chemistry technology

Most municipalities must use a source of water in which the probability of pollution is rather high. Certainly, all our natural rivers and lakes and even the water stored in most reservoirs may be subjected to pollution,  and  generally  cannot  be  considered  safe  for  drinking  purposes  without  some  forms  of treatment. The type and extent of treatment will vary from city to city, depending upon the conditions of
the  raw  water.  Treatment  may  comprise  various  processes  used  separately  or  in  combinations,  such  as storage,  aeration,  sedimentation,  coagulation,  rapid  or  slow  sand  filtration,  and  chlorination,  or  other accepted forms of disinfection.
When  surface  waters  serve  as  a  municipal  water  supply,  it  is  generally  necessary  to  remove suspended solid, which can be accomplished either by plain sedimentation or sedimentation following the addition of coagulating chemicals. In the water from most streams that are suitable as a source of supply,
the sediment is principally inorganic, consisting of particles of sand and clay and small amount of organic matter.  In  this  water  there  will  also  be  varying  numbers  of  bacteria,  depending  upon  the  amount  of
bacteria  nutrients,  coming  from  sewage  or  other  sources  of  organic  matter,  and  upon  the  prevailing
temperature. Many of the bacteria may have come from the soil and, as a result, during a season of high turbidity when there is a large amount of eroded soil in the water, the bacterial count from this source
may be relatively high. If the organisms are derived from sewage pollution, the number will be highest during periods of low flow when there is less dilution, and at this time the turbidity will, in general, be low.  The  amount  of  sediment  may  vary  a  great  deal  from  one  river  to  another,  depending  upon  the
geological character of the various parts of the drainage system. The size of the suspended particles can also vary greatly. In some waters the clay particles may be extremely fine, in fact, they may be smaller
than bacteria. The time required for satisfactory sedimentation differs for different waters, and generally must  be  established  by  actual  experiments.  Some  waters  can  be  clarified  satisfactorily  in  a  few  days,
while others may require weeks or months. As far as total weight of sediment is concerned, the bulk of it
is  probably  removed  in  a  few  days,  but  this  may  not  bring  about  a  corresponding  change  in  the appearance of the water, since the smaller particles may have greater influence than the large ones upon
the apparent color and turbidity. When plain sedimentation is used primarily as a preliminary treatment, a high degree of clarification is not needed and, as a result, shorter periods of settling are adequate.
After  flocculation  treatment,  water  is  passed  through  beds  of  sand  with  diatomaceous  earth  to accomplish  sand  filtration.  As  we  mentioned  previously,  some  protozoan  cysts,  such  as  those  of G.lamblia, appear to be removed from water only by such filtration treatment. The microorganisms are trapped mostly by surface adsorption in the sand beds. They do not penetrate the tortuous routing of the sand beds, even through the openings might be larger than the organisms that are filtered out. These sand filters are periodically backflushed to clear them of accumulations. Water systems of cities that have an exceptional  concern  for  toxic  chemicals  supplement  sand  filtration  with  filters  of  activated  charcoal (carbon).  Charcoal  has  the  advantage  of  removing  not  only  particulate  matter  but  also  some  dissolved organic chemical pollutants.
Before entering the municipal distribution system, the filtered water is chlorinated. Because organic matter neutralized chlorine, the plant operators must pay constant attention to maintaining effective levels
of chlorine. There has been some concern that chlorine itself might be a health hazard, that it might react
with organic contaminants of the water to form carcinogenic compounds. At present, this possibility is considered minor when compared with the proven usefulness of chlorination of water.
One substitute for chlorination is ozone treatment. Ozone (O3) is a highly reactive form of oxygen that  is  formed  by  electrical  spark  discharges  and  ultraviolet  light.  (The  fresh  odor  of  air  following  an electrical storm or around an ultraviolet light bulb is from ozone). Ozone for water treatment is generated electrically  at  the  site  of  treatment.  Use  of  ultraviolet  light  is  also  a  possible  alternative  to  chemical disinfection. Arrays of ultraviolet tube lamps are arranged in quartz tubes so that water flows close to the lamps. This is necessary because of the low penetrating power of ultraviolet radiation.

