Question

1- A 0.0456 g sample of an unknown sample was titrated using the EDTA titrant from question 1 and the procedure below. The starting burette volume was 0.05 mL. The ending burette volume was 42.35 mL. Calculate the % calcium oxide (CaO; 56.0774 g/mol) by mass in the sample. Show all work.

2-  100.0 mL of an unknown water sample was titrated using the EDTA from question 1 and the procedure below. The starting volume was 0.25 mL and the ending volume was 20.53 mL. Calculate the concentration of Ca2+ in the tap water. Show all work.

Answer 1

1- A 0.0456 g sample of an unknown sample was titrated using the EDTA titrant from question 1 and the procedure below. The starting burette volume was 0.05 mL. The ending burette volume was 42.35 mL. Calculate the % calcium oxide (CaO; 56.0774 g/mol) by mass in the sample. Show all work.

the reaction with EDTA is this...

Ca+2 + EDTA-4 ----> CaEDTA-2

volume of EDTA = 42.35 Ml-0.05 mL

= 42.30 mL

= 0.0423 L

Moles of EDTA = molarity * volume in L

= 0.010 M*0.0423 L

= 0.00423 Moles EDTA

According to reaction moles of EDTA equal to moles of Ca2+

And one mole CaO gives one mole Ca2+, therefore the moles of CaO = 0.00423 Moles

Amount of CaO = Molar mass* number of moles

= 56.0774 g/mol *0.00423 Moles

=0.02372 g CaO

% of CaO = Amount of CaO/ amount of sample *100

= 0.02372 g CaO/0.0456 g*100

= 52.02%