Combustion analysis and DBE Flashcards
How do you do combustion analysis?
Weigh the pure sample very accurately
Combust the material in the presence of excess O2
Weigh the products
How would you calculate the percentage of an element in a compound?
(Mass of element in sample / total mass of sample) x 100
How would you work out the empirical formula?
(% of element as a decimal/mr of element) x molecular mass of the compound
What is the formula of an alkane?
CnH2n+2
What is the formula of a cycloalkane or alkene?
CnH2n
What is the formula of an alkyne?
CnH2n-2
What happens to the hydrogen number when a triple bond is added?
Molecular formula reduced by 4
What happens when a ring or a pi bond is added?
The number of hydrogens in the formula reduces by 2
What happens to the formula when you add group 5 element?
One more hydrogen is added
What happens to the formula when you add group 6 elements?
No change in the number of hydrogens
What happens to the formula when you add group 7 elements?
One hydrogen is subtracted
What is the formula to work out double bond equivalents?
((2a+2)-b) /2
In the formula ((2a+2)-b) /2, what are a and b?
CaHb
How do oxygen molecules affect the equation for DBE? (CaHbOc)
They aren’t included in the equation
How do group 5 elements (eg. N) affect the equation for DBE? (CaHbNd)
((2a+2)-(b-d))/2
