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Molality
(moles solute)/(kg solvent)
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ppm
- (μg sample)/(mL solute)
- (mg sample) / (L solute)
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When dealing with concentration problems, what are top three key things to think about?
- 1) Density, concentration, molartiy... etc. of the solvent, solute and all else. Sometimes these do not correlate. Watch out for it!
- 2) Think of when to use M1V1 = M2V2 rule. It is normally for getting a volume to a desired molarity. (Left side is moles taken from concentrated solution, and right side is moles placed in dilute solution)
- 3) Think of it like a puzzle, or stoichiometry stuff :)
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Kilo to pico
- Kilo (1000)
- Hecto (100 - h)
- Deca (10 - da)
- Deci (.1)
- Centi (.01)
- Mili (.001)
- Micro (.000001)
- Nano (.000000001)
- Pico (.000000000001)
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What are the steps in chemical analysis?
- -inject solution into chromatogram
- -wash with solvent to flush it through column
- -chromatogram separates analytes
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What does it mean to mask an interfering species?
It means that a reagent is used that react with the interfering species, to prevent detection.
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What is the difference between random and segregated heterogeneous material?
- Random: differences in composition, appear randomly and on a fine scale
- Segregated: large regions have obvious different compositions
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ppb
- (ng sample) / (mL solute)
- (μg sample)/(L solute)
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Calculating quantities of reagents needed to prepare solution
- M1V1 = M2V2
- (moles taken from concentrated solution) = (moles added to dilute solution)
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Uncertainty in Addition and Subtraction from Absolute Values
e 4 = √e 12 + e 22 + e 32
- e = uncertainty value
- absolute uncertainty = actual value
- relative uncertainty = wt% or fraction
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Uncertainty in Multiplication and Division
e 4 = √(%e 1) 2 + (%e 2) 2 + (%e 3) 2
- e = uncertainty value
- You have to convert to relative uncertainty first!
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Significant figure rule for ubcertianties
First digit of absolute uncertainty is the last significant figure of answer
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Significant figures when taking log of something or solving log
- log339 = 2.530 (mantissa takes sig figs)
- 104.36 = 2.3 x 104
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How are uncertainties in atomic masses obtained?
- 2C = 2(12.0106 (± 0.0010))
- 2C = 24.0210 ± 0.002
- 4H = 4(1.00798 (± 0.00014))
- 4H = 4.03192 ± 0.00028
So all the above uncertainties were multiplied by 2 then use the addition / subtraction rules to add them
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How does the uncertainty change for a calibrated and uncalibrated pipet?
- Uncalibrated - multiply uncertainty by number of deliveries
- Calibrated - addition / subtraction rule
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Coefficient of variation
Stdev expressed as a percentage of the mean value. Also known as the relative stdev.
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What does it mean to find the area of a certian range?
Using the z chart, it is also the probablitity of measuring z in a certian range.
z = (x - xavg) / s
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Using the F test
Answers: Is s from the instrument "significantly" greater than s from original instrument.
- Fcalculated = s12 / s22
- The larger stdev is in the numerator.
If F calc > F table then there is a significant difference. This is because there is 5% probability of finding F above the table value. The significant difference means the null hypothesis is rejected and the values probably come from different populations.
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Null Hypothesis
Two sets of data are drawn from populations with the same properties. There are no significant differences between populations.
Rejected if there is less than 5% probability of finding observed value.
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Confidence Interval
Tool used to test probability of finding a range of values within a given location. You get t from a chart.
Just plug and chug the values in
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Comparing a measured result with known result. Given:
-set of values or mean
-commercial value.
Calculate the confidence interval of 95% and then see if the commercial value agrees with it.
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Grubbs test
To see if a value should be part of the measurements.
Gcal = (questionable value - avg) / stdev
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How would your compare replicate measurements?
Found from F test (p.76)
- Significantly Different: use a more complicated it test that pools it all together
- Not Significantly Different: conduct a t test
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