Following lab 9, resequence labs 10 & 11: 09_colorful_chemical_clues/ 11_disappearing_xls/ (Disappearing Powder) 10_the_name_is_bond/ Rationale: You have to get chemical compounds in solution BEFORE you can measure their conductivity! -- "If there are no ions in solution, then there is no conductivity!" DrV [see Logger Pro resource, described below....] Suggested activity extensions: [at a minimum, use the following scenarios as EDD-related PODs] 1. Scenario: At a constant temperature, vary the concentration of an aqueous solution of NaCl; test its conductivity. Title: The Effect of Solution Concentration [IV] on Conductivity [DV] Hypothesis: IF the concentration of a solution [IV] is greater, THEN its conductivity [DV] is greater. IV: solution concentration Levels of the IV (incl. control, if there is one): 4-5, for example 0.1 M, 0.2 M, 0.3 M, 0.4 M, and 0.5 M; there is no control DV: conductivity Constant(s), incl. measurements where needed: aqueous solutions of NaCl, concentration of solutions measured by molarity (M); temperature of solution, e.g., 20degC ***Use the following scenario*** 2. Scenario: At a constant solution concentration, vary the temperature of an aqueous solution of NaCl; test its conductivity. Title: The Effect of Solution Temperature on Conductivity Hypothesis: IF the temperature of a solution (at a constant concentration) is higher, THEN its conductivity is greater. IV: temperature (of the aqueous solution of NaCl) Levels of the IV (incl. control, if there is one): 4-5, for example 20-, 25-, 30-, 35-, & 40degC; there is no control Repeated Trials: 1 (per temperature) DV: conductivity Constant(s), incl. measurements where needed: aqueous solution of NaCl; solution concentration, measured by molarity (M) [empirical test results for the two preceding scenarios shown below...] [Results from two different simulators.] (x)Use button to build Microsoft Excel spreadsheet of the following data points; enhance spreadsheet and add chart (graph). Done! ***Revise in order to better display molarity data.*** [left of forward slash (/)] http://antoine.frostburg.edu/chem/senese/101/kits/conductivitysimulation3.html [right of forward slash (/)] http://web.umr.edu/~gbert/conductivity/cond.html cation: sodium (+) anion: chloride (-) >> concentration versus conductivity 0.001 M NaCl : 0.124 mS at 24.6degC / 125.8 MuS/cm 0.002 M NaCl : 0.254 mS at 24.6degC / 248.5 MuS/cm (309.3 MuS/cm at 0.0025 mol/L) 0.005 M NaCl : 0.601 mS at 24.6degC / 609.3 MuS/cm 0.007 M NaCl : 0.833 mS at 24.6degC / 845.6 MuS/cm (904.2 MuS/cm at 0.0075 mol/L) 0.010 M NaCl : 1.180 mS at 24.6degC / 1195 MuS/cm [Note: Only one of the simulators enables the user to change the temperature of the solution.] http://web.umr.edu/~gbert/conductivity/cond.html cation: Na+ anion: Cl- concentration: 0.0010 moles/liter (mol/L) >> temperature versus conductivity t = 15 C | 98.5 MuS/cm t = 20 C | 112.2 MuS/cm t = 25 C | 125.8 MuS/cm t = 35 C | 153.1 MuS/cm t = 45 C | 180.4 MuS/cm Note: Greek letter "Mu", used in science to mean "micro." For example, MuS means microsiemens (10^-6), that is, millionths of a siemens. DO NOT confuse with millisiemens (mS) (10^-3), that is, thousandths of a siemens. "...each pole will attract the opposing charge. Anions (-) will flow to the positive plate and cations (+) to the negative plate." "Cathode (negative pole, attracts cations); Anode (positive pole, attracts anions)." http://en.wikipedia.org/wiki/Cathode "A cathode is the electrode...." "Flow of Electrons The flow of electrons is always from anode to–cathode outside of the cell or device, and from cathode to–anode inside the cell or device, regardless of the cell or device type. Inside a chemical cell, ions are carrying the electrons but the flow is still from cathode–to–anode inside the cell." http://www.av8n.com/physics/anode-cathode.htm How to Define Anode and Cathode == Logger Pro 3.4.6 "Vernier Software" folder contains the following possible resource: C:\Program Files\Vernier Software\Logger Pro 3\Experiments\Sample Data\Chemistry\conductivity electrolytes.cmbl [Demo file for Dr.V in order to determine its usefulness and accuracy of my inference (see below).] Sample data file shows a graph of conductivity (MuS/cm) versus volume; all solutions at same concentration (1 M). Three substances (in order of least to most conductive): NaCl; CaCl2; AlCl3. Inference: More ions in solution = more conductivity! == [notes from TRG] T 186 ESSENTIAL LEARNINGS > When two non-metal elements react, atoms share electrons, forming COVALENT BONDS. [For more info, see ...] All About Covalent Compounds http://misterguch.brinkster.net/covalentcompounds.html http://www.chemistrycoach.com/tutorials-1.htm#Bonding2 -- Note: According to ACS Periodic Table, the following elements are non metals (x = inert): 1. H; xHe 2. ... C; N; O; F; xNe 3. P; S;Cl; xAr 4. Se;Br; xKr 5. I; xXe 6. xRn (Radon) Virtually all other elements are metals with the exception of the metaloids: Boron (B); Silicon (Si); Germanium (Ge); Arsenic (As); Antimony (Sb); Tellurium (Te); Polonium (Po). -- > When a metal element reacts with a non-metal element, their atoms gain and lose electrons respectively, forming IONIC BONDS. > ***When dissolved in water, ionic compounds are good conductors of electricity and demonstrate high conductivity. Solutions of substances with covalent bonds have low conductivity.