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General Chemistry 2 summary wur
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A summary of the General Chemistry 2 syllabus. It includes chapter 1-7, for the biotechnology programm.
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General Chemistry 2 summaryBy Emma Burgwal, wur
Chapter 1
Friction or drag: this is a type of force which works against other forces; if you stop pedalling, your
bike will eventually stop rolling.
Moving particles slow down because of friction, unless we apply a force. When something has a
f
constant force (f), it will eventually have a constant velocity (drift velocity). v= , in which ζ is the
ζ
friction coefficient. This is a constant or can be determined with Stokes’ law for spherical objects:
ζ =6 πηr , in which η is the viscosity of the fluid medium.
Flux (J): the amount of material that is transported per unit time through an area.
J=cv , in which c is the concentration.
Sedimentation: heavy particles dispersed in a liquid settle to the bottom of a vessel under influence
of gravity. Force here: f =mg− ρVg=ΔρVg , where ρ is the density and g is 9,81. This gives:
ΔρVg
v= . Creaming: particles that are lighter than their surrounding move upwards.
ζ
Diffusion: particles spread from an area of high concentration to an area with low concentration. In a
collection of random movements, the average particle will move from high to low, not every particle
goes from high to low!
δc
Diffusion follows Fick’s laws: J=−D , where D is the diffusion coefficient. This is a measure for
δx
how rapidly the particles are diffusing.
δc
The total flux can also be calculated: Jtot=Jdrift+ Jdif =vc −D . After some time an
δx
mg δc
equilibrium will be reached. For molecules in a gravitational field Jtot=0., because Jtot= −D .
ζ δx
kbT
This gives that D= , the Einstein relation. This formula can only be used to calculate the
ζ
diffusion coefficient of microscopic objects (like ions etc). For a spherical particle, the following
kbT
equation is used: D= .
6 πηr
Brownian motion: in his study, pollen grains were always moving around even though this
phenomenon had noting to do with life. This motion is caused by constant collisions between the
particles.
This gives us an understanding about diffusion; the random collisions are a random walk. A particle
only has a small probability to be found near its starting point, due to the mean square displacement:
√ x 2=√1∗λ 2+1∗¿ ¿ ¿, where λ the length is. So ¿ x 2 ≥ i λ 2 and ¿ x 2> ¿<v > λt .
The relation between x and the diffusion coefficient is: ¿ x 2> ¿ 2 Dt and for three-dimensional object
¿ x 2> ¿ 6 Dt .
Ecell
Electric fields can also drag particles through a solution. ε = and f =zeε .
l
ze ze
Velocity: v= ε . Ze/ζ is a constant, defined as the mobility of ions: u= . We can combine this
ζ ζ
, ze
equation with Stokes’ law: u= , table 1.1 has listed the mobility u of several ions. R is this
6 πηr
formula is the hydrodynamic radius; the effective radius of the ion in water. Protons have very high
mobilities, because the move by different transport. This involves a rearrangement of covalent
bonds.
kbT
The diffusion coefficient can also be calculated with the mobility: D= u . Electrophoresis is the
ze
migration of macroions in an electric field. The net charge of a protein depends on its pH. There is a
pH-charge where the net charge of an ion is zero; iso-electric point.
In membranes a difference in concentration gradient leads to diffusion. This can be done by passive
transport through channels. The potential difference can be calculated with the Nernst equation:
−kbT cout
Emem , eq=Eout−Ein= ln .Membrane potential difference are important for a lot of
ze cin
things, for example the signalling in cells.
With two electrodes, the total current can be found. Each kind of ion contributes to this number:
Ii= AJ ∨z∨F , where zF is the charge per mole of ions of type i.
AFΣc|z|u
This leads to: I =( ) Ecell .
l
AFΣc∨z∨u
We can rewrite Ohm’s law for conductance: C= and I =CEcell . We can also define
l
the conductivity: κ=Σλc=FΣ |z|uc .
Chapter 2
Volta discovered that electricity can be produced with two different metals. The chemical reactions
involved here are redox reactions. Electrons move from one species to another. The species that
loses electrons is oxidized, the one that gains electrons is reduced. The one that gets oxidized is de
reducing agent and vice versa.
A redox reaction is the sum of half-reactions.
To systematically track change of electrons, chemists use the oxidation number. A few rules can help
with predicting the oxidation number:
1. The oxidation number of an atom in an element is zero
2. The oxidation number of a mono-atomic ion is equal to its charge (Cu 2+ has +2)
3. H is +1, O is -2 and F, Cl, Br, I are -1
So: a redox reaction is a reaction in which two or more atoms change their oxidation number.
How to balance a half-reaction:
1. Balance the elements other than hydrogen and oxygen
2. Balance O by adding H2O or OH-
3. Balance H by adding H+
4. Acidic: at H+ to both sides. Alkaline: at OH- to both sides.
5. Balance the charge of electrons
6. Make the number of electrons in each half-reaction equal (multiplying)
7. Add or subtract half-reactions
8. Get rid of redundant terms.
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