Work Problem: Calculation of Molar Mass of Unknown Base Using Titration With a Strong Acid

 

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Given Question: A student titrates 2.0135 grams of an unknown monobase weak base to the equivalence point with 67.02 mL of .5003 M HCl(aq). What is the molar mass of the weak base? 

Step 1: This is to sort out what we’re given in the equation, as well as some previous knowledge. We’ll use the first equation, but I wanted to show that it also works for base concentrations as well. The reaction scheme is modeled on the right, with ‘B’ standing for the monoprotic base.

Step 2: We’re gonna plug and chug on a modification of the first equation, where we can find moles of HCl titrated.  You can use the equation above, or if it’s preferable you can also probably use the M=moles/Liter equation.

Step 3: Since we wrote out the reaction scheme earlier, we know the molar ratio of compound A to compound B. Since it’s 1:1, we can assume that .0335 moles of HCl react with .0335 moles of BOH.

Step 4: Now we can use the grams used to titrate and the moles derived from the 1:1 relationship to find the molar mass of BOH. The final molar mass is 60.158 grams/mole BOH.

 

If there are any questions, comments, or concerns, contact us at heychemistryblog@gmail.com. A special thanks to the professors of general chemistry at Oregon State University.

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