (60.2%) and Ga-71 (39.8%). (ii) Magnesium has 3 common isotopes : Mg-24 (78.6%), Mg-25 (10.1%) and Mg-26 (11.3%). b) Use the information displayed in the chart to calculate the average atomic mass of Germanium ? c) 8 u Radioactive Decay 3 types of decay : alpha, beta and gamma. Questions to try - on radioactive decay: 14] Copy and complete the following: 9 u Light Reactions There are 2 equations that you need to know: [For all Qs: speed of light = 3x108 m/s and Planck’s constant = 6.63x10-34 j/Hz ] Questions to try - on light: 15] a) What is the wavelength of light with a frequency of 500 Hz ? b) What is the wavelength of light which has an energy of 210 joules ? c) Xrays have a frequency of 7.02x1015 Hz. What is the energy of a photon of this radiation ? u Bond enthalpy calculations: You will need this data to help you (all are measured in Kj/mol) : [ It’s always worth drawing out the structural formula of the compounds to help you determine the number of each type of bond !] Questions to try - on bond enthalpy: 16] Calculate the enthalpy change for each of the following reactions using bond enthalpy data (note: O=O is 798 kj/mol and Br-Br is 183 kj/mol) a) C2H4 + HBr g C2H5Br b) CH2=CH-CH3 + Br2 g CH2BrCHBrCH3 c) C6H13OH + 9.5O2 g 6CO2 + 7H2O 10 Answers to MODULE 1 practice Qs – skills 11 12 13 14 15 16 17 18 19 20 21