UNIT 10 Titrations 2 Flashcards
What is the standard solution for titrating bases?
Hydrochloric acid
What form of HCl is stable indefinetely?
Dilute solutions
Chloride ion are soluble in aq solution
What solutions are stable and useful when chloride ion interferes with precipitaes?
Perchloric acid and sulfuric acid
Why isnt nitric acid solution used?
oxidizing properties
How are standard acid solution prepared?
Concentrated reagent is first siluted to approximate concentration then standardized against primary standard base
What is desirable in a primary standard?
High mass per proton consumed due to the larger mass of reagent to be used… decreases weighing error
What endpoint is used for stnadardization?
the sharper endpoint
How can a sharper endpoint be made in the titration of sodium carbonate?
Boiling the solution to get rid of the buffer solution ( gets rid of carbonic acid and the arbondioxide)
What is used for the standardization of bases?
Sodium hydroixed Potassium hyroxide Barium Hydroxide --> cannot be obtained inprimary standard purity --> Standardized after they are prepared
What do hydroxides os Na, K and Ba react with?
Atmospheric carbon dioxide toproduce carbonate
How many hydroniums are consuemd in an acid range indicator?
2 Hydroniums
carbonate and hydronium –> H2CO3 and water
How many hydroniums are consumed in a basic reange indicator?
1 Hydronium ion by carbonate
What is the effect of carbon dioxide on standard base solution?
The effective concentration of the base is thus dimished by the absorption fo CO2
–> negative systematic error called carbonate error
Is there systematic error with an acidic range?
No
How do you make a carbonate free sodium hydroxide soluton?
50% aq solution of sodium hydroxide
Why do you make that type of solution?
Sodium carbonate has a very low solubility on concentrated solution of base
The water must be free of carbon dioxide
The conc solution is diluted to desired concentration
How do you eliminate CO2 from water?
Distilled water boiled briefly
Deionized water usually does not contain significant amounts of CO2
How do you store bases to protect against atmospheric carbon dioxide? What leads to a decreased strength?
A tightly capped low density polyethylene bottle provides short term protection against atm CO2
Glass container leads to decreased strength due to silicates
What are some characteristics of Potassium Hydrogen phthalate
KHC8H4O4
- non hygroscopic
relatively large molar mass
What are some characteristics of benzoic acid?
Limited solubility in water, dissolved in ethnaol prior to dolution with water and titration
Commercial alcohol is slighly acidic hence blank titration required
What are the characteristics of standarizing Potassium hydrogen iodate
KH(IO3)2
- high molar mass per mole of protons
Strong acid
Can be titrated using any indicator with a transition range between 4-10
What is an application of neutralization titrations?
Inorganic, organic and biological species that posess acidic or basic properties
analytes converted to acid/base
titrated with a standard strong base or acid
What are the two end points that can be observed?
Visual enpoint based on inidcators
Potentiometric end point using pH meter
What are some more applicaiton of neutralization titration
elemental analysis
inorganic substnaces
organic functional groups
salts
What is the kjeldajl method?
Sample is decomposed in sulfuric acid to convert the bound nitrogen to ammonium ion
Solution is cooled, made basic collected in an acid solution and determined via neutralization titration
Percent total nitrogen is determined by multiplying the N by a factor (6.25)
Why can’t there exist all three constituents of a polyprotonated molecules in a titration reaction?
Because any solution reaction eliminates the third
In carbonate and carbonate mixutres, what titration are required?
two titrations witha strong aci: one under alkaline indicator (phenolphthalein) and the other with a acid range indicator (bromocresol green)
Composition of solution is deduced from the relative volumes of acid needed to titrate equal volumes of the sample
