Units
7 fundemental units
| Measurement |
Unit |
Symbol |
| Time |
Second |
s |
| Displacement |
Metre |
m |
| Mass |
Kilogram |
Kg |
| Current |
Ampere |
A |
| Temperature |
Kelvin |
K |
| Amount of substance |
Mole |
mol |
| Luminous Intensity |
Candela |
cd |
Derived quantities
To convert between the derived and fundemental units, look at the formula and subsitute the units.
E.g Momentum has derived unit - p.
To find fundemental, subsitute units into the formula.
p = mass*velocity = kgms-1
dimensional consistency
This is checking if the units are correct for a meaurement by converting it to fundemental units and seeing if it fits the equation.
E.g are the units for velocity at2?
ms-1 ≠ ms-2s2 Therefore this is not dimensional consistent.
Metric multipliers and si prefixes
| Factor |
Name |
Symbol |
Factor |
Name |
Symbol |
| 101 |
deca |
d |
10-1 |
deci |
d |
| 102 |
hecto |
h |
10-2 |
centi |
c |
| 103 |
kilo |
k |
10-3 |
milli |
m |
| 106 |
mega |
M |
10-6 |
micro |
μ |
| 109 |
giga |
G |
10-9 |
nano |
n |
| 1012 |
tera |
T |
10-12 |
pico |
p |
| 1015 |
peta |
P |
10-15 |
femto |
f |
Order of magnitude
The nearest power of 10.
6.5 x 105 has magnitude of 106 because 6.5 rounds up to 10.
Significant figure
Equal to least precise significant figures in question. Very important
Uncertainties
What is uncertainty
This is how much a value measured may vary from the actual value.
Absolute uncertainty: same units as the measurements
percentage uncertainty: Given as a percentage as measurement
Types of error
| Type |
Description |
Effect on graph |
| Random |
Changes every trial |
Best fit line will not pass through all the error bars. |
| Systematic |
Caused by equipment, which is constant for every trial. |
Shifts grpah vertically or/and horizontally. Error bars represent this error. |
Rules to determine uncertainty
Rounding: 1 sig fig on exam OR don't round for lab report
Averages: Range / 2
Analog Measurements: For reliable equipment use half smallest division else use just the smallest division
Combining Uncertainties
Addition/subtraction:Add al uncertainties
Multiplication/division: Sum of percentage uncertainties
Uncertainty graphs
Gradient uncertainty: (Maximum graident - minimum gradient)/2
Y-intercept: Maximum/minimum y-intercept - bestfit y-intercept (largest difference determines maximum or minimum)
Error bars: Shows the uncertainty of the best line based on the systematic error.
Analytical techniques
In organic chemistry with isomers, the molecular formula is no longer enough to figure out what the structure of a molecule is. In addition, we need to apply analytical techniques.
Overview of analytical techniques
There are 4 analytical techniques that you are required to know, each provides different information which is needed to build a full picture:
| Technique |
Description |
information it provides |
| Index of hydrogen deficiency (IHD) |
This is a number which tells us how many hydrogens are missing from what the saturated form of the molecule would have. |
Degree of saturation in molecule |
| Mass spectrometry (MS) |
Sample of molecule is put into mass spectrometer which ionises the molecule forming different fragments with different masses, which can be detected.
|
Spikes tell us mass of fragments, which depending on mass, gives possible fragments that may exist in the molecule. |
| Infrared spectroscopy (IR) |
Shows different absorptions by bonds in the molecule of different frequencies of light shined on it. |
Frequency of spikes can be compared with data booklet to tell what bonds are present |
| proton nuclear magnetic resonance spectroscopy (1H NMR) |
In strong magnetic field the hydrogen atoms which possess a spin will align with or against the magnetic field.The shift in frequency of the nuclei, gives the chemical shift. |
- Chemical shift gives the chemical environment of the hydrogens
- Integration trace tells the relative number of hydrogens in each environment.
|
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