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Unit 5: Chemical Kinetics Unit 5: Chemical Kinetics

Unit 5: Chemical Kinetics - PowerPoint Presentation

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Unit 5: Chemical Kinetics - PPT Presentation

Day 5 Begin Kinetics Lab Warm Up If you are given 15 M stock solution and you need to make ONLY 20 mL of a 6 M solution how much of the stock solution should you use Agenda Demonstration ID: 798900

crystal violet x10 kinetics violet crystal kinetics x10 rate fading concentration naoh lab absorbance solution reaction constant ions law

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Slide1

Unit 5: Chemical Kinetics

Day

5: Begin Kinetics Lab

Slide2

Warm Up

If you are given

15 M

stock solution and you need to make

ONLY 20 mL

of a

6 M solution

, how much of the stock solution should you use?

Slide3

Agenda

Demonstration

Begin

Lab Set

Up

Purpose

Hypothesis

Materials

Pre-Lab Questions

If Time:

B

egin Introductory Activity

Slide4

Kinetics of Crystal Violet Fading

Pre-Lab

1.

Concentration

(

mol

/L)

Volume of

2.5 x10

-5

CV (mL)

Volume of distilled

water

2.5 x10

-5

= 25

μ

M

10.0 mL

0.0 mL

2.5 x10

-6

= 2.5

μ

M

5.0 x10

-6

= 5.0

μ

M

7.5 x10

-6

= 7.5.0

μ

M

10.0 x10

-6

= 10.0

μ

M

12.5 x10

-6

= 12.5

μ

M

5.0 mL

5.0 mL

Slide5

Kinetics of Crystal Violet Fading

Guided Inquiry Design and Procedure

Part A

CV

+

+ OH

-

 CVOH

What percent of OH

-

ions will remain at the end of a reaction if the initial concentrations of each reactant were equal (1:1 ratio)?

Slide6

Kinetics of Crystal Violet Fading

Review:

CV

+

+

OH

-

CVOH

purple

colorless

Rate

= k[CV

+

]

m

[OH

-

]

n

Slide7

Kinetics of Crystal Violet Fading

Rate Law:

Rate = k’ [CV

+

]

m

where k’ = k [OH

-

]

n

The constant k’ is a new “pseudo” rate constant. The new pseudo rate law is valid when the concentration of OH

-

ions is much greater than the concentration of CV

+

ions. Under these conditions, the [OH

-

] term in the original rate law will not change much over the course of the reaction and may be treated as a constant in the rate equation.

Slide8

Kinetics of Crystal Violet Fading

Slide9

Kinetics of Crystal Violet Fading

BIG IDEA:

The more color, the more concentrated, the more absorbance.

Absorbance = Concentration

Slide10

Part B: Procedure Outline

NaOH

conc. needs to be changed, not CV

+

, so that the effect on k’ can be calculated and the order of reaction with respect to OH

-

determined

Colorimeter must be zeroed with a blank, equal volumes 0.01 M

NaOH

and water

To make 10 mL of 0.01 M

NaOH

, measure 5.0 mL of 0.02 M

NaOH

in a serological pipet and…

Clean the pipet with small portions of crystal violet solution. Measure 10 mL of 25

uM

crystal violet solution…

After the absorbance vs. time data are recorded, the absorbance values need to be converted into concentration, then separate data columns for

ln

[CV

+

] and 1/[CV

+

] need to be created and analyzed to determine k’ for the new concentration of

NaOH

, 0.01 M.