Tooth enamel consists mostly of hydroxyapatite, whose formula unit is Ca5(PO4)3(OH). In an acidic medium of sulphuric acid, it can be decomposed according to the following reaction:
Ca5(PO4)3(OH) + 4H+ → 5(Ca)2+ (+) 3(HPO4)2- + H2O
How many moles of H2SO4 are needed to produce 0.3 moles of ions?
A. 0.2
B. 0.4
C. 0.3
Q. 0.1
E. 0.5
Answer: A
This seems a bit different then usual stoichiometry questions and I couldn’t figure out how to approach and solve it. Maybe someone can help?
could you tell me which year’s question this one is. i want to read the Italian version as there are usually translation errors as well
My apologies, I forgot to mention it. This is year 2019, question 47, and I used the test from testbusters.it
no problems!
here is how you can solve it:
in order to have 0.3 moles of HPO-2 the amount of H+ you need is
0.3* 4/3= 0.4 mol H+
as we know that H2SO4 is a diprotic molecule, it will donate 2H+ molecules instead of one.
that is why we divide 0.4 mol/2 to get the amount we want.
When it says produce ‘0.3 moles of ions’ its just referring to the HPO4 ions then?
Does that mean the Ca2+ ions are not relevant because the H2SO4 is not linked to the number of Ca2+ produced?
yes! i believe the problem is the translation. i tried to find the solution via Italian version