Arock weighing 75.0 g is placed in a graduated cylinder displacing the volume from 31.4 ml to 36.5 ml. what is density of the rock in grams/cubic centimeter?
1. calculate the mass of each element
mass of c = 1.45 mg co₂ × (12.01 mg c/44.01 mg co₂) = 0.3957 mg c
mass of h = 0.89 mg h₂o × (2.016 mg h/18.02 mg h₂o) = 0.0996 mg h
mass of o = mass of compound - mass of c - mass of h = (1.55 – 0.3957 – 0.0996) mg = 1.055 mg
2. calculate the moles of each element
moles of c = 0.3957 mg c × 1mmol c/12.01 mg c = 0.03295 mol c
moles of h = 0.0996 mg h × 1 mmol h/1.008 mg h = 0.0988 mol h
moles of o = 1.055 mg o × 1 mmol o/ 16.00 mg o = 0.06592 mol o
3. calculate the molar ratios
divide all moles by the smallest number of moles.
c: 0.032 95/0.032 95 = 1
h: 0.0988/0.032 95 = 2.998
o: 0.065 92/0.032 95 = 2.001
4. round the ratios to the nearest integer
c: h: o = 1: 3: 2
5. write the empirical formula
the empirical formula is ch₃o.
specifically, i would use a 250 ml graduated beaker.
a beaker is appropriate to measure 100 ml of stock solution, because it's easy to pour into itscwide mouth from a large stock bottle.
you don't need precisely 100 ml solution.
if the beaker is graduated, you can easily measure 100 ml of the stock solution.
even if it isn't graduated, 100 ml is just under half the volume of the beaker, and that should be good enough for your purposes (you will be using more precise measuring tools during the experiment).
moles of excess reactant remaining: 0.67 mol cs2
moles of each product formed: 0.33 mol co2 and 0.67 mol so2
your coefficients in the chemical equation reveal the molar ratio of the reactants that must be present to give a complete reaction of both reactants. in this case each mole of cs2 requires 3 moles of o2 to form the products given. if you start with equimolar amounts of both reactants then the o2 must be in insufficient supply to completely react with all of the cs2. if only 1 mole of o2 is present, it will be consumed by one third that amount of cs2. all o2 will react. 0.67 mole of cs2 will remain. the co2 comes from the carbon in cs2, so 0.33 mole of co2 will be produced. since 2 moles of so2 are produced for each mole of co2 produced, then the amount of so2 produced will be 0.67 mol.