OG unit 1.3

Question 1

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

Answer 1

You raise a good point!

he definitely raised a good point guys

Question 2

For different isotopes (¹²C₆, ¹³C₆, ¹⁴C₆), what would be the difference in terms of protons, neutrons and electrons?

Answer 2

Protons - stays the same (atomic number)
Neutrons - changes (probably cuz mix of protons & electrons type shi)
Electrons - stays the same (perhaps atomic number too?)

Question 3

Formula for relative atomic mass?

75% Cl-35 and 25% Cl-37

Answer 3

% x atomic number / 100
also add em at the top

(75x35)+(25x37)/100
= 35.5

Question 4

What’s a mass spectrometer?
(3 things)

Answer 4

• An analytical technique
• Used to identify different isotopes
• And find overall relative atomic mass of an element

Question 5

Explain step 1: Ionisation in mass spectrometry?
(5 things)

Answer 5

1. 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

Question 6

Explain step 2: Acceleration in mass spectrometry?
(2 things)

Answer 6

2. Positively charged ions are accelerated towards
   - Negatively charged detection plate

Question 7

Explain step 3: Ion drift in mass spectrometry?
(4 things)

Answer 7

3. Ions deflected by magnetic field
   - Into a curved path
   - Radius of their path dependent on
   - Charge & mass of ion

Question 8

Explain step 4: Detection in mass spectrometry?
(4 things)

Answer 8

4. When positive ions hit negatively charged detection plate,
   - They gain an electron
   - Producing flow of charge
   - Greater current produced = greater abundance

Question 9

Explain step 5: Analysis in mass spectrometry?
(4 things)

Answer 9

5. Current values used in combination
   - With flight times to produce
   - Spectra print-out
   - With relative abundance of each isotope displayed

Question 10

In mass spectrum, why do we see a half traced version of the ion?
(5 things)

Answer 10

• 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

Question 11

In mass spectrum:
What m/z?
What relative abundance?

> _>

Answer 11

1. Mass to charge ratio
2. 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

Question 12

For mass spectra graph, how u gain mass for the 2 isotopes

Answer 12

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)

Question 13

How to gain empirical formula?

48.38% carbon, 8.12% hydrogen, rest is O2 (43.50%)

% = their mass

Answer 13

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

Question 14

How to gain molecular formula?

CH has molar mass of 78.1g/mol

Answer 14

molar mass/mr empirical formula

CH = 12 + 1.01 = 13.01

78.1/13.01 = 6.00 = 6

C6H6

Question 15

What are the 3 different formulas for moles ?

Answer 15

Solid - Mass/molar mass = n
Liquid - concentration x volume = n
Gas - volume/molar volume = n

Question 16

How to gain mass of one molecule?

H2

Answer 16

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

Question 17

How to gain number of molecules in a compound?

1.058 mole of H2O

Answer 17

n x avogadro’s constant

1.058 x (6.02x10^23) = 6.37x10^23

Question 18

How to gain moles from molar volume + volume?

120cm^3 of hydrogen at RTP (24.5 molar volume)

(the liquid type shi)

Answer 18

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

Question 19

How to understand mole ratio?

H2O + 2H2O

Answer 19

1. Gain moles (so use n = m/M)
2. The 2 on the second H2O is very important (lol)
   1:2 mole ratio
3. So then that means mols for second H2O
   is double mols of first H2O

:v

Question 20

What is the ideal gas equation?

and what’s the 3 points to note?

Answer 20

pV = nRT

1. Temp must be kelvin (0 degrees = 273K)
2. Pressure must be in pascals (1atm = 101325 Pa)
3. Volume must be m^3 (convert cm by dividing by 10^6)

Question 21

Define each symbol from ‘pV = nRT’

Answer 21

P = pressure (Pa)
V = volume (m^3)
n = number of moles (mols)
R = molar gas constant (8.31Jmol^-1 K-1)
T = temperature (K)

Question 22

What’s the simplified gas equation?
and when to use it?

