Title: CHE2FCA concept questions

Q: The pK_a value of acetic acid is 4.76. In an aqueous solution at pH=3, most of the acetic acid will exist in:
- the deprotonated form (i.e, CH_3COO^-)
- the protonated form (i.e, CH_3COOH)
- an equal mixture of the protonated and deprotonated forms
- More information is needed to answer this question
A: the protonated form (i.e, CH_3COOH)

Q: A hydrochloric acid sample (25 mL) with the approximate concentration of [HCl]=0.02 mol/L is titrated with a 0.100 mol/L sodium hydroxide solution.  At pH 7 (see arrow in the graph), which of the following statements is true?

[Image]
- The volume of NaOH added is equal to the volume of the HCl sample.
- The volume of NaOH added is half the volume of the HCl sample.
- The number of moles of NaOH added is equal to number of moles of HCl in the sample.
- The number of moles of NaOH added is half the number of moles of HCl in the sample.
A: The number of moles of NaOH added is equal to number of moles of HCl in the sample.

Q: Recall that pH= -log[H^+].  A solution with pH=5 is 100 times more acidic than a solution with pH= ?
- 7
- 3
- 0.05
- 5.5
A: 7

Q: Which of the following numbers have the same number of significant figures: (i) 2.348;  (ii) 0.041;  (iii) 49.940;  (iv) 1339?
- (i) and (ii)
- (i) and (iii)
- (i) and (iv)
- (i), (ii) and (iv)
A: (i) and (iv)

Q: The mass of a sample was determined to be 1.93 pounds with a standard error of 3.4 %.  To convert the value to kilograms, it must be multiplied with 0.453. What happens to the error after conversion to kilograms?
- The error will be smaller than 3.4 %.
- The error will be larger than 3.4 %.
- The error will remain 3.4 %.
A: The error will remain 3.4 %.

Q: Figure A shows a red laser source directed onto a solar cell, which detects light as photocurrent. A blue copper salt solution reduces the amount of laser light reaching the solar cell by half (Fig. B). How much light is detected if a second solution (same concentration as the first one) is added (Fig. C)?

[Image]
- 0 (no light)
- between 0 and 0.25
- 0.25
- 0.50
A: 0.25