2 amount of substance

Question 1

what is Mr?

Answer 1

relative molecular mass

Question 2

what is Ar?

Answer 2

relative atomic mass

Question 3

define Mr

Answer 3

the mean mass of a molecule of a compound divided by 1/12 of the mass of a carbon12 isotope

Question 4

define Ar

Answer 4

the mean mass of an atom of an element divided by 1/12 of the mean mass of an atom of carbon12 isotope

Question 5

what is avogadros constant?

Answer 5

6.022x10^23

Question 6

define avogadros constant

Answer 6

the number of atoms in 12g of C12

Question 7

how do you calculate moles from mass and Mr/Ar?

Answer 7

moles = mass/Mr

Question 8

where do you find the Ar of an element on the periodic table?

Answer 8

above the letters

Question 9

what is the ideal gas equation?

Answer 9

pV=nRT

Question 10

what do the letters stand for in the ideal gas equation?
what are all the units for each?

Answer 10

p= pressure (Pa)
V= volume (m^3)
n= moles
R= molar gas constant (always 8.31JKmol)
T= temp (K)

Question 11

how do you go from dm^3 to m^3?

Answer 11

divide by 1000

Question 12

how do you go from cm^3 to m^3?

Answer 12

divide by 1000000

Question 13

how do you go from °C to K?

Answer 13

+273

Question 14

how do you go from kPa to Pa?

Answer 14

x1000

Question 15

define empirical formula

Answer 15

simplest whole number ratio of atoms of each element

Question 16

define molecular formula

Answer 16

actual number of atoms of each element

Question 17

how do you find the empirical formula?

Answer 17

1. divide mass of each element by Ar of that element (moles)
2. divide all moles by the smallest number of moles

Question 18

how do you find the molecular formula of an element?

Answer 18

1. divide mass of each element by Ar of that element (moles)
2. divide all answers by smallest value of moles
3. find the total mass of empirical formula
4. divide Mr given by mass of empirical formula

Question 19

what is the equation for % atom economy?

Answer 19

mass of desired product/mass of reactants
x100

Question 20

what is the formula for % yield?

Answer 20

amount of specific product formed/ theoretical mass
x100

Question 21

what does a high atom economy mean?

Answer 21

• produce less waste
• less expensive

Question 22

why are %yields almost always under 100%?

Answer 22

• side reactions occur
• reaction doesn’t go to completion
• waste

Question 23

how do you find moles from concentration and volume?

Answer 23

moles = conc x vol

Question 24

what is 1dm in cm?

Answer 24

10

Question 25

what are the steps in a titration?

Answer 25

1. fill burette with acid of known conc
2. measure 25cm^3 or alkali using a pipette and transfer to conical flask
3. slowly add acid from burette into conical flask while swirling
4. as soon as indicator changes colour the solution is neutral so record the volume of acid added
5. repeat process until you get results within 0.1cm^3

Question 26

how do you make up a standard solution?

Answer 26

1. transfer known mass of solid
2. dissolve in water
3. transfer to flask

Question 27

how do you calculate % error?

Answer 27

error of equipment / amount measured x100