still with hexaaquochromium(II)
This is the speedwell; which also looks good on frogeye Sprites! The ion also resembles this colour too
Colour in TM ions
When a TM ion is dissolved in water it will form a hexaaquo complex ion. Six water molecules acting as lizards will form dative bonds to suitable receptor orbitals on the cation. This has an effect on the energies of the d set of orbitals. Due to their profiles, and the octahedral geometry of the complex ion, their gas-phase degeneracy is lost; three fall to a lower energy level and two move to a higher level. This means that an energy seperation exits between these two sets. The d electrons are fed into these orbitals, filling up from low level as usual.
An electronic transition from low level to high level requires the absorption of some energy, and it so happens that the energy seperation corresponds to energy carried by photons of visible readiation. So, if the red end of the white light spectrum is absorbed by electron excitation, the ion will appera blue. The complementary colour is seen.
PLEASE do not reply as one candidate did one year : "The electrons get excited and jump up and down." They are NOT small children who have just heard that they are going to McDonalds for tea!
Acid sand base s
These may be helpful...
Buffers
Solns of KNOWN pH that RESIST CHANGES in ph casued by addition of SMALL amounts of acid or alkali. I have stressed the important words to use....
Continue reading "Buffers"...pH of alkaline solutions
Remember that pH is defined in terms of the concentration of hydrogen ions in the aqueous solution. If a solution contains a strong alkali [such as KOH] the concentration of hydroxide ions will be the same as that of the solute. The corresponding [H+(aq)] may then be found by utilising the ionic product of water, which happens to have a value of 1 x 10-14 mol2 dm-6 at 298K. Knowing the value of the product of two ionic concentartions, and one of those, enables the evaluation of the other...hence the pH.
The value of Kw is temperature dependent, becoming larger with an increase in temperature. This is a consequence of its definition, and of the fact that the dissociation of water to which it relates is an endothermic process.
If you are asked to complete calculations at a different temperature, then the value of Kw would be given.
some thoughts on buffers..
Weak acids are because in aqueous solutions the solute species undergoes only very limited or partial ionisation into its conjugate base and the H3O+ ion. Due to the very low standing concentration of the conjugate base, these solutions cannot function as buffers.
Adding to the weak acid solution some salt of the same acid will give immediately a large concentration of anion [i.e. conjugate base]. This will have the effect of driving the weak acid dissociation equilibrium position leftwards, thus suppressing even further its dissociation. The result is a solution with high concentrations of BOTH undissociated acid solute species AND its conjugate base. Buffer action is optimised if these two concentrations happen to be high and equal to each other.
Transition metal slides... updated...
these may be useful to you...
Download file
Coursework dates for mocks
Please put these dates into your diaries
For a little light relief...
if you have an idle moment or two...
UP
I will keep bringing this note to the top... it IS helpful and useful...
http://www.knockhardy.org.uk/sci.htm
Keeping it all in perspective..
I was going to put a sign: "YOU ARE HERE"...
Results Day
I have been informed that results are published on Thursday March 18th
Discussion Forum
this is a new BBS for you chemists
Visit the site, apply for membership, and get chatting... ...
http://www.bodmas.org/vanilla
Good web site
this is well worth a look:
http://www.knockhardy.org.uk/sci.htm
copy and paste I'm afraid... ...
Kinetics definitions
The RATE CONSTANT is a constant of proportionality that links the reaction rate to the concentrations of the reagents that actually affect the rate.
The concentration terms in the rate equation may be raised to various indices called ORDERS. The overall order of a rate equation is thus the sum of the individual orders. Remember that the orders HAVE to be determined experimentally.
Thus, if rate =k [X][Y]2 then the rate order with respect to [X] is 1 and the order with respect to [Y] is 2 and the overall order is (1+2) =3.