calculations

Question 1

relative isotopic mass

Answer 1

same as mass number

Question 2

calculating Mr + relative formula mass

Answer 2

add together relative atomic masses of each atom making up a molecule

Question 3

calculating relative atomic mass from mass spec

Answer 3

(mass x abundance) + (mass x abundance)/ total abundances

Question 4

calculating abundance from mass spec

Answer 4

height peak/total height of peaks x 100

Question 5

calculating number of atoms

Answer 5

• calculate number of moles

- x Avogadro’s constant

Question 6

predicting ionic formulaes

Answer 6

• overall charge has to be 0

- add as many + and - ions required to balance out the charge

Question 7

calculating number of atoms from the number of molecules

Answer 7

• calculate number of moles
• x 6.02 x 10^23
• multiply by number of calculated molecules in the element

Question 8

calculating number of electrons

Answer 8

• find the number of atoms

- x by atomic number

Question 9

number of mole, involving mass

Answer 9

n=m/mr

Question 10

calculating empirical formula

Answer 10

• calculate the number of moles of each element
• divide all elements by the smallest number of moles
• write the ratio in the formula

Question 11

calculating molecular formula from the empirical formula

Answer 11

• calculate the Mr of the empirical formula
• divide by the relative molecular mass of the empirical formula
• multiply the empirical formula by the number

Question 12

calculating molecular formula from the empirical formula

Answer 12

• calculate the Mr of the empirical formula
• divide by the relative molecular mass of the empirical formula
• multiply the empirical formula by the number

Question 13

writing ionic equations

Answer 13

• write the ions involved including there state and charges
• cross out the spectator ions
• form the equation from the rest

Question 14

calculating concentration of a solution

Answer 14

• c=n/m

- make sure given volume is in dm3 divide by 1000 if in cm3

Question 15

calculating number of moles of a gas at RTP

Answer 15

-n=v(dm3)/24

Question 16

ideal gas equation

Answer 16

PV=NRT

• kpa to pa x1000
• degree to K +273
• R = 8.314
• volume in m3 dm3 to m3 divide by 1000

Question 17

determining the value of x for water of crystallisation

Answer 17

• calculate the mass of water alone by subtracting the formula mass by the mass of the element
• divide by the Mr of water (18)

Question 18

calculating value water of crystallisation from a experiment

Answer 18

mass of hydrated element - mass of the anhydrous element

• use this to calculate the mass of water
• calculate the amount of moles in the anhydrous element and water
• calculate the ratio by dividing both by the smallest number

Question 19

calculating atom economy

Answer 19

atom economy = molecular mass of desired product/ sum of molecular mass of all reactants x 100

Question 20

calculating percentage yield

Answer 20

percentage yield = actual yield/theoretical yield x 100
theoretical yield: find the amount of moles of element desired product in a reactant
-look at the mole ratio between reactant and products
-use the mole number to find the mass of desired product