Previous Quizzes Analytical Chemistry Exam 2

Chapters 6-10

Compounds A and B react as follows: A + B = C + D.  The equilibrium constant is 2.0 x 10². If 0.20 mol A and 0.80 mol B are mixed into 1 liter of water, what is the concentration of "A" after reaction?

3.3x10^–4 M

At equilibrium, _______________.

the rate of the reverse reaction equals the rate of the forward reaction

If Q < K, ______________________.

then the reaction must proceed to the right to reach equilibrium

According to Bronsted-Lowry's definition, an acid is any substance _______________.

that can donate a proton

The dissociation constant for a weak, monoprotic electrolyte is 1.23x10^-3. Calculate the percent dissociation (to 3 significant figures) of the compound if you have a 9.46x10^-2 M solution.

10.8

Phosgene (COCl2) is a potent chemical warfare agent that is now outlawed by international agreement. It decomposes by the reaction,  COCl2(g)    ↔     CO(g)  +  Cl2(g)       Kc = 8.3 x 10−4 (at 360°C). Calculate the concentration of COCl2 when 0.010 mols of phosgene decomposes and reaches equilibrium in a 10.0 L flask. Don't forget that you vessel is 10.0 L, not 1 L.

4.1×10^-4

Given the chemical equilibrium HC₂H₃O₂ (aq)  +  H₂O (l)  ↔ C₂H₃O₂^- (aq)  +  H₃O⁺(aq), which of the following best represents the mathematical expression of this equilibrium?

[H₃O⁺] f(_H3O⁺) [C₂H₃O₂^-] f(_C2H3O2-) / [HC₂H₃O₂] f(_HC2H3O2) = K_a

Upon standardization of a NaOH solution at 0.1350 M, you neutralized a diprotic acid by titrating 39.65 mL into an Erlenmeyer flask containing 0.5034 g of the unknown acid and about 50 mL of DI water. What is the molecular weight (to 4 significant figures) of the unknown acid?

188.1

An activity coefficient _________________.

measures the deviation of behavior of ions from ideality

The pH of an acetic acid solution is 3.32.  Assuming that the acid dissociation constant (K_a) is 1.75x10^-5, calculate the percent ionization of the acetic acid.

3.53

Calculate the pH of a solution obtained by mixing equal volumes (1 mL each) of 0.117 M H₂SO₄ and 0.348 M NaOH.

12.8

At what pH is the buffering capacity of a buffer solution the greatest?

pH = pKa

The concentration of total phosphorous (HPO₄^2– and H₂PO₄^–) found in a blood sample is determined by spectrophotometry to be 0.00359 M.  If the pH of the blood sample is 7.39 and the pKa is 7.21, what is the concentration of H₂PO₄^– in the blood?

0.00143

In lab, the purpose of boiling the solution near the end point for the titration of sodium carbonate with hydrochloric acid is to _____________.

increase the sharpness of the endpoint

Calculate the pH of a solution prepare by mixing 5.49 mL of 0.106 M NH₃ with 10.09 mL of 0.0259 M HCl.  Assume that the pK_b is 4.76.

9.33

What is the minimum pH change required for a sharp indicator color change at the end point?

2.0

What is the net ionic reaction at the second equivalence point in the reaction between hydrochloric acid and sodium carbonate?

HCO₃⁻ + H⁺ → H₂O + CO₂

Which one of the following equations is correct for the reaction between hydrochloric acid and sodium carbonate?

Na₂CO₃ + 2HCl   →  2NaCl + H₂O + CO₂

What volume (mL) of concentrated HCl is needed to make 0.897 liter of a 0.100 M HCl solution?  Concentrated HCl has a density of 1.18 g/mL and contains 37.0% by weight HCl.

7.49

Potassium Hydrogen Phthalate (KHP) is a weak acid that is commonly used as a primary standard in the standardization of dilute solutions of NaOH for use as titrants. A mass of 0.7500 g of KHP is dissolved in approximately 50 mL of de-ionized water in a 250 mL Erlymeyer flask and titrated with an 0.1050 M NaOH solution.  Determine the titration volume (in mL to the correct number of significant figures) required to reach the phenolphthalein endpoint.

34.98

For the standardization of NaOH with potassium hydrogen phthalate (KHP), the Q-test should be performed on which set of values to determine if an outlier exists in one of the titration trials?

NaOH concentration

For the Acid-Base 1 lab, you will be standardizing a NaOH solution for use in determining the molecular weight of an unknown (solid) acid.  Calculate the amount of solid NaOH required to prepare a 0.458 liter 0.1176 M solution.

2.15