1.3 chemical calculations

Question 1

what does the term relative atomic mass mean

Answer 1

the average mass of one atom of an element relative to 1/12th the mass of an atom of carbon-12

Question 2

what does the term relative formula mass mean

Answer 2

the weighted average of the masses of the formula units compared to 1/12th the mass of an atom of carbon-12

Question 3

what does the term relative isotopic mass mean

Answer 3

the mass of one atom of an isotope compared to 1/12th the mass of an atom of carbon-12

Question 4

what is mass spectrometry

Answer 4

mass spectrometry is a type of analytical technique which measures the mass to charge ratio of ions. it also measures how abundant each ion is so it can be used to calculate the relative atomic mass

Question 5

define empirical formula

Answer 5

the simplest whole number ratio of atoms of each element in a compound

Question 6

define molecular formula

Answer 6

the actual number of atoms of each present in a compound

Question 7

define the Avogadro constant

Answer 7

the number of particles in one mole of a substance. this is 6.02 x 10^23 particles

Question 8

what is the equation linking Avogadro’s constant to moles

Answer 8

number of particles =
moles x Avogadro’s constant

Question 9

define molar mass

Answer 9

the mass per mole of a substance measured in g mol-1

Question 10

what is the equation that links moles to mass

Answer 10

moles =
mass(g) x relative atomic mass

Question 11

define concentration

Answer 11

the amount of moles per unit volume

Question 12

how can concentration be calculated in g/dm^3

Answer 12

concentration =
mass (g) / volume (dm^3)

Question 13

how can concentration be calculated in mol/dm^3

Answer 13

concentration (mol/dm^3) =
moles / volume

Question 14

what is the molar volume of any gas at room temperature and pressure

Answer 14

24 dm^3

Question 15

how is molar volume at a given pressure affected if temperature is increased

Answer 15

an increase in temperature reduced the molar volume at a given temperature

Question 16

how is the molar volume affected if the pressure is increased

Answer 16

an increase in pressure will mean the maximum molar volume reduces. up to this maximum, increasing the pressure will increase the molar volume

Question 17

what is the ideal gas equation

Answer 17

pV=nRT

p - pressure (pa)
V - volume (m^3)
n - number of moles
R - gas constant (8.31 J K-1 mol-1)
T - temperature (K)

Question 18

how can percentage yield be calculated

Answer 18

percentage yield =
(actual yield / theoretical yield) x 100

Question 19

why might the actual yield of product be less than expected

Answer 19

-incomplete reaction
-unwanted side reactions
-practical losses(solid may get lost when being transferred between beakers

Question 20

what is the atom economy of a reaction

Answer 20

atom economy is a measure of the efficiency of the reaction. it looks at the amount of reactants that get turned into useful products

Question 21

how can atom economy be calculated

Answer 21

atom economy =
(mr of desired product , total mr of reactants) x 100

Question 22

fill in the gap : ‘The ___ the atom economy the more sustainable and efficient the process

Answer 22

higher

Question 23

how can percentage error be calculated

Answer 23

% error =
(absolute uncertainty / calculated value) x 100