Chem Lab 1412 mid-term

What is the concentration of a solution of a monoprotic acid (i.e., HA) which required 19.25 mL of 0.0965 M KOH to titrate 15.00 mL of the acid solution? Report the answer with the correct number of significant figures.

.124M

A 0.458 g sample of KHP (molar mass 204.22 g/mol) is titrated to a pink phenolphthalein endpoint with 12.84 mL of a NaOH solution. What is the concentration of the solution?

.175 M

If you dilute 175 mL of a 1.6 M solution of LiCl to 1.0 L, determine the new concentration of the solution.

.28 M

What is the concentration of a solution of a diprotic acid (i.e., H2A) which required 19.25 mL of 0.0965 M KOH to titrate 15.00 mL of the acid solution? Report the answer with the correct number of significant figures.

.062 M

A 0.385 g sample of KHP (HKC8H4O4, MM=204.23 g/mol) required 18.50 mL of NaOH solution to reach a phenolphthalein endpoint. Determine the molarity of the NaOH:

1) convert .385 g into mol 2) convert 18.50 mL to L 3) mol/L .102 mol/L

Calculate the volume of 0.505 M KOH necessary to titrate 0.0151 moles of hydrochloric acid, HCl, to a phenolphthalein end-point. Report the answer with three significant figures.

1) convert .505 M to mol per liter 2) .0151/.505 .0299 L

Use Beer's Law, A = ebc, and calculate the absorbance of a solution with a molar absorbtivity of 105 M-1 cm-1 if the analyte's concentration in that solution contained in a 1.01 cm path length cuvette is 9.80 x 10-3 M.

1.04

How many moles of phosphoric acid (a triprotic acid, H3A) can be completely neutralized by 20.0 mL of 0.252 M potassium hydroxide?

1.68 mol

What is the molar mass of an unknown monoprotic acid which required 15.90 mL of 0.101 M KOH to titrate 0.205 g? Report the answer with the correct number of significant figures.

128 g/mol

An acid with molar mass 84.48 g/mol is titrated with 0.650 M KOH. What volume of KOH solution is needed to titrate 1.70 grams of the acid to the equivalence point.

13.08 mL

What is the molar mass of lauric acid (monoprotic) if 14.06 mL of 0.355 M KOH is needed to neutralize 1.000 g of the acid.

200.35 g/mol

According to Beer's Law, on which of the following does absorbance NOT depend?

Color of the solution

What is the molar mass of an unknown triprotic acid, H3A, which required 84.70 mL of 0.554 M KOH to titrate 0.889 g?

56.8 g/mol

An unknown diprotic acid, H2A, is titrated with a solution of 0.350 M NaOH in order to determine its molar mass. If 15.74 mL are needed to neutralize 0.245 g of the acids, what is the molar mass of the acid?

88.94 g/mol

The color of a solution is related to the amount of light of a certain frequency that the solute absorbs. Beer's Law expresses this relationship. Which best describes Beer's Law. (A = absorbance, L = path length, C = concentration)

A µ L and A µ C

For the reaction PbI2(s) ↔ Pb2+(aq) + 2 I-(aq) a value for the equilibrium constant should be calculated from equilibrium concentrations as:

Keq = [Pb2+][I-]2

For the gas phase reaction 2 SO2 + O2 ↔ 2 SO3 a value for the equilibrium constant should be calculated from equilibrium concentrations as:

Keq = [SO3]2 / [O2][SO2]2

For the equilibrium reaction whose equation is written below, predict the shift in the reaction to re-establish equilibrium conditions resulting from the actions described below. Cr2O72- (aq) + H2O (l) ↔ 2 CrO42- (aq) + H1+ (aq) Addition of several drops of potassium hydroxide solution will:

Shift to the right

Adding Fe(NO3)3 to the aqueous equilibrium system: Fe3+ + SCN- ↔ FeSCN2+ (light yellow) ↔ (deep red) will produce which of the following changes?

The color in the test tube becomes a deeper red because the equilibrium will shift to make more products.

If fingerprints are not wiped off of the sample cell, how will the data be affected?

The concentration will be inaccuratly high

In the reaction CO(g) + NO2(g) ↔ CO2(g) + NO(g), which of the following changes would result in the formation of more products at equilibrium?

adding NO2 to the reaction

A potassium hydroxide solution, previously standardized against KHP, is added from a burette to a beaker that contains hydrochloric acid of unknown concentration. One to two drops of phenolphthalein have been added to the acid in the beaker. Hydrochloric acid is the _____.

analyte

A colored solution of concentration 0.0100 mol/L has an absorbance of 0.50. What is the concentration a solution of the same solute with an absorbance of 0.75? Assume that the same sample cell is used for both readings.

c1/c2=a1/a2 .0150 mol/L

A student performs a titration in order to determine the concentration of a nitric acid solution. The buret containing the titrant, NaOH, has a number of bubbles clinging to the inside throughout the procedure. How will this error affect the calculated value of the HNO3 concentration?

calculated value < actual value

A student performed a titration to standardize a NaOH solution. After measuring the mass of KHP to be titrated, a small number of crystals are spilled during the transfer to an Erlenmeyer flask. How will this error affect the determination of the concentration of the NaOH solution?

calculated value > actual value

In the titration of a monoprotic acid with a monoprotic base, the point at which the same number of moles of acid and base have been added is called the ______________.

equivalence point

A 0.54 gram sample of a solid acid is dissolved in a minimal amount of water and titrated to a phenolphthalein endpoint with 15.45 mL of 0.125 M KOH. Determine the number of moles of acid in the sample.

m1v1=m2v2 1) convert 15.45 mL into L 2) .125 M is .125 mol/L 3) plug in/ (.125)(1)=(.01545)(m2) .00193 mol

Which one of the following is a correct expression for the concentration term "molarity"?

mol solute/L solution

Calculate the volume of 0.310 M KOH necessary to titrate 0.0255 moles of acetic acid (HOAc, H3CCOOH) to a phenolphthalein end-point. Report the answer with three significant figures.

mol=Molarity*Volume 82.3 mL

At equilibrium, __________

the rates of the forward and reverse reactions are equal