Antacid tablets are used to neutralize excess stomach acid (HCI). The active ing

Question

Antacid tablets are used to neutralize excess stomach acid (HCI). The active ingredient in these tablets is CaCO_3, which is basic. A conventional acid/base titration is very difficult in this case as the active ingredient is barely soluble in water. In order to overcome this limitation, antacid tablets (which also contain inert binders like starch) are dissolved in an excess of acid. Some of the HCI will be neutralized by the CaCO_3, but there will be some HCI remaining. A subsequent titration with NaOH can be used to determine the amount of this remaining acid, which can be related back to the amount of CaCO_3 just as you did in your lab for this course. Below is the data for one trial of the experiment. Determine the %(w/w) of CaCO_3 in the antacid tablet. The two reactions involved are: Data. Mass of antacid tablet: 1.27 g Antacid tablet was dissolved using 30.0 mL of 1.00 M HCI. Back-titration of remaining HCI required 19.89 mL of 0.885 M NaOH

Explanation / Answer

Determination of mass of antacid in tablet

CaCO3 + 2HCl = CaCl2 + H2CO3

HCl + NaOH ---> NaCl + H2O

From above,

moles of HCl used = 1 M x 0.03 L

                              = 0.03 mol

moles of NaOH used = 0.885 M x 0.01989 L

                                  = 0.0176 mol

HCl reacted with antacid = 0.03 - 0.0176

                                        = 0.0124 mol

moles of antacid present = 0.0124/2

                                        = 0.0062 mol

mass of antacid present = 0.0062 mol x 100.087 g/mol

                                       = 0.6205 g

Percent antacid in tablet = 0.6205 x 100/1.27

                                        = 48.86%

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