chemistry ch2011a teacher-marked assignment measurement and moles student instructions Overview This assignment is designed to give you practice in demonstrating your understanding of the fundamental concepts of chemistry. It is not for NCEA credit, but it will help you to develop your skills, so that you do well in future assessments. Conditions • This is a closed book assessment; you may not refer back to any booklets. • There is no time limit for this assignment, but allow about one hour to finish it. You will need: • a pen or pencil and a calculator. If you do not understand any of these conditions, please phone, fax or email your teacher now. Supervisor requirements You and your supervisor (if applicable) must sign the cover sheet at the back of the assessment to verify that the work is your own. Assessment criteria Not Attempted Did not attempt to complete. Not yet on target for Achieved Did not demonstrate an understanding of simple calculations. On target to Achieved Demonstrated an understanding of simple calculations. On target to Achieved with Merit On target to Achieved with Excellence Demonstrated an in-depth understanding of simple calculations. Demonstrated a comprehensive understanding of simple calculations. For teacher use only © te aho o t e k ur a p o un a m u 2012/2 ch2011a teacher-marked assignment answer all the questions question one Calculate the molar mass for each of the following substances. Show all your working. a. CHCl3 ram values H = 1.0 Li = 6.9 C = 12.0 O = 16.0 P = 31.0 Cl = 35.5 Ca = 40.1 b. Li2CO3 c. Ca3(PO4)2 question two Calculate the molar mass of a compound if 0.372 mole of it has a mass of 152 g. question three How many molecules of ethane (C2H6) are present in 0.334 g of C2H6? M = 30.0 g mol-1. 2 CH2011A © te ah o o te k u ra p ou n a mu ch2011a teacher-marked assignment question four The formula for rust can be represented by Fe2O3 a. How many moles of Fe2O3 are present in 24.6 g of the compound? ram values O = 16.0 Fe = 55.8 b. How many moles of Fe are present in 24.6 g of the compound? question five Allicin is the compound responsible for the characteristic smell of garlic. Its composition by mass is as follows: C: 44.4% H: 6.21% a. Calculate its empirical formula. S: 39.5% O: 9.86% ram values H = 1.0 C = 12.0 O = 16.0 S = 32.1 b. What is the molecular formula, given that its molar mass is about 162 g mol–1? © te ah o o t e k ur a p o un a m u CH2011A 3 ch2011a teacher-marked assignment question six Tin(II) fluoride (SnF2) is often added to toothpaste as an ingredient to prevent tooth decay. a. Calculate the number of moles of fluorine in 24.6 g of the compound. ram values F = 19.0 Sn = 118.7 b. What is the mass of F in grams in 24.6 g of the compound? c. Calculate the percentage of tin in the compound. question seven 4.96 g of hydrated sodium thiosulfate (Na2S2O3.xH2O) were dehydrated and formed 3.16 g of anhydrous salt. Calculate the empirical formula for the hydrated crystals. ram values H= 1.0 O = 16.0 Na = 23.0 S = 32.1 4 CH2011A © te ah o o te k u ra p ou n a mu ch2011a teacher-marked assignment what to do next When you have finished this teacher-marked assignment, please make sure that you have written your name and ID number on the back cover. You can also use a label if you have one on hand. By post: Put the assignment in the plastic envelope provided. Make sure that the address card shows the address for Te Aho o Te Kura Pounamu. Seal the envelope with tape before you post it. Do not include booklets from other subjects with this Science work. By email: Scan the pages including the cover sheet and email to your teacher. The standard format for Te Kura teacher email addresses is: firstname.lastname@tekura.school.nz If you aren’t sure who your teacher is, call 0800 65 99 88. If you do not have your next set of study materials, contact your teacher immediately. If you are not sure what to do next, ask your teacher for advice. © te ah o o t e k ur a p o un a m u CH2011A 5 cover sheet – ch2011a students – place student address label below or write in your details. Full Name ID No. Address (If changed) authentication statement I certify that the assessment work is the original work of the student named above. Signed Signed (Student) (Supervisor) for school use only assessment www.tekura.school.nz Copyright © 2012 Board of Trustees of Te Aho o Te Kura Pounamu, Private Bag 39992, Wellington Mail Centre, Lower Hutt 5045, New Zealand. