Name: chemical equilibrium shifts in a color test
Uploaded: 2023-04-30T06:41:21.000Z
Duration: 8 min 37 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Chemistry

Matter And Its Interactions

HS-PS1-6

Le Ch&#226;telier's Principle

1. Preparation of the Iron(III) Thiocyanate Equilibrium Solutions
<ol>
	<li>Place 1 drop of 1 M Fe(NO3)3 solution in a&#160;test tube and dilute with 2 mL of water. Place 1 drop of 1 M KSCN in another test tube and dilute with 2 mL of water. These two test tubes serve as controls to compare against the other test tubes.</li>
	<li>Place 1 drop of 1 M Fe(NO3)3 solution in a&#160;test tube.</li>
	<li>Add 1 drop of 1 M KSCN to the test tube.</li>
	<li>Add 16 mL of water to the test tube and thoroughly mix the contents.</li>
	<li>Record any observations.</li>
	<li>Divide the mixture into 2 mL portions in 8&#160;test tubes. One of the test tubes remains untouched and serves as a FeSCN2+ control. Number the other test tubes 1&#8211;7.</li>
</ol>
2. Addition of Iron(III) and Thiocyanate Ions to the Equilibrium Solution
<ol>
	<li>To test tube 1, add 1 drop of 1 M Fe(NO3)3 solution.</li>
	<li>Shake to mix and record any observations.</li>
	<li>To test tube 2, add 1 drop of 1 KSCN solution.</li>
	<li>Shake to mix and record any observations.</li>
</ol>
3. Addition of Silver Nitrate to the Equilibrium Solution
<ol>
	<li>To test tube 3, add 3 drops of 0.1 M AgNO3 solution.</li>
	<li>Shake to mix and record any observations.</li>
	<li>Add 3 drops of 1 M Fe(NO3)3 to the test tube.</li>
	<li>Shake to mix and record any observations.</li>
	<li>To test tube 4, add 3 drops of 0.1 M AgNO3 solution.</li>
	<li>Shake to mix and record any observations.</li>
	<li>Add 3 drops of 1 M KSCN to the test tube.</li>
	<li>Shake to mix and record any observations.</li>
</ol>
4. Addition of Potassium Phosphate to the Equilibrium Solution
<ol>
	<li>To test tube 5, add 3 drops of 0.5 M K3PO4 solution.</li>
	<li>Shake to mix and record any observations.</li>
	<li>Add 3 drops of 1 M Fe(NO3)3 to the test tube.</li>
	<li>Shake to mix and record any observations.</li>
	<li>To test tube 6, add 3 drops of 0.5 M K3PO4 solution.</li>
	<li>Shake to mix and record any observations.</li>
	<li>Add 3 drops of 1 M KSCN to the test tube.</li>
	<li>Shake to mix and record any observations.</li>
</ol>
5. Changing the Temperature of the Equilibrium Solution
<ol>
	<li>Place test tube 7 in a 70&#8211;80 &#176;C water bath for 1&#8211;2 min.</li>
	<li>Compare the warm solution to the solution in the unheated test tube (the FeSCN2+ control), and record any observations.</li>
	<li>Collect the contents of test tubes 3 and 4 in the laboratory waste jar labeled &#34;Silver.&#34; Pour the contents of all the other test tubes down the drain.</li>
</ol>

Le Châtelier's principle is at work in human bodies. Oxygen is transported from the lungs to muscle and other tissues by a protein called hemoglobin (Hb) that is found in the blood. The oxygen molecule binds to this protein in a reversible reaction that can be described by an equilibrium equation:
Hb + 4 O2 <img alt="Reversible reaction symbol used in chemical equations." src="/files/ftp_upload/10138/reversible.jpg" data-altupdatedat="1761830439000" data-alt="Reversibly Equals"> Hb(...

le ch&#226;telier's principle

Source: Laboratory of Dr. Lynne O'Connell — Boston College
When the conditions of a system at equilibrium are altered, the system responds in such a way as to maintain the equilibrium. In 1888, Henri-Lewis Le Châtelier described this phenomenon in a principle that states, "When a change in temperature, pressure, or concentration disturbs a system in chemical equilibrium, the change will be counteracted by an alteration in the equilibrium composition."
This experiment demonstrates Le Châtelier's principle at work in a reversible reaction between iron(III) ion and thiocyanate ion, which produces iron(III) thiocyante ion:
Fe3+(aq) + SCN- (aq) <img alt="Reversible reaction symbol used in chemical equations." src="/files/ftp_upload/10138/reversible.jpg" data-altupdatedat="1761830439000" data-alt="Reversibly Equals"> FeSCN2+ (aq)
The concentration of one of the ions is altered either by directly adding a quantity of one ion to the solution or by selectively removing an ion from the solution through formation of an insoluble salt. Observations of color changes indicate whether the equilibrium has shifted to favor formation of the products or the reactants. In addition, the effect of a temperature change on the solution at equilibrium can be observed, which leads to the ability to conclude whether the reaction is exothermic or endothermic.

