General Chemistry Week Four Notes
General Chemistry Week Four Notes CHEM103090
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This 7 page Class Notes was uploaded by Nina Drachman on Tuesday October 6, 2015. The Class Notes belongs to CHEM103090 at University of Delaware taught by Graves PhD,Kimberly Susan in Fall 2015. Since its upload, it has received 56 views. For similar materials see General Chemistry in Health and Human Services at University of Delaware.
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Date Created: 10/06/15
Chemistry Lecture Sep 22 Chapter 3 Aqueous Solutions and Concentrations Focus Question Water Quality Water quality refers to what is found in it bene cial compounds or harmful compounds Ex microbial toxin in ohio iron ions that support bacterial growth or lead ions that are generally toxic o How can we talk about the amounts of compounds in water 0 How can we measure them Solution De nitions Concentration is generally the amount of solute compared to the amount of solution More concentrated more solute Homogeneous mixture looks all the same solution Amount can be moles mass volume Concentration Units Amount of solute can be measure as 0 Mass of solute 0 Volume of solute o Moles of solute Compared to amount of solution as 0 Mass of solution 0 Volume of solution 0 Don t talk about moles of solution mostly mass and volume Percent Composition as a Concentration Ex SO3401 sulfur 599 oxygen how much compared to the whole Percent composition of a solution 0 Mass of solutemass of solution or volume of solutevolume of solution Concentration Units by Mass Parts per million ppm o Ppmgrams of solute10quot6 grams of solution 1 mg of solute1 kg of solution 0 Parts per billion ppb Ppbgrams of solute10quot9 grams of solution1 microgram of solute1kg of solution 0 Useful for very small amounts of solute Molarity Most common concentration used Moles of soluteliters of solution moles per liter Molethow many particles of solute If given grams how do you get to moles 0 Divide by molar mass from periodic table LitersVolume of solution Preparing Solutions by Dilution Stock solution a concentrated solution of a substance used to prepare solutions of lower concentration Dilution the process of lowering the concentration of a solution by adding more solvent Moles of solute before dilutionmoles of solute after dilution solute doesn t change during dilution only the concentration and the amount of solution Dilution Calculations Moles of solute before dilutionmoles of solute after dilution How can we nd moles if we know concentration and volume multiply by liter Molaritymoles of soluteliters of solution Mstock x Vstock Mdilute x Vdilute can t use compound if using different compounds Measuring Concentration Intensity of color can be used to measure concentrations Beer s Law A epsilon x b x c Where o A absorbance amount of light absorbed by sample o E molar absorptivity depends on compound absorbing light Bpath length C concentration of absorbing species 0 Spectrometer shining light on something and measuring it 00 Beer s Law and Dilutions A E x b x c What do you do to make the line change the concentration Absorbance is related to concentration Chemistry Lecture Sep 24 Chapter 3 Aqueous Solutions and Concentrations Focus Questions Hard Water Hard water is water with a large amount of calcium and magnesium compounds dissolved in it Water that travels through rocks or pipes something releasing metal ions in water mostly calcium and magnesium Hard water can cause some serious problems with piping and some annoying problems like soap scum What causes hard water to form soap scum Solubility Solubility is the ability of a solute to dissolve in a certain solvent If something dosslves in water it has high solubility If something is insoluble it will crash out as a precipitate when something doesn t dissolveljprecipitate Some things dissolve some things don t but why What does dissolving really mean Electrolytes When ionic compounds are put into water they become electrolytes Strong electrolytes 0 Nearly 100 dissociated into ions 0 Conducts current ef ciently Ex solutions of NaCl if you put sodium chloride into water it dissolves the sodium chloride breaks into sodium ions and chloride ions NaClsH20 Naaq Claq When we separate the charges it can conduct electricity so it is electrolytes lnsolubility What causes something to be insoluble Forces involved in holding solid together win over forces wanting to dissociate ions in solution Greater attraction between the ions than the ions in the water it cannot be broken apart Solubility Rules Soluble cations 0 Group ions alkali metals and NH4 ammonium Soluble anions 0 N03 nitrate CH3COO acetate CIO3 chlorate o Halides group 17 except doesn t dissolve Ag Pb2Hg22 o Sulfates 5042 except doesn t dissolve Pb2 Hg22 Ca2 Ba2 Sr2 Combining anions and cations not listed above results in formation of an insoluble compound Soluble cations and soluble anions listed above can be paired up to form a soluble compound Nonelectrolytes There are compounds that dissolve in water that AREN T electrolytes called nonelectrolytes they don t conduct electrical current Substance in which no ionization occursn molecular compounds contain covalent bonds that can t be broken by dissolving No conduction of electrical current Ex aqueous solutions or sugar ethanol ethylene glycol compounds that dissolve in water that are covalent compounds and do not break apart into ions and are therefore not electrolytes What happens to polyatomic ions going to stay together but will separate with whatever ion it is paired with polyatomic ions are held together by covalent bonds C02Dwill not dissociate into ions because it s a covalent compound nonmetals it is a molecule but it WILL dissolve Mixing Solutions Many important solutions are mixtures of multiples compounds Ex Ringer s solution used in IVs for rehydration is made by adding solid NaCl KCI and CaCl2 all ionic compounds to water to match body conditions What ions are present K Na Cl Ca they are all soluble Closer Look at Mixing Solutions KBr aq NaCl aq mixture K aq Br aq Na aq Claq all ions Has a reaction occurred NO just mixing together two solutions Mixing lonic Compounds in Water Kl Pb22NO3 Has a reaction occurred YES something has chemically changed Pbl is insoluble and they bumped into each other when mixed Precipitation Reactions Precipitate 0 Solid product formed from a reaction in solution 0 PbNO32 aqmeans it dissociates into ions 2 Kl aq l 2 KNO3 aq Pbl2s Can predict formation of precipitates based on solubility quotrulesquot Precipitation reactions can be written using net ionic equations Precipitation Combining insoluble cation with insoluble anion precipitate Ex PbNO32 aq 2 Kl aq Cations Pb2 2K Anions 2NO3 2 Rednot soluble when together Spectator Ions A spectator ion is any ion that appears the same before and after mixing CI aq Agaq D AgCl S Net ionic equation shows only ions that react with each other Describing Precipitation with Equations Na2CO3 aq CaC2 aq mixed together Total ion equation 2Naaq CO32aq Ca2aq 2C aqCaCO3s 2 Naaq 2 CIaq Net ionic equation Ca2aq CO32aqCaCO3s