1.3 Chemical calculations (re)
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This may be our downfall, for such a teacher we were given it’s basically gon be solo yolo, but what is the purpose for teachers? Bruh
You raise a good point! he definitely raised a good point guys
Formula for relative atomic mass? 75% Cl-35 and 25% Cl-37
% x atomic number / 100 also add em at the top (75x35)+(25x37)/100 = 35.5
What’s a mass spectrometer? (3 things)
• An analytical technique • Used to identify different isotopes • And find overall relative atomic mass of an element
Explain step 1: Ionisation in mass spectrometry? (5 things)
• A sample of an element is vapourised and injected - Into mass spectrometer - Where high voltage passed over chamber - Causes electrons to be removed from atoms (ionised) - Leaving 1+ charged ions in chamber
Explain step 2: Acceleration in mass spectrometry? (2 things)
• Positively charged ions are accelerated towards - Negatively charged detection plate
Explain step 3: Ion drift in mass spectrometry? (4 things)
• Ions deflected by magnetic field - Into a curved path - Radius of their path dependent on - Charge & mass of ion
Explain step 4: Detection in mass spectrometry? (4 things)
• When positive ions hit negatively charged detection plate, - They gain an electron - Producing flow of charge - Greater current produced = greater abundance
Explain step 5: Analysis in mass spectrometry? (4 things)
• Current values used in combination - With flight times to produce - Spectra print-out - With relative abundance of each isotope displayed
In mass spectrum, why do we see a half traced version of the ion? (5 things)
• During ionisation process, 2+ charged ion may be produced • Will be affected more by magnetic field • Producing curved path of a smaller radius • As a result, mass to charge ratio (m/z) is halved • Can be seen on spectra as a trace at half the expected m/z value
In mass spectrum: What m/z? What relative abundance? > _>
• Mass to charge ratio • Relative atomic mass? icl i haven’t seen where u had to put a number for a certain bar so i reckon u don’t get fucked up by this one I changed it lol
For mass spectra graph, how u gain mass for the 2 isotopes
Formula for mass of 2 isotopes: 1(relative abundance x m/z)+2(relative abundace x m/z)/ra1 + ra2 May seem a lil hard to remember but gl bro B)
How to gain empirical formula? 48.38% carbon, 8.12% hydrogen, rest is O2 (43.50%) % = their mass
mass/mr = a number (mols?) then divide that number with it (the smallest number u’ve gained) double it if the number is not whole 48.38/12 = 4.03 divided by 2.72 8.12/1.01 = 8.02 divided by 2.72 43.5/16 = 2.72 divided by 2.72 (O has a 2, perhaps i should’ve done that 2 to gain real empirical formula) 2.72 is the smallest number C = 1.5 x 2 = 3 H = 3 x 2 = 6 O = 1 x 2 = 2 C3H6O2
How to gain molecular formula? CH has molar mass of 78.1g/mol
molar mass/mr empirical formula CH = 12 + 1.01 = 13.01 78.1/13.01 = 6.00 = 6 C6H6
Formula for moles?
Mass/molar mass = n
How to gain mass of one molecule? H2
Mr x number of atoms then divide it by avogadro’s constant (6.02x10^23) 1.01 x 2 = 2.02 mr 2.02/6.02x10^23 = 3.36x10^-24
How to gain number of molecules in a compound? 1.058 mole of H2O
n x avogadro’s constant 1.058 x (6.02x10^23) = 6.37x10^23
How to gain moles from molar volume + volume? 120cm^3 of hydrogen at RTP (24.5 molar volume)
Volume (v) = number of moles (n) x molar volume (Vm) (also divide volume into dm^3) 0.12/24.5 = 0.0049 or 4.89 x 10^-3
How to understand mole ratio? H2O + 2H2O
• Gain moles (so use n = m/M) • The 2 on the second H2O is very important (lol) 1:2 mole ratio • So then that means mols for second H2O is double mols of first H2O :v
What is the ideal gas equation? and what’s the 3 points to note?
pV = nRT • Temp must be kelvin (0 degrees = 273K) • Pressure must be in pascals (1atm = 101325 Pa) • Volume must be m^3 (convert cm by dividing by 10^6)
Define each symbol from ‘pV = nRT’
P = pressure (Pa) V = volume (m^3) n = number of moles (mols) R = molar gas constant (8.31Jmol^-1 K-1) T = temperature (K)
What’s the simplified gas equation? and when to use it?
P1V1/T1 = P2V2/T2 Only when the moles remain constant
What equation if number of moles and volume remain constant? (simplified gas equation)
P1/T1 = P2/T2
What equation if number of moles and temperature remain constant? (simplified gas equation)
P1V1 = P2V2
What equation if number of moles and pressure remain constant? (simplified gas equation)
V1/T1 = V2/T2