Answer 22

P1V1/T1 = P2V2/T2
Only when the moles remain constant

Question 23

What equation if number of moles and volume remain constant?

(simplified gas equation)

Answer 23

P1/T1 = P2/T2

Question 24

What equation if number of moles and temperature remain constant?

(simplified gas equation)

Answer 24

P1V1 = P2V2

Question 25

What equation if number of moles and pressure remain constant? (simplified gas equation)

Answer 25

V1/T1 = V2/T2

Question 26

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**)

Answer 26

Know this: n = cv and rearrange for n = c = n/v and also know n = m/M 1. Since it's moldm^-3, - Convert 250cm^3 to dm^3 = 250/1000 = 0.25dm^-3 2. Gain mr of NaOH - 25 + 16 + 1.01 = 40.01 3. Gain moles - 4/40.01 = 0.0999 4. Divide Tingy n stuff - 0.0999/0.25 = 0.3996moldm^-3 (you are using both solid & liquid formulas)

Question 27

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?

Answer 27

n = m/M moles = mass/mr 1. When u convert for dm^3, mass gotta be times by 10 - 37.2 & 100cm^3 = 372 & 1dm^3 2. 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 :(

Question 28

Wat percentage yield?

Answer 28

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

Question 29

2 reasons for how percentage yield may be below 100%?

Answer 29

1. Not all reactants react 2. Impurities in reactants

Question 30

The simplified formula for percentage yield?

Answer 30

(what you get/what you should get) x 100

Question 31

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

Answer 31

1. 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) 2. mass = mols x mr - 0.06 x 60.04 = 3.60g <-- that's the theoretical yield ig (don't include the 2 in front)

Question 32

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

Answer 32

1. 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**) 2. Do mass/mr = mols - 18/60.08 = 0.29 - 7.20/58.06 = 0.12 3. The real percentage yield (actual/theoretical) x 100 - 0.12/0.29 x 100 = 41.4%

Question 33

What 2 things atom economy check?

Answer 33

1. How much of the reactants are turned into desirable products 2. And how much is waste product

Question 34

Formula for atom economy?

Answer 34

(molecular mass of desired product/sum of molecular masses of all products) x 100

Question 35

How to calculate atom economy for this one? CH3CH2OH + HBr --> CH3CH2Br + H2O The desired product is bromoethane

Answer 35

1. Gain mr of CH3CH2Br (that's bromoethane) - 24 + 5.05 + 79.9 = 108.95 2. Add mr of bromoethane with water - mr of H2O = 2.02 + 16 = 18.02 - 108.95 + 180.02 = 126.97 3. (Mr of bromoethane/Mr of resultant products altogether) x 100 - (108.95/126.97) x 100 = 85.8%

Question 36

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??**

Answer 36

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

Question 37

We just keep continuing. Also questions are good for answering so ye idk do something, am currently sick rn Sick of you losing

Answer 37

¬.¬ >:|

Question 38

How to do percentage errors? (mass and time are the same, volume is a lil different D:)

Answer 38

1. Say u want to find the percentage error for mass 1g 2. For 2 decimal place balance, nearest would be 0.01g 3. Formula: (0.01/1g) x 100 = 1% 4. For 3 decimal place: (0.001/1g) x 100 = 0.1% 5. How how about 2 decimal place for 10g?: (0.01/10g) x 100 = 0.1% 1. Say for time, 100s, it's probably 2 decimal places depending on how many 0s in decimal place thingy 2. soooo: (0.01/100) x 100 = 0.01% 1. Now for volume 2. Consider measuring 25cm³ in a 25cm³ measuring cylinder 3. Apparently it's the nearest 0.5cm³ and idk why 4. Therefore: (0.5/25) x 100 = 2.0% 5. For a burette, nearest 0.05cm³ as well? 6. Aiming for a titre of 25cm³ as well? 7. 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