Measurement and analysis

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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