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means without the written permission of Te Aho o Te Kura Pounamu. chemistry ch2012a teacher-marked assignment calculations in chemistry student instructions Overview This assignment is designed to give you practice in demonstrating your understanding of the fundamental concepts of chemistry. It is not for NCEA credit, but it will help you to develop your skills, so that you do well in future assessments. Conditions •• This is a closed book assessment; you may not refer back to any booklets. •• There is no time limit for this assignment, but allow about one hour to finish it. You will need: •• a pen or pencil and a calculator. If you do not understand any of these conditions, please phone, fax or email your teacher now. Supervisor requirements You and your supervisor (if applicable) must sign the cover sheet at the back of the assessment to verify that the work is your own. Assessment criteria Not Attempted Did not attempt to complete. Not yet on target for Achieved Did not demonstrate an understanding of simple calculations. On target to Achieved Demonstrated an understanding of simple calculations. On target to Achieved with Merit On target to Achieved with Excellence Demonstrated an in-depth understanding of simple calculations. Demonstrated a comprehensive understanding of simple calculations. For teacher use only © te aho o t e k ur a p o un a m u 2012/2 ch2012a teacher-marked assignment answer all the questions NOTE: The ram values are given by the relevant question. NA = 6.02 × 1023 Use the appropriate number of significant figures. Show all your working. question one How many moles of MgSO4 are present in 60.0 mL of a 0.100 mol L-1 solution? question two 2.54 × 10-2 mole of substance was dissolved in 25.0 mL of solution. Calculate the concentration of the solution. question three What mass of NaHCO3 is required to prepare 2.50 × 102 L of a 0.200 mol L-1 solution? ram values H = 1.0 C = 12.0 O = 16.0 Na = 23.0 2 CH2012A © te ah o o te k u ra p ou n a mu ch2012a teacher-marked assignment question four How many grams of KOH are present in 35.0 mL of a 5.50 mol L-1 solution? ram values H = 1.0 O = 16.0 K = 40.1 question five Hydrochloric acid reacts with sodium carbonate according to the equation: 2HCl + Na2CO3 2NaCl + CO2 + H2O a. What mass of sodium chloride will be produced from 0.153 mol of HCl? ram values H = 1.0 C = 12.0 O = 16.0 Cl = 35.5 Na = 23.0 b. What mass of carbon dioxide will be formed from 5.00 g of Na2CO3? c. What mass of sodium chloride will be formed from 5.00 tonnes of Na2CO3? © te ah o o t e k ur a p o un a m u CH2012A 3 ch2012a teacher-marked assignment question six The fertiliser ammonium sulfate [(NH4)2SO4] is prepared by the reaction between ammonia and sulfuric acid. 2NH3(g) + H2SO4(aq) (NH4)2SO4(aq) How many kilograms of NH3 are needed to produce 1.00 × 105 kg of (NH4)2SO4? ram values H = 1.0 N = 14.0 O = 16.0 S = 32.1 question seven a. A standard solution of oxalic acid has to be made. What is a standard solution? b. How many grams of oxalic acid (C2O4H2.2H2O) are required to make up a 0.100 mol L-1 solution in a 250.0 mL volumetric flask? ram values H = 1.0 C = 12.0 O = 16.0 4 CH2012A © te ah o o te k u ra p ou n a mu ch2012a teacher-marked assignment what to do next When you have finished this teacher-marked assignment, please make sure that you have written your name and ID number on the back cover. You can also use a label if you have one on hand. By post: Put the assignment in the plastic envelope provided. Make sure that the address card shows the address for Te Aho o Te Kura Pounamu. Seal the envelope with tape before you post it. Do not include booklets from other subjects with this Science work. By email: Scan the pages including the cover sheet and email to