Chapter 35: Dissolving the sample Flashcards
is an excellent solvent for inorganic samples but finds limited application for decomposing organic materials.
conc HCl
is resistant to heat and attack by strong chemical agents.
refractory substance
TRUE or FALSE
Ideally the reagent selected should dissolve the entire sample, not just the analyte.
TRUE
Sources of error in decomposition and dissolution
- Incomplete dissolution of the analytes
- Losses of the analyte by volatilization
- Introduction of analyte as a solvent contaminant
- Introduction of contaminants from reaction of the solvent with vessel walls
When a sample is introduced/ dissolved in an acid, what possible error occurs?
Losses of the analyte by volatilization
It is widely used for
dissolving many metal oxides as well as metals more easily oxidized than hydrogen.
conc HCl
is a strong oxidant that dissolves all common metals with
the exception of aluminum and chromium, which become passive to this reagent due
to surface oxide formation
hot conc HNO3
is widely used for decomposing organic samples for determining their trace metal content.
HNO3 combined with other acids and oxidizing agents such as H2O2 and bromine
is a process of oxidative
decomposition of organic samples
by liquid oxidizing reagents, such as
HNO3, H2SO4, HClO4, or mixtures
of these acids.
Wet ashing
effective solvent as many materials are decomposed and dissolved, which owes part of its effectiveness as a solvent to its high boiling point (about 340 C)
sulfuric acid
a potent oxidizing agent that attacks a number of iron alloys and stainless steels that are not affected by other mineral acids, which is potentially explosive in nature.
perchloric acid
TRUE or FALSE
The cold conc perchloric acid is not explosive, nor are heated dilute solutions. Violent explosions occur, however, when hot concentrated perchloric acid comes into contact with organic materials or easily oxidized inorganic substances.
TRUE
a mixture containing three volumes of concentrated hydrochloric acid and one volume of nitric acid, is well known mixture containing three volumes of concentrated hydrochloric acid and one volume of nitric acid, is well known
aqua regia
primary use of is for the decomposition of silicate rocks and minerals in the determination of species other than silica
hydrofluoric acid
TRUE or FALSE
Treatment with a dilute solution of calcium ion in HF affected area on the skin, which precipitates fluoride ion, may also be of help.
TRUE
can be carried out in either closed or
open vessels, but closed vessels are more popular because of the higher pressures and higher temperatures that can be achieved.
Microwave digestion
is a process of oxidizing an
organic sample with oxygen or air at
high temperature, leaving the
inorganic component for analysis.
dry ashing
is the simplest method for decomposing organic compounds, it is often the least reliable depending on the sample
dry ashing
simplest method for decomposing an organic sample prior to determining the cations it contains is to heat the sample over a flame in an open dish or crucible until all carbonaceous material has been oxidized to carbon dioxide.
combustion over an open flame (dry ashing)
is the thermochemical decomposition of organic compounds at elevated temperature in the absence of oxygen.
pyrolysis
is the thermochemical decomposition of organic compounds at elevated temperature in the presence of oxygen.
combustion
can be combined with techniques such as mass spectrometry or gas chromatography to separate and determine the volatile compounds
pyrolysis decomposition
TRUE or FALSE
Another limitation is that most high-pressure vessels are restricted in sample sizes to less than 1 g of material.
TRUE
The limitations of closed-vessel microwave digestion systems just noted have led to the development of atmospheric-pressure units, often called
open-vessel systems
It is designed to heat simultaneously 12 of the moderate-pressure vessels. The vessels are held on a turntable that rotates continuously through 360 deg so that the average energy received by each of the vessels is approximately the same.
Microwave oven
have been developed for performing fusions and for dry ashing samples containing large amounts of organic materials before acid dissolution, which temperatures of 1000°C are reached in two minutes
microwave furnaces
what method is capable of analyzing volatile compounds quantitatively as organic compounds are converted to gaseous products as the sample is pyrolyzed, which the analysis is completed within 15 mins
combustion-tube method
in decomposing inorganic materials with fluxes, the sample is mixed with an alkali metal salt, called the ______, and the combination is then fused to form a water-soluble product called the ______.
flux
melt
It decomposes most substances by virtue of the high temperature required for their use (300°C to 1000°C) and the high concentration of reagent brought in contact with the sample.
fluxes
TRUE or FALSE
the high temperatures required for a fusion increase the danger of volatilization losses.
TRUE
is a potent acidic flux that is particularly useful for attacking the more intractable metal oxides. Fusions with this reagent are performed at about 400°C. At this temperature, the slow evolution of the highly acidic sulfur trioxide
potassium pyrosulfate
Silicates and certain other refractory materials can be decomposed by heating to 1000°C to 1200°C with _________. This treatment generally converts the cationic constituents of the sample to acid-soluble carbonates or oxides
sodium carbonate
by itself or mixed with lithium tetraborate finds considerable use for attacking refractory silicate and alumina minerals, particularly for AAS, ICP emission, and X-ray absorption or emission determinations.
lithium metaborate
