Calculations

Question 1

What equation should be used to find the number of moles if you have the mass and Mr?

Answer 1

moles=mass/Mr

Question 2

How do you find the Mr?

Answer 2

Add up all of the Ar’s in the compound.

Question 3

How do you find the number of moles if you have volume and concentration?

Answer 3

moles= volume X concentration

Question 4

What are the units for moles?

Answer 4

mol

Question 5

What are the units for mass?

Answer 5

g

Question 6

What are the units for Mr?

Answer 6

gmol^-1

Question 7

What are the units for concentration?

Answer 7

mol dm^-3

Question 8

What are the units for volume in the moles and centration equation and in the moles and volume, 24 e

Answer 8

dm^3

Question 9

How do you get from cm3 to dm3?

Answer 9

/1000

Question 10

What is the equation for moles if you know only the volume?

Answer 10

moles=volume/24

Question 11

What conditions are required for the following reaction: moles=volume/24?

Answer 11

RTP

Question 12

What is the ideal gas equation?

Answer 12

pV=nRT

Question 13

In the ideal gas equation, what does R stand for?

Answer 13

Gas constant

Question 14

What is the value of R in the ideal gas equation?

Answer 14

8.314 Jmol^-1k^-1

Question 15

What does n stand for in the ideal gas equation?

Answer 15

Number of moles.

Question 16

What are the units for p in the ideal gas equation?

Answer 16

Pa

Question 17

What are the units of V in the ideal gas equation?

Answer 17

m^3

Question 18

What are the units of T in the ideal gas equation?

Answer 18

K

Question 19

How do you get from C to K?

Answer 19

+273

Question 20

How do you get from KPa to Pa?

Answer 20

x10^3

Question 21

How do you get from cm^3 to m^3?

Answer 21

x10^-6

Question 22

How do you get from dm^3 to m^3?

Answer 22

x10^-3

Question 23

How do you find the percentage yield?

Answer 23

(actual yield/ theoretical yield) x100

Question 24

How do you find the atom economy?

Answer 24

(sum of molar masses of desired products/ sum of molar masses of all products)x100

Question 25

How do you find the water of crystallisation?

Answer 25

Calculate the number of moles of anhydrous compound present. Calculate the moles of water produced. Find the simplest whole number ratio.

Question 26

How do you calculate the mass of product formed?

Answer 26

Find the moles of reactant. Find the moles of product formed using ratios. Calculate the mass of product formed.

Question 27

How do you calculate the theoretical yield?

Answer 27

Using ratios (for product)

Question 28

How do you calculate the actual yield?

Answer 28

By using the relevant mathematical equations.

Question 29

How do you find the empirical formula from mass?

Answer 29

Find the number of moles. Divide by the smallest. Multiply for whole numbers.

Question 30

How do you find the molecular formula?

Answer 30

Find the empirical formula. Find the relative mass. Divide the relative molecular mass by relative formula mass. Multiply the empirical formula by the result of the previous step.