OG unit 1.3 Flashcards
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
For different isotopes (12C6, 13C6, 14C6), what would be the difference in terms of protons, neutrons and electrons?
Protons - stays the same (atomic number)
Neutrons - changes (probably cuz mix of protons & electrons type shi)
Electrons - stays the same (perhaps atomic number too?)
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
What are the 3 different formulas for moles ?
Solid - Mass/molar mass = n
Liquid - concentration x volume = n
Gas - volume/molar volume = 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)
(the liquid type shi)
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
How to gain concentration of a certain chemical present in a solution?
Conc. of NAOH solution when 4.0g of NaOH powder dissolved in 250cm^3 of distilled water? (in moldm^-3)
Know this:
n = cv
and rearrange for n =
c = n/v
and also know n = m/M
- Since it’s moldm^-3,
- Convert 250cm^3 to dm^3
= 250/1000 = 0.25dm^-3 - Gain mr of NaOH
- 25 + 16 + 1.01 = 40.01 - Gain moles
- 4/40.01 = 0.0999 - Divide Tingy n stuff
- 0.0999/0.25 = 0.3996moldm^-3
(you are using both solid & liquid formulas)
How to find concentration of chemicals with just their solubility?
Solubility of ammonium chloride , NH4Cl is 37.2g/100g water. What is the concentration in moldm^-3?
n = m/M
moles = mass/mr
- When u convert for dm^3, mass gotta be times by 10
- 37.2 & 100cm^3
= 372 & 1dm^3 - n = m/M with the NH4Cl
- 372/(14 + 4.04 + 35.5)
= 6.95 moldm^-3
Doesn’t make sense but just go with it man :(
Wat percentage yield?
uhhh idk the info it no say, only for actual and theoretical
How effective a reaction is
But here’s the formula:
Percentage yield = (Actual yield/Theoretical yield) x 100
2 reasons for how percentage yield may be below 100%?
- Not all reactants react
- Impurities in reactants
The simplified formula for percentage yield?
(what you get/what you should get) x 100
How would u get the theoretical yield specifically?
3.00g of ethanoic anhydride reacts with water to give ethanoic acid.
(CH3CO)2O + H2O –> 2CH3COOH
Calculate theoretical yield
- Mole ratio first
- Gain mr for that specific compound (CH3CO)2O and then do mass/mr
- It’s 1:2 so 0.03 x 2 = 0.06 mols (Look in book for more details) - mass = mols x mr
- 0.06 x 60.04 = 3.60g <– that’s the theoretical yield ig
(don’t include the 2 in front)
How to really get the percentage yield?
When 18.0g of propan-1-ol (C3H8O) was reacted with excess acidified sodium dichromate, 7.20g of propanol (C3H6O) were obtained. Calculate percentage yield given the equation
3C3H8O + Na2Cr2O7 + 4H2SO4 –> 3C3H6O + Na2SO4 + 7H2O
- We got the masses for the propanols sooo we gain mr first for both
- 3C3H8O =
36 + 8.08 + 16 = 60.08
- 3C3H6O =
36 + 6.06 + 16 = 58.06
(DON’T INCLUDE THE NUMBERS INFRONT OF EM) - Do mass/mr = mols
- 18/60.08 = 0.29
- 7.20/58.06 = 0.12 - The real percentage yield (actual/theoretical) x 100
- 0.12/0.29 x 100 = 41.4%
What 2 things atom economy check?
- How much of the reactants are turned into desirable products
- And how much is waste product
Formula for atom economy?
(molecular mass of desired product/sum of molecular masses of all products) x 100
How to calculate atom economy for this one?
CH3CH2OH + HBr –> CH3CH2Br + H2O
The desired product is bromoethane
- Gain mr of CH3CH2Br (that’s bromoethane)
- 24 + 5.05 + 79.9 = 108.95 - Add mr of bromoethane with water
- mr of H2O = 2.02 + 16 = 18.02
- 108.95 + 180.02 = 126.97 - (Mr of bromoethane/Mr of resultant products altogether) x 100
- (108.95/126.97) x 100 = 85.8%
Look at the last question of atom economy in the book cuz it has both atom economy and percentage yield soooo ye
How do u comment on atom economy and percentage yield??
Ohhhhh kayyyyyyy.
Atom economy
- High % = Efficient reaction
- Low % = Not efficient at all, high waste products, not sustainable
Percentage yield
- High % = Effective reaction
- Low % = Not an effective reaction, impurities probably present
We just keep continuing. Also questions are good for answering so ye idk do something, am currently sick rn
Sick of you losing
¬.¬
> :|
How to do percentage errors?
(mass and time are the same,
volume is a lil different D:)
- Say u want to find the percentage error for mass 1g
- For 2 decimal place balance, nearest would be 0.01g
- Formula: (0.01/1g) x 100 = 1%
- For 3 decimal place: (0.001/1g) x 100 = 0.1%
- How how about 2 decimal place for 10g?: (0.01/10g) x 100 = 0.1%
- Say for time, 100s, it’s probably 2 decimal places depending on how many 0s in decimal place thingy
- soooo: (0.01/100) x 100 = 0.01%
- Now for volume
- Consider measuring 25cm3 in a 25cm3 measuring cylinder
- Apparently it’s the nearest 0.5cm3 and idk why
- Therefore: (0.5/25) x 100 = 2.0%
- For a burette, nearest 0.05cm3 as well?
- Aiming for a titre of 25cm3 as well?
- Formula: (2x0.05/25) x 100 = 0.4%
My question is, why the 2x there?
Concluding tho:
- Look at the minimum number u can get (it’s the decimal places)
- grams always denominator
- And tbh it’s like finding any other percentage in general
