CHM 12 Fall 2012
Lab 3 Le Chatelier's Principle- And Chemical Equilibrium Introduction All chemical chemical reactions proceed proceed until equilibrium equilibrium is is reached, provided provided none of th e re actan ts o r th e pr od uc ts ar e re move mo ve d from fr om the th e re ac tion ti on mixt mi xt ur e. Le Chate C hatelier lier's 's princ p rinciple iple describe desc ribess what wh at happens to an equilibrium after it has been disturbed.
Purpose You will study the application of Le Chatelier's principle by seeing the effect of the addition of e!" and #C$%& to an equilibrium mixture of e!", #C$%&, and e#C$()" * the effect of the addition of an acid to an equilibrium mixture of $i)", $+!, and $i$+!()"* the effect of the addition of an acid and a base on the equilibrium involving an indicator* the effect of acids and bases on the solubility of Ca-+() in water* and the effect of temperature on an equilibrium mixture of Co)", Cl%&, and CoCl)%. /n this experiment you will encounter some substances that you may not have seen before. 0he reaction between e!" and #C$%&thiocyanate ion( gives e#C$()". 0his substance is a deeply colored complex ion. -ther complex complex ions that you will w ill encounter are a re $i$+!()" and CoCl)%. 0hese substances result from the reaction between $i)" and $+! and from the reaction between Co)" and Cl%&, respectively. You You will also study an equilibrium involving methyl orange, an indicator. indicator.
Experimental Concepts Le Chatelier's principle can be described in the following way1 23hen a system in chemical equilibrium is disturbed disturbed by a change of temperature, pressure, or a conc entration, the system shifts in equilibrium composition in a way that tends to counteract this change of variable2 This statement explains the effects that you ill encounter in this experiment!
Procedure &. -btain ! small small test tubes tubes and a piece piece of filter filter paper. ). -btain directions for discarding the solutions that you will use in this experiment. !. 0a4e 0a4e care in handling the solutions used in this experiment. CA"TI#$% &olutions of ammonia' hydrochloric acid' and sodium hydroxide can cause chemical burns in addition to ruinin( your clothin(! )o not use your fin(er as a stopper hen mixin( these solu tions ! I f y ou s pill any of thes e solutio solutions ns on you' you' ash ash the the conta contamin minate ated d area area thorou(hly and report the incident to your laboratory instructor! i nstructor! *ou may require further treatment!
CHM 12 Fall 2012
&tudyin( the equilibrium of +e 3, and &C$- ith +e.&C$/ 0,
&. 5ar4 each of the test tubes with an identification number &, ), and !(. ). Add )6 mL of distilled water from a graduated cylinder to a &66%mL bea4er. $ext add )6 drops of 6.& M e$-!(! and )6 drops of 6.& M 7#C$ to bea4er. 0he color is due to the e#C$( ") ion. #tir the solution thoroughly. !. 8sing a &6%mL graduated cylinder, add ! mL of this solution to each of test tubes. ). Add )6 drops of 6.& M e$-!(! to test tube &. 5ix by gentle sha4ing. !. Add )6 drops of 6.& 5 7#C$ to test tube ). 5ix by gentle sha4ing. . Add )6 drops of distilled water to test tube ! and mix. 0he color of the contents of this tube will serve as your reference. 9. Compare the colors in test tubes & and ) with the color in the reference tube 0he intensity of the color in each test tube will indicate the relative concentration of e#C$(")ion that test tube. or best results, view the tubes down their lengths against a white paper. :ecord your observation.
&tudyin( the equilibrium of $i 0, and $1 3 ith $i$+ !()"
&. Add &6 drops of 6.& 5 $i$-!() to a clean test tube. :ecord the color. ). Add drops of 5 $+! until the color changes and intensifies. :ecord color. !. Add drops of 5 +C& until the color changes once again. :ecord the color. 0he acid has reacted with $+! to form $+" ions.
&tudyin( the equilibrium in2ol2in( methyl oran(e
&. 5ar4 each of two small bea4ers with an identification letter A for acid* ; for base(. ). Add &6 mL of distilled water and drops of 5 +C& to the bea4er mar4ed A. #wirl. !. Add &6 mL of distilled water and drops of 5 $a-+ to the bea4er mar4ed ;. #wirl. . Add & mL of distilled water to a clean test tube. 0hen add drops of the indicator solution and ) drops of the dilute acid solution. #ha4e gently. :ecord the color. 9. Add drops of the dilute base solution until the color changes. #ha4e gently. :ecord the color. . Add drops of the dilute acid solution un til the color changes again. #ha4e gently. :ecord the color. 2
CHM 12 Fall 2012
&tudyin( the solubility of Ca.#1/ 0
&. 8sing a &6%mL graduated cylinder, add 9 mL of M $a-+ to a small, clean bea4er. ). :inse the graduated cylinder, then use it to add 9 mL of & M Ca$-!() to the same bea4er. !. #tir the mixture thoroughly with a stirring rod. A white precipitate of Ca-+() should be present. . 8sing gravity filtration described in the /ntroduction to this manual(, filter the mixture. 0his filtration may require a rather long time. 3hile you are waiting, you may wish to begin your study of the equilibrium involving CoCl)%. 9. 3ash the precipitate on the filter paper with 9 mL of distilled water. . 3ith a metal spatula, remove as much of the wet precipitate from the filter paper as you can. #uspend this solid in &6 mL of distilled water in a small, clean bea4er. lace a piece of wire gau?e on the ring. [email protected]
the height of the ring so that the wire gau?e will be in the hottest part of the flame from a laboratory burner. o not light the burner until this [email protected]
has been made. CA"TI#$% A2oid burnin( your fin(ers! )o not touch the iron rin( or the ire (au4e at any time hile the flame is bein( used!
). >lace a small bea4er containing distilled water on the wire gau?e, and heat the water to a gentle boil. !. Add 9 drops of 6.& 5 Co$-!() to a clean test tube. :ecord the color. . Add 9 drops of concentrated +C& do not use 5 +C&(. #ha4e the test tube gently, and record the color. 0his is the characteristic color of the CoCl%) ion.. 9. Add 9 drops of distilled water. #ha4e gently. :ecord the color. . >lace the test tube in the bo iling water, and wait a few minutes until the color has changed again. :ecord the color.