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CHEM 111 Lab Final

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complex ions
brightly colored species produced by the reaction of dissolved metals with certain substances
iron (III) reacts with thiocyanate ion (SCN1-) producing
a bright red color
complex ions indicate
the position of equilibrium
a saturated solution represents equilibrium between the solution and any undissolved solute because
a saturated solution is formed when the maximum amount of the solute is dissolved in an amount of solution so the ratio between the two is constant, representing equilibrium
effect of adding 12M HCl to saturated NaCl
HCl precipitated at the bottom because more Cl- ions were added, shifting the reaction to the left to form more NaCl, which is already saturated so precipitate forms
effect of adding 1M HCl to saturated NaCl
because smaller amount of HCl is added, precipitate still forms, because Cl- ions are being added , but in a smaller amount and at a slower rate
effect of adding Fe3+ to FeSCN3+
causes FeSCN3+ to turn darker red
effect of FeCl3 solution on FeSCN3+ using Le Chatelier's
the bright red color produced indicates that the addition of Fe3+ ions shifts the reaction to the right, producing more of the complex ion that produces the color
effect of the addition of a reagent (Ag+)
removed thiocyanate ion from the system forming AgSCN, shifting the rxn left, reducing the complex ion and removing color
in acid base equilibrium, what is added to indicate the equilibrium. why?
acid/base indicator (phenolphthalein) that changes color with pH because there are no colored components in the system
effect of adding NH4Cl to ammonia solution
the color changes to pale pink because the addition of the NH4+ ion shifts the reaction to the left, reducing the OH- ions and shifting the pH
hydrolysis
the reaction of ions with water producing acidic or basic solutions
indicators
substances which are weak acids that change color in a specific pH range
salt of a strong acid and a strong base
neither cation or anion undergoes hydrolysis so solution is neutral and pH=7
salt of a strong acid and weak base
the cation undergoes hydrolysis, forming H+ ions and the pH is less than 7 so the solution is acidic
salt of a weak acid and a strong base
the anion undergoes hydrolysis, forming OH- ions and the pH is above 7 so the solution is basic
salt of a weak acid and weak base
both cation and anion undergo hydrolysis and the pH is determined by the relative acid strength of the cation and the base strength of the anion (compare Ka to Kb)
strong acids have a _______ Ka value and ______ conjugate bases
larger, weaker
weak acids have a ________ Ka value and _______ conjugate bases
smaller, stronger
strong acids
HCl, HBr, HI, HClO4, HNO3, HIO4, H2SO4, HClO3
strong bases
LiOH, NaOH, KOH, Sr(OH)2, Ca(OH)2, Ba(OH)2
methyl orange
In a solution becoming less acidic, methyl orange moves from red to orange and finally to yellow with the reverse occurring for a solution increasing in acidity
methyl red
changes from red to yellow as pH increases higher then a pH of 6
bromothymol blue
blue in high pH levels then changes to yellow as pH decreases below 7
phenol red
red in high pH levels then changes to yellow as pH decreases below 8
phenolphthalein
colorless in low pH solution, changes to dark pink as pH increases above 7
Alizarin yellow
yellow in low pH solution, changes to red in high pH levels
chemical equilibrium
a reversible reaction that does not go to completion
equilibrium constant
the ratio of the product concentration to the reactant concentration remain after equilibrium is reached
bronsted-lowry acid
a substance that transfers an H+
bronsted-lowry base
a substance that accepts an H+
equivalence point
the point in the titration at which stoichiometrically equivalent quantities of reactants have been mixed together
endpoint
the point in the titration at which a color change occurs due to an indicator (approximates the equivalence point)
1/2 equivalence point
50% acid and 50% salt present so the ratio is 1, making the pH=pKa
determining the Ka from 1/2 equivalence point
since pH=pKa at this point, the pH at the 1/2 equiv. point (determined from titration curve) can be substituted into the equation, pKa=-logKa, in order to solve for the constant
mixing solutions (5 ways)
1)using a clean stirring rod
2)covering the top of the test tube with parafilm and inverting several times
3)pouring back and forth between test tubes
4)stroking test tube with finger
5)drawing solution with a pipet then squatting it back into the container
decantant
liquid above the precipitate
decantation
best way is to withdraw it by means of a capillary pipet, another way is pouring test tubes lip to lip
why it is necessary to wash precipitant
because the precipitant is still wet with excess decant liquid so it is necessary to wash it free of contaminating ions
washing decant
add 10 drops of distilled water to precipitate, stirring with stirring rod, and repeating the centrifuging and decanting
testing acidity/basicity
make sure solution is throughly mixed, then by means of a clean stirring rod, remove a drop of the solution and apply it to the proper litmus paper setting on a watch glass
red litmus paper tests for
base
blue litmus paper tests for
acid
evaporation
heat the solution in a casserole by moving it in and out of the flame, not directly in the flame because it may over heat and bump or pop dangerously or char, decompose, or fuse the ions to the casserole
flame test
dip platinum or nichrome wire in 12M HCl and heat the wire in the hottest part of the flame, repeat until no cold is seen when the wire is placed in the flame. then place 10 drops of solution in a test tube and before test tube on wire
colored cations
Fe3+ (rust to yellow), Cr3+ (blue-violet), Ni2+ (green)
why its important to balance centrifuge
tubes are spun at high velocities so unbalanced masses can cause instability in the system
precipitating reagent
converts a completely soluble ion into a slightly soluble compound after being added to a sample solution
what does a colorless cation tell you
indicated the absence of iron, chromium, or nickel
test for Na+ ion
flame test because sodium salts produce yellow color in a flame
Na+ and NH4+ ion test first
because they are added as reagents in the analysis of the general unknown
test for NH4+
because adding a strong base to an ammonium salt produces NH3 gas when heated, by doing so NH4+ can be detected by the presence of NH3 gas on red litmus paper
serperating Ag+ from other ions
by adding HCl, Ag+ precipitates and separates from the other ions
separating Fe,Cr, and Al from other ions
by making the solution alkaline and precipitating these ions with their corresponding hydroxides
why is NH4 added to NH3 in 3a
creates an alkaline buffer that provides hydroxide ion concentration high enough to percipitate Fe, Cr, Al but low enough to prevent unwanted precipitation of other ions
why are NaOH and H2O2 added in 3b
to separate Fe(OH)3 from other hydroxides by dissolving them
amphoteric
having the ability to react as both a base and an acid
complex ion
structure consisting of a combination of simpler ions
confirmatory test
confirms the presence of an ion by dissolving the compound containing that ion and then repercipitating it again in the presence of its precipitating reagent
aluminon reagent test for what ion
aluminum
"red lake"
red coloration of aluminum hydroxide when it precipitates and absorbs the aluminon reagent
DMG test for what ion
nickel
DMG
dimethylglyoxime
"brick red" flame indicaties
calcium
"yellow" flame indicates
sodium
use of DI water
used to guarantee the absence of unwanted ions
"blue lake" confirms what ion
magnesium