*** TEACHER INFORMATION Salt [NaCl], baking soda, copper sulfate, and magnesium citrate (milk of magnesia, a common laxative) used in this investigation are ionic compounds and will conduct electricity quite well (~2,800 microsiemens). Sugar, cornstarch, Equal(R) sweetener, and acetone are covalently bonded compounds and will not conduct electricity very well (~400 microsiemens). ***[Note: Milk of magnesia -- Mg(OH)2 -- IS NOT the same formulation as magnesium citrate!]*** TEACHING SUGGESTIONS Prepare solutions - Combine 125 mL distilled water (solvent) with the following solutes: <-- Check molarity (M). Sample | Amount | Formula | Common Name | Bond Type A 0.5g NaCl salt I B 0.5g CxH2yOy starch C <-- Note: x & y are subscripts. C 0.5g CuSO4 copper sulfate I D 0.5g C6H12O6 sugar C E 2 mL C3H6O acetone C F 2 mL Mg3(C6H5O7)2 magnesium citrate I G 0.5g C14H18N2O5 aspartame C H 0.5g NaHCO3 sodium bicarbonate I Alternate recipe: Mix 1 liter (1 L) of distilled water with 8x the amounts listed in the preceding table. <-- Check molarity (M). [Note: One (1) packet of "Equal" (aspartame) equals one (1) gram. Add ~2 packets. Equal Packets: http://www.equal.com/products/product_detail/packets.html Ingredients: http://www.equal.com/products/ingredient.html -- The reading for covalent solutions should be ~400 microsiemens/cm and ~3,000 microsiemens/cm for ionic compounds. [Note: Using distilled water to mix solutions (at 0.1 M concentration), covalent colutions should be ~38 MuS/cm (the "control" value for distilled water) and ~12,000 for ionic compounds.] Note: Greek letter "Mu", used in science to mean "micro." For example, MuS means microsiemens (10^-6). DO NOT confuse with millisiemens (mS) (10^-3). == Misc. Planning Notes re: Bonding Lab: A water molecule is formed by *covalent* bonds. Q. Why 0.1 M concentration for solutions? A. It was chosen because it's easy to calculate. Also, the 0.1 M solutions will show conductivities that fall w/in the range of the Vernier(R) conductivity probe (0-20K MuS/cm). Hardware/software: Set the conductivity probe to the 0-20,000 (MuS/cm) range. Using Logger Pro, open the following file: Physical Science with Computers/16 Conducting Solutions.xmbl (or .cmbl) Conducting Solutions Activity Enrichment/Extension: Using Logger Pro, open the following file(s): 1. Physical Science with Computers/17 Saltwater.xmbl (or .cmbl) Conductivity of Saltwater: The Effect of Concentration 2. Physical Science with Computers/18 Acid Strengths.xmbl (or .cmbl) Acid Strengths Addenda to Procedure: 1. In order to determine a baseline reading for conductivity, test the conductivity of: distilled water (used to prepare solutions); and tap water. 2. Double the concentration of at least one of the covalent solutions (e.g., sugar); greater concentration shouldn't change conductivity. 3. Add substance(s) that have more ions, such as two of the three substances from Vernier sample data file (in order of least to most conductive): NaCl (two ions); *CaCl2* (three ions); *AlCl3*[1] (four ions); or sodium sulfate (Na2SO4) (three ions), as per Dr.V's suggestion. Inference: More ions in solution = more conductivity! Qualification: Given equal numbers of ions, the mobility of the ions comes into play (based upon, in part, the size of the molecules). [1]Order aluminum chloride from suppliers as AlCl3.6H20. Substance | Conductivity (MuS/cm) [TRG] | 1 M (g/L) | 0.1 M (g/100mL) NaCl (2 ions) | 2,875 | 58.5g/L | 0.6g/100mL Starch (covalent) | 360 | (use arbitrary amt., e.g., 0.5 g) [formula weight of insoluble starch we use is unknown] CuSO4 (2 ions) | 3,000 | 249.7* | 2.5* Sugar (covalent) | 387 | (use arbitrary amt.) Acetone (covalent) | 420 | (use arbitrary amt.) Magnesium Citrate (?2? ions) | 2,500 | Aspartame (covalent) | 387 | (use arbitrary amt.) Sodium Bicarbonate (?2? ions) | 2,875 | 84.0 | 0.8 *(with 5 "waters" of hydration) [Anhydrous = NO water] Note: FCPS "recipe" calls for either 0.5g or 2mL per 125mL distilled water. == Notes re: moles: 1 mole = the number of molecules in one (1) formula weight, e.g., 1 mol of NaCl = 58.5g Problem: You can't mass one molecule, so... Solution: ...the mole is a practical work-around to the problem. Use 6.02x10^23 atoms, or 1 mol.