Some physical methods used in gas analysis

The relative proportions of various components of gas mix­tures can be determined by merely measuring some physical constants of the mixture: the density, the viscosity, the thermal conductivity, heat of combustion, ionization potential.

Condensation methods are often applicable in the separa­tion of complex mixtures of gases. This method has been applied to the gases of the argon group and of natural gas mixtures.

The application of the methods of mass spectrometry to gas analysis has been extensive. The use of a mass spectrometer in analysis enables one to determine the components of mixtures of hydrocarbons, fuel gases, rare gases, etc.

Thermal conductivity applied to gas analysis is rapid, simple to carry out and adaptable to continuous operation.and process control.

Some attempts to apply the methods of emission and ab­sorption spectroscopy to gas analysis have been made.

Other miscellaneous methods include magnetic suscepti­bility, micro-wave analysis, acoustical method based on the principle that the velocity of sound in a gas is a function of the molecular weight of the gas, inferometric methods, diffusion methods and others.

NOTES AND COMMENTARY

enables one -обеспечивает simple to carry out -прост в поизводстве

based on -основан на

ANALYSIS OF MIXTURES

Many problems of quantitative chemistry are more complex than determining the amount of a pure substance or the com­position of an aqueous solution of a pure compound. Often the problem arises simply because the compound or solution has an unknown or complex composition.

There are three fundamental schemes than can be used in the problem at hand.

1. Phase separation: The metal ion, A, can be determined
without interference front B if we separate A from B. We do
this by preparing a two-phase system such that all of A is in
one phase and all of B is in the other phase.

2. Selective determination: The metal ion, A, can be deter­
mined in the presence of B if we can find a determination
which is selective toward A, ignoring B.

3. Combined determination: The two metal ions, A and B,
can be determined together. This type of measurement com­
bined with another independent measurement gives the amount
of each ion.

NOTES AND COMMENTARY

are more complex than -более сложны чем

the problem at hand -рассматриваемая проблема

 

EXTRACTION

Liquid-liquid phase separations are possible when a metal forms a compound soluble in two immiscible liquids. The dis­tribution of the compound between the two liquids can be con­sidered to be a solubility contest. Practical considerations dictate that one of the liquids must be water. Among the liquids other contestants are: carbon tetrachloride, chloroform, carbon disulfide, ethers, paraffin hydrocarbons, and aromatic hydro­carbons. Alcohols cannot be added to this list.

Most inorganic compounds just are not interested in the organic solvents which are immiscible with water. Sometimes, however, a complexing agent can be found which will coach an inorganic substance into an organic solution. Cupric, lead, zinc, silver, mercuric, and cadmium salts, for example, will dissolve, in either chloroform or carbon tetrachloride if it con­tains some dithizone.

PRECIPITATION

The most generally useful technique for accomplishing a phase separation is the solid-liquid separation, obtained in a precipitation.

To have wide applicability a precipitant should form com­pounds with many metal ions, and these compounds should have a wide range of solubility. To obtain proper conditions, the concentration of the precipitant should be controlled easilly.

What sort of precipitant is most desirable depends upon many variables: how many samples must be determined, what constituents are present, what reagents are at hand, what time is available, what accuracy is desired, etc.

ELECTROLYSIS

Another type of solid-liquid phase separation is furnished by electrolytic techniques. Two electrodes are placed in the solution of interest, and a current is passed through the solu­tion at a voltage sufficient to reduce some but not all of the metals present. If the current and concentrations are adjusted properly, the metals which are reduced will plate out on the electrode in a pure metallic deposit which can be dried and weighed directly.

NOTES AND COMMENTARY

the solution of interest -исследуемый раствор will plate out -отлагается

to reduce some but not all -для частичного удаления

ION EXCHANGE

Another procedure utilizing the elution technique is the ion exchange separation. This time the solid (which is called the substrate) is a salt or compound with salt-forming capacity, something like a sulfonic acid group. When a solution con­taining metal ions is passed through such an acid substrate, the ions can replace the protons, forming salts. Further elution repeats many times the cycle of ion exchange, replacement of a proton by a salt ion, followed by replacement of the metal ion by proton. As in chromatography, the repetitious procedure magnifies small differences in saltforming capacity and per­mits separations which are extremely difficult by any other method.

