A 2.20-g sample of an unknown acid (emperical formula=C3H4O3) is dissolved in 1.0 L of water. A titration required 25.0 mL of 0.500 M NaOH to react completely with all the acid present. Assuming the unknown acid has one acidic proton per molecule, what is the molecular formula of the unknown acid?
2006-09-03 06:10:49 · 2 answers · asked by xxxlovelymoi 1 in Science & Mathematics ➔ Chemistry
I had already answered to a similar question but obviously the question was removed (tried to llok for the link but it wasn't there...) so here it goes again:
The empirical formula is C3H4O3. So if you have n C atoms in the molecule, the molecular formula will be (C3H4O3)n or C3nH4nO3n and the molecular weight MW=(3*12+4+3*16)n= 88n
It is a monoprotic acid and it reacts with a monovalent base.
Therefore for the titration mole acid=mole base
but mole acid= mass acid/MWacid
and mole base= Cbase*Vbase
Thus mass acid/MWacid = Cbase*Vbase
and 2.2/88n=0.5*0.025 => n=2.
Thus the molecular formula is C6H8O6
If you had polyvalent acid and/or base then you would have
a(acid)*mole acid=a(base)*mole base
where a(acid) and a(base) is the valency of the acid and the base respectively.
2006-09-03 06:29:56 · answer #1 · answered by bellerophon 6 · 2⤊ 0⤋
A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. For molecular compounds, it identifies each constituent element by its chemical symbol and indicates the number of atoms of each element found in each discrete molecule of that compound. If a molecule contains more than one atom of a particular element, this quantity is indicated using a subscript after the chemical symbol (although 19th-century books often used superscripts). For ionic compounds and other non-molecular substances, the subscripts indicate the ratio of elements in the empirical formula.
2006-09-03 16:17:53 · answer #2 · answered by azy t 2 · 0⤊ 1⤋