2. At this point, measure a volume of vinegar, between 5.0 -6.0 cups, convert th

Question

2. At this point, measure a volume of vinegar, between 5.0 -6.0 cups, convert this to milliliters. Show all your work in your notebook. But wait, it vinegar is 5% v/v volume solute per volume of solution then it is mostly water. Research the density of vinegar and use that value to determine the mass of your volume of vinegar. If 5% of this amount is acetic acid, calculate the mass, in grams, of only the acetic acid in the vinegar sample 3. We are now ready to do stoichiometry. If the reactants combine in a 1:1 manner, then we need an amount of baking soda that is in a 1:1 ratio. However, this cannot be determined in a mass to mass ratio, but in a mole to mole ratio. Therefore, determine the number of moles of acetic acld from the mass determined earlier, using the molar mass of acetic acid. See the example problems at the end of section 2.4 in your textbook. 4. Now, use the fact that the mole ratio is 1:1 for baking soda and acetic acid to determine the amount, in moles, of baking soda that is required to completely react with your vinegar, and convert this to tablespoons, given the mass of one tablespoon of baking soda is approximately 14.8 grams. (Hint: convert moles of vinegar to moles baking soda (1:1), to mass of baking soda to tablespoons).

Explanation / Answer

Ans. #2. Given- vol. of vinegar = 6 cups = 1500.0 mL

#Step I: Volume of acetic acid in vinegar = 5 % (v/v) of 1500.0 mL = 75.0 mL

#Step II: Mass of acetic acid = Volume x Density = 75.0 mL x (1.05 g / mL) = 78.75 g

Note: Vinegar is 5 % v/v – i.e. there is 5.0 mL of acetic acid per 100.0 mL of vinegar solution. We can’t use a v/v % to calculate the mass of acetic acid as presented by you.

That is ( as your presentation)-

            Mass of vinegar soln. = 1500.0 mL x 1.05 g mL-1 = 1575.0 g

            Mass of acetic acid = 5 % (v/v) of 1575.0 g

            Error: A v/v % can’t be multiplied to mass to get another mass. To get the mass of acetic acid from mass of vinegar soln., the % content must be in terms of (w/w) %. So, the question indeed puts “incorrect and confusing” wordings.

# So, it’s advised to calculate the mass of as described above if content is % (v/v).

#3. Moles of acetic acid = Mass / MW = 78.75 g / (60.05256 g/mol) =1.3114 mol

#4. Required moles of baking soda (NaHCO3) = Moles of acetic acid = 1.3114 mol

Required mass of baking soda = Moles x MW = 1.3114 mol x 84.007 g mol-1

= 110.16 g

Now,

            Required quantity in tablespoons = Required mass / mass per tablespoon

                                                = 110.16 g / (14.8 g tablespoon-1)

                                                = 7.44 tablespoons

# Therefore, required amount of baking soda = 7.5 tablespoons

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