Moles, Calculations, Dimensional Analysis!!!


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Moles, Calculations, Dimensional Analysis!!!

  1. 1. Moles, Calculations, Dimensional Analysis!!!<br />
  2. 2. Calculating with significant digits<br />When performing any calculations with significant digits, always use the number with the lowest number of significant digits.<br />This allows us to maintain the proper degree of precision and accuracy when calculating our yields and points to the sources of error and ways to improve.<br />
  3. 3. Calculations<br />Example: 100g+299g=400g<br />100 has 1 significant figure, 299 has 3. Use the number with the lowest sig figs.<br />Why??? Because we do not know the degree of precision was obtained.<br />Let’s think about the bean lab. One group could have measured 47.99g and another gave us 50g. Therefore, 47.99g+50g=100g<br />
  4. 4. Labeling<br />When performing any calculation it is also of extreme importance to label answers.<br />Remember our base units of measure.<br />Grams=mass<br />Liters=volume<br />Meters=length<br />An answer without a label will have points deducted!!!<br />
  5. 5. Dimensional Analysis<br />We will use this as a way to check our work and cancel out units.<br />You may already know how to do this, but do not recognize what it is called.<br />We have done something like this in our density lab.<br />
  6. 6. Example problem<br />You have a substance with a density of 63g/L.<br />How will you find out the number of grams in 500ml?<br />
  7. 7. Dimensional Analysis<br />In NASCAR racing we did not have a fuel gauge in the race car. Instead we had to estimate how much fuel was consumed and when we would have to stop again.<br />Fuel has a density of 800.00g/L<br />The race car holds 51.2kg of fuel<br />You are at a race track 1.0 mile per circuit and the race car will run 4.5 miles on 4.0L of fuel.<br />Problem: how many circuits before we stop?<br />
  8. 8. Setting up the problem<br />How do we set up the problem???<br />First, let’s determine the volume of fuel we have. We do that based on density and the mass.<br />
  9. 9. Setting up the problem<br />Now that we have a volume we need to calculate our consumption.<br />64L of fuel<br />How many laps (miles) can we run?<br />4.5mile/4.0L<br />
  10. 10. Setting up the problem<br />1.125 mile/L<br />Now given the volume of 64L at what point do we need to stop and re-fuel?<br />64Lx1.125mile/L=<br />72miles x 1.0lap/mile= Lap 72<br />
  11. 11. Moles<br />Wasn’t that fun???????? Just wait until we really get to practice this stuff every day!!!<br />Avagadro’s Number is 6.02 x 1023<br />This represents one Mole of any given substance.<br />
  12. 12. Moles<br />We use moles to calculate how many molecules, concentrations, particles, etc… It represents very large quantities of items.<br />Molecules and atoms are very small objects so we need any easy way to count them.<br />How large is a mole? A mole of pennies stacked would the sun and back 500 million times!<br />A mole is almost a trillion trillion!!!!<br />
  13. 13. Atomic Mass and Moles<br />The atomic mass of an atom is the molar mass in grams.<br />For example, helium has an atomic mass of 4. It’s molar mass is 4g.<br />If you have .3mol of Helium, how many grams?<br />
  14. 14. Diatomic Molecules<br />Remember with diatomic molecules (2 or more atoms) you must account for both!<br />F has a mass of 19g/mol, but F2 has a mass of 38g/mol!<br />
  15. 15. Compounds<br />Count all the atoms in a compound!!!<br />Let’s look at lithium hydroxide. What is the formula?<br />LiOH<br />1 Li, 1 O, 1H<br />Ans: 7+16+1=24g<br />