Study Guides
(238,270)

Canada
(115,049)

McMaster University
(6,958)

ENGTECH 1AC3
(1)

D R.
(1)

Midterm

# Analytical Chemistry Midterm Review

Unlock Document

McMaster University

Engineering Technology

ENGTECH 1AC3

D R.

Winter

Description

Equations//Symbols//Calculations
Absolute error(E) = x xi - t
Relative error (E r)
100% = 10 ppt = 1000ppm
Sample mean ( )x=
If N is large then the mean (x) is called the population mean, (μ) and if it is in the
absence of errors then μ or the population mean is called the true result
Spread = (highest – lowest)
Mean deviation (d) = average value of result mean result
x x x x
x
Standard deviation (σ or s)
Detailed results show that when we calculate the
standard deviation, we can predict the following if
the result is repeated many times;
- 68% of results will be within 1 σ of the mean
- 96% of results will be within 2σ of the mean
- 99.7 of results will be within 3σ of the mean
Population standard deviation (σ):
If N > 20
x x x x
Sample standard deviation (s):
If N < 20
x x x x
The mean ( X ) and the standard deviation (σ or s) values apply to the numerical value of the
result Coefficient of variation (CV):
x x
Relative error (Relative.Standard.Deviation%):
x x
6
1L = 1000mL = 1000g = 1000000 mg - (mass of solute(mg) / 10 mg solution = ppm
Buoyancy error
Temperature correction
Error caused by buoyancy is < 0.1% for objects with density > 2g/cm 2
Volume, mL Volume, mL
Temperature, T, ºC At T Corrected to 20ºC
20 ºC 1.0028 1.0028
//other temperatures // //
25 ºC 1.0040 1.0037
Ex. A 25mL pipet delivers 24.976 g of water weighed against steel mass at 25 ºC
- @ 25 ºC: V = 24.976 g 1.0040 mL/g
o V = 25.076 mL
- @20 ºC: V = 24.976 g 1.0037 mL/g
o V = 25.068 mL
Rounding
Going from infinite set of #’s to a finite set of #’s
When rounding calculations, carry at least one extra digit beyond significant digits
through calculations to avoid rounding error Significant digits
- Magnitude
- Units
- Error
Rules for “Sig figs”
- All non-zero digits are significant
- Zeros are significant if:
o Between significant figures
o Right of decimal and right of significant figures
- For logarithms anything before decimal is not significant and anything after the decimal.
Rules for significant figures in calculations
- Addition and/or subtraction
o Round answer to the “least reliable” decimal place
- Multiplication and/or division
o Round answer to match the factor with the fewest number of significant figures
- Mixed calculations
o Determine the number of significant digits in the same order for which you
perform the calculation B.E.D.M.A.S
- Multiple calculations
o Save any round until the end of the problem
- Mean ( X )
o Decimal places for the mean should match the decimal places of the
measurements used to calculate the mean
- Standard deviation (σ or s)
o Decimal places for the standard deviation should match the decimal places of the
measurements used to calculate the standard deviation
Error propagation (σ propagation)
- Addition/subtraction
- Multiplication/division
Then multiply by y
Rounding error propagation
- Round the S ty appropriate significant figures
- Round answer y to the same # of decimal places as the error term Practice Quiz 1:
Four solutions prepared by dissolving appropriate amounts to make 250mL solution in flask
1 2 3 4 5 6 7 8 9
Solution Compound g mg g/mol # of # of concentration ppm
# moles mL [mol/L]
1 A 200.0 39.99
2 B 1.260 0.0210
3 C 18.00 2000.0
4 C 3.600 100.0
Gravimetric analysis (Weighing)
Sample variance (s ):

More
Less
Related notes for ENGTECH 1AC3