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Experiment #5

Experiment #5. Avagadro’s Number 6.02 x 10 23 And The Standard Deviation x  S. Introduction. Purpose : Relate a gram formula weight to Avogadro’s number by using the dimensional analysis approach and determine the correct number of significant figures in your applications.

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Experiment #5

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  1. Experiment #5 Avagadro’s Number6.02 x 10 23 And The Standard Deviation x  S

  2. Introduction • Purpose: • Relate a gram formula weight to Avogadro’s number by using the dimensional analysis approach and determine the correct number of significant figures in your applications. • Compute the standard deviation for the volume of water delivered by a 10 mL Graduate Cylinder.

  3. Key Ideas • Amu Vs. Gram – • Atom Vs. Ion – • Atom Vs. Mole – • Formula Weight – • GFW,GAW,GMW – • Dimensional Analysis – • Standard Deviation –

  4. Amu – We use if we are talking about the mass of an atom. Ex. the mass of an iron atom is 55.8 amus. Gram – We use if we are talking about the mass of a mole or fraction of a mole. Ex. The mass of one mole of iron is 55.8 grams. Amu Vs. Gram

  5. Ion Atoms Not on the Periodic Table On Periodic Table Have a charge; can be positive or negative. Do not have a charge Do not React React Only one atom Canbe more then one atom Equal number of Protons & Electrons Unequal number of Protons and Electrons AtomVs. Ion

  6. Mole Atom 6.02X10 23 Atoms 1Atom Larger mass measured in grams Very small mass measured in Amus Larger in size Can be seen Very Small in size Can’t be seen Atom Vs. Mole

  7. Formula Weight Formula weight – the mass of the collection of atoms represented by a chemical formula. For Ex. water contains two hydrogen atoms and one oxygen atom. 1 x 16.00 (mass of O) = 16.00 2 x 1.01 (mass of H) = + 2.02 Formula Weight  18.02 The formula weight tells us the mass of one mole of our substance.

  8. GFW – Gram Formula Weight This refers to the mass of an ion or ionic compound Ex. Mass of a Cl- GAW – Gram Atomic Weight This refers to the mass of a atom Ex. Mass of a Cl atom GMW Gram Molecular Weight This refers to the mass of a molecule or molecular compound Ex. Mass of one molecule of H2O

  9. How do Avagadro’s number, Mole and GAW Apply to each other? • One mole of Tin has a mass of 118.69g. • One atom of Tin has a mass of 118.69 Amu. • One mole of Tin contains 6.02X1023 atoms.

  10. Dimensional Analysis Convert 10 m to mm Remember 1 m = 1000mm They both mean the same thing it all depends on what you need.

  11. What you are given always over 1 The 1 is a filler. # 1 The unit you want to eliminate is placed in the lower right so it will cancel out with your original unit. # 2 # 3 Mult. left to right divide top to bottom Dimensional Analysis

  12. X going and / going Keep in mind

  13. Find the # of moles in the sample of Tin. Given the sample has a mass of 29.04g Ex#1 pg 51

  14. To determine the g formula wt. determine the mass of all atoms present. To determine #g / moleculethink about the units Think how can we compare grams and molecules? We need to use moles. So # grams per mole / number of parts in 1 mole To determine the number of atoms per mole add up the number of atoms in the formula Chart on pg 55

  15. X = Avg Standard Deviation • This is how much your value is off from the actual answer. Can be used as a correction factor. • Ex. A 1mL pipette delivers 1mL + or - .007mL • So the pipette delivers .9993mL or 1.007 mL.

  16. Mass of Beaker 110.51g 110.51g 110.51g 110.51g 110.51g Mass of Beaker & water 109.50g 111.53g 109.50g 109.50g 111.53g M H2O 1.01g 1.02g 1.01g 1.01g 1.02g Density of H20 = 0.9982 g/mL Vol. of pipet 1.01mL 1.02mL 1.01mL 1.02mL 1.02mL Use V= M/D to determine volume delivered Standard Deviation Ex. 1 mL Pipette

  17. #1 X avg.= 1.02 mL (Xi-Xavg.)2 (a).01 =1.0X10-4 (b) 0 = 0 (c).01 =1.0X10-4 (d) 0 = 0 (e) 0 = 0 #3 Xi-Xavg. (a)1.01-1.02=.01 (b)1.02-1.02= 0 (c)1.01-1.02=.01 (d)1.02-1.02= 0 (e)1.02-1.02= 0 #2 #5 ∑(Xi-X avg.)2/N-1 #4 ∑(Xi-X avg.)2 Take Square Root of Step #5 #6 Final Answer: +/- 0.007 mL. N= number of trials

  18. Due Next Week • Pages 51 & 53 we are determining the number of atoms / ions or moles that are asked for. • YOU MUST SHOW ALL WORK FOR CREDIT!! • Page 55 complete the table and show all work. • Pages 61 determine the St. Dev. for 1 mL pipette ( I do as a example) • Page 63 determine the St. Dev. for a 10mL. graduated cylinder.

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