A Guide To Quantitative Aspects Of Chemical Change

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESA Guide to Quantitative Aspects ofChemical ChangeTeaching ApproachQuantitative chemistry has considerable importance in the chemistry curricula in the FETCAPS curriculum, since it is a topic that is studied in both Grade 10 and 11 and it is includedin the final Grade 12 chemistry exam. With this in mind it is very important that enough timeis spent on making sure that students understand the concepts and the relationshipsbetween them.The approach that needs to be followed is to make sure that students first understand themeaning of the mole and grasp the size of Avogadro’s number. They need to realise that amole is a measure of the amount (or number) of items. These items may be atoms,molecules or ions. Make sure that learners know the difference between molecular massand molar mass.Secondly they need to understand the four different ways to calculate the number of molesof a substance i.e. making use of the mass, the number of particles, the concentration andthe molar volume.Once these concepts are in place, the focus should change to solving stoichiometriccalculations. Four basic steps need to be followed to solve this type of calculation.The steps are1. Balance the equation.2. Convert the amounts of a given substance to moles.3. Using the mole ratio, calculate the moles of substance yielded by the reaction.4. Convert moles of the required substance back to the desired quantity.The only way to make sure that the concepts discussed in this series is thoroughlyunderstood is by making use of extensive practice.MINDSET LEARN TEACHING RESOURCES – PUBLISHED 20131

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESVideo SummariesSome videos have a ‘PAUSE’ moment, at which point the teacher or learner can choose topause the video and try to answer the question posed or calculate the answer to the problemunder discussion. Once the video starts again, the answer to the question or the rightanswer to the calculation is given.Mindset suggests a number of ways to use the video lessons. These include:Watch or show a lesson as an introduction to a lessonWatch or show a lesson after a lesson, as a summary or as a way of adding in someinteresting real-life applications or practical aspectsDesign a worksheet or set of questions about one video lesson. Then ask learners towatch a video related to the lesson and to complete the worksheet or questions, either ingroups or individuallyWorksheets and questions based on video lessons can be used as short assessments orexercisesAsk learners to watch a particular video lesson for homework (in the school library or onthe website, depending on how the material is available) as preparation for the nextday’s lesson; if desired, learners can be given specific questions to answer inpreparation for the next day’s lesson1. Atomic MassIn this lesson we define mole and look at the difference between relative molecular mass.We also do some calculations.2. The Mole ConceptIn this lesson we will look at how to find the number of particles in a sample of asubstance.3. Mole CalculationsWe discuss the relationship between the number of moles, mass and the molar mass.The second concept is the number of particles in a mole.4. Introducing Empirical Formula and Percentage CompositionAny element and compound known to us has an empirical formula. In this lesson weinvestigate how this formula is calculated from given values, and determined throughexperiments. The percentage composition of compounds is also determined.5. Working with Empirical Formula and Percentage CompositionIn this lesson we do complex examples of questions that involve empirical formula andpercentage composition6. Molar ConcentrationsIn this video we define and calculate the concentration of a solution as the number ofmoles per volume.MINDSET LEARN TEACHING RESOURCES – PUBLISHED 20132

MINDSET LEARN GRADE 10 PHYSICAL SCIENCES7. Molar Volume of GasesThe definition of molar volume is stated as: one mole of gas occupies 22,4 dm 3 at 0 Cand 1 atmosphere. In this lesson we explain the molar volume and do some calculationsto calculate the number of moles under these conditions.8. Introducing Stoichiometric CalculationsIn this lesson we look at how stoichiometric calculations are done by making use of fourbasic steps. We also visit a laboratory where we see the difference between a qualitativeexperiment and a quantitative calculation.9. Exploring Stoichiometric CalculationsIn this lesson we use everything that we studied so far to do some stoichiometriccalculations.MINDSET LEARN TEACHING RESOURCES – PUBLISHED 20133

