CHEM, Week 2 Notes
CHEM, Week 2 Notes CHEM 1500
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This 2 page Class Notes was uploaded by D Holley on Saturday September 3, 2016. The Class Notes belongs to CHEM 1500 at Ohio University taught by Corey Beck in Fall 2016. Since its upload, it has received 59 views. For similar materials see Concepts in Chemistry in Chemistry at Ohio University.
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Date Created: 09/03/16
Week 2 CHEM 1500 8/30 & 9/1 This week we covered three main topics: density, significant figures and calculations of significant figures. We focused on significant figures (sig figs, SF) and ran over the basis of density. Let’s start with density. Only a brief overview. Density is referred to as the ratio of a mass and a volume. As chemists, scientists and engineers we can use that to create a formula: d=m/v. That is density equals mass over (divided by) volume. The units for density have to be related to both units of mass and volume and will always be mass over volume (m/v). Ex. g/mL. The one density you should know is the density of water (dwater=1g/mL). In Chemistry we will be using this density to relate to all others. Density is also referred to an intensive property, but mass and volume are extensive properties. Well, what the heck is that. An intensive property has nothing to do with the amount of the material and there for there will be no change. Meaning if we have a cup of water that’s density is 1g/mL, then the swimming pool in our backyard has the density of 1g/mL. An extensive property is the exact opposite; the mass will change if the amount of the material changes, as well as, the volume. Since d=m/v and d is an intensive property, m/v must also be intensive. Now for Significant Figures. First, let’s go over the rules for using sig figs: All nonzero digits are significant figures: 1, 2, 3, 4, 5, 6, 7, 8, 9. All leading zeros are not significant figures, even if a decimal is present. In mathematics we read our numbers left to right and any zero read before a nonzero digit will not be a significant figure. All captive zeros are significant figures: 1004, 20005, 403, etc. Captive zeros are withheld between two nonzero digits that are ALWAYS significant. Trailing zeros are only significant figures if a decimal is present: 644.00. Significant figures are used to identify how precise and accurate a measured value is. Every instrumentation in a Chemistry laboratory will have a given set of sig figs. Whenever we are dealing with significant figures in this class, you ALWAYS have to RECORD the number of sig figs in each calculation at the end. Significant Figure Calculation On top of all the general rules of significant figures there are two separate rules for performing multiplication/division and addition/subtraction. Multiplication/Division: Depends on the number of significant figures being multiplied or divided. After undergoing the process, take the least number of sig figs present in the initial problem. Ex. 3.4*2.111, 3.4 has two sig figs and 2.111 has four sig figs, so after multiplying the two you would make the product have two significant figures because two is the least of the initial problem. Addition/Subtraction: Has nothing to do with significant figures. Depends on the number of available decimal places of each number being added or subtracted. Like multiplication and division the final solution will take form of the least of the initial problem. Ex. 3.4+2.111, 3.4 have one available decimal place and 2.111 has three available decimal places, so the sum of the two will have one available decimal place. dp=decimal place. You ALWAYS have to keep tract of the significant figures during each process of a complex problem. You CAN NOT DROP the insignificant figures after establishing the significant figures, this will skew the data on a large scale. Use PEMDAS to perform the processes in the correct order and keep tract of the correct number of significant figures. Don’t forget to do the homework! I hope this helps.
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