Analysis of strong and weak electrolytes using a

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Analysis of strong and weak electrolytes using a conductivity apparatus Presentation to Accompany the

Analysis of strong and weak electrolytes using a conductivity apparatus Presentation to Accompany the Conductivity of Solutions Lecture Demonstration Includes student activities Chemistry Education Research Group Department of Chemistry & Biochemistry University of Oregon Eugene, Oregon 97403 USA

Animal of the Day Caribou? Caribou B. A. Antelope D. C.

Animal of the Day Caribou? Caribou B. A. Antelope D. C.

H 2 partial negative charge H 2 O partial positive charge In the H

H 2 partial negative charge H 2 O partial positive charge In the H 2 O molecule, sharing is not equal. The electron density is centered around the oxygen nucleus. Water is a polar molecule (also referred to as a dipole)

Net dipole moment of water (physics) Oxygen is more electronegative compared to hydrogen. vectors

Net dipole moment of water (physics) Oxygen is more electronegative compared to hydrogen. vectors

Net dipole moment of water (physics)

Net dipole moment of water (physics)

Forces of attraction between water molecules Physics: opposite charges attract Intermolecular force (IMF) A

Forces of attraction between water molecules Physics: opposite charges attract Intermolecular force (IMF) A force of attraction between molecules The type of IMF: dipole-dipole

Forces of attraction between water molecules

Forces of attraction between water molecules

Representation of liquid water molecules

Representation of liquid water molecules

Movement of liquid water molecules

Movement of liquid water molecules

Analysis of Aqueous Solutions • Many reactions occur in aqueous solutions, especially reactions of

Analysis of Aqueous Solutions • Many reactions occur in aqueous solutions, especially reactions of ionic compounds. • A solution consists of one or more solutes (minor component) dissolved in a solvent (the major component).

Supplementing with electrolytes Cells use electrolytes to maintain voltages across cell membranes and to

Supplementing with electrolytes Cells use electrolytes to maintain voltages across cell membranes and to carry electrical impulses for nerve signaling and muscle contractions. Electrolytes, particularly sodium ions and potassium ions, are lost when you sweat.

Because of the polar nature of water, it is often able to dissolve other

Because of the polar nature of water, it is often able to dissolve other polar covalent substances or ionic substances. (Opposite charges attract) Let’s consider a couple of common substances • Sodium chloride, Na. Cl (table salt) • Sucrose, C 12 H 22 O 11 (sugar)

Substances that dissolve in water are “soluble” Sodium chloride, Na. Cl (table salt) Sucrose,

Substances that dissolve in water are “soluble” Sodium chloride, Na. Cl (table salt) Sucrose, C 12 H 22 O 11 (sugar) Once dissolved, do they have the same behaviors?

Detecting Ions in Aqueous Solution Using a Conductivity Tester Lecture Demonstration Conductivity Apparatus

Detecting Ions in Aqueous Solution Using a Conductivity Tester Lecture Demonstration Conductivity Apparatus

What does a battery do? e- e- A cell or battery provides the electromotive

What does a battery do? e- e- A cell or battery provides the electromotive force that pushes electrons out of the negative terminal and pulls electrons into the positive terminal. https: //www. lightrocket. com/russellkightley/galleries/go/12734/electricity-animations

Physics: circuit diagram Electrons are pulled into the positive terminal of the battery. Electrons

Physics: circuit diagram Electrons are pulled into the positive terminal of the battery. Electrons are pushed out of the negative terminal of the battery. e- Direction of e- flow ee. Physics circuit diagram

Detecting Ions in Aqueous Solution using a Conductivity Tester This solution contains ions. Conductivity

Detecting Ions in Aqueous Solution using a Conductivity Tester This solution contains ions. Conductivity Apparatus This solution does not contain ions.

What is electrical current? Electrical current is electrical charges in motion. What are the

What is electrical current? Electrical current is electrical charges in motion. What are the electrical charges? Electrical charges can be electrons in a wire, or ions moving in a solution.