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESResource Material1. Atomic 94.cw/index.htmlA resource on atomic mass and themole concept.http://en.wikipedia.org/wiki/Mole (unit)An encyclopaedia on mole (unit).2. Mole 30494.cw/index.htmlA resource on atomic mass and themole concept.https://www.youtube.com/watch?v Ik4zE8lXWs8A video on how to Calculate thenumber of moles, given the mass ofa substance.http://chemwiki.ucdavis.edu/Physical Chemistry/Atomic Theory/TheMole and Avogadro's ConstantA resource on mole and nversions and mole nding/empirical.htmEmpirical and ss/majors/tutorialnotefiles/empirical.htmThis page defines empirical formulaand gives step by step instructionson determining an empirical /percentcomp.htmA video demonstration on how tocalculatethepercentagecomposition by .htmA resource on molarity, volumes andthe concentration of ionworksheets.htmlWorksheet about dissolved stuff.http://en.wikipedia.org/wiki/Molar volumeAn encyclopaedia on molar /Unit5MolarVolume.htmThis page provides instructions onhow to do calculations usingstandard molar volume.3. Mole Calculations4. EmpiricalFormulaandPercentage Composition5. Working with EmpiricalFormula and PercentageComposition6. Molar Concentrations7. Molar Volume of GasesMINDSET LEARN TEACHING RESOURCES – PUBLISHED 20134formula

MINDSET LEARN GRADE 10 PHYSICAL SCIENCES8. Introducing StoichiometricCalculations9. rown.info/page04/473calcs09mvg.htmThis page describes and explains,with fully worked out examples, howto calculate the volume of gasformed from given masses ofreactants. You need to know theformula connecting moles, mass andformula mass AND know how to usethe molar volume in these gasvolume calculation itativeaspects-of-chemical-change04.cnxmlplusThis page defines stoichiometry andgives examples of /watch?v 65ogAbpko8IStoichiometric calculations wers/6.answers.htmA worksheet on stoichiometry.MINDSET LEARN TEACHING RESOURCES – PUBLISHED 20135

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESTaskQuestion 1Calculate the relative molecular or formula mass of1.1 ammonium nitrate1.2 aluminium oxide1.3 ethanoic acid, CH3COOHQuestion 2Calculate the molar mass of2.1 Sodium carbonate Na2CO32.2 Hydrated magnesium sulfate MgSO4.7H2O2.3 Calcium phosphateQuestion 33.1 Calculate the number of moles in 7g of nitrogen gas3.2 Calculate the mass of 0,4 moles of water.3.3 Calculate the number of moles in 0,25 kg of Ca(OH)2.Question 44.1 Calculate the number of molecules in 3 g of chlorine gas4.2 Calculate the mass of 3,01 x 1023 molecules of iodineQuestion 513 g of zinc reacts with 6,4 g of sulfur. What is the empirical formula of zinc sulfide?Question 6Determine the empirical formula of a compound that is composed of 36,5% sodium, 25,4%sulfur, and 38,1% oxygen.Question 710,2 g of aluminium oxide is strongly heated in the presence of hydrogen gas until it isreduced to 5,4 g of aluminium metal. Determine the empirical formula of aluminium oxide.Question 8Calculate the percentage composition by mass of nitrogen present in ammonium phosphate.Question 987 g of potassium sulfate makes a solution with a concentration of 0,8 mol dm-3 . What is thevolume of this solution?Question 10VM 22,4 dm3 at S.T.P308 g of CO2 are released into the atmosphere at STP. What volume will the gas occupy?MINDSET LEARN TEACHING RESOURCES – PUBLISHED 20136

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESQuestion 11If 33 g of hydrogen gas is produced when aluminium metal is dissolved in hydrochloric acid,what mass of aluminium was dissolved?Question 12Consider this balanced equation2 NaOH H2SO4 Na2SO4 2 H2O12.1 How much Na2SO4 is formed if 58 g of H2SO4 reacts with an excess of NaOH ?12.2 What mass of Na2SO4 is formed if 62 g of NaOH reacts with an excess of H2SO4?Question 13Determine the volume of oxygen, calculated at STP, which is liberated when 43,4 g mercuryoxide decomposes completely into mercury and oxygen gas.MINDSET LEARN TEACHING RESOURCES – PUBLISHED 20137

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESTask AnswersQuestion 11.1 Mr(NH4NO3) 2x14 4x1 3x16 801.2 Mr(A 2O3) 2x27 3x16 1021.3 Mr(CH3COOH) 2x12 4x1 2x16 60Question 22.1 M(Na2CO3) 2x23 12 3x16-1 106 g·mol2.2 M(MgSO4.7H2O) 24 32 4x16 7(2x1 16)-1 246 g·mol2.3 M(Ca3(PO4)2 3x40 2x31 8x16-1 310 g·molQuestion 33.1mM7n 28n 0,25 moln 3.2mMm n x M 0,4 x 18 7,2 gmn M250n 74n 3,38 moln 3.3Question 44.1n NNAmMNNA371N6, 02 x1023N 2,54 x 1022 molecules of CMINDSET LEARN TEACHING RESOURCES – PUBLISHED 201328

