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Post Lab: Electrolytes

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

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Post Lab: Electrolytes

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  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. LED Drop of CaCl2 (aq) Conduction Illustrated Resistor 330 Ω (ohms) • Electric current : flow of charged particles. • One type of current is electrons flowing through a wire, from cathode(negative electrode) to anode(positive electrode). • 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!

  5. Is it a strong electrolyte, a weak electrolyte, or a nonelectrolyte? • Strong electrolytes include: • Strong acids (all acids begin with H) • Ex: HCl, HBr, HI, HNO3, H2SO4, HClO4) • 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)

  6. 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)

  7. 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

  8. Nonelectrolytes • Dissolve as molecules only • No ions are produced in water • Do not conduct an electric current H2O C6H12O6(s) C6H12O6(aq) glucose

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

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

  11. * Dissolving Ionic Solutes

  12. Solid ionic compounds ~ Ions not free to move not current ~ Must be dissolved in H2O

  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. Ionic equations for each electrolyte

  15. Questions for Analysis • 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-Electrolytesdo not have ions to dissociate

  16. 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

  17. 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,

  18. 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) 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.

  19. Dissociation + H H O O Cl Na Na Cl H H Ionization + H H O H O Cl Cl H H H 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. + + + + +

  20. Sources of error: contamination spilled solution misreading the conductivity apparatus the conductivity apparatus shorts out Not drying off the probes H2SO3: CH3OH: organic, acid, KOH: base, HC3H5O2: acid, Na2C2H3O2: salt, Ba(OH)2: base

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