quantitative chemistry

Question 1

what is gas chromatography

Answer 1

separating substances in a mixture depending on how long they stay in a column

Question 2

what is mass spectrometry

Answer 2

measuring the relative molecular mass of a substance

Question 3

what are isotopes

Answer 3

atoms of the same element (same proton number) but with a different number of neutrons

Question 4

what is the RAM

Answer 4

the average of mass numbers from all isotopes

Question 5

what is the empirical formula

Answer 5

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

Question 6

how do we find the empirical formula?

eg. empirical formula of a compound containing 7g of iron and 3g of oxygen

Answer 6

1) divide by RAM of each element to get moles eg.7/56=0.125 3/16=0.1875
2) divide by smallest number to get simplest ratio eg. 0.125/0.125=1 0.1875/0.125=1.5
3) ratio is 1:1.5 or 2:3 so empirical formula is Fe2O3

Question 7

what mass of CaO forms from 25g of CaCO3

Answer 7

1) look at equation: CaCO3–>CaO+CO2
2) use RAMs: 100g–>56g+44g
3) scale up or down: 25g–> 14g+11g

Question 8

what is the percentage yield equation

Answer 8

actual mass of product obtained/maximum theoretical mass of product x100

Question 9

what is the %yield of CaCO3–>CaO+CO2

Answer 9

1) work out theoretical mass- from 25g that is 14g

2) if actual mass obtained was only 10g then the % yield = 10/14x100=71.4%

Question 10

what is paper chromatography

Answer 10

separating colours in a mixture, depending on how well they dissolve in a solvent