your teacher. The standard format for Te Kura teacher email addresses is: firstname.lastname@tekura.school.nz If you aren’t sure who your teacher is, call 0800 65 99 88. If you do not have your next set of study materials, contact your teacher immediately. If you are not sure what to do next, ask your teacher for advice. © te ah o o t e k ur a p o un a m u CH2012A 5 cover sheet – ch2012a students – place student address label below or write in your details. Full Name ID No. Address (If changed) authentication statement I certify that the assessment work is the original work of the student named above. Signed Signed (Student) (Supervisor) for school use only assessment www.tekura.school.nz Copyright © 2012 Board of Trustees of Te Aho o Te Kura Pounamu, Private Bag 39992, Wellington Mail Centre, Lower Hutt 5045, New Zealand. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means without the written permission of Te Aho o Te Kura Pounamu. chemistry ch2013a teacher-marked assignment acid-base titrations student instructions Overview This assignment is designed to give you practice in demonstrating your understanding of the fundamental concepts of chemistry. It is not for NCEA credit, but it will help you to develop your skills, so that you do well in future assessments. Conditions •• This is a closed book assessment; you may not refer back to any booklets. •• There is no time limit for this assignment, but allow about one hour to finish it. You will need: •• a pen or pencil and a calculator. If you do not understand any of these conditions, please phone, fax or email your teacher now. Supervisor requirements You and your supervisor (if applicable) must sign the cover sheet at the back of the assessment to verify that the work is your own. Assessment criteria Not Attempted Did not attempt to complete. Not yet on target for Achieved Did not demonstrate an understanding of titrations and related calculations. On target for Achieved Demonstrated an understanding of titrations and related calculations. On target for Achieved with Merit On target for Achieved with Excellence Demonstrated an in-depth understanding of titrations and related calculations. Demonstrated a comprehensive understanding of titrations and related calculations. For teacher use only © te aho o t e k ur a p o un a m u 2012/2 ch2013a teacher-marked assignment answer all the questions NOTE: The ram values are given by the relevant question. NA = 6.02 × 1023 Use the appropriate number of significant figures. Show all your working. question one Explain the following terms. Give an example in each case. a. Strong acid b. Weak base c. Concentrated acid d. Dilute acid e. Indicator 2 CH2013A © te ah o o te k u ra p ou n a mu ch2013a teacher-marked assignment question two Explain why each of the following procedures is incorrect. a. Filling a burette above eye level. b. Holding the pipette by the bulb. c. Emptying the pipette into a conical flask and immediately removing the pipette. d. Leaving the funnel in the burette during the titration. e. Wiping the outside of the pipette after the bottom of the meniscus is level with the marked line on the pipette. f. Holding the pipette close to the surface of the solution, when sucking up the solution. © te ah o o t e k ur a p o un a m u CH2013A 3 ch2013a teacher-marked assignment question three In a titration involving 25.0 mL potassium hydroxide solution against a solution containing 0.132 mol L-1 sulfuric acid, 28.2 mL of the acid was found to just neutralise the alkali completely. The unbalanced equation is: H2SO4 + KOH K2SO4 + H2O a. Write the balanced equation. b. Name a suitable indicator for the titration and state the colour change you would observe for this titration. c. Calculate the concentration of the alkali in mol L-1. 