General Chemistry CHM 11500
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This 3 page Class Notes was uploaded by Austen Pollich on Saturday September 19, 2015. The Class Notes belongs to CHM 11500 at Purdue University taught by Staff in Fall. Since its upload, it has received 44 views. For similar materials see /class/207976/chm-11500-purdue-university in Chemistry at Purdue University.
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Date Created: 09/19/15
Chemistry 115 and Chemistry 116 Answer Formatting in WebCT Important If you close the main WebCT webpage before submitting your answers or homework your homework will be listed as ungraded You must click Submit Finish OK ViewResulls for your homework to be graded Your homework must have been graded for you to be able to go back and review your questions and answers WebCT does not recognize certain functions in the answer fields of the program and the following guidelines will be used for entering answers unless directed otherwise CHEMICAL FORMULAS IN WebCT Answers 1 When entering chemical formulas in answer fields the subscript and superscript fonts are not available For molecular formulas H2504 must be entered as H2SO4 just as you would read the formula leftto right but without subscripts the formula for ammonium phosphate would be entered as NH43PO4 The number 1 is not used as a subscript since it is implied as soon as you write the symbol for the element in a formula For ions alone SOL2 39 must be entered as SO42 parentheses around the chemical composition followed by the charge number first then sign The number one is omitted For example the formula for the ammonium ion would be entered as NH439 the formula for the nitration ion would be entered as N03 39 the chloride ion would be Cl39 the sulfide ion would be S2 the zinc ion would be Zn2 etc For hydrates Use an asterisk with no spaces to separate the formula of water from the other component For example the formula for cobaltII nitrate hexahydrate would be entered as CoNO326H20 2 Watch your zeros and quot039squot and well as spaces Entering H20 or H2 0 instead of H20 for water will be counted as a wrong answer NAMES OF COMPOUNDS and IONS in WebCT Answers 1 Spelling and spacing are important If an answer is not spelled correctly it is wrong Spelling of the names of elements and compounds will follow the conventions in your textbook For example if you enter flourine instead of fluorine then your answer will be counted as a wrong answer 2 Enter your answers for names of elements compounds and ions using all lower case letters For example oxygen calcium nitride carbon dioxide sulfate ion copperII ion 3 For names of ions where you need to show the ion charge no space between the symbol of the element and its ion charge which is in parentheses For example the name of the Co ion is entered as cobaltII CALCULATING MOLAR MASS 0r MOLECULAR WEIGHT VALUES and ENTHALPY FREE ENERGY AND ENTROPY VALUES FOR CHEMICAL SYSTEMS All molar mass values used in the computations for the problem answers were calculated using atomic mass values given in the Periodic Table on the inside front cover of your textbook The computation of molar mass values is based on the math concept of addition NOT multiplication Expressing 7990 gmol 7990 gmol as 27990 gmol is merely a simplification in writing format Therefore the significant figure rules for addition and subtraction apply to calculation of molar mass values and are based on number of digits after the decimal point The same principles of addition and subtraction apply in thermochemistry Chapter 6 and thermodynamics Chapter 20 when two or more equations are added andor subtracted in order to obtain the enthalpy Hess s Law free energy andor entropy for some overall or combined reaction BALANCED CHEMICAL EQUATIONS Generally chemical equations are balanced using smallest integer values as coefficients Exceptions In therm ochemistry Chapter 6 and thermodynamics Ch 20 balancing an equation so that the substance of interest is expressed as 1 mole is common Therefore fractions are often used to balance thermochemical equations For example H2g 12 Ozg 9 HZOg NUMERICAL ANSWERS 1 Unless instructed to do otherwise it is advisable to enter your answers in scientific notation format E For example 345E34 34E3 3E3 In other words replace quotx 10quot with E for example 000345 becomes 345E3 in WebCT If standard decimal notation is required include any leading zeroes For example enter 0123 not 123 to be consistent with the format in your textbook For very large numbers such as 2500000 enter the commas if standard decimal notation is required otherwise enter in scientific notation as shown above 2 Don39t forget to use the correct numbers of significant figures in your answers for all homework assignments 3 Special note about special significant figure cases For a temperature value given with a zero in the one s place eg 20 0C the zero is normally considered to be a significant digit Therefore 20 0C would be precise to 2 significant figures the 2 as well as the 0 in the one s place not 1 significant figure Changing 20 0C to K increases the number of significant digits by 1 20 273 293 K for computation purposes 760 torr 1 atm is considered to have 3 significant digits CONSTANTS Values for constants will be found in your textbook Use the value given don t round off for your computations UNITS 1 The answer fields labeled as units are where the appropriate unit abbreviation must be typed Most of the time these abbreviations are the same as what you will find in your Silberberg textbook for other situations use the units indicated in the problem set or those in the table below 2 When entering units just enter the accepted abbreviation for that unit The unit for 18 grams of H20 is entered as g39 for 10 mol H20 enter the unit as mol 3 If a unit box does not appear after the question units are not required 4 Units are case sensitive Area m2 cm2 inZ etc Hertz Hz Molar mass gmol Atomicisotopic mass amu Hours h Molar solubility molL Atmosphere atm Joules etc J kl Moles mol Becquerels Bq Joulesmole Jmol kJmol Molecules molecules QC degrees C Kelvin K Moles per liter per second molLlsl Concentration M Liters etc L mL Particles particles Coulombs C Meters etc m cm km Percent Curies Ci Meters per second ms Pounds lbs Days day Metric tons metric tons Seconds s Density gmL Miles mi Per second sl Gallons gal Miles per hour mih Torr torr Grams etc g kg mg Minutes min Volts V Molality m Molarity M Years yr
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