Mole Calculations A1

Question 1

What is the equation linking mass, moles and Mr? What are the units?

Answer 1

Mass (g) = Moles (mol) x Mr (g mol-1)

Question 2

What is the equation for percentage yield?

Answer 2

Actual yield/Theoretical yield x 100

Question 3

What are the two equations to work out concentration? What are the units?

Answer 3

Concentration (g dm-3) = mass (g) / volume (dm3)

Concentration (mol dm-3) = moles / volume (dm3)

Question 4

What is the equation for atom economy?

Answer 4

Mr or mass of desired product / Mr or mass of all products x 100

Question 5

What is the equation for molar gas volume? What are the units?

Answer 5

Volume (dm3) = moles x 24

Question 6

What is the Ideal Gas Equation? What are the units?

Answer 6

pV = nRT

p (Pa) x V (m3) = n (mol) x R (8.314) x T (K)

Question 7

How do you convert from MPa and kPa to Pa?

Answer 7

MPa x 1,000,000 = Pa

kPa x 1000 = Pa

Question 8

How do you convert from cm^3 and dm^3 to m^3?

Answer 8

cm3 / 1,000,000 = m3

dm3 / 1000 = m3

Question 9

How do you convert from degrees C to K?

Answer 9

+273

Question 10

What is the equation for percentage uncertainty?

Answer 10

Measurement uncertainty (half the increments or to the d.p.) / reading taken x 100

note: with titrations, 2 readings taken so measurement of uncertainty is squared, and the reading is the mean titres

Question 11

What is the definition for Relative Isotopic Mass?

Answer 11

The mass of an atom of an isotope of an element compared with 1/12 the mass of an atom of Carbon-12

Question 12

What is the definition for Relative Atomic Mass?

Answer 12

The weighted mean mass of an atom of an element compared with 1/12 the mass of an atom of Carbon-12

Question 13

What is Molar Mass (Mr)?

Answer 13

The mass of a substance per mole (g mol-1)

NOTE: you can use this to work out mass!

Question 14

What is the empirical formula?

Answer 14

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

Question 15

What is the molecular formula?

Answer 15

The formula that shows the actual number of atoms of each element in a compound

Question 16

What is the difference between a hydrous and anhydrous salt?

Answer 16

The hydrated compound has ‘water of crystallisation’ in it’s crystal structure, anhydrous has no water.

Question 17

When heating to remove all water of crystallisation, how can you be sure that all water is gone?

Answer 17

Reheat and reweigh the salt until a constant mass is reached.

Question 18

How do you convert concentration in mol dm-3 to g dm-3?

Answer 18

Multiply by the Mr of the solute

Question 19

How can you increase the atom economy of a reaction?

Answer 19

Find a use for all the products, so none of them are ‘waste’.

Question 20

What is avogadro’s number?

Answer 20

6.02 x 10^23

Question 21

What is the equation for density?

Answer 21

Density = mass / volume