4 CH2013A © te ah o o te k u ra p ou n a mu ch2013a teacher-marked assignment question four A student needed to find the exact concentration of an HCl solution. He used 20.00 mL aliquots of a 0.237 mol L-1 sodium carbonate solution. He recorded his results as follows. Rough 2nd titration 3rd titration 4th titration 5th titration Burette reading at the end /mL 23.20 45.85 23.90 46.65 23.14 Burette reading at the start /mL 0.05 23.20 1.30 23.90 0.20 Volume of HCl used (titre) /mL a. Calculate each titre value for each titration in the table above. b. Calculate the average titre using only concordant results. c. Write the balanced equation for the reaction. d. Calculate the amount in moles of Na2CO3 in each 20.0 mL aliquot. e. Calculate the amount in moles of HCl in the average titre. f. Calculate the concentration of the HCl solution in mol L-1. © te ah o o t e k ur a p o un a m u CH2013A 5 ch2013a teacher-marked assignment what to do next When you have finished this teacher-marked assignment, please make sure that you have written your name and ID number on the back cover. You can also use a label if you have one on hand. By post: Put the assignment in the plastic envelope provided. Make sure that the address card shows the address for Te Aho o Te Kura Pounamu. Seal the envelope with tape before you post it. Do not include booklets from other subjects with this Science work. By email: Scan the pages including the cover sheet and email to your teacher. The standard format for Te Kura teacher email addresses is: firstname.lastname@tekura.school.nz If you aren’t sure who your teacher is, call 0800 65 99 88. If you do not have your next set of study materials, contact your teacher immediately. If you are not sure what to do next, ask your teacher for advice. 6 CH2013A © te ah o o te k u ra p ou n a mu ch2013a teacher-marked assignment © te ah o o t e k ur a p o un a m u CH2013A 7 cover sheet – ch2013a students – place student address label below or write in your details. Full Name ID No. Address (If changed) authentication statement I certify that the assessment work is the original work of the student named above. Signed Signed (Student) (Supervisor) for school use only assessment www.tekura.school.nz Copyright © 2012 Board of Trustees of Te Aho o Te Kura Pounamu, Private Bag 39992, Wellington Mail Centre, Lower Hutt 5045, New Zealand. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means without the written permission of Te Aho o Te Kura Pounamu. chemistry ch2071a teacher-marked assignment oxidation-reduction chemistry student instructions Overview This assignment is designed to give you practice in demonstrating your understanding of the fundamental concepts of chemistry. It is not for NCEA credit, but it will help you to develop your skills, so that you do well in future assessments. Conditions •• This is a closed book assessment; you may not refer back to any booklets. •• There is no time limit for this assignment, but allow about one hour to finish it. You will need: •• a pen or pencil and a calculator. If you do not understand any of these conditions, please phone, fax or email your teacher now. A Periodic Table and tables of species and their colours are supplied near the back of this assignment. You can tear out this page to refer to the tables more easily. Supervisor requirements You and your supervisor (if applicable) must sign the cover sheet at the back of the assessment to verify that the work is your own. Assessment criteria Not Attempted Did not attempt to complete. Not yet on target for Achieved Did not demonstrate an understanding of oxidationreduction chemistry. On target for Achieved Demonstrated an understanding of oxidationreduction chemistry. On target for Achieved with Merit On target for Achieved with Excellence Demonstrated an in-depth understanding of oxidationreduction chemistry. Demonstrated a comprehensive understanding of oxidationreduction chemistry. For teacher use only © te aho o t e k ur a p o un a m u 2012/2 ch2071a teacher-marked assignment answer all the questions question one a. Complete the table with the oxidation number of each underlined element. The first one has been done for you. Species NH3 Oxidation number -3 H2SO4 Cl2 NO3- HCl b. The reaction between magnesium and hydrochloric acid is represented by the following equation: Mg + 2HCl MgCl2 + H2 Identify the oxidant in this reaction. Explain your answer with reference to oxidation numbers. 