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Things I get wrong > Chem - Physical Yr 1 > Flashcards

Chem - Physical Yr 1 Flashcards

1
Q

Time of flight mass spectrometer - Steps of electron impact

A
  • an electron gun fires high energy electrons at the sample
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2
Q

Time of flight mass spectrometer - steps of electrospray ionisation

A
  • sample dissolved in a polar solvent
  • injected through a fine needle with a high voltage
  • sample gains a proton
  • forms MH+
  • solvent evaporates and MH+ move towards negative plate
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3
Q

What happens when electron impact is used on larger organic molecules?

A

They fracture

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4
Q

Which type of ionisation for a low formula mass substance

A
  • electron impact
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5
Q

Which type of ionisation for larger organic molecules?

A
  • electrospray ionisation
  • ‘softer’ conditions - less likely to fragement
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6
Q

Time of flight mass spectrometer - detection

A
  • ions hit a detector and gains an electron - this generates a current
  • the current is proportional to the abundance
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7
Q

State and explain the trend of 1st Ionisation energy down a period

A
  • decreases
  • outer electron in shells further away from the nucleus
  • increased shielding
  • attraction becomes smaller
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8
Q

State and explain the tend in 1st ionisation energy across a period

A
  • increases
  • same shell - same shielding
  • number of protons increases
  • nuclear attraction becomes greater
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9
Q

State and explain what happens in the 1st ionisation energy between Mg and Al

A
  • decrease
  • Al is 3p whereas Mg is 3s
  • electrons in 3p are easier to remove
  • electrons are higher energy and more shielding
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10
Q

State and explain what happens in the 1st ionisation energy between P and S

A
  • decrease
  • 4 electron in 3p in S
  • slight repulsion between two negatively charged electrons
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11
Q

Define a mole

A
  • amount of substance in grams that has the same number of particles as there are in 12 grams of carbon-12
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12
Q

Define relative atomic mass

A
  • the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
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13
Q

Define relative molecular mass

A
  • average mass if a molecule compared to one twelfth of a mass of one carbon-12
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14
Q

Define Avogadro’s constant

A
  • one mole of any specified entity contains 6.022x10^23 of that entity
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15
Q

Avogrado’s formula

A

particles = moles X Avogadro’s constant

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16
Q

Define empirical formula

A
  • simplest ratio of atoms of each element in a compound
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17
Q

Define molecular formula

A
  • actual number of atoms of each element in the compound
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18
Q

Why do we use a lid in experiments?

A
  • improves the accuracy - prevents loss of solid but gas should still be able to escape
19
Q

How do you convert m^3 to dm^3

A
  • times by 1000
20
Q

How do you convert from g dm^-3 to moldm^-3

A
  • divide by mr
21
Q

How do you make a solution?

A
  • weigh mass of weighing boat and required mass on a balance
  • transfer to a beaker and reweigh the weighing boat
  • record the difference in mass
  • add 100cm^3 to the beaker - use a glass rod to stir - helps to dissolve
  • ( if not dissolving in cold water, you could gently heat until solid is dissolved)
  • pour solution into a 250cm^3 graduated flask using a funnel
  • rinse the beaker and funnel and add the washings from the beaker and glass rod to the volumetric flask
  • make up to the mark with distilled water using a dropping pipette for last few drops
  • invert the flask several times to ensure a uniform solution is produced
22
Q

How do you dilute a solution?

A
  • pipette 25cm^3 of the solution into a 250cm^3 volumetric flask
  • make up to the mark with distilled water - use dropping pipette for last few drops
  • invert the flask several times to ensure a uniform solution is produced
23
Q

Why use a volumetric pipette instead of a measuring cylinder

A
  • more accurate - smaller uncertainty
24
Q

Dilutions formula

A

new diluted concentration = original concentration x (original volume/ new diluted volume)

25
Q

What are the units for the different things in: pV = nRT

A
  • pressure = Pa
  • volume = m^3
  • Temp = K
  • n = moles
26
Q

What are the potential errors in using a gas syringe?

A
  • gas escapes before bung is inserted
  • the syringe sticks
  • some gases like CO2 are soluble in water - true amount of gas is not measured
27
Q

What is the volume of 1 mole of any gas at room temperature and pressure?

A

24dm^3

28
Q

Do chemists want a high percentage yield?

A
  • yes - means there has been an efficient conversion of reactants to products
29
Q

Do chemists want a higher percentage atom economy?

A
  • yes - maximum mass of reactants ends up in the desired product
30
Q

How do you do a titration?

A
  • rinse equipment ( burette with acid, pipette with alkali and conical flask with distilled water)
  • pipette 25cm^3 of alkali into conical flask
  • touch surface of alkali with the pipette - ensures the correct amount was added
  • pour acid solution into burette
  • make sure jet space is filled with acid
  • add a few drops of indicator
  • use a white tile underneath whilst swirling and add acid dropwise at end point
  • note burette reading before and after addition of acid
  • repeat titrations until concordant results are reached - two within 0.1 of each other
31
Q

What happens if the jet space isn’t filled properly prior to titration

A
  • leads to larger than expected reading
32
Q

How do you reduce the % uncertainty in a burette reading?

A
  • increase the volume and concentration of the substance in the conical flask
  • decreasing the concentration of the substance in the burette
33
Q

If % uncertainity due to apparatus < % difference - what does this mean?

A
  • there is a discrepancy in the result due to other errors
34
Q

If % uncertainity due to apparatus > % difference - what does this mean?

A
  • there is no discrepancy and all the difference between the values can be explained by the sensitivity of the equipment
35
Q

Define enthalpy change

A
  • amount of heat energy taken in or given out during any change in a system provided the pressure is constant
36
Q

What happens in an exothermic reaction and what is the sign?

A
  • energy is transferred from the system to the surroundings
  • the products have less energy than the reactants
  • enthalpy change is negative
  • (also feel hot)
37
Q

What happens in an endothermic reaction and what is the sign?

A
  • energy is transferred from the surroundings to the system
  • require an input of heat energy
  • products have more energy than the reactants
  • enthalpy change is positive
  • (also feels cold)
37
Q

Define standard enthalpy of formation

A
  • one mole of the compound is formed from its elements under standard conditions and all reactants and products are in their standard states
37
Q

Define standard enthalpy of combustion

A
  • one mole of a substnace is combusted completely in oxygen under standard conditions and all the reactants and products are in their standard state
38
Q

What are the standard conditions?

A
  • 100 kPa pressure
  • 298K temperature
  • solutions at 1 moldm^-3
  • all substances should have their normal state at 298K
39
Q

what are the errors in measuring the enthalpy of combustion using calorimetry?

A
  • energy losses from the calorimeter
  • incomplete combustion of fuel
  • incomplete energy transfer
  • evaporation of fuel after weighing
  • heat capacity of calorimeter not included
  • measurements not carried out under standard conditions
40
Q

Define Hess’s law

A
  • total enthalpy change for a reaction is independent of the route by which the chemical change takes place
41
Q

define mean bond energies

A
  • the enthalpy needed to break the covalent bond into gaseous atoms, arranged over different molecules
42
Q
A

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