Gen Chem 2 lab midterm

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.

.124 M

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

Light is passed through a solution with a path length of 2.0 cm and absorbance is recorded as 0.40. If light is passed through the same solution at the same wavelength and the path length is reduced to 1.0 cm, the absorbance should be _____.

.20

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

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.

0.00193 moles

A 0.401 g sample of KHP (HKC₈H4₄O₄, MM=204.23 g/mol) required 31.00 mL of NaOH solution to reach a phenolphthalein endpoint. Determine the molarity of the NaOH:

0.0633 mol/L

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:

0.102 mol/L

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:

.102 mol/L

A 0.86 gram sample of a solid acid is dissolved in a minimal amount of water and titrated to a phenolphthalein endpoint with 18.35 mL of 0.250 M KOH. Determine the number of moles of acid in the sample. (3 SF)

.005

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.

.0299 L

A solution containing an unknown analyte measured an absorbance of 0.51. If the lengh of the cuvetter was 1.00 cm and the molar absorptivity of the analyte was determined as 50450 M-1 cm‑1. Calculate the concentration of analyte:

1.01 x 10-5 M

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

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

Calculate the absorbance of 5.3x10-4 moles in 23.3mL solution given the molar absorptivity is 1050 M-1 cm-1 and the path length is 0.8 cm.

19.1

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

An acid of molar mass 121.1 g/mol is titrated with a 0.700 M NaOH solution. What volume of titrant is needed to reach the equivalence point when titrating 0.450 g of the acid?

5.3 * 10^-6 mL

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

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.

82.3 mL

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 absorbance of an iron (III) thiocyanate, Fe(SCN)3 (MM= 230.09 g/mol), solution containing 0.00500 mg/mL is reported as 0.4900 at 540 nm. Calculate the specific absorptivity, including units, of iron (III) thyocyanate on the assumption that a 1.00 cm cuvette is used.

98.0 cm-1 (mg/mL)-1

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

At equilibrium

Q = K

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

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

mol solute/L solution

The "KHP" is used to prepare:

our standardized acid

Why is light exiting a test tube or cuvette containing a colored analyte of lower intensity than light entering that sample?

the analyte absorbs part of the light

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. Potassium hydroxide is the _____.

titrant