Ok, so... 20.219 grams is the mass of the flask with the water in it.
10.267 grams is the mass of only the flask. Subtract them to find the water mass.
20.219 g (flask+water) - 10.267 g (flask) = 9.952 g (water)
Answer:

Explanation:
Hello,
In this case, the dissociation of the given weak acid is:

Therefore, the law of mass action for it turns out:
![Ka=\frac{[H^+][A^-]}{[HA]}](https://tex.z-dn.net/?f=Ka%3D%5Cfrac%7B%5BH%5E%2B%5D%5BA%5E-%5D%7D%7B%5BHA%5D%7D)
That in terms of the change
due to the reaction extent is:

Thus, by solving with the quadratic equation or solver, we obtain:

Which clearly matches with the hydrogen concentration in the solution, therefore, the pH is:

Regards.
This requires familiarity with the different theories (or concepts) of acids and bases.
On the Arrhenius concept, an acid is a substance that produces an H⁺ ion in water such that the H⁺ concentration increases, and a base is a substance that produces an OH⁻ ion in water such that the OH⁻ concentration increases.
On the Brønsted–Lowry concept, an acid is a substance that donates a proton (which is basically an H⁺ ion) in a solvent, and a base is a substance that accepts a proton in a solvent.
On the Lewis concept, an acid is a substance that accepts an electron pair in a solvent, and a base is a substance that donates an electron pair in a solvent.
The concepts become progressively broader, i.e., the Arrhenius concept is the most restrictive and the Lewis concept is the least restrictive. As a corollary, an Arrhenius acid or base is also both a Brønsted–Lowry acid or base and a Lewis acid or base, respectively; a Brønsted–Lowry acid or base is not necessarily an Arrhenius acid or base, but an Arrhenius acid or base is also a Lewis acid or base, respectively. And finally, a Lewis acid or base may not necessarily be either an Arrhenius or a Brønsted–Lowry acid or base.
So, with the above concepts in mind, we can match the statements in column A with the type of acid or base in column B:

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