Chem Unit 1 (Amount of substance)

Question 1

Relative atomic mass

Answer 1

average mass of an atom of an element/ 1/12 of a mass of carbon-12
Number of protons and neutrons added together

Question 2

Relative molecular mass

Answer 2

average mass of a molecule/ 1/12 of the mass of an atom of carbon-12
add together the number of atoms in each element in a molecule

Question 3

Relative formula mass

Answer 3

mass of the formula unit (ratio of each type of atom in a lattice)
adding the number of atoms of each element in the lattice

Question 4

Avogadro’s constant

Answer 4

number of atoms in 12g of carbon-12
6.023 x 10 23
a mole of particles contains 6.023 x 10 23 particles.

Question 5

How do you use Avogadro’s constant?

Answer 5

To work out the number of moles of a substance you times the mass of a single atom x Avogadro’s constant.

Question 6

How do you work out the mass of a single atom?

Answer 6

Example: 1 H - You would add together 1 proton and 1 electron
1 H + - You would add together 2 protons
3 H - You would add 2 neutrons and 1 proton
If it just asks yo to work out the MASS you don’t need to times by the Avogadro’s constant next.
If it gives you Mr moles = mass / Mr

Question 7

Empirical formula

Answer 7

Simplest whole number ratio of atoms of each element in a compound.

Question 8

Molecular formula

Answer 8

Actual number of atoms of each element in a compound.

Question 9

How do you work empirical and molecular formula out?

Answer 9

Empirical: Divide % or given mass by atomic mass
Divide by smallest number to get simplest ratio
Molecular: Divide Mr of whole thing (given) by the Mr of empirical formula (Atomic masses of each of the elements in the compound.

Question 10

What is percentage yield?

Answer 10

actual yield / theoretical yield x 100

Question 11

How do you work out % yield?

Answer 11

Theoretical mass: Mr of reactants
moles = mass/Mr [DON’T RATIO HERE]
ratio out moles for products
Mass = moles x Mr of products
Actual yield (given) / Your theoretical yield x 100
Reasons why it was less: reversible reactants in impurities

Question 12

What is atom economy?

Answer 12

mass of desired products / total mass of reactants x 100

Question 13

How do you work out atom economy?

Answer 13

No given numbers
Divide the Mr of the desired product / Mr of ALL THE REACTANTS x 100
NO RATIO

Question 14

If there is only one product…

Answer 14

The atom economy must be OVER 100%

Question 15

Why is a higher atom economy better?

Answer 15

• less disposable cost
• less waste
• cheaper to manufacture

Question 16

What are isotopes?

Answer 16

Atoms of the same element with the same number of protons but a different number of neutrons.

Question 17

Chemical and physical properties of isotopes?

Answer 17

Chemical: same because the arrangement of electrons are the same.
Physical: Different because the mass will slightly vary.

Question 18

% isotopic abundance?

Answer 18

The % of each isotope that naturally occurs o earth
Different in space- different %’s (isotopic signature)
Values in data book and mass spec data is going to be different because the % isotopic abundance is going to be different.

Question 19

Ideal Gas properties and realistic?

Answer 19

Particles are constantly in motion
They’re constantly colliding
These collisions don’t produce reactions
Kinetic energy is conserved
No intermolecular forces that divert their path range.
Real gasses DO have intermolecular forces that divert the path of particles.
Some can act like ideal gasses under limited temperature and pressure ranges.

Question 20

Idea; Gas Equation?

Answer 20

pv = nRT

Question 21

Conversions for cm3, dm3> m3?

Answer 21

cm3 x 10-3 = dm3
dm3 x 10-3 = m3
cm3 x 10-6 = m3

Question 22

Conversions for degrees>kelvin

kPa/Mpa>Pa

Answer 22

Degrees + 273 = K
kPa x 10-3 = Pa
mPa x 10-6 Pa

Question 23

To work out Mr for ideal gas equation?

Answer 23

n = PV/RT
n (moles) = mass/Mr
Mr = moles / mass

Question 24

How do you work out concentration?

Answer 24

conc = moles/ vol

Question 25

standard solutions?

Answer 25

solutions where a known volume is used

Question 26

titrations are used for?

Answer 26

used to find out a volume of an an acid of a base at a particular concentration.

Question 27

Conversion for dm3?

Answer 27

cm x 10-3 = dm3

1l = 1dm3

Question 28

To find it in g/dm-3 instead of mol/dm-3?

Answer 28

work out concentration in mol/dm-3 and x Mr

Question 29

if it gives you a neutrilisation reaction to work out the unknown concentration?

Answer 29

work out the moles of the other thing using conc and vol
ratio out the moles
work out the conc using the moles and the volume it gave

Question 30

If it gives you a amount of the original soltution and asks you to work out the mass used in the original soltuion?

Answer 30

Work out the moles conc x vol
This is for the sample (e.g. 25 cm3 of the original 250 cm3)
Times the moles by the same amount for the sample to go into the original amount e.g. 25 x 10 = 250
Do mass = moles x Mr

Question 31

Mass spectromy can be sued to find?

Answer 31

% isotiopic abundance

realtive atomic mass

Question 32

Low-resolution mass soectormy is..?

Answer 32

uslly used (1 d.p)
high= 5 d.p

Question 33

Steps of mass spectrometer?

Answer 33

1) Vaporization- mas is heated into solid
2) Ionisation- beam of electorns form a high-energy elctron gun>remove electrosn to make atoms into 1+ ions
3) Acceleration= The ions are attratced tp th negatively charged plates>produce an electric field acclerates them twowards the electromagnet
4) Deflection- The elctromagnet produces a magnetic field>deflects them at right-snglers from direction of travel
5) Hit a detector (straight line down)- small electric signal generates current (gives you the % abundance)

Question 34

What infleunces the deflection?

Answer 34

• lighter ions deflecte dmore (away)/heaveir less
  -ions wiht positive charge deflected more
  -operating conditions- stronger magnetic field deflect them more
  temperature no difference

Question 35

working out relatvie siotopic aabundance?

Answer 35

m/z value x % abundance divided by 100

Question 36

working out relative atomic mass/intensity?

Answer 36

m/z value x relative atomic/intensity divied by sum of the relatve atomic mass/intensity
assume the % abundanc/relative aotmic mass/intensity is 1 unless it tells you

Question 37

if one moelcuel has got a lone pair and the other hasn’t got any lone pairs it might be?

Answer 37

dative/co-ordiante bonding by the one that has got a lone pair

Question 38

selenium deviates from the trend in Group 7 as?

Answer 38

it should take a huigher meltng point but they are psired electorns in the 4p orbital