Conductivity Observations Light Bulb D. I. Water Na. Cl(s) Na. Cl(aq) Inference What is

Conductivity Observations Light Bulb D. I. Water Na. Cl(s) Na. Cl(aq) Inference What is present in solution?

Will pure water conduct electricity? A. Yes B. No C. Somewhat D. Not sure

Will pure water conduct electricity? A. Yes B. No C. Somewhat D. Not sure

Experimental Observations: the light bulb does not light up Inference: the conductivity tester is

Experimental Observations: the light bulb does not light up Inference: the conductivity tester is not detecting any mobile ions. Deionized water is water that has had many of the ions removed. D. I. water Solid Na. Cl(aq) What is happening at the molecule level? Pure water consists mostly of H 2 O molecules.

What about the water? Deionized and distilled water are pure, with no ions present.

What about the water? Deionized and distilled water are pure, with no ions present. Tap water contains ions and does conduct electricity.

Will Na. Cl(solid) conduct electricity? A. Yes B. No C. Somewhat D. Not sure

Will Na. Cl(solid) conduct electricity? A. Yes B. No C. Somewhat D. Not sure

Conductivity Observations Light Bulb D. I. Water Na. Cl(s) Na. Cl(aq) Inference What is

Conductivity Observations Light Bulb D. I. Water Na. Cl(s) Na. Cl(aq) Inference What is present in the substance?

Conductivity Observations Light Bulb Inference What is present in the substance? D. I. Water

Conductivity Observations Light Bulb Inference What is present in the substance? D. I. Water Light blub does not light up no ions detected in the liquid Water molecules H 2 O Na. Cl(s) Light blub does not light up no ions detected in the solid In the solid, there are Na+ cations and Clanions, but these ions are not mobile. Na. Cl(aq)

Will Na. Cl(aq) conduct electricity? A. Yes B. No C. Somewhat D. Not sure

Will Na. Cl(aq) conduct electricity? A. Yes B. No C. Somewhat D. Not sure

Demo

Demo

When an aqueous solution of Na. Cl(aq) is tested for conductivity the light bulb

When an aqueous solution of Na. Cl(aq) is tested for conductivity the light bulb glows brightly. Draw a picture diagram of how solid Na. Cl dissolve in water to form a solution. Include the orientation of the water molecules. Save your diagram for later.

Conductivity Observations Light Bulb Inference What is present in the substance? D. I. Water

Conductivity Observations Light Bulb Inference What is present in the substance? D. I. Water Light blub does not light up no ions detected in the liquid Water molecules H 2 O Na. Cl(s) Light blub does not light up no ions detected in the solid In the solid, there are Na+ cations and Clanions, but these ions are not mobile. Na. Cl(aq) Bright glow Ions present H 2 O molecules in solution solvent Na+(aq), Cl-(aq) ions solute

Experimental Observations D. I. water What is happening at the atom level? Solid Na.

Experimental Observations D. I. water What is happening at the atom level? Solid Na. Cl(aq)

 • Write a chemical equation representing solid Na. Cl dissolving in water H

• Write a chemical equation representing solid Na. Cl dissolving in water H 2 O Solid Na. Cl

 • Soluble ionic compounds dissolved in water will support a movement of current

• Soluble ionic compounds dissolved in water will support a movement of current when subjected to why? H 2 O Solid Na. Cl Initial 100 Na. Cl Final 0 Na. Cl Na+(aq) and Cl-(aq) ions All of the Na. Cl units in the solid are pulled apart and become Na+ and Cl- ions. 0 Na+ 100 Na+ 0 Cl 100 Cl- 100% Dissociated Soluble ionic compounds fully dissociate into ions. (But, not all ionic compounds are soluble in water… more on that later. )

Dissociation and Dissolving An electrolyte is a substances that dissociates into ions when dissolved

Dissociation and Dissolving An electrolyte is a substances that dissociates into ions when dissolved in water. A short computer animation illustration how positive and negative ions in a solid ionic compound dissolve in water might be used to accompany dissolving salts in water demonstration https: //www. youtube. com/watch? v=betb. KEJf 7 j. Q

 • Draw a particle diagram of the species existing in a solution of

• Draw a particle diagram of the species existing in a solution of sodium chloride, Na. Cl(aq).