MINDSET LEARN GRADE 10 PHYSICAL SCIENCES4.2n NNAmMNNAm3, 01x10 23254 6, 02 x10 23m 127 g of I 2Question 5Zn13g0,2 mol0,2 / 0,21massn m/MRatioS6,4g0,2 mol0,2 / 0,21Thus the empirical formula is ZnSQuestion 6Na36,5g1,59 mol1,59 / 0,792massn m/MRatioS25,4g0,79 mol0,79 / 0,791O38,1g2,38 mol2,38 / 0,793Thus the empirical formula is Na2SO3Question 7massn m/MRatio(x2)A O5,4g0,2 mol0,2 / 0,21210,2 - 5,4 4,8g0,3 mol0,3 / 0,21,53Thus the empirical formula is A 2O3Question 8M((NH4)3PO4) 3x14 12 x 1 31 4x16-1 149 g·molThe3x14x100149N 28,19N MINDSET LEARN TEACHING RESOURCES – PUBLISHED 20139

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESQuestion 9M(K 2SO 4 )2 x39 32 4 x16174g mol1nVmc MVc 87174V87V (0,8)1740,8V 0,63 dm 3Question 10M(CO2 ) 12 16 x 2 44 g mol 1n mMVVmVVm308V44 22, 4(22, 4)(308)V 44V 156,80 dm3Question 112 Al 6 HCl 2 AlCl3 3 H2mM33n 2n 16,5 mol of hydrogenn 3 to 2 ratio, therefore 11 mol of Al was dissolved.mMm1127m 11x27m 297 g of aluminiumn MINDSET LEARN TEACHING RESOURCES – PUBLISHED 201310

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESQuestion 1212.12 NaOH H2SO4 Na2SO4 2 H2Othe mole ratio 1 mol H2SO4 : 1 mol Na2SO4n mM582 32 4 x16n 0,59 mol of H 2SO 4nNote that the questions asks “How much?” so the answer is a quantity in mol.12.2The mole ratio is 2 mol NaOH : 1 mol Na2SO4n mM6223 16 1n 1,55 mol of NaOHnTherefore 1,55 / 2 0,775 mol will formn mMm2 x 23 32 4 x16m 110,05 g of Na 2SO 40, 775The question asks “What mass?” so the answer is in grams.Question 132HgO(s) 2Hg(s) O2(g)The mole ratio 2mol HgO : 1 mol O2mM43, 4n217n 0,2 mol of HgOn Therefore 0,1 mol of oxygen gas will formn 0,1VVmV22, 4V 2,24 dm3 of O 2MINDSET LEARN TEACHING RESOURCES – PUBLISHED 201311

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESAppendixMINDSET LEARN TEACHING RESOURCES – PUBLISHED 201312

MINDSET LEARN GRADE 10 PHYSICAL SCIENCESAcknowledgementsMindset Learn Executive HeadContent Manager Classroom ResourcesContent Coordinator Classroom ResourcesContent AdministratorContent DeveloperContent ReviewersDylan BusaJenny LamontHelen RobertsonAgness MunthaliIzelle MüllerBruce NoziacLiz HarrisProduced for Mindset Learn by TrafficFacilities CoordinatorProduction ManagerDirectorEditorPresenterStudio CrewGraphicsCezanne ScheepersBelinda RenneyAlriette GibbsNonhlanhla NxumaloNiki MontgomeryAbram TjaleJames TselapediWilson MthembuWayne SandersonCreditsThis resource is licensed under a Attribution-Share Alike 2.5 South Africa licence. When usingthis resource please attribute Mindset as indicated athttp://www.mindset.co.za/creativecommonsMINDSET LEARN TEACHING RESOURCES – PUBLISHED 201313

Chemical Change Teaching Approach Quantitative chemistry has considerable importance in the chemistry curricula in the FET CAPS curriculum, since it is a topic that is studied in both Grade 10 and 11 and it is included in the final Grade 12 chemistry exam. With this in mind it is very important that enough time