Chem 1412 lab -Midterm

A colored solution of concentration 0.0562 mol/L has an absorbance of 0.423. What is the concentration a solution of the same solute with an absorbance of 0.841? Assume that the same sample cell is used for both readings.

0.112 *concentration is directly proportional to absorbance

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.

.124 mol

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?

0.175 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 _____.

0.20

The observed intensity of light (I) after passing through the sample cell is one-fourth the initial intensity (I0) from the light source. The absorbance (A) of the sample solution is

0.602

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.

0.0150 mol/L *absorbance is directly proportional to concentration

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.

0.0299 L

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.

0.062 M

A second calibration standard solution of an iron(III) salicylate complex was prepared in two steps. First, 29.1 mL of a 0.272 M stock solution was diluted with solvent to make 100.0 mL of the first calibration standard solution and, secondly, 80.8 mL of that first calibration solution was diluted to 100 mL to make the second calibration standard. What is the molar concentration of the second calibration standard solution? Report your answer to 3 significant figures.

0.0639 asking for molar concentration means they want in moles

In this colorimetry experiment we used a Spectronic-20 with a monochrometer that allows us to select visible light of specific wavelength. The unit of measure best used to express these wavelengths is:

-nm (nanometer)

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.

.00193 mol

For the general gas phase reaction A + 2 B ↔ 2 C + 2 D calculate the value of the equilibrium constant given the following equilibrium concentrations (report your answer to 3 significant figures in decimal format, not scientific notation): concentration of A = 1.2 Mconcentration of B = 1.68 Mconcentration of C = 0.471 Mconcentration of D = 0.254 M

.00423

For the general gas phase reaction 2 A + 3 B ↔ 2 C the equalibrium constant is 5.00. Calculate the equilibrium quotient based on the following initial concentrations and predict whether the system with shift left or shift right. Report your answer to 3 significant figures, not scientific notation, using the format "1.23 left" or "9.87 right". A0 = 0.111 MB0 = 1.66 MC0 = 0.0298 M

.0158 right

The concentration of an unknown acid solution with general formula H3A is to be determined by titration with a 0.850 M KOH solution. Determine the concentration of the acid solution given that 38.34 mL of KOH solution were needed to fully neutralize 15.00 mL of the acid solution.

0.724 M

What will be the corresponding absorbance for a solution having a concentration of 0.0025 mol L-1 and a molar absorptivity of 320 L mol-1 cm-1. (path length = 1.0 cm)

0.80 a=ebc

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

Calculate the absorbance of 0.00042 moles in 24.7 mL of solution given the molar absortivity is 1,392 M-1 cm-1 and the path length is 0.9 cm. Report your answer to 3 decimal places.

21.3 *a= ebc *remember to convert concentration from mole/ mL to mole/Liter

A 15.0 mL portion of a 0.400 M solution of acetic acid is to be titrated with a standarized 0.250 M solution of KOH. What is the expected volume of the KOH solution needed to reach the phenolphthalein end point?

24 ml

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.

30.96 ml

What is the molar mass of an unknown monoprotic acid, HA, which required 34.70 mL of 0.554 M KOH to titrate 0.889 g?

46.2 g/mol

A solution of cobalt(II) chloride is observed to be red in color. The maximum absorbance is expected to occur in what wavelength range?

500-560 nm (green)

A solution of copper(II) sulfate is observed to be blue in color. The maximum absorbance is expected to occur in what wavelength range

580-595 nm (yellow)

A second calibration standard solution of an iron(III) salicylate complex was prepared in two steps. First, 10.0 mL of a 0.100 M stock solution was added to 90.0 mL of solvent to make 100.0 mL of the first calibration standard solution and, secondly, 80 mL of that first calibration solution plus 20.0 mL of solvent were mixed to make the second calibration standard. What is the concentration of the second calibration standard solution?

8 mM

What will be the corresponding concentration for a solution having an absorbance of 0.350 and a molar absorptivity of 420 L mol-1 cm-1. (path length = 1.0 cm)

8.33 x 10^-4 M .350=(420)(1.0)(x)

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 cm^-1 (mg/mL)^-1

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.

A= ebc 1.04

KHP is titrated with a solution of KOH in order to determine the concentration of the KOH solution. The calculated concentration of the KOH solution is significantly higher than expected, leading the experimenter to believe that an error has occurred. Which of the following could account for the error of the calculated KOH concentration being too high?

KHP has spilled before adding it to the flask

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

For the equilibrium reaction whose equation is written below, predict the experimental observation resulting from the actions described below. [Co(H2O)6]2+(aq) (pink) + 4 Cl-(aq) <===> [CoCl4]2-(aq) (blue) + 6 H2O(l) Addition of several drops of cobalt(II) nitrate, Co(NO3)2, solution will:

becomes more blue, less pink *reaction shifts right

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

The point in a titration at which the indicator changes and the addition of titrant is stopped is called the ______________.

end point

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

For the equilibrium reaction whose equation is written below, predict the experimental observations resulting from the actions described below. Fe(H2O)6+3(aq) (light yellow) + 4 NCS- (aq) <===> Fe(NCS)4(H2O)2-(aq) (deep red) + 4 H2O(l) Addition of several drops of iron(III) chloride (FeCl3) to a red solution at equilibrium, will:

intensify the red color of the solution

For the equilibrium reaction whose equation is written below, predict the experimental observation resulting from the actions described below. Cr2O72-(aq) (orange) + H2O(l) <===> 2 CrO42-(aq) (yellow) + 2H1+(aq) Addition of several drops of hydrochloric acid to a yellow solution at equilibrium, will:

produce an orange color in the solution

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 hydrochloric acid solution will:

shift left the addition of HCL increases hydrogen ions, so the reactions shifts left to consume some of the product.

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. [Co(H2O)6]2+(aq) + 4 Cl-(aq) <===> [CoCl4]2-(aq) + 6 H2O(l) Addition of several drops of hydrochloric acid (HCl) solution will:

shift right

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 right this is because adding a base decreases the number of Hydrogen Ions. The reaction shifts right to replace the lost hydrogen.

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) (orange) + H2O(l) <===> 2 CrO42-(aq) (yellow) + 2H1+(aq) Addition of several drops of sodium hydroxide solution will:

shift to the right

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