2 CH2071A © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment c. For each of the following reactions, identify the underlined product, the oxidant and the reductant. i. Chlorine gas is bubbled through a colourless potassium bromide solution, turning it yellow-orange. product oxidant reductant ii. When hydrogen peroxide is added to an acidified potassium permanganate solution, the purple solution becomes colourless and bubbles of gas are seen. product oxidant reductant iii. When zinc is added to an iodine solution, the brown solution becomes colourless. product oxidant reductant iv. When aluminium foil is added to bromine liquid, the mixture burns and white smoke is produced. product oxidant reductant © te ah o o t e k ur a p o un a m u CH2071A 3 ch2071a teacher-marked assignment question two a. Sulfur dioxide gas (SO2) is bubbled through a solution of acidified potassium permanganate (KMnO4). An oxidation-reduction reaction occurs. The unbalanced equation for this reaction is: MnO4– + SO2 Mn2+ + SO42– A student wrote the two following half-equations: Mn2+ + 4H2O Equation One MnO4– + 8H+ + 5e– + – SO42– + 2H2O Equation Two SO2 + 4H + 2e It is not possible to combine these two half-equations as the student had written Equation Two incorrectly. i. Describe the mistake that was made in Equation Two. ii. Write Equation Two correctly. iii. Discuss, in terms of oxidation-reduction principles, electron transfer and charge, why Equation One and the original Equation Two cannot be combined into an overall balanced equation. 4 CH2071A © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment b. Hydrogen peroxide is added to a solution of potassium bromide. You may use the resource tables given at the end of this assignment to help you answer the following questions. i. Identify which substance is being reduced. Use oxidation numbers and the transfer of electrons to justify your choice. ii. Describe what you would expect to observe for this reaction. Link all observations to the species concerned. (Tip: remember to describe both reactants and products.) iii. Write the balanced oxidation half reaction. iv. Write the balanced reduction half reaction v. Write the full balanced equation. © te ah o o t e k ur a p o un a m u CH2071A 5 ch2071a teacher-marked assignment question three Acidified potassium dichromate, K2Cr2O7, is a common oxidant used in aqueous solution. You may use the resource tables given at the end of this assignment to help you answer the following questions to explain the chemistry when acidified potassium dichromate solution is added to a solution of potassium iodide, KI. a. Describe what you would expect to observe for this reaction. Link all observations to the species concerned. (Tip: remember to describe both reactants and products.) b. Write the balanced oxidation half reaction. c. Explain why this is the oxidation half reaction. Refer to changes in oxidation number and the number of electrons transferred. d. Write the balanced reduction half reaction. e. Explain why this is the reduction half reaction. Refer to changes in oxidation number and the number of electrons transferred. f. Write the full balanced equation. 6 CH2071A © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment question four: Drops of iron(II) sulfate are added to a chlorine solution. The very pale green solution began to turn colourless. You may use the resource tables given at the end of this assignment to help you answer the following questions. a. Describe what you would expect to observe for this reaction. Link all observations to the species concerned. (Tip: remember to describe both reactants and products.) b. Write the balanced oxidation half reaction. c. Explain why this is the oxidation half reaction. Refer to changes in oxidation number and the number of electrons transferred. d. Write the balanced reduction half reaction. e. Explain why this is the reduction half reaction. Refer to changes in oxidation number and the number of electrons transferred. f. Write the full balanced equation. © te ah o o t e k ur a p o un a m u CH2071A 7 ch2071a teacher-marked assignment Extra space. Label each question clearly. 