Post Lab: Electrolytes. Electrolytes Are substances that form positive(+) and negative (-) ions in water Conduct an electric current.

Post Lab:Electrolytes

Electrolytes

Are substances that form positive(+)

and negative (-) ions in water

Conduct an electric current

Electrolytes in the Body

Carry messages sent to and from the

brain as electrical signals

Maintain cellular function with the correct

concentrations electrolytes

• Electric current : flow of charged particles.

• One type of current is electrons flowing through a wire, from cathode (negative electrode) to anode (positive electrode).

Conduction Illustrated

• Another type of current: anions and cations moving through a solution Cations move to the cathode, anions move to the anode.

• External source of potential (voltage) is required in both cases!

Drop of CaCl2 (aq) LED

Resistor 330 Ω (ohms)

– Strong electrolytes include:

– Strong acids (all acids begin with H)

– Ex: HCl, HBr, HI, HNO3, H2SO4, HClO4)

Is it a strong electrolyte, a weak electrolyte, or a nonelectrolyte?

– Strong bases (bases end in –OH (Hydroxide)– (IA and IIA hydroxides)– Ex: NaOH, Ca(OH)2, KOH, Ba(OH)2

– Soluble Salts (Most water-soluble ionic compounds) Ex: metal – nonmetal (NaCl)

metal - polyatomic ion (Na2SO4 )

Strong Electrolytes are 100% ionized

salts H2O 100%ions

NaCl(s) Na+(aq) + Cl-(aq)

H2O

CaBr2(s) Ca2+(aq) + 2Br- (aq)

acids H2O

HCl(g) H3O+(aq) + Cl-(aq)

Bases H2O NaOH(s) Na+(aq) + OH-(aq)

Weak electrolytes

Most of the solute exists as molecules in solution

Only a few solute particles produce ions

HF + H2O H3O+(aq) + F- (aq)

acid

NH3 + H2O NH4+(aq) + OH- (aq)

base

Nonelectrolytes

Dissolve as molecules only

No ions are produced in water

Do not conduct an electric current

H2O

C6H12O6 (s) C6H12O6

(aq)

glucose

• Electrolytes dissociate to produce ions.

Electrolytic Properties

of Aqueous Solutions

The more the electrolyte dissociates, the more ions it produces.

• Dissolving Polar Covalent Compounds

Some dissolve only as molecules

EX: Sucrose

Timberlake, Page 239

Dissolves but does

not dissociate into ions

* Dissolving Ionic Solutes

Solid ionic compounds

~ Ions not free to move not current

~ Must be dissolved in H2O

Observations coming up

• Substance tested

• Scale (0-4)

• Conductivity ( low, medium, high, none)

• Strong, Weak or Non-Electrolyte

• Classification of Electrolyte (acid/base, Ionic salt, alcohol, covalent organic molecule

1 C3H7OHPropanol

O None Non-electrolyte Large organic molecule

2 KCl (aq)Potassium Chloride

4 Very high strong Soluble

Ionic salt

3 H2SO4 (aq)Sulfuric Acid

4 Very High strong Strong acid

4 H2ODeionized water

1 Low weak Weak acid /base

5 Na2SO4 (aq)Sodium sulfate

4 Very High strong Soluble

Ionic salt

6 HCl (aq)Hydrochloric Acid

4 Very High strong Strong acid

7 NaOH (aq)Sodium Hydroxide

3 High strong Strong base

8 C2H5OH2

Ethanol O None Non-electrolyte Large organic

molecule

(alcohol)

9 H2O

Tap water

3 High strong Acid/base

10 HC2H3O2

Acetic Acid1 Low-2 Medium

weak Weak organic acid

Ionic equations for each electrolyte

1. C3H7OH

2. KCl (aq) K+(aq) + Cl-(aq)

3. H2SO4 (aq) 2H+(aq) + SO42-(aq)

4. Deionized H2O(l) H+(aq) + OH-(aq)

5. Na2SO4 (aq) 2Na+(aq) + SO42-(aq)

6. HCl(aq) H+(aq) + Cl-(aq)

7. NaOH(aq) Na+(aq) + OH-( aq)

8. C2H5OH2

9. Tap H2O(l) H+(aq) + OH-(aq)

10. HC2H3O2 (aq) H+(aq) + C2H3O2- (aq)

Questions for Analysis1. Some substances conduct electricity

because of the ions present. Those substances that do not dissociate into ions do not conduct electricity.

Electrolytes=dissociate to produce ions

Non-Electrolytes do not have ions to dissociate

2. Could any of these substances conduct electricity in the solid form? Explain

None of the substances can conduct electricity in the solid form .

EX: Ionic compound. When a salt is in a molten state / dissolved in water, the ions can move and carry the electric current.

in SOLID STATE= the ions cannot move, so the current cannot flow.

COVALENT COMPOUNDS (non metal bonded with non metal), the outer shell electrons are used up to form the covalent bonds. thus, there are no free electrons to conduct electricity. (examples include diamond, PURE water etc)

METALS: metals have free electrons which allow them to conduct electricity in both solid and molten state.

EX: Copper,steel,water,plasma and most metals conduct electricity in solid form

3. Explain some possible reasons for a high conductivity measurement in a freshwater sample from a lake, stream or pond.

High concentration of ions (unusual anions and cations)

Nutrients

(e.g., phosphorus, nitrogen, carbon, silicon, calcium, potassium, magnesium, sulfur, sodium, chloride, iron) are primarily transported to ponds and lakes via streamflow, surface runoff and groundwater,

ConclusionConclusionAn electrolyte is a compound that, in aqueous solution,

conducts electricity. As liquids: salts, bases. When aq: salts, acids, bases. When ions are present it can conduct electricity.

ex> HCl(aq): H+(aq) + Cl –(aq) NaOH(aq): Na+(aq) + OH–(aq)

CuSO4(aq): Cu2+(aq) + SO42–(aq)

Nonelectrolytes do not conduct electricity. They do not ionize and therefore have no moveable ions.

Acid: a compound that ionizes in water to form hydrogen ions.

Base: an ionic hydroxide that dissociates in water to produce hydroxide ions

A strong electrolyte has a greater percentage ionization (most molecules are converted to ions).. Weak have a few ions and more molecules so they conduct electricity at a lesser percentage.

Ionization

Dissociation

Conclusion thoughtsConclusion thoughtsDissociation occurs when a (ionic) compound breaks

into its ions in water. Ionization occurs when a neutral atom or molecule is converted into an ion (e.g. by water). Ionic compounds and bases dissociate. Acids ionize.

+Cl HH

HO

+H

HH O Cl+

+Cl NaH

HO

H

HO Cl+ + Na

+

Sources of error: contamination spilled solution misreading the conductivity

apparatus the conductivity apparatus

shorts out Not drying off the probes

H2SO3: acid, KOH: base, CH3OH: organic,HC3H5O2: acid, Na2C2H3O2: salt, Ba(OH)2: base