21, Antacids are commonly determined by acid-base back titrations because the lo

Question

21, Antacids are commonly determined by acid-base back titrations because the low solubility of the antacid slows the direct reaction with acid. A 0.3251 g sample of a leading antacid (active ingredient: CaCO3) is added to 50.00 mL of 0.1102 M HCI. After the reaction, the excess acid is titrated with 29.43 mL of 0.1006 M NaOH. Calculate the number of milligrams of CaCO3 per tablet, assuming that an average tablet has a mass of 1.28 g. Also assume the CaCO3 to be totally neutralized. Molar Mass CaCO3 100. g-mol-1 (A) 392 mg (C) 784 mg (B) 502 mg (D) 1004 mg 22. Benzoic acid, C6 H5 COOH, is a weak, monoprotic organic acid in aqueous medium. However, in the nonaqueous solvent methylamine, CH3 NH2, benzoic acid is readily ionized. Identify the conjugate acid for this ionization, (A) C6H5 COOH2+ (C) C6Hs COo (B) CH3NH3+ (D) CH3NH

Explanation / Answer

NO OF mol of NaOH consumed = 29.43*0.1006 = 2.96 mmol

No of mol of HCl taken = 50*0.1102 = 5.51 mmol

No of mol of HCl reacted = 5.51 - 2.96 = 2.55 mmol

1 mol CaCo3 = 2 mol HCl

Noof mol of CaCo3 present in sample = 2.55 /2 = 1.275 mmol

mass of CaCo3 = n*Mwt

              = 1.275*10^-3*100

              = 0.1275 g

mass of caCo3 in 1 tablet = 1.28*0.1275/0.3251 = 0.502 g

                 = 502 mg

answer: 502 mg

22. answer: CH3NH3+

C6H5COOH + CH3NH2 ---> C6H5COO- + CH3-NH3+

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