Exp 9-11 Flashcards
(43 cards)
What form of titration was done in exp 9 Determination os soluble chloride in swimming pool water using fajan’s method?
Why is it called that way?
Precipitimetry
precipitimetry since the reaction between tirant and titrand produces a precipitate
There are different titrants for precipitimetry but the most common is ___________
what do you call the titration if this titrant is used?
silve (I) ions in the form of silver nitrate
titration is called argentometry
Type of titration that determines the amount of soluble chloride in a sample
What are the three methods of this type?
Argentometry
3 argentometric methods
1. Volhard
2. Mohr
3. Fajan (what we used)
What adsorption indicator does Fajan’s method rely on?
what does this indicator form as they absorb to the surface of particles in the solution?
dichlorofluorescein
it forms as colored layer as it absorbs to the surface of particles in the solution
In exp 9, what will preferntially adsorb the excess chloride ions over any indicator ions
the silver chloride particles that form before the equivalence point in an argentometric tritration
In exp 9, what prevents the adsorption of dichlorofluoresceinate ions
However what happens once the equivalence point is reached, all choride ions have reacted?
the negative charge surrounding the silver chloride particles
silver cations (Ag+) will begin to adsorb on the surface of the precipitate
Exp 9
Attracted by the positive charge of the silver cations, the dichlorofluoresceinate anions form __________
what does this formation signal?
Attracted by the positive charge of the silver cations, the dichlorofluoresceinate anions form a pink layer as they absorb to the surface of the silver chloride precipitate.
it signals the titration’s endpoint: reaction is Cl- + Ag+ –> AgCl(s)
exp 9
What makes argentometric methods challenging?
- light sensitive nature of silver nitrate solutions
- difficulty recognizing the endpoint of a precipitation reaction
exp 9
Why are silver solutions typically stored in dark-colored containers and titrations are performed in low light?
Silver cations are reduced to silver metal in bright light
SILVER SOLUTIONS CONTAINING A FINE GRAY PRECIPITATE, REDUCED SILVER, SHOULD NOT BE USED!!
exp 9
The endpoints of precipitation titrations are not often sharp. How can you promote more adsorption of the indicator and a sharper endpoint?
Increasing precipitate surface area
Exp 9
What prevents the silver chloride particles from coagulating – thereby increasing the surface area of the precipitate?
what does this provide in terms of the color? why?
addition of carbohydrate dextrin to the analyte solution
Provides a pinker color due to a higher degreee of association between the silver cations and dichlorofluoresceinate anions
exp 9
what is the molarity of standard silver nitrate solution used in exp. 9?
what glasswares were used?
0.2 M?
buret
10-ml pipet
250-ml erlenmeyer flask
10-ml graduated cylinder
How many percent was the dextrin suspension used in exp 9? How many drops of dichlorofluorescein indicator solution?
10 ml of 1% dextrin suspension
10 drops of dichlorofluorescein indicator
What type of titration is used in exp 10. Determination of the Total Hardness of Water?
This titration involves the formation of ________________?
Complexometric titration
involves the Formation of a colored complex that indicates the endpoint of a titration
In exp 10, how does the formation of a colored complex occur?
it occurs when a metal ion accepts electrons from a donor called a LIGAND
Exp 10
the most common ligand (titrant) in complexometric titrations is
EDTA-ethylenediaminetetraacetic acid or its disodium salt (Na2EDTA)
Exp 10
The reaction of a metallic ion and EDTA is sensitive to varying _______?
Thus what is required by the reaction for the metal of concern to react with EDTA?
pH values
the reaction requires appropriate pH for the metal of concern to react with EDTA.
What is a characteristic required from the indicator in experiment 10?
What are the common/typical indicators used?
What does the color change show in the endpoint?
What is the color of the endpoint?
The titration requires an indicator capable of producing an unambiguous color change to detect the endpoint of the titration
Fast Sulphon black and Erichrome Black T
Color change shows that the indicator has been displaced (usually by EDTA) from the metal cations in solution upon reaching the endpoint
endpoint is BLUE
In exp 10, what is the endpoint indicator?
the free indicator rather than the metal complex
exp 10
complexometric titrations are beneficial for __________?
OR it is used to determine?
what is determined in the experiment?
determining a mixture of different metal ions in a solution
The experiment determmines the amount of calcium in a water sample
exp 10
amount of calcium in water affects its properties, specifically, it contributes to the water’s?
water hardness
it measures (or a measure) the concentration of all the polyvalent cations dissolved in the water
what are the most common polyvalent cations?
Water hardness
Calcium and magnesium are the most common
although iron, strontium, and manganese may contribute
Exp 10
Water hardness is the sum of the ______
what does “hard’ indicate?
concentrations of Ca2+ and Mg2+ in water
Hard water indicates that the water typically contains high concentrations of Ca2+ and Mg2+ which react with fatty acids in soap, causing them to precipitate
Exp 10
what do you call a water that has very little Ca2+ and Mg2+?
what are examples of this?
Soft water
rainwater or water passing though a water softener
