1.3 Chemical Calculations

Question 1

How do you work out the number of moles using mass?

Answer 1

number of moles = mass/mr

Question 2

How do you work out the number of moles using concentration?

Answer 2

number of moles = concentration x volume

Question 3

In what units should volume always be in?

Answer 3

dm^3

Question 4

What is the unit for concentration?

Answer 4

mol dm^-3

Question 5

What is mr?

Answer 5

relative atomic mass

Question 6

How do you work out the empirical formula?

Answer 6

mass of the substances
divided by it’s mr
divide again by the lowest
work out the ratio

Question 7

What is the ideal gas equation

Answer 7

PV= nRT

Question 8

What does P stand for in the ideal gas equation? units?

Answer 8

pressure (Pascals/Pa)

Question 9

What does V stand for in the ideal gas equation? units?

Answer 9

Volume (m^3)

Question 10

What does n stand for in the ideal gas equation? units?

Answer 10

moles (mol)

Question 11

What does R stand for in the ideal gas equation?

Answer 11

molar/ideal gas constant
always 8.31

Question 12

What does T stand for in the ideal gas equation? units?

Answer 12

temperature (Kelvin/K)

Question 13

How do you convert from *C to Kelvin (temperature)?

Answer 13

+273

Question 14

How do you convert cm^3 to dm^3?

Answer 14

divide 1000

Question 15

How do you convert dm^3 to m^3?

Answer 15

divide 1000

Question 16

How do you convert m^3 to dm^3?

Answer 16

divide 1000

Question 17

How do you convert dm^3 to cm^3?

Answer 17

x 1000

Question 18

How do you convert cm^3 to m^3?

Answer 18

divide 1000000

Question 19

How do you convert m^3 to cm^3?

Answer 19

x 1000000

Question 20

How do you work out the atom economy?

Answer 20

(mass of useful product / total mass of reactants) x 100

Question 21

What is the unit of atom economy?

Answer 21

%

Question 22

How do you work out the molecular formula?

Answer 22

Divide the molar mass by empirical formula molar mass
then multiply that number by the empirical formula

Question 23

how do you calculate a back titration?

Answer 23

1. Calculate the moles of acid added
2. Calculate the moles of alkali added
3. Subtract the moles of alkali from the moles of acid to give the number of acid reacted
4. Calculate the moles of base that reacted
5. Calculate the mass of base reacted
6. Calculate % mass (mass reacted/mass of tablet x 100)

Question 24

How do you work out percentage yield?

Answer 24

mass of required product/theoretical x 100

Question 25

second pv=nrt equation

Answer 25

V2 = P1 V1 T2 / P2 T1