8 CH2071A © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment appearance of redox reactants and their products redox reactants and their products Species Appearance Br2 → Br– Br– colourless ion Cl2 → Cl– Br2 red/orange liquid C black solid CO2 → C → Cr3+ CO2 colourless gas which turns lime water milky Cr2O7 /H Cu2+ → Cu Cl– colourless ion Fe3+ → Fe2+ Cl2 pale green gas H+ → H2 Cr2O72–/H+ orange ion H2O2 → H2O Cr3+ green ion HNO3(conc) → NO2 Cu Pinkish/red-brown solid I2 → I– Cu2+ blue ion IO3– → I2 Fe pale green ion MnO4 /H → Mn2+ Fe3+ orange (brownish) ion → H colourless ion O2 H2O2 + → O2– H2 colourless gas O2 OCl– → Cl– H2O colourless liquid H2O2 colourless liquid S H2S colourless gas HNO3(conc) colourless liquid HSO3 colourless ion I colourless ion I2 brown solution, black solid 2+ – – – + → H2S 2– → HSO3– SO42– → SO2 SO4 → SO32– SO4 2– colourless ion IO3– colourless ion Mn 2+ MnO4 /H purple ion NO2 brown gas O2 colourless gas 2– O colourless ion OCl– colourless ion S yellow solid SO2 colourless gas SO32– colourless ion SO42– colourless ion Zn colourless ion – 2+ + 2– + © te ah o o t e k ur a p o un a m u CH2071A 9 10 CH2071A Y 226 223 262 261 262 105 263 264 107 265 108 268 109 192 77 Ir 103 45 Rf Db Sg Bh Hs Mt 106 104 103 88 190 87 Fr Ra Lr 186 184 181 179 175 137 76 133 75 101 W Re Os 74 98.9 56 73 95.9 44 55 72 92.9 43 58.9 195 78 197 79 108 47 63.6 201 80 112 48 65.4 204 81 115 49 69.7 Pt Au Hg Tl 106 46 58.7 31 Zr Nb Mo Tc Ru Rh Pd Ag Cd In 91.2 42 Cs Ba Lu Hf Ta 71 88.9 41 55.8 28 30 87.6 Rb Sr 40 54.9 27 Si P 207 82 Pb 119 209 83 Bi 122 51 74.9 33 31.0 S Cl 210 84 I 210 85 127 53 79.9 35 35.5 17 19.0 9 F 17 Ar Kr 222 86 131 Xe 54 83.8 36 40.0 18 20.2 10 Ne 4.0 He Po At Rn 128 52 79.0 34 32.1 16 16.0 8 O 16 Sn Sb Te 50 72.6 32 28.1 15 14.0 7 N 15 Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br 52.0 26 29 85.5 12 39 11 38 V 50.9 25 10 37 Ti 47.9 24 9 45.0 Ca Sc 23 7 8 40.1 K 22 6 39.1 21 5 20 4 19 3 Al 27.0 24.3 23.0 14 13 Na Mg 12.0 6 C 14 10.8 12 1.0 11 Molar mass/g mol-1 5 B 9.0 1 H 6.9 Atomic Number Be 4 3 13 Li 2 1 2 18 ch2071a teacher-marked assignment periodic table © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment what to do next When you have finished this teacher-marked assignment, please make sure that you have written your name and ID number on the back cover. You can also use a label if you have one on hand. By post: Put the assignment in the plastic envelope provided. Make sure that the address card shows the address for Te Aho o Te Kura Pounamu. Seal the envelope with tape before you post it. Do not include booklets from other subjects with this Science work. By email: Scan the pages including the cover sheet and email to your teacher. The standard format for Te Kura teacher email addresses is: firstname.lastname@tekura.school.nz If you aren’t sure who your teacher is, call 0800 65 99 88. If you do not have your next set of study materials, contact your teacher immediately. If you are not sure what to do next, ask your teacher for advice. © te ah o o t e k ur a p o un a m u CH2071A 11 cover sheet – ch2071a students – place student address label below or write in your details. Full Name ID No. Address (If changed) authentication statement I certify that the assessment work is the original work of the student named above. Signed Signed (Student) (Supervisor) for school use only assessment www.tekura.school.nz Copyright © 2012 Board of Trustees of Te Aho o Te Kura Pounamu, Private Bag 39992, Wellington Mail Centre, Lower Hutt 5045, New Zealand. