physical chemistry Flashcards
explain the existence of iscotopes
Isotopes are atoms of the same element with the same atomic number, but with a different number of neutrons, resulting in a different mass number
principles of a simple time of flight (TOF) mass
spectrometer
- vaporization (ensure molecules are seperated)
- ionisation ( turning molecules into overall posative ions)
- aceleration (a negatively charged plate attracts and acellerates all ions to move with same amount of Ek)
- Ion detection (the more posative ions, the more difference in charge, the greater the current is indduced)
- speed of ions ( mass and speed are iversley porportional, so higher speed means lower mass)
what is tof mass spectrometer use for?
-determining abundunce of iscotopes
-determining the mass of iscotopes
-determining the number of the types of iscotopes
( in a sample)
what is electron bombardment?
- electrons are fired at sample molecules via an electron gun
- electrons in the orbit of molecules are knock away by the high speed elcetrons from the gun
- thus molecules turns ino a posative ion
what is electrospray?
- sample is inserted into a hypothermic neddle
- a posative terminal is attatched at the end of the neddle
- thus an extra photon is attatched to each molecule passing through the end of needle
- the needle will then release the sample as mist
how to read a simple mass spectra? (without fragmentation)
- x axis is mass divided by charge (Q is usually +1)
- number of vertcal lines = no of iscotopes
how to read simple mass spectra? (with fragmentation)
- fragmentation is when molecules are broken down into fragments due to colliding with hign speed electrons from electron bombardment
- thus the no. of vertical lines > no. of iscotopes
- vertical line with highest mass = original molecule
how to caculate mass of molecule in tof ms? (with 2 sets of iscotopes with 2 known time but only one known mass)
√(Mr1/Mr2) x t of Ar2
Ar applies as well
It is ok to use mass number instead of mass in Kg
how to caculate the V of an iscotope in Tof ms? (with known Ek and mass)
use Ek = 0.5m x v^(2)
how to caculate abundence of iscotope (with 2 known masses of iscotope and the average mass of element)
average mass number = Ar1(X)+Ar2(100-X))/100
let X be one of the abundence of the iscotopes
def of 1st ionisation energy
the E needed to remove 1 mole e- from the most outer shell from 1 mole of an element in gas state
electron configuration hierachy accordingfrom low to high energy level
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6
how does sucessive ionisation E show the group no.
-a high jump in sucessive E shows that there is a change in the energy level
-just count back how many e- are removed before the jump to infer the no of e- in outer shell
why are there dips in period 3 1st ionisation energy trend
-Mg Al dip
* Mg has an electron configuration of 1s2 2s2 2p6 3s2
* Al has an electron configuration of 1s2 2s2 2p6 3s2 3p1
* 3p orbital has more E than 3s
- P S dip
* P has paired electrons
* S has unpaired electrons
* paired electrons repeal
def of reletive atomic mass:
mass of the element compare to the mass of 1 12th of the mass of C12
same appleies for reletive molecular mass but replace element with molec
ideal gas equation
PV=nRT
* P is preasure in pa
* v is volume m^3
* n is number of moles
* T is temperature in k
converting pa to atm
101325pa is 1amt
what is empiral fomula
the simplest hole number ratio of each atoms in a compound
how to caculate emprial fomula ( with mass no of elements and their abundence in the compound)
- divide the percentages with the corresponding mass number of the same element
- divide each ratio by the smallest ratio
- those numbers can then be round to the nearest whole number and apply on empiral fomula
percentage yield and atomic economy
percentage yeild: actual yeild divided by theroetical yeild
atom economy : percentage of product moles produced from reactant moles
conducting RP1a
making a standard solution:
1. measure 2 g of NaOH powder from a weighing boat
2. pour powder into beaker and half fill it with distiled water
3. rinse the weighing boat with distilte water and pour the rinse water into beaker
4. mix the solution with glass rod until no deposits are seen at the bottom
5. pour solution into a volumetric flask through a funnel
6. rinse the glass rod and beaker with distilte water and pour the rinse water into volumetric flask
7. topple the volumetric flask to the 250cm^3 mark, with the local minimum of the miniscus just touching the mark
8. redo the whole process if you pour too much water
9. invert the volumetric flask few times to ensure the solution is well mixed
conducting RP1b
conducting a titration
1. caculate the concentration of standard solution of NaOH
2. prepare 25 cm^3 of unknown HCl soultion
3. set up tirtation with HCl being tirated
4. add methyl orange to HCl
5. adding NaOH drop by drop through the use of burret
6. as the coulour changes from orange to red, the tiration is complete
remeber to swirl it ocassionally
place a white tile under HCl to enthzize the colour change
trends of melting/boiling point of metals
- as going down the group, the melting point decrease
- more e- means there is more distance between posative nulceus and sea of e-
- thus weakens the electrostatic attraction
