CHEM 111 Lab Final

Created by greerwchambers 

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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

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