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means without the written permission of Te Aho o Te Kura Pounamu. chemistry ch2011a teacher-marked assignment measurement and moles student instructions Overview This assignment is designed to give you practice in demonstrating your understanding of the fundamental concepts of chemistry. It is not for NCEA credit, but it will help you to develop your skills, so that you do well in future assessments. Conditions • This is a closed book assessment; you may not refer back to any booklets. • There is no time limit for this assignment, but allow about one hour to finish it. You will need: • a pen or pencil and a calculator. If you do not understand any of these conditions, please phone, fax or email your teacher now. Supervisor requirements You and your supervisor (if applicable) must sign the cover sheet at the back of the assessment to verify that the work is your own. Assessment criteria Not Attempted Did not attempt to complete. Not yet on target for Achieved Did not demonstrate an understanding of simple calculations. On target to Achieved Demonstrated an understanding of simple calculations. On target to Achieved with Merit On target to Achieved with Excellence Demonstrated an in-depth understanding of simple calculations. Demonstrated a comprehensive understanding of simple calculations. For teacher use only © te aho o t e k ur a p o un a m u 2012/2 ch2011a teacher-marked assignment answer all the questions question one Calculate the molar mass for each of the following substances. Show all your working. a. CHCl3 ram values H = 1.0 Li = 6.9 C = 12.0 O = 16.0 P = 31.0 Cl = 35.5 Ca = 40.1 b. Li2CO3 c. Ca3(PO4)2 question two Calculate the molar mass of a compound if 0.372 mole of it has a mass of 152 g. question three How many molecules of ethane (C2H6) are present in 0.334 g of C2H6? M = 30.0 g mol-1. 2 CH2011A © te ah o o te k u ra p ou n a mu ch2011a teacher-marked assignment question four The formula for rust can be represented by Fe2O3 a. How many moles of Fe2O3 are present in 24.6 g of the compound? ram values O = 16.0 Fe = 55.8 b. How many moles of Fe are present in 24.6 g of the compound? question five Allicin is the compound responsible for the characteristic smell of garlic. Its composition by mass is as follows: C: 44.4% H: 6.21% a. Calculate its empirical formula. S: 39.5% O: 9.86% ram values H = 1.0 C = 12.0 O = 16.0 S = 32.1 b. What is the molecular formula, given that its molar mass is about 162 g mol–1? © te ah o o t e k ur a p o un a m u CH2011A 3 ch2011a teacher-marked assignment question six Tin(II) fluoride (SnF2) is often added to toothpaste as an ingredient to prevent tooth decay. a. Calculate the number of moles of fluorine in 24.6 g of the compound. ram values F = 19.0 Sn = 118.7 b. What is the mass of F in grams in 24.6 g of the compound? c. Calculate the percentage of tin in the compound. question seven 4.96 g of hydrated sodium thiosulfate (Na2S2O3.xH2O) were dehydrated and formed 3.16 g of anhydrous salt. Calculate the empirical formula for the hydrated crystals. ram values H= 1.0 O = 16.0 Na = 23.0 S = 32.1 4 CH2011A © te ah o o te k u ra p ou n a mu ch2011a teacher-marked assignment what to do next When you have finished this teacher-marked assignment, please make sure that you have written your name and ID number on the back cover. You can also use a label if you have one on hand. By post: Put the assignment in the plastic envelope provided. Make sure that the address card shows the address for Te Aho o Te Kura Pounamu. Seal the envelope with tape before you post it. Do not include booklets from other subjects with this Science work. By email: Scan the pages including the cover sheet and email to your teacher. The standard format for Te Kura teacher email addresses is: firstname.lastname@tekura.school.nz If you aren’t sure who your teacher is, call 0800 65 99 88. If you do not have your next set of study materials, contact your teacher immediately. If you are not sure what to do next, ask your teacher for advice. © te ah o o t e k ur a p o un a m u CH2011A 5 cover sheet – ch2011a students – place student address label below or write in your details. Full Name ID No. Address (If changed) authentication statement I certify that the assessment work is the original work of the student named above. Signed Signed (Student) (Supervisor) for school use only assessment www.tekura.school.nz Copyright © 2012 Board of Trustees of Te Aho o Te Kura Pounamu, Private Bag 39992, Wellington Mail Centre, Lower Hutt 5045, New Zealand. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means without the written permission of Te Aho o Te Kura Pounamu.