Chapter 35: Dissolving the sample

Question 1

is an excellent solvent for inorganic samples but finds limited application for decomposing organic materials.

Answer 1

conc HCl

Question 2

is resistant to heat and attack by strong chemical agents.

Answer 2

refractory substance

Question 3

TRUE or FALSE
Ideally the reagent selected should dissolve the entire sample, not just the analyte.

Answer 3

TRUE

Question 4

Sources of error in decomposition and dissolution

Answer 4

1. Incomplete dissolution of the analytes
2. Losses of the analyte by volatilization
3. Introduction of analyte as a solvent contaminant
4. Introduction of contaminants from reaction of the solvent with vessel walls

Question 5

When a sample is introduced/ dissolved in an acid, what possible error occurs?

Answer 5

Losses of the analyte by volatilization

Question 6

It is widely used for
dissolving many metal oxides as well as metals more easily oxidized than hydrogen.

Answer 6

conc HCl

Question 7

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

Answer 7

hot conc HNO3

Question 8

is widely used for decomposing organic samples for determining their trace metal content.

Answer 8

HNO3 combined with other acids and oxidizing agents such as H2O2 and bromine

Question 9

is a process of oxidative
decomposition of organic samples
by liquid oxidizing reagents, such as
HNO3, H2SO4, HClO4, or mixtures
of these acids.

Answer 9

Wet ashing

Question 10

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)

Answer 10

sulfuric acid

Question 11

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.

Answer 11

perchloric acid

Question 12

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.

Answer 12

TRUE

Question 13

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

Answer 13

aqua regia

Question 14

primary use of is for the decomposition of silicate rocks and minerals in the determination of species other than silica

Answer 14

hydrofluoric acid

Question 15

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.

Answer 15

TRUE

Question 16

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.

Answer 16

Microwave digestion

Question 17

is a process of oxidizing an
organic sample with oxygen or air at
high temperature, leaving the
inorganic component for analysis.

Answer 17

dry ashing

Question 18

is the simplest method for decomposing organic compounds, it is often the least reliable depending on the sample

Answer 18

dry ashing

Question 19

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.

Answer 19

combustion over an open flame (dry ashing)

Question 20

is the thermochemical decomposition of organic compounds at elevated temperature in the absence of oxygen.

Answer 20

pyrolysis

Question 21

is the thermochemical decomposition of organic compounds at elevated temperature in the presence of oxygen.

Answer 21

combustion

Question 22

can be combined with techniques such as mass spectrometry or gas chromatography to separate and determine the volatile compounds

Answer 22

pyrolysis decomposition

Question 23

TRUE or FALSE
Another limitation is that most high-pressure vessels are restricted in sample sizes to less than 1 g of material.

Answer 23

TRUE

Question 24

The limitations of closed-vessel microwave digestion systems just noted have led to the development of atmospheric-pressure units, often called

Answer 24

open-vessel systems

Question 25

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.

Answer 25

Microwave oven

Question 26

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

Answer 26

microwave furnaces

Question 27

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

Answer 27

combustion-tube method

Question 28

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 ______.

Answer 28

flux
melt

Question 29

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.

Answer 29

fluxes

Question 30

TRUE or FALSE
the high temperatures required for a fusion increase the danger of volatilization losses.

Answer 30

TRUE

Question 31

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

Answer 31

potassium pyrosulfate

Question 32

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

Answer 32

sodium carbonate

Question 33

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.

Answer 33

lithium metaborate