Conductivity Observations Light Bulb Inference What is present in solution? D. I. Water Light

Conductivity Observations Light Bulb Inference What is present in solution? D. I. Water Light blub does not light up no ions detected in the liquid Water molecules H 2 O Na. Cl(s) Light blub does not light up no ions detected in the solid In the solid, there are Na+ cations and Clanions, but these ions are not mobile. Na. Cl(aq) Bright glow Ions present H 2 O molecules in solution solvent Na+(aq), Cl-(aq) ions solute

Dissociation and Dissolving An electrolyte is a substances that dissociates into ions when dissolved

Dissociation and Dissolving An electrolyte is a substances that dissociates into ions when dissolved in water. A short computer animation illustration how positive and negative ions in a solid ionic compound dissolve in water accompanies the dissolving salts in water demonstration. https: //www. youtube. com/watch? v=betb. KEJf 7 j. Q

 • Soluble ionic compounds dissolved in water will support a movement of current

• Soluble ionic compounds dissolved in water will support a movement of current when subjected to … why? Na. Cl(aq) is a strong electrolyte H 2 O Na+(aq) and Cl-(aq) ions 100 100 Solid Na. Cl Soluble ionic compounds fully dissociate into ions. (But, not all ionic compounds are soluble in water… more on that later. )

 • Draw a particle diagram of the species existing in a solution of

• Draw a particle diagram of the species existing in a solution of sodium chloride, Na. Cl(aq).

The orientation of the water molecules toward the Na+ cation and Cl- anion matters!

The orientation of the water molecules toward the Na+ cation and Cl- anion matters! Think physics: opposite charges attract. The partial negative oxygen end of the water molecule will be attracted to the positive charge Na+ cation.

 • The partial positive hydrogen end of the water molecule will be attracted

• The partial positive hydrogen end of the water molecule will be attracted to the negative charge Cl- anion.

What occurs in the Na. Cl solution between the electrodes during a conductivity test?

What occurs in the Na. Cl solution between the electrodes during a conductivity test? • Draw a particle diagram.

Experimental Observations What is happening at the atom level? Na. Cl(aq)

Experimental Observations What is happening at the atom level? Na. Cl(aq)

To which electrode are the cations attracted? To which electrode are the anions attracted

To which electrode are the cations attracted? To which electrode are the anions attracted

To which electrode are the cations attracted? To which electrode are the anions attracted

To which electrode are the cations attracted? To which electrode are the anions attracted

To which electrode are the cations attracted? To which electrode are the anions attracted

To which electrode are the cations attracted? To which electrode are the anions attracted

Anions Cations

Anions Cations

Insert URL computer animation of ion movement on solution.

Insert URL computer animation of ion movement on solution.

There is a migration of cations and anions in opposite directions.

There is a migration of cations and anions in opposite directions.

Caribou Antelope Caribou and antelope migrate in opposite directions.

Caribou Antelope Caribou and antelope migrate in opposite directions.

Animation of migration of cations and anions in Na. Cl(aq) Anions Cations Antelope Caribou

Animation of migration of cations and anions in Na. Cl(aq) Anions Cations Antelope Caribou https: //www. youtube. com/watch? v=hh. GVh. LLXRz. M

Animation of migration of cations and anions in Na. Cl(aq) during conductivity testing -

Animation of migration of cations and anions in Na. Cl(aq) during conductivity testing - + Anions Cations Antelope Caribou https: //www. youtube. com/watch? v=hh. GVh. LLXRz. M

What occurs in the Na. Cl solution between the electrodes during a conductivity test?

