A. A chemistry student comes home from school and finds a leaky battery lying on the new living room carpet, where it's left a dark stain. Having just learned about acids and bases in school, he dashes to the kitchen, grabs something from the cupboard, and uses it to treat the stain.
Should he have grabbed a bottle of vinegar (acetic acid) or a box of baking soda (which contains HCO3–) to treat the spill? Explain your reasoning. (2 points)

b. Some substances, such as HPO42–, can act as acids or as bases. (2 points)
i. When HPO42– acts as an acid, what is its conjugate base? When it acts as a base, what is its conjugate acid? (1 point)
ii. The reaction between HPO42– and its conjugate acid creates a very important buffer inside your cells. Explain what a buffer does. (1 point)