Chem 2 lab final

Suppose you measure the absorbance of a yellow dye solution in a 1.00 cm cuvette (b=1.00 cm). The absorbance of the solution at 427 nm is 0.76 . If the molar absorptivity of yellow dye at 427 nm is 27400 M-1cm-1, what is the concentration of the solution in M?

0.0000277 or 2.77E-5

The molar absorptivity of a compound at 500 nm wavelength is 252 M-1cm-1. Suppose one prepares a solution by dissolving 0.00140 moles of a solute in enough water to make a 500.0 mL solution. What would be the absorbance in a 3 .00 mm pathlength cell?

0.212

Glucose (molar mass=180.16 g/mol) is a simple, soluble sugar. Glucose solutions are used to treat patients with low blood sugar. Suppose you prepare a glucose solution using the described procedure. Step 1: Dissolve 291.8 g of glucose in enough water to make 500.0 mL of solution. Step 2: Transfer 22.0 mL of the solution to a new flask and add enough water to make 250.0 mL of dilute solution. What is the concentration (in M) of the glucose solution at the end of the procedure?

0.285 M

A sample in a spectrophotometer gives a percent transmittance of 49.2 %. What is the absorbance of the sample?

0.308

The concentration of many colorful solutions can be determined by the amount of light absorbed by the solution. The relationship between absorbance and concentration is a linear relationship known as Beer's law. The data below show the absorbance of a series of solutions of known concentrations of Substance A. Plot these data using Excel and determine the equation of the trendline. Use that equation to determine the concentration (M) of an unknown sample of Substance A.

0.350

Identify the color absorbed by a solution that should appear as the given color. 1. Red ____ 2. Blue ____ 3. Green ____ 4. Orange ____

1. Green 2. Orange 3. Red 4. Blue

Arrange the colors of the visible spectrum in order from highest to lowest energy. orange, yellow, blue, green, red, violet 1. Highest Energy 2. 3. 4. 5. 6. Lowest Energy

1. Violet 2. Blue 3. Green 4. Yellow 5. Orange 6. Red

Match the correct name with the correct formula. 1. NH3 2. NH4+ 3. Na2Sn(OH)4 4. K4[Fe(CN)6] 5. OH- 6. S2-

1. ammonia 2. ammonium ion 3. sodium stannite 4. potassium hexacyanoferrate(ii) 5. hydroxide ion 6. sulfide ion

Identify the color flame each element that produces in a flame test. 1. K 2. Na

1. fleeting lavender flame 2. brilliant yellow flame

Match the correct sentence to the ions. 1. Na+, K+, and NH4+ 2.Ag+ 3. NH4+ 4. Na+ and K+ 5. Cu2+ and Bi3+

1. produces soluble salts of these ions 2. the chloride salt is insoluble 3. this ion tested when the pH increases and releases gas 4. these ions can be tested using the flame test 5. sulfide salts of these ions are considered insoluble.

Suppose you are working with a NaOH stock solution but you need a solution with a lower concentration for your experiment. Calculate the volume (in mL) of the 1.412 M stock NaOH solution needed to prepare 250.0 mL of 0.1444 M dilute NaOH solution.

25.57mL

What is the correct reading of the temperature in the pictured thermometer? Make sure to report your reading with the appropriate significant figures.

40.6

Determine whether each salt is generally classified as soluble or insoluble in water. A. Ca₃(PO₄)₂ B. AgCl C. PbSO₄ D. MgCO₃ E. Ba(NO₃)₂ F. Al₂(SO₄)₃ G. NaNO₃ H. Na₂SO₄

A. Insoluble B. Insoluble C. Insoluble D. Insoluble E. Soluble F. Soluble G. Soluble H. Soluble

Beer's Law states that concentration is proportional to ____________ of light. Select one:

Absorption

When hydrochloric acid is added to a solution containing Ag+ ions, _____________.

AgCl precipitates

What is the best way to stop a centrifuge from spinning after it is turned off?

Allow the centrifuge to stop spinning completely on its own.

Identify the common indicators that a chemical reaction has occurred. Select one or more: A solid being dissolved Bubbles being produced A color change Precipitate being formed A phase change A change in temperature

Bubbles being produced A color change Precipitate being formed A change in temperature

Fill in the expression for the equilibrium constant Kc for the reaction given. A(aq)+2B(aq)−⇀↽−2C(aq)+D(aq)A(aq)+2B(aq)↽−−⇀2C(aq)+D(aq) Kc=

C²D/AB²

The equilibria studied in the lab procedure include which two reactants? Select one or more: FeCl3 Fe3+ Co(SCN)2(H2O)3 [CoCl4]2−

Fe3+ [CoCl4]2−

___________________occurs when potassium hexacyanoferrate(II), K4[Fe(CN)6], is added to a solution containing copper Bi3+ and Cu2+ cations.