What occurs in the Na. Cl solution between the electrodes during a conductivity test? • Answer: a migration of cations toward the cathode and anions toward the anode. Electrical current is electrical charges in motion. Electrical charges can be electrons in a wire, or ions moving in a solution.

 • How about covalent compounds? for example, sucrose, C 12 H 22 O

• How about covalent compounds? for example, sucrose, C 12 H 22 O 11, or table sugar Red = O, grey = H, black = C • Covalent compounds must have a polar portion to be soluble in water. Covalent compounds can contain C, H, O, N, or P (non-metals).

Conductivity Observations Water Sucrose(s) Sucrose(aq) Light Bulb Inference What is present in the substance?

Conductivity Observations Water Sucrose(s) Sucrose(aq) Light Bulb Inference What is present in the substance? Light blub does not light up no ions detected in the liquid Water molecules H 2 O

Conductivity Observations Light Bulb Inference What is present in solution? Water Light blub does

Conductivity Observations Light Bulb Inference What is present in solution? Water Light blub does not light up no ions detected in the liquid Water molecules H 2 O Sucrose(s) Light blub does not light up no ions detected in the solid In the solid, there are no cations and anions Sucrose(aq)

Demonstration Sucrose is added to water, stirred and it dissolves. The solution is tested

Demonstration Sucrose is added to water, stirred and it dissolves. The solution is tested with the conductivity apparatus. H 2 O sucrose, C 12 H 22 O 11

Two sucrose molecules (solid) dissolving in water

Two sucrose molecules (solid) dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water H 2 O(l) sucrose, C 12 H 22 O 11

Sucrose dissolving in water H 2 O(l) sucrose, C 12 H 22 O 11 (s) C 12 H 22 O 11 (aq)

A representation of solid sucrose dissolving in water sucrose, C 12 H 22 O

A representation of solid sucrose dissolving in water sucrose, C 12 H 22 O 11 (s) Insert URL sucrose dissolving in water computer animation

Sucrose dissolving in water

Sucrose dissolving in water

One Sucrose molecule dissolving in water

One Sucrose molecule dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water

Sucrose dissolving in water Glucose and fructose are not ions!!

Sucrose dissolving in water Glucose and fructose are not ions!!

Strong electrolytes: fully dissociated into ions when dissolved in water (ionic solutions such as

Strong electrolytes: fully dissociated into ions when dissolved in water (ionic solutions such as Na. Cl(aq)). Non-electrolytes: remain in molecular form when dissolved in water (covalent compounds such as sucrose) Note: dissolved ≠ dissociated

Conductivity Observations Light Bulb Inference What is present in solution? Water Light blub does

Conductivity Observations Light Bulb Inference What is present in solution? Water Light blub does not light up no ions detected in the liquid Water molecules H 2 O Sucrose(s) Light blub does not light up no ions detected in the solid In the solid, there are no cations and anions Sucrose(aq) Light blub does not light up no ions detected in the solution In the solution, there are no cations and anions

Role of the water molecules when sucrose dissolves in water Electrostatic forces of attraction

Role of the water molecules when sucrose dissolves in water Electrostatic forces of attraction A sucrose solution is a non-electrolyte. Partial charges shown on selected atoms

Role of the water molecules when sucrose dissolves in water URL computer animation dissolving

Role of the water molecules when sucrose dissolves in water URL computer animation dissolving sucrose in water

Representing a sucrose solution at the particle level

Representing a sucrose solution at the particle level

 • A sucrose solution does not conduct electricity. Why not? What must be

• A sucrose solution does not conduct electricity. Why not? What must be missing? No dissociation, no charged particles Covalent compounds do not dissociate and do not conduct electricity. • When dissolved, covalent compounds do not dissociate and will exist as molecules. • No charged particles – no conduction of electricity

Demonstration Test the conductivity of a solution acetic acid HC 2 H 3 O

Demonstration Test the conductivity of a solution acetic acid HC 2 H 3 O 2(aq)

