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

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Presentation on theme: "Post Lab: Electrolytes. Electrolytes Are substances that form positive(+) and negative (-) ions in water Conduct an electric current."— Presentation transcript:

1 Post Lab: Electrolytes

2 Electrolytes Are substances that form positive(+) and negative (-) ions in water Conduct an electric current

3 Electrolytes in the Body Carry messages sent to and from the brain as electrical signals Maintain cellular function with the correct concentrations electrolytes

4 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 CaCl 2 (aq) LED Resistor 330 (ohms)

5 –Strong electrolytes include: –Strong acids (all acids begin with H) – Ex: HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 4 ) 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 (Na 2 SO 4 )

6 Strong Electrolytes are 100% ionized salts H 2 O 100%ions NaCl(s) Na + (aq) + Cl - (aq) H 2 O CaBr 2 (s) Ca 2+ (aq) + 2Br - (aq) acids H 2 O HCl(g) H 3 O + (aq) + Cl - (aq) Bases H 2 O NaOH(s) Na + (aq) + OH - (aq)

7 Weak electrolytes Most of the solute exists as molecules in solution Only a few solute particles produce ions HF + H 2 O H 3 O + (aq) + F - (aq) acid NH 3 + H 2 O NH 4 + (aq) + OH - (aq) base

8 Nonelectrolytes þ Dissolve as molecules only þ No ions are produced in water þ Do not conduct an electric current H 2 O C 6 H 12 O 6 (s) C 6 H 12 O 6 (aq) glucose

9 Electrolytes dissociate to produce ions. Electrolytic Properties of Aqueous Solutions The more the electrolyte dissociates, the more ions it produces.

10 Dissolving Polar Covalent Compounds Some dissolve only as molecules EX: Sucrose Timberlake, Page 239 Dissolves but does not dissociate into ions

11 * Dissolving Ionic Solutes

12 Solid ionic compounds ~ Ions not free to move not current ~ Must be dissolved in H 2 O

13 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

14 1C 3 H 7 OH Propanol O NoneNon- electrolyte Large organic molecule 2 KCl (aq) Potassium Chloride 4 Very highstrong Soluble Ionic salt 3 H 2 SO 4 (aq) Sulfuric Acid 4 Very High strong Strong acid 4 H 2 O Deionized water 1 Lowweak Weak acid /base 5 Na 2 SO 4 (aq) Sodium sulfate 4 Very High strong Soluble Ionic salt 6 HCl (aq) Hydrochloric Acid 4 Very Highstrong Strong acid 7 NaOH (aq) Sodium Hydroxide 3 Highstrong Strong base 8 C 2 H 5 OH 2 Ethanol O NoneNon- electrolyte Large organic molecule (alcohol) 9H 2 O Tap water 3 High strong Acid/base 10 HC 2 H 3 O 2 Acetic Acid 1 Low- 2 Medium weak Weak organic acid

15 Ionic equations for each electrolyte 1. C 3 H 7 OH 2. KCl (aq) K + (aq) + Cl - (aq) 3. H 2 SO 4 (aq) 2H + (aq) + SO 4 2- (aq) 4. Deionized H 2 O(l) H + (aq) + OH - (aq) 5. Na 2 SO 4 (aq) 2Na + (aq) + SO 4 2- (aq) 6. HCl(aq) H + (aq) + Cl - (aq) 7. NaOH(aq) Na + (aq) + OH - ( aq) 8. C 2 H 5 OH 2 9. Tap H 2 O(l) H + (aq) + OH - (aq) 10. HC 2 H 3 O 2 (aq) H + (aq) + C 2 H 3 O 2 - (aq)

16 Questions for Analysis 1.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

17 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

18 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,

19 Conclusion An 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) CuSO 4 (aq):Cu 2+ (aq) + SO 4 2– (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.

20 Ionization Dissociation Conclusion thoughts Dissociation 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. + ClH H H O + H H HO + + Na H H O H H O Cl ++ Na +

21 Sources of error: contamination spilled solution misreading the conductivity apparatus the conductivity apparatus shorts out Not drying off the probes H 2 SO 3 : acid,KOH:base, CH 3 OH:organic, HC 3 H 5 O 2 :acid,Na 2 C 2 H 3 O 2 :salt,Ba(OH) 2 :base

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