Formation of a red-brown precipitate of Cu2[Fe(CN)6]

________________occurs when aqueous ammonia is added to a solution containing Bi3+ and Cu2+ions.

Formation of a soluble deep blue Cu2[Fe(CN)6]

Identify the correct equation for the equilibrium constant K for the reaction given. Cu(s)+2AgNO3(aq)−⇀↽−Cu(NO3)2(aq)+2Ag(s)

K=[Cu(NO3)2][AgNO3]2

If you plot the absorbance measurements of solutions vs. their concentrations, what is the slope equal to?

Molar absorptivity, if the path length is 1 cm.

Identify some of the cations that will be detected in the procedure Qualitative Analysis of Some Cations and Anions. Select one or more: NH4+ Cu2+ Ni2+ Bi3+ Pb2+ Ag+

NH4+ Cu2+ Bi3+ Ag+

Consider the given plot of absorbance vs. concentration. Which line is the best-fit line to represent the black data points?

Red line (B)

Addition of sodium stannite solution, Na2Sn(OH)4 to white bismuth hydroxide, Bi(OH)3, results in ________________.

Reduction to black bismuth metal

What visible signs indicate a precipitation reaction when two solutions are mixed? Select one or more: Solid settling out in the test tube Bubbling in the test tube A color change A hazy or cloudy appearance

Solid settling out in the test tube A hazy or cloudy appearance

Which species is responsible for the blue color that appears during the iodine clock reaction?

Starch-triiodide complex

Which statement is true about a chemical reaction at equilibrium?

The forward reaction rate is equal to the reverse reaction rate.

Suppose you prepare a 5μM solution of red dye and a 5μM solution of blue dye and observe them in two identical test tubes. Why might the blue dye solution appear more intensely colored than the red dye solution?

The molar absorptivity of the blue dye is greater than the molar absorptivity of the red dye.

When any reversible reaction is at equilibrium, what conditions are necessarily true? The conversion between reactants and products has stopped. The rate of the forward reaction equals the rate of the reverse reaction. Reactants and products are both present in the reaction mixture. The amount of products equals the amount of reactants. The amounts of reactants and products has stopped changing

The rate of the forward reaction equals the rate of the reverse reaction. Reactants and products are both present in the reaction mixture. The amounts of reactants and products has stopped changing

Suppose that you are performing a flame test with multiple solutions. First, you test a potassium compound, which appears violet. Then, you test a calcium compound, which should produce a brick red flame. However, you do not see the correct flame color. For each incorrect flame appearance, select the most likely error responsible and the necessary action to address it. Incorrect appearance 1: The flame appears weakly yellow.

There is a sodium impurity somewhere. Compare to a known sodium compound to distinguish.

Suppose that you are performing a flame test with multiple solutions. First, you test a potassium compound, which appears violet. Then, you test a calcium compound, which should produce a brick red flame. However, you do not see the correct flame color. For each incorrect flame appearance, select the most likely error responsible and the necessary action to address it. Incorrect appearance 2: The flame remains blue.

There is not enough solution on the wire. Dip it back in the solution and try again.

Suppose that you are performing a flame test with multiple solutions. First, you test a potassium compound, which appears violet. Then, you test a calcium compound, which should produce a brick red flame. However, you do not see the correct flame color. For each incorrect flame appearance, select the most likely error responsible and the necessary action to address it. Incorrect appearance 3: The flame appears violet.

There is some of the previous metal left on the wire. Clean with acid and try again.

Identify the first step in preparing a spectrophotometer for use.

Turn on the light source and the spectrophotometer.

When a Cu²⁺solution is added to a solution containing S²⁻, the result is ________ brought about by _______.

a black precipitate formation of CuS

When testing the pH of a solution with litmus paper, dip _________ in the solution. Add a ________ of the solution to the paper. Observe the ______ of the litmus paper and determine whether the solution is acidic or basic.

a stirring rod drop color

Suppose you are studying the kinetics of the reaction between the peroxydisulfate ion and iodide ion. You perform the reaction multiple times with different starting concentrations and measure the initial rate for each, resulting in this table. Based on the data, choose the correct exponents to complete the rate law. rate=k[S2O82-]a[I-]b

a=1 b=1

The amount of light absorbed in spectroscopy is defined by _______.

absorbance

To find the order of a reaction with respect to one reactant, you will monitor the _______ as the ______ of ______ is changed.

change in rate of reaction concentration the reactant

The process of separating a liquid/solid mixture by slowly pouring the liquid component into a new vessel as the solid settles to the bottom of the original vessel is known as

decanting

According to the Beer-Lambert Law, absorbance is

directly proportional to the molarity (M) of the color absorbing chemical.

