UNIT 10 Titrations 2

Question 1

What is the standard solution for titrating bases?

Answer 1

Hydrochloric acid

Question 2

What form of HCl is stable indefinetely?

Answer 2

Dilute solutions

Chloride ion are soluble in aq solution

Question 3

What solutions are stable and useful when chloride ion interferes with precipitaes?

Answer 3

Perchloric acid and sulfuric acid

Question 4

Why isnt nitric acid solution used?

Answer 4

oxidizing properties

Question 5

How are standard acid solution prepared?

Answer 5

Concentrated reagent is first siluted to approximate concentration then standardized against primary standard base

Question 6

What is desirable in a primary standard?

Answer 6

High mass per proton consumed due to the larger mass of reagent to be used… decreases weighing error

Question 7

What endpoint is used for stnadardization?

Answer 7

the sharper endpoint

Question 8

How can a sharper endpoint be made in the titration of sodium carbonate?

Answer 8

Boiling the solution to get rid of the buffer solution ( gets rid of carbonic acid and the arbondioxide)

Question 9

What is used for the standardization of bases?

Answer 9

Sodium hydroixed
Potassium hyroxide 
Barium Hydroxide
--> cannot be obtained inprimary standard purity
--> Standardized after they are prepared

Question 10

What do hydroxides os Na, K and Ba react with?

Answer 10

Atmospheric carbon dioxide toproduce carbonate

Question 11

How many hydroniums are consuemd in an acid range indicator?

Answer 11

2 Hydroniums

carbonate and hydronium –> H2CO3 and water

Question 12

How many hydroniums are consumed in a basic reange indicator?

Answer 12

1 Hydronium ion by carbonate

Question 13

What is the effect of carbon dioxide on standard base solution?

Answer 13

The effective concentration of the base is thus dimished by the absorption fo CO2
–> negative systematic error called carbonate error

Question 14

Is there systematic error with an acidic range?

Answer 14

No

Question 15

How do you make a carbonate free sodium hydroxide soluton?

Answer 15

50% aq solution of sodium hydroxide

Question 16

Why do you make that type of solution?

Answer 16

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

Question 17

How do you eliminate CO2 from water?

Answer 17

Distilled water boiled briefly

Deionized water usually does not contain significant amounts of CO2

Question 18

How do you store bases to protect against atmospheric carbon dioxide? What leads to a decreased strength?

Answer 18

A tightly capped low density polyethylene bottle provides short term protection against atm CO2
Glass container leads to decreased strength due to silicates

Question 19

What are some characteristics of Potassium Hydrogen phthalate

Answer 19

KHC8H4O4
- non hygroscopic
relatively large molar mass

Question 20

What are some characteristics of benzoic acid?

Answer 20

Limited solubility in water, dissolved in ethnaol prior to dolution with water and titration
Commercial alcohol is slighly acidic hence blank titration required

Question 21

What are the characteristics of standarizing Potassium hydrogen iodate

Answer 21

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

Question 22

What is an application of neutralization titrations?

Answer 22

Inorganic, organic and biological species that posess acidic or basic properties
analytes converted to acid/base
titrated with a standard strong base or acid

Question 23

What are the two end points that can be observed?

Answer 23

Visual enpoint based on inidcators

Potentiometric end point using pH meter

Question 24

What are some more applicaiton of neutralization titration

Answer 24

elemental analysis
inorganic substnaces
organic functional groups
salts

Question 25

What is the kjeldajl method?

Answer 25

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)

Question 26

Why can’t there exist all three constituents of a polyprotonated molecules in a titration reaction?

Answer 26

Because any solution reaction eliminates the third

Question 27

In carbonate and carbonate mixutres, what titration are required?

Answer 27

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