So in my Gen Chem II class we did a lab for CaCO3
+ 2 HCl
We are to find the % of "junk" in the Tums/Equate antacids and determine which is the better buy. It doesn't seem hard, although I'm not sure if my calculations are correct. If not, I'd like to fix my mistake. I previously did a similar titration with vitamin C and found that "pure vit. C" tabs were anything but.
The three things we tested were pure calcium carbonate powder, Tums, and Equate brand antacids. For example, when doing the Tums portion of the lab I ground a tablet and added 0.1513 g of the tums tablet to 10 ml of 0.484 M HCl. Then titrated with 0.260 M NaOH. The initial tums tablet was completely neutralized by the excess of HCl, then doing a back titration I am supposed to be able to find the % of calcium carbonate and junk in the tablet sample by neutralizing the remaining HCl with NaOH.
Here's the part I'm not completely sure if I did right. The calculations. I believe I should go as followed:
moles HCl - moles NaOH = moles HCl reacted with CaCO3
/ 2 (because HCl to CaCO3
ratio is 2:1) = moles CaCO3
in sample (then convert to grams)
initial sample size (in grams) - CaCO3
reacted (grams) = weight of "filler/junk" in sample (grams) / initial sample = % of junk in sample
Using the numbers gathered from titration.
0.00484 mol HCl - 0.003692 mol NaOH = 0.001148 mol HCl that reacted with CaCO3
/ 2 (2:1 ratio) = 0.000574 mol CaCO3
0.000574 mol CaCO3
x (100.06 g / 1 mol) = 0.057434 g CaCO3
0.1513 g initial sample - 0.0574 g CaCO3
reacted = 0.0939 g filler / 0.1513 g initial sample x 100% = 62.06% junk
Is my math right or am I mixing up something small like dividing by the 2:1 ratio if I'm supposed to multiply? I appreciate everyone who takes the time to read this, it would mean a lot to me to get some other opinions on it before I hand it in.