According to Beer-Lambert law, when concentration of color absorbing Cu2+(aq) is doubled, the absorbance Select one:

doubles (2x).

Determine whether each description corresponds to an endothermic reaction or an exothermic reaction. Heat is a product in the reaction. The reaction mixture feels cool from the outside. The reaction mixture feels warm from the outside. Heat is a reactant in the reaction.

exothermic endothermic exothermic endothermic

Concentration data is commonly monitored during a reaction to determine the order with respect to a reactant. Consider the types of observations listed, and determine which order is likely for that reactant. Assume all other factors are held constant. The reaction rate increases in direct proportion to the concentration of the reactant in solution. ______ An increase in the concentration of the reactant in solution causes the reaction rate to increase exponentially. ______ The reaction rate is constant regardless of the amount of reactant in solution. _____

first order second order zero order

Identify each category of substance as soluble or insoluble in water. Most carbonate and phosphate salts ____ Most silver salts_____ Salts of Group 1 elements ______ Most nitrate salts ______ Most halide (Br-, cl-, and i-) salts _______

insoluble insoluble soluble soluble soluble

Which warning about iodine is accurate?

iodine can stain the body and other surfaces

A colorimeter is an instrument used to measure the amount of ______ absorbed by a solution. This absorbance is proportional to the _________ of the solute in solution.

light concentration

Determine the best position for the lid of the centrifuge during each phase of operation. Loading samples into the centrifuge _____ Turning the centrifuge on and starting the separation of the sample ____ Waiting for the centrifuge to come to a complete stop after it has been turned off ______ Retrieving the sample after the centrifuge has completely stopped _______

open closed closed open

When aqueous ammonia is added to a solution containing Bi3+ and Cu2+ cations, ____________ occurs.

precipitation of white bismuth hydroxide

When using the method of initial rates for a kinetic study, the reaction is performed _______ One reactant concentration is kept constant, and the other ________.

several times varies

Consider the two reactions of iron ions, one with thiocyanate ( SCN−SCN−) ions and one with chloride (Cl−Cl−) ions. Fe3++SCN−−⇀↽−FeSCN2+Fe3++SCN−↽−−⇀FeSCN2+ Fe3++4Cl−−⇀↽−FeCl4−Fe3++4Cl−↽−−⇀FeCl4− If you create an equilibrium mixture from Fe3+Fe3+ and SCN−SCN− ions, adding Cl−Cl−ions will __________ because _______.

shift the iron-thiocyanate equilibrium to the reactant side it removes iron from the iron-thiocyanate equilibrium mixture.

The purpose of a centrifuge is to separate a sample into a ______ component and a ____ component.

solid liquid

In a spectrophotometer, both absorbance and transmittance indicate _________ passing through a sample. A high absorbance corresponds to a ________ transmittance.

the amount of light low

According to Le Châtelier's Principle, heat applied to an exothermic reaction will shift the reaction towards ______ Heat applied to an endothermic reaction will shift the reaction towards ________.

the reactants the products

In the Kinetics of an Iodine Clock Reaction procedure, the initial rate is calculated by multiplying the initial concentration of _________ by half, and dividing by the elapsed time as measured with a ________.

the thiosulfate ion stopwatch

To run a spectrophotometry experiment, begin by ______ the spectrophotometer and preparing the samples. Be sure to select the correct ______, then run a measurement on the _______ solution. Follow up by running measurements on ______ solutions. Once data is collected, turn off the instrument, clean the area, and discard the samples.

warming up wavelength blank sample

The ammonium ion is a

weak acid

Suppose you are studying the kinetics of the reaction between nitrogen monoxide and hydrogen gas. You perform the reaction multiple times with different starting concentrations and measure the initial rate for each, resulting in this table. Based on the data, choose the correct exponents to complete the rate law. rate=k[NO]x[H2]y

x=2 y=1

Identify the formatting aspects of the pictured Beer's Law plot graph that contain errors, such as missing information.

y-axis numeric range Title