Conductivity Observations Light Bulb Inference What is present in solution? Na. Cl(aq) Bright glow

Conductivity Observations Light Bulb Inference What is present in solution? Na. Cl(aq) Bright glow Ions present in solution H 2 O solvent Na+(aq), Cl-(aq) solute Sucrose(aq) No light No ions present in solution H 2 O solvent C 12 H 22 O 11 (aq) solute Acetic acid(aq)

Demonstration

Demonstration

Acetic acid CH 3 COOH(aq) What do you observe about the light bulb? What

Acetic acid CH 3 COOH(aq) What do you observe about the light bulb? What does this imply about the solution?

Consider the conductivity of aqueous acetic acid, HC 2 H 3 O 2. This

Consider the conductivity of aqueous acetic acid, HC 2 H 3 O 2. This indicates that acetic acid A. fully dissociates into ions. B. does not dissociate and remains in the molecular form. C. partially dissociates to form a mixture of ions and molecules.

Conductivity Observations Light Bulb Inference What is present in solution? Acetic acid(aq) dim Some

Conductivity Observations Light Bulb Inference What is present in solution? Acetic acid(aq) dim Some ions H 2 O solvent, Mostly HC 2 H 3 O 2 molecules; some H+ ions, C 2 H 3 O 2 - ion Na. Cl(aq) Bright glow Ions present in solution H 2 O solvent Na+(aq), Cl-(aq) solute Sucrose(aq) No light No ions present in solution H 2 O solvent C 12 H 22 O 11 (aq) solute

Acetic acid CH 3 COOH(aq) An acetic acid solution is a weak electrolyte. What

Acetic acid CH 3 COOH(aq) An acetic acid solution is a weak electrolyte. What is present in the solution? Draw a picture diagram.

Weak electrolytes - partially dissociated into ions H 2 O HC 2 H 3

Weak electrolytes - partially dissociated into ions H 2 O HC 2 H 3 O 2 D H+ + C 2 H 3 O 2~ 99% ~ 1% Double reaction arrow indicates that the reaction is significant in both directions. An acetic acid solution establishes a dynamic equilibrium

Weak electrolytes - partially dissociated into ions H 2 O HC 2 H 3

Weak electrolytes - partially dissociated into ions H 2 O HC 2 H 3 O 2 D H+ + C 2 H 3 O 2~ 99% ~ 1% Double reaction arrow indicates that the reaction is significant in both directions. Sketch a picture diagram representing an aqueous solution of acetic acid at the molecular level.

Draw a particle level diagram for a solution of acetic acid Dynamic equilibrium of

Draw a particle level diagram for a solution of acetic acid Dynamic equilibrium of a weak acid solution An animation of a strong acid solution dissociation. https: //www. youtube. com/watch? v=r. Kq. YE 5 s. Zi 1 s

Only some ions present

Only some ions present

Demonstration Test the conductivity of a solution hydrochloric acid HCl(aq)

Demonstration Test the conductivity of a solution hydrochloric acid HCl(aq)

Write a chemical equation representing dissolving gas phase HCl(g) in water to form a

Write a chemical equation representing dissolving gas phase HCl(g) in water to form a solution of hydrochloric acid

Demonstration hydrochloric acid reacts with water

Demonstration hydrochloric acid reacts with water

Conductivity Observations Water HCl(aq) Light Bulb Inference What is present in the substance? Light

Conductivity Observations Water HCl(aq) Light Bulb Inference What is present in the substance? Light blub does not light up no ions detected in the liquid Water molecules H 2 O

Demonstration HCl(aq) solution

Demonstration HCl(aq) solution

Conductivity Observations Water HCl(aq) Light Bulb Inference What is present in the substance? Light

Conductivity Observations Water HCl(aq) Light Bulb Inference What is present in the substance? Light blub does not light up no ions detected in the liquid Water molecules H 2 O

