Solving Acid Base Problems

For all acid-base equilibrium calculations that are properly set up, these roots will be real, and only one will be positive; this is the one you take as the answer.

Solving Acid Base Problems-40Solving Acid Base Problems-50

As we will explain farther on, in most practical cases we can make some simplifying approximations which eliminate the need to solve a quadratic.], thus shifting the dissociation process to the right.But dilution similarly reduces [HA], which would shift the process to the left.The very important first step is to make sure you understand the problem by writing down the equation expressing the concentrations of each species in terms of a single unknown, which we represent here by x: , you just substitute the x's into the latter, and you're off!If you feel the need to memorize stuff you don't need, it is likely that you don't really understand the material — and that should be a real worry!Even if the acid or base itself is dilute, the presence of other "spectator" ions such as Na values to be accurate to ±5 percent at best, and even more uncertain when total ionic concentrations exceed 0.1 M.As a consequence of this uncertainty, there is generally little practical reason to express the results of a p H calculation to more than two significant digits.This raises the question: how "exact" must calculations of p H be?It turns out that the relation between p H and the nominal concentration of an acid, base, or salt (and especially arbitrary mixtures of these) can become quite complicated, requiring the solution of sets of simultaneous equations.And when, as occasionally happens, a quadratic is unavoidable, we will show you some relatively painless ways of dealing with it.What you do will depend on what tools you have available.

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