For an aqueous solution of acetic acid to be called...

For an aqueous solution of acetic acid to be called "distilled white vinegar" it must contain $5.0 \%$ acetic acid by mass. A solution with a density of $1.05 \mathrm{~g} / \mathrm{mL}$ has a $\mathrm{pH}$ of $2.95 .$ Can the solution be called "distilled white vinegar"?

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Key Concepts

Acid Dissociation and the Acid Dissociation Constant (Ka)

Weak acids like acetic acid do not completely dissociate in water. The acid dissociation constant, Ka, quantifies the extent of this dissociation. Understanding Ka is essential to relate the measured hydrogen ion concentration (via pH) to the initial concentration of the acid present in the solution. This equilibrium concept is key to determining if the solution's measured pH aligns with the expected concentration for distilled white vinegar.

pH and Hydrogen Ion Concentration

pH is a logarithmic measure of the concentration of hydrogen ions in a solution. It is used to quantify the acidity or basicity of the solution. In acid-base chemistry, knowing the pH allows one to deduce the concentration of hydrogen ions, which is critical when evaluating whether the acid concentration in a solution meets a certain standard.

Percent Composition by Mass

This concept defines the concentration of a solute in a solution expressed as a percentage of the total mass. In this context, a 5% acetic acid solution means that 5% of the total mass of the solution is acetic acid, a criterion used to classify distilled white vinegar. Understanding percent composition by mass is essential when comparing measured values (like density and mass) to specified product standards.

Transcript

00:01 Well, we know that we have a 5 % solution if we want to call it white vinegar.

00:08 So i'm going to work from there and see if i can find the ph of that solution and see if it matches the ph that it's supposed to have.

00:16 So if it's 5%, i can say that i have 5 grams, right, and that's of my vinegar, which is my acetic acid.

00:29 So we'll go ahead and change grams to moles here, using the molar mass, which is 60 .06.

00:35 So that'll be .0833 moles.

00:43 And that would be 5 grams and 100 grams of solution.

00:47 That's how we would get our 5%.

00:49 So i've got our density.

00:52 So we go ahead and change grams to milliliters here.

00:55 It's 1 .05 grams per milliliter is going to give us 95 .2 milliliters.

01:06 So the concentration of our acetic acid.

01:11 Is going to be our moles, 0 .833 moles, divided by our volume in liters.

01:27 Okay, so we would get a 5 % solution would be 0 .875 molar.

01:35 So what i'm going to do now is see if i can find the ph of a 0 .875 molar solution of acetic acid.

01:42 So it's a weak acid, so it's going to ionize slightly into h plus and acetate.

01:58 I'm going to make an ice box to keep track of what's happening here.

02:03 We decided that this was 0 .875...

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