Draw a particle level diagram representing a solution of hydrochloric acid

Draw a particle level diagram representing a solution of hydrochloric acid

Particle level diagram of a solution of HCl(aq)

Particle level diagram of a solution of HCl(aq)

Draw a particle level diagram representing HCl(g) molecules reacting with water molecules Dynamic equilibrium

Draw a particle level diagram representing HCl(g) molecules reacting with water molecules Dynamic equilibrium of a weak acid solution An animation of a strong acid solution dissociation. https: //www. youtube. com/watch? v=r. Kq. YE 5 s. Zi 1 s Insert computer animation of HCl(aq)

Electrolytes • A strong electrolyte dissociates completely when dissolved in water. • A weak

Electrolytes • A strong electrolyte dissociates completely when dissolved in water. • A weak electrolyte only dissociates partially when dissolved in water.

Strong Acids • You need to memorize the following seven strong acids in life.

Strong Acids • You need to memorize the following seven strong acids in life. • All other acids are considered as weak acids. HCl HBr HI – Hydrochloric acid – Hydrobromic acid – Hydroiodic acid HNO 3 H 2 SO 4 HCl. O 3 HCl. O 4 – Nitric acid – Sulfuric acid – Chloric acid – Perchloric acid H 2 SO 4 is a diprotic acid. Only the first H+ off is considered strong Strong acids are strong electrolytes – They 101 completely dissociate in water!

Demonstration Test the conductivity of a solution sodium hydroxide Na. OH(aq)

Demonstration Test the conductivity of a solution sodium hydroxide Na. OH(aq)

Conductivity Observations Light Bulb Inference What is present in the substance? Water Light blub

Conductivity Observations Light Bulb Inference What is present in the substance? Water Light blub does not light up no ions detected in the liquid Water molecules H 2 O HCl(aq) Light bulb lights up brightly mobile ions in solution Water molecules H 2 O H 3 O+ and Cl- ions Na. OH(aq)

Conductivity Demonstration sodium hydroxide solution

Conductivity Demonstration sodium hydroxide solution

Demonstration Na. OH(aq) solution

Demonstration Na. OH(aq) solution

Conductivity Observations Water HCl(aq) Na. OH(aq) Light Bulb Inference What is present in the

Conductivity Observations Water HCl(aq) Na. OH(aq) Light Bulb Inference What is present in the substance? Light blub does not light up no ions detected in the liquid Water molecules H 2 O

Write a chemical equation representing dissolving solid sodium hydroxide in water to form a

Write a chemical equation representing dissolving solid sodium hydroxide in water to form a solution of sodium hydroxide

Write a chemical equation representing dissolving solid sodium hydroxide in water to form a

Write a chemical equation representing dissolving solid sodium hydroxide in water to form a solution of sodium hydroxide

Draw a particle level diagram for a solution of sodium hydroxide

Draw a particle level diagram for a solution of sodium hydroxide

Particle level diagram for a solution of Na. OH(aq)

Particle level diagram for a solution of Na. OH(aq)

Demonstration sodium hydroxide interacts with water

Demonstration sodium hydroxide interacts with water

Selected Strong Bases and Weak Bases Strong bases are strong electrolytes – they completely

Selected Strong Bases and Weak Bases Strong bases are strong electrolytes – they completely dissociate in water. Weak Acids sodium hydroxide, Na. OH potassium hydroxide, KOH calcium hydroxide, Ca(OH)2 strontium hydroxide, Sr(OH)2 barium hydroxide, Ba(OH)2 Weak Bases hydrofluoric acid, HF ammonia, NH 3 phosphoric acid, H 3 PO 4 Methyl amine, CH 3 NH 2 acetic acid, CH 3 COOH (or HC 2 H 3 O 2) and many more…

To recap… • Substances that dissolve in water are water soluble. • Substances that

To recap… • Substances that dissolve in water are water soluble. • Substances that fully dissociate in water are strong electrolytes. • All ionic compounds, that are water soluble, are strong electrolytes.