bridge to a level: content

Question 1

name and describe the relevant models of the atom used in OCR a level

Answer 1

plum pudding
- J J Thompson 1897
- areas of negative charge embedded in a ball of positive charge

nuclear model
- Ernest Rutherford 1909
- alpha scattering experiment
~ ⍺²⁺ particles fired at a thin sheet of Au
~ plum pudding model: expect most to be slightly deflected
~ most passed through with no deflection: atoms are mainly empty space
~ some were fully deflected: small dense positively-charged nucleus

Question 2

how to calculate empirical formula

Answer 2

set up a table
elements:
measured mass:
relative mass Mr:
mass/mr = moles:

divide by the smallest value
scale up to find the smallest whole number ratio

** might not be perfect: often from experimental data (you can give approximations/round)

Question 3

how to calculate water of crystallisation

Answer 3

mass of anhydrous salt - mass of water lost
empirical formula method: find the ratio of anhydrous salt to water