Important Bits Atomic Structure and Amount of Substance

Question 1

Why is it necessary to ionise atoms in the sample?

Answer 1

Turn into positive ions to be detected and accelerated.

Question 2

What is adjusted so each isotopes can be detected in turn?

Answer 2

Magnetic field, different fields of different masses reaching the detector.

Question 3

Why is actual yield not 100 percent?

Answer 3

• Incomplete reactions
• Practical losses (eg. pouring or filtering)
• Side reactions
• Reversible reactions
• Impurities in reactants

Question 4

Convert degrees C to K

Answer 4

+273

Question 5

Convert KPa to Pa

Answer 5

x1,000

Question 6

Convert cm^3 to m^3

Answer 6

x10^-6

Question 7

Convert dm^3 to m^3

Answer 7

x10^-3

Question 8

Easiest moles equation?

Answer 8

Moles = mass/Mr

Question 9

Moles equation using volume of gas using dm^3?

Answer 9

Moles = volume of gas in dm^3 / 24

Question 10

Moles equation using volumes of gas in cm^3?

Answer 10

Moles = volume of gas in cm^3 / 24,000

Question 11

Equation for concentration in moldm^-3?

Answer 11

Conc. in moldm^-3n = conc in gdm^-3 / Mr

Question 12

Factors that affect ionisation energy.

Answer 12

Atomic radius, nuclear charge, shielding.

Question 13

Explain how atomic radius affects ionisation energy.

Answer 13

The closer the e-s to the nucleus the stronger the attraction from the nucleus to the e-s.

Question 14

Explain how nuclear charge affects ionisation energy.

Answer 14

The more protons in the nucleus the stronger the attraction from the nucleus to the e-s.

Question 15

Explain how shielding affects ionisation energy.

Answer 15

The less shells of e-s shielding/repelling the e-s the stronger the attraction from the nucleus to the e-s.

Question 16

Equation for electron impact.

Answer 16

X(g) -> X+(g) + e-

Question 17

Equation for electrospray.

Answer 17

X(g) + H+ -> XH+(g)

Question 18

Electron impact summary.

Answer 18

• Sample vaporised
• ‘Electron gun’ fires high energy e-s at sample
• Knocks e- off
• Becomes 1+ ion

Question 19

What is electron impact used for?

Answer 19

Low Mr compounds and elements.

Question 20

Electrospray summary.

Answer 20

• Sample dissolved in volatile solvent
• Injected through fine hypodermic needle to give aerosol at high pressure
• High voltage applied through needle
• Each particle gains a proton (H+) ion
• Solvent evaporates
• Leaves 1+ ions

Question 21

What is electrospray used for?

Answer 21

High Mr compounds (eg. proteins).

Question 22

Define rel. atomic mass.

Answer 22

One atom of an element / 1/12 mass of one atom of carbon-12

Question 23

Calculate Ar.

Answer 23

Total mass of all atoms / total number of atoms

Question 24

What is special about Cr e- arrangement?

Answer 24

4s1, 3d5

Question 25

What is special about Cu e- arrangement?

Answer 25

4s1, 3d10

Question 26

Define 1st ionisation energy

Answer 26

The energy required to remove 1 e- from each atom in a mole of gaseous atoms producing 1 mole of gaseous 1+ atoms.

Question 27

Ionisation energy trend down a group.

Answer 27

Downward trend. Bigger atomic radius, more shielding so weaker attraction from nucleus to e- in outer shell.

Question 28

Ionisation energy trend across a period.

Answer 28

Upward trend. Increased nuclear charge, smaller atomic radius, similar shielding so stronger attraction from nucleus to e- in outer shell.

Question 29

Exceptions to ionisation energy trend across a period.

Answer 29

Group 2-3 dip. Electron in p orbital higher energy than s subshell, extra shielding from extra s orbital so easier to remove e-.
Group 5-6 dip. G6 loses e- from orbital with 2 e-s (p4), G5 loses e- from orbital with 1 e- (p5) so extra electron repulsion makes it easier to lose form p4 than p5.

Question 30

Define empirical formula.

Answer 30

The simplest whole no. ratio of atoms of each element in a compound.

Question 31

Define molecular formula.

Answer 31

The actual no. of atoms in each element in a compound.

Question 32

Steps to calculate empirical formulae.

Answer 32

% / mass in periodic table, / lowest no. from step 1, if fraction x to get whole no.s.

Question 33

Steps to calculate molecular formulae.

Answer 33

Find empirical mass (little no. x mass in periodic), Mr/empirical mass, scale up by result in step 2.

Question 34

Steps to calculate water of crystallisation.

Answer 34

% / formula mass of compound, / by lowest no. from step 1, that number is .x .

Question 35

Define relative molecular mass (Mr).

Answer 35

Mr = average mass of one molecule / 1/12 mass of one element of carbon-12

Question 36

Avagadro’s constant?

Answer 36

6.022 x 10^-23`

Question 37

Define molar mass.

Answer 37

Mass of 1 mole of a substance in g.

Question 38

Steps to reacting mass calculations.

Answer 38

Find moles of one you know, use ratio in equation to get moles of unknown, mass = moles x Mr.

Question 39

Steps to calculating volumes of gases in equations.

Answer 39

Moles of one you know, ratio to find one you don’t, vol. = moles x 24.

Question 40

Equation for % yield?

Answer 40

% yield = actual yield / theoretical yield x 100

Question 41

Define actual yield.

Answer 41

What you make in the lab.

Question 42

Define theoretical yield.

Answer 42

What you should make using a calculation.

Question 43

% atom economy equation?

Answer 43

% atom economy = total Mr of desired product / total Mr of all reactants x 100

Question 44

For % atom econ. what should you include in calculations?

Answer 44

BIG NUMBERS!

Question 45

Moles equation using conc. and vol.?

Answer 45

Moles = conc. x vol. in dm^3

Question 46

Steps to titration calculations.

Answer 46

Find the moles of one you know (use vol. and conc.), find moles of unknown with equation, find conc. of unknown (conc. = moles/vol. in dm^3)