Observations of the initial solutions and the mixture of the two solutions can be seen in Table 1.
Observations of the equilibrium mixtures upon addition of various reagents can be seen in Table 2.
Observation when the temperature is changed: In test tube 7, the solution turns more orange in color (less red, more yellow) when heated.</...

Source: Laboratory of Dr. Lynne O&#39;Connell &#8212; Boston College
When the conditions of a system at equilibrium are altered, the system responds in ...

According to Le Ch?telier's Principle, if the equilibrium of a system is disturbed by a stress, the system will shift to compensate.When a chemical system is at equilibrium, there is no net change in the concentration of its reactants or products. If any parameter, such as concentration or temperature, is altered, the equilibrium will be disturbed.The system readjusts by shifting the direction of the reaction until a new equilibrium is reached.This video will demonstrate Le Ch?telier's Principle by showing the influence of concentration and temperature on chemical reactions at equilibrium.Reversible chemical reactions consist of two competing processes: the forward reaction, and the reverse reaction. When these two processes occur at the same rate, the system is at equilibrium. Le Ch?telier's Principle states that, when a system at equilibrium is stressed, it will shift to counteract the disturbance.For instance, if the concentration of a reactant species in an equilibrium solution is increased, the equilibrium will shift towards the products, increasing the rate of the forward reaction. Eventually, the system will reach a new equilibrium.Temperature can also be thought of as a rea

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chemical equilibrium shifts in a color test

Chemical equilibrium shifts are shown with a color test using iron(III) ions and thiocyanate ions. In this reversible reaction, Fe3+ and SCN- combine to form FeSCN2+. The changing color of the solution helps show which side of the equilibrium is favored.

The experiment follows Le Châtelier's principle. This principle says that when temperature, pressure, or concentration changes disturb a system at equilibrium, the system responds by counteracting that change. Here, the focus is on concentration and temperature changes in a chemical equilibrium.

One ion is added directly to the solution to change concentration. Another ion can also be removed by forming an insoluble salt. These changes shift the equilibrium toward either the products or the reactants, and the color change gives a clear clue about the direction of the shift.

The solution is also heated or cooled to test the effect of temperature. From the observed response, students can tell whether the reaction is exothermic or endothermic. This makes the iron(III) thiocyanate system a simple way to observe equilibrium behavior in action.

Chemical Equilibrium Shifts in a Color Test

chemical-equilibrium-shifts-in-a-color-test

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Explore how iron(III) and thiocyanate ions change color as equilibrium shifts with concentration and temperature changes under Le Châtelier's principle.

Chemical Equilibrium Shifts in a Color Test | JoVE K12

Arizona Science Standards

Physical Science

HS+C.P1

HS+C.P1U1.6

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New Jersey Student Learning Standards for Science

Matter and Its Interactions

Next Generation Science Standards

HS-PS1-4

Florida Department of Education

SC.912.P.10

SC.912.P.10.7

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South Carolina College and Career Ready Science Standards

C-PS1-6

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Structure and Properties of Matter

HS-PS2-6.

HS-PS1-10.

HS. Chemical Reactions

HS-PS1-2.

HS-PS1-4.

HS-PS1-6.

HS-PS1-11.

HS-PS1-12.

Earth and Space Sciences

Earth’s Systems

HS-ESS2-2.

Georgia Standards of Excellence

9-12

SC4.

lechateliers-principle-and-chemical-equilibrium

LeChatelier’s Principle and Chemical Equilibrium

Lynne O'Connell

Boston College

Overview

Le Ch&#226;telier&#8217;s Principle

Preparation of Iron(III) Thiocyanate Equilibrium Solutions

Altering Reaction Parameters

Applications

Summary

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

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The Periodic Table And Organismal Elements

Atomic Structure

The Greek philosopher Democritus proposed that everything on Earth is made up of tiny particles called atomos, Greek for &#34;indivisible,&#34; from which ...

Electron Configurations

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Electronic Structure of Atoms


An atom comprises protons and neutrons, which are contained inside the dense, central&#160;core called the nucleus, with electrons present around the ...

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Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

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Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

Coulomb's Law

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Van der Waals Interactions

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Chemical Bonds


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Electron Behavior

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Subatomic Particles

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Electric Field

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Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

Electric Dipoles and Dipole Moment

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HS-PS1-3

Chemical Equilibrium Shifts in a Color Test

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