(moles solute)/(kg solvent)
- (μg sample)/(mL solute)
- (mg sample) / (L solute)
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 :)
Kilo to pico
- Kilo (1000)
- Hecto (100 - h)
- Deca (10 - da)
- Deci (.1)
- Centi (.01)
- Mili (.001)
- Micro (.000001)
- Nano (.000000001)
- Pico (.000000000001)
What are the steps in chemical analysis?
- -inject solution into chromatogram
- -wash with solvent to flush it through column
- -chromatogram separates analytes
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.
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
- (ng sample) / (mL solute)
- (μg sample)/(L solute)
Calculating quantities of reagents needed to prepare solution
- M1V1 = M2V2
- (moles taken from concentrated solution) = (moles added to dilute solution)
Uncertainty in Addition and Subtraction from Absolute Values
- e = uncertainty value
- absolute uncertainty = actual value
- relative uncertainty = wt% or fraction
Uncertainty in Multiplication and Division
- e = uncertainty value
- You have to convert to relative uncertainty first!
Significant figure rule for ubcertianties
First digit of absolute uncertainty is the last significant figure of answer
Significant figures when taking log of something or solving log
- log339 = 2.530 (mantissa takes sig figs)
- 104.36 = 2.3 x 104
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
How does the uncertainty change for a calibrated and uncalibrated pipet?
- Uncalibrated - multiply uncertainty by number of deliveries
- Calibrated - addition / subtraction rule
Coefficient of variation
Stdev expressed as a percentage of the mean value. Also known as the relative stdev.
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
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.
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.
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.
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
Comparing a measured result with known result. Given:
-set of values or mean
Calculate the confidence interval of 95% and then see if the commercial value agrees with it.
To see if a value should be part of the measurements.
Gcal = (questionable value - avg) / stdev
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