One important factor in any chemical synthesis is the actual quantity of desired

Question

One important factor in any chemical synthesis is the actual quantity of desired product obtained compared to the theoretical amount predicted on the basis of the stoichiometry of the reaction. The ratio of the mass of product obtained to the theoretical quantity, expressed as a percentage, is referred to as the "percent yield" or more simply the "yield". For example: if we react HCl with excess NaOH one of the products will be NaCl. If we assume that all of the Cl in HCl ends up as NaCl we know that each mole of HCl consumed should produce a mole of NaCl product. Suppose that in a particular reaction 10.7 grams of HCl (36.5 g/mol) react with excess NaOH and 20 grams of NaCl (58.5 g/mol) are isolated from the reaction mixture by crystallization. What is the percent yield of NaCl in the experiement?

Explanation / Answer

m = 10.7 g of HCl react with NaOH in exces

m = 20 g of NaCl are isolated...

find % yield

so

the reaction

HCl + NaOH = H2O + NaCl

mol of HCl = mol of NaCl since ratio is 1:1

mol of HCl = mass/MW = 10.7/36.5 = 0.29315 mol of HCl

then, we will expect:

0.29315 mol of H2O AND 0.29315 mol of NaCl

mass of NaCl = mol*MW = 0.29315 *58.5 = 17.149275 g of NaCl

mol of NaCl produced = mass/MW = 20/58.5 = 0.34188 mol of NaCl produced

so

%yield = real / theoretical * 100% = 0.34188/0.29315 * 100 = 116.622 %

which can't be, since we are producing much more NaCl as we could expect... so there must be an error, probably, the total amount is hydrated

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