Ion exchange substrates fall into two groups: cation ex­changers and anion exchangers. Acidic functional groups are

effective as cation exchangers. These groups include sulfonic acids,— SO₃H; carboxylic acid,— COOH; phenols or alcohols,— OH; and mercaptans,— SH. These interact only with cations and by an exchange reaction of the following sort:

— SO₃H + M⁺ = — SO₂M + H⁺.

Most anion exchangers are amines, depending upon one of the functional groups — NH_2,— NHR, and NR₂. These groups form ammonium type salts, and the anion can be displaced:

— NH₂ • HC1 + X = — NH₂ • HX + Cl.

 

NOTES AND COMMENTARY

saltforming capacity -способность солеобразования something like -нечто вроде

by any other method -любым другим методом fall into two groups -разделяются на две разные группы

 

Unit 7. Famous chemists.

Task: 1) read the texts

Answer the questions

Make up a report about any famous chemist you like

Antoine Lavoisier.

Antoine Laurent Lavoisier is a French chemist, was the founder of modern chemistry.

Lavoisier carefully measured the weights of substances involved in chemical reactions. In 1772 he began a series of experiments that demonstrated the nature of combustion. He concluded that combustion results from the union of a flammable material with a newly discovered gas, which he called oxygen. Lavoisier published his findings in his Elementary Treatise on Chemistry (1789).

With French astronomer and mathematician Pierre Simon Laplace, Lavoisier conducted experiments on respiration in animals. Their studies demonstrated a similarity between common chemical reactions and the processes that occur in living organisms. These experiments provided the foundation for the science now known as biochemistry. Lavoisier also helped to develop a system for naming chemical substances based on their composition. This system is still in use.

Lavoisier was born in Paris. He received an excellent education and developed an interest in all branches of science, especially chemistry. He was elected to the French Academy of Sciences in 1768.

Lavoisier was arrested in 1793 by the leaders of the French Revolution. Many years earlier, he had become a partner in a firm that collected a number of taxes for the government. In spite of his achievements, Lavoisier was found guilty of conspiracy with the enemies of France because of his involvement in tax collection. He was executed by guillotine.

 

Questions

1) What famous scientist did Lavoisier work with?

2) What experiments did they conduct?

3) The foundation of what science did their experiments provide?

4) Why was he arrested?

5) What series of experiments did Lavoisier begin in 1772?

 

Alfred Nobel.

Alfred Bernard Nobel, a Swedish chemist, invented dynamite and founded the Nobel Prizes. As a young man, Nobel experimented with nitroglycerin in his father’s factory. He hoped to make this dangerous substance into a safe and useful explosive. He prepared a nitroglycerin explosive, but so many accidents occurred when it was put on the market that for a number of years many people considered Nobel almost a public enemy.

Finally in 1867 Nobel combined niter with an absorbent substance. This explosive could be handled and shipped safely. Nobel named it dynamite. Within a few years he became one of the world’s richest men. He set up factories throughout the world and bought the large Bofors armament plant in Sweden. He worked on synthetic rubber, artificial silk and many other products.

Nobel was never in good health. In later years he became increasingly ill and nervous. He suffered from a feeling of guilt at having created a substance that caused so much death and injury. He hated the thought that dynamite could be used in war when he had invented it for peace. Nobel set up a fund of about 9 million U.S. dollars. The interest from the fund was to be used to award annual prizes, one of which was for the most effective work in promoting international peace.

Alfred Nobel was born on October, 21, 1833 in Stockholm. He was the son of an inventor. He was educated in St. Petersburg, Russia, and later studied engineering in the United States.

 

Questions

1) Who was Nobel’s father?

2) What was Nobel’s chief invention?

3) Why did people consider him a public enemy for a number of years?

4) What kind of Prizes did he set up?

5) What was the interest from these fund?

 

Final test.

I. Match the words.