A Student Titrates an Unknown Weak Acid, HA, to a Pale

question 134

Multiple Choice

A student titrates an unknown weak acid, HA, to a pale pink phenolphthalein endpoint with 25.0 mL of 0.100 M NaOH. The student then adds 13.0 mL of 0.100 M HCl. The pH of the resulting solution is 4.7. Which of the following statements is true?

• A) At pH 4.7, half of the conjugate base, A^-, has been converted to HA.
• B) The pK_a of the acid is 4.7.
• C) The pK_a of the acid is less than 4.7.
• D) The pK_a of the acid is greater than 4.7.
• E) More than one of the above statements are correct.

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Definitions:

Shaping

A method of operant conditioning in which successive approximations of a desired behavior are reinforced until the exact behavior is achieved.

Reinforcer

In operant conditioning, any event that strengthens the behavior it follows.

Conditioned Stimulus

An initially neutral stimulus that, upon association with an unconditioned stimulus, elicits a conditioned response.

Unconditioned Stimulus

A trigger that inherently and effortlessly evokes a reaction without the need for previous learning.