Conductivity Lab

Warm Up 1. Why is it not a good idea to take a hair dryer into the bathtub? EQ: What is the difference between an ionic compound and a molecular compound? HOT Q1: How can we distinguish between ionic and molecular compounds based on their conductivity? HOT Q2: What are the properties of ionic compounds? HOT Q3: What are the properties of molecular compounds?

Agenda Warm Up Agenda Quiz Conductivity Lab Exit Ticket QUIZ MONDAY! (on nomenclature and properties of molecular vs. ionic compounds) TEST WEDNESDAY!

Lab: Conductivity Date Intro: Purpose: To distinguish between ionic and molecular compounds based on their conductivity. Hypothesis: I think molecular compounds do/do not conduct electricity, while ionic compounds do/do not conduct electricity. Background info: Conductivity: the ability of a substance to conduct electricity Electricity : ______________________________________________

Materials: Methods: Conductivity probes Salt, tap water, sugar, and distilled water Methods: Test samples of ionic compounds, molecular compounds, and solutions for electrical conductivity

Data: Substance Conductivity Tap water Distilled water Distilled water with sugar Sugar Distilled water with salt Salt Analysis: 1. Which substances conducted the most electric current? Which substances conducted the least?

Discussion Which substances did not conduct electricity in their solid form but did conduct electricity when they were dissolved in water? Which substances did not conduct electricity either as a solid or dissolved? The formula for sugar is C6H12O6 and the formula for salt is NaCl. Sugar is a molecular compound and salt is an ionic compound. Looking at the formula, are they made of metal elements, nonmetal elements or both? Based on this and your knowledge of their conductivity, what is the difference between ionic and molecular compounds? Based on your knowledge of electricity, attempt to explain why sugar water will not conduct electricity as well as salt water. Use particle diagrams to support your answer.

Video: Dissociation of Salt http://www.youtube.com/watch?v=CLHP4r0E7hg

Electrolytes

Conclusion 1) What is the difference between distilled water and faucet water at the particle level? 2)What is the difference at the particle level between solid salt and salt dissolved in water? 3) What is the difference at the particle level between salt water and sugar water? The formula for sugar is C6H12O6 and the formula for salt is NaCl

Consensus Electricity is the free movement of charged particles When ionic solids are melted or dissolved, oppositely charged ions are free to move and can conduct electricity When molecular compounds are melted or dissolved, the molecules are electrically neutral and do not conduct electricity

MOLECULAR COMPOUNDS Properties -do NOT conduct electricity -low melting pt. and boiling pt. Basic structural unit -building block: The molecule -made of 2 or more nonmetal atoms bonded together - weak attractions between molecules Molecular compounds are made of two or more nonmetals bonded together. Molecular compounds DO NOT break up into ions when they are melted and dissolved so they are poor conductors.

Molecular Compounds Solid Dissolved/Melted

Ionic Compounds Properties -generally have high melting pt. and boiling pt. -conduct electricity when molten (melted) and dissolved (electrolytes). Basic Structural Unit -Formula Unit (FU) ex: NaCl which is Na+ and Cl- -As a solid many formula units come together to form a crystal lattice. -As a liquid they separate into ions, not molecules or formula units. NaCl crystal lattice

Ionic Compounds Solid Dissolved/Melted

Crystal Lattice http://www.avogadro.co.uk/structure/chemstruc/ionic/g-ionic.htm

Exit Ticket 1. What type of bonding is associated with compounds that have the following characteristics: •high melting points •conduct electricity in the molten state •solutions conduct electricity •normally crystalline solids at room temperature. A) covalent B) ionic C) hydrogen D) metallic