A piece of zinc was added to 1000 cm3 of 0.2M hydrochloric acid. After effervescence had stopped. 30 cm3 of the resulting solution required 22 cm3 of 0.08M sodium trioxocarbonate (IV) solution for complete neutralization, calculate the mass of the zinc added. (Zn = 65, HCl = 36.5, Na2CO3 = 106)
NOTE: One name for Na2CO3 acceptable by IUPAC (International Union of Pure and Applied Chemistry) is sodium carbonate. The name you used is NOT an acceptable name by the IUPAC.
.................Zn + 2HCl ==> ZnCl2 + H2
millimoles HCl initially = mL x M = 1000 mL x 0.2 M = 200
Excess HCl titrated with Na2CO3 as follows:
2HCl + Na2CO3 ==> CO2 + H2O + 2NaCl
millimoles Na2CO3 in 30 cc solution = mL x M = 22 mL x 0.08 M = 1.76 in 30 mL. How much if we had titrated all of the acid left. That's 1.76 millimols x (1000/30) = 58.86 millimoles Na2CO3 or 2*58.86 = 117.72 millimoles HCl NOT used by the Zn reaction. How much was used? That's 200 initially- 117.72 not used = 82.28 millimoles HCl used by the reaction with Zn. That's 0.08228 moles HCl used. Half of that (0.08228/2 = 0.0411) mols Zn reacted or 0.08228 x 65.39 = 5.38 grams Zn initially.