A  systematic  nomenclature  was  devised  towards  the  end  of  the  18th  century.  Elements  already known  retained  their  old  names,  e.g.  silver,  tin,  gold,  mercury,  etc.,  but  newly  discovered  elements generally have their names ending in -um if they are metals, and-on if they are non-metals/e.g. sodium, potassium, argon /.
The  names  of  compounds  are  formed  from  those  of  their  components  so  as  to  indicate  their composition. In the names of binary compounds /i.e., compounds of two elements/ the name of the metal comes first, followed by that of the other element ended in -ide, e.g. sodium chloride /NaCl/, zinc oxide
/ZnO/, aluminum oxide /Al2O3/. When a metal forms two compounds with oxygen, the two oxides are distinguished  by  adding  -ous  and  -ic  to  the  Latin  name  of
 the  metal,  signifying  the  lower  and  higher oxidation  states  respectively,  e.g.,  cuprous  oxide  /Cu2O/,  cupric  oxide  /CuO/,  and  ferrous  oxide  /FeO/, ferric  oxide  /Fe2O3/.  The  salts  corresponding  to  cuprous  oxide  are  called  cuprous  salts,  e.g.  cuprous chloride and cupric chloride. Another way  of distinguishing between different compounds of the same element is by the use of the Greek prefixes to the names of the elements. These prefixes are as follows: mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octo-. To these we may add the Latin hemi-, meaning one half, and sesqui-, meaning one and a half, and per-. By the use of these prefixes we can designate the compounds more precisely than by means of the prefixes -ous and -ic, especially when more than two compounds exist. As examples of the use of these prefixes we may mention carbon monoxide /CO/ and carbon  dioxide  /CO2/,  phosphorus  trichloride  /PCl3/  and  phosphorus  pentachloride  /PCl5/,  chromium sesquioxide /Cr2O3/ and chromium trioxide /CrO3/, lead hemioxide /Pb2O/, hydrogen peroxide /H2O2/.
Oxides, which form salts with acids, are known as basic oxides; by combination with water, basic oxides form bases. These  contain the metal united  with the group of atoms -OH/ the hydroxyl group/; they are, therefore, called hydroxides. Thus NaOH is sodium hydroxide, Cu(OH)2  is copper hydroxide,
and the compounds Fe(OH)2  and Fe2O3.H2O are ferrous hydroxide and ferric hydroxide, respectively.
The endings -ous, -ic are also applied to acids, the -ous acid containing less oxygen than the -ic acid, e.g. sulphurous acid /H2SO3/ and sulfuric acid /H2SO4/, chlorous acid /HClO2/. In addition to HClO2 and HClO3, the acids having the formulas HClO and HClO4  are also known, the former having the name hypochlorous acid, the latter being designated by the name perchloric acid.
Salts  are  named  in  relation  to  the  acids  from which  they  are  derived  according  to  the  following
rules:
1. If the name of the acid ends in -ous, the name of the salt ends in -ite/ sodium chlorite, NaClO2/.
2. If the name of the acid ends in -ic, the corresponding salt ends in -ate/ sodium chlorate, NaClO3/
3. If the name of the acid involves also a prefix such as per- or hypo-, the prefix is retained on the name  of  the  salt/  sodium  hypochlorite,  NaClO,  and  sodium  perchlorate,  NaClO4/.  Accordingly, salts of sulfurous acid are called sulfites, those of sulfuric acid, sulfates. Salts of phosphorous acid
are phosphites, of phosphoric acid, phosphates, etc.

Laboratories have now become indispensable in schools, factories and research institutes to test, confirm, or demonstrate on a small scale, phenomena and processes which occur in nature or which may find application in industry or be of importance to science.
The equipment of a chemical laboratory varies according to the nature of the work, which is to be carried  out.  It  may  be  intended  for  the  student  to  put  to  the  test  his  theoretical  knowledge/  school laboratory, for the technician/ technologist to verify and check processes to be employed in the factory/ works  laboratory  or  to  help  the  scientist  and  research  worker  to  discover  or  confirm  scientific  facts/ research laboratory.
Every chemical laboratory should be provided with running water, gas and electricity. The water supply is conducted from the mains by means of pipes, the piping terminating in taps under, which there
are sinks to take away waste water and other non-objectionable liquids. When one needs water one turns the tap on and stops it flowing by turning the tap off.
Similarly a system of pipes is attached to the gas main from where gas reaches the various kinds of burners.  They  serve  for  producing  flames  of  different  intensity,  the  Bunsen  burner  being  the  most common type used.
Apart from a gas supply there is electricity which serves for lighting and as a driving power. For operating electricity, switches or switch buttons are employed. That is why we talk about switching on the light or switching it off.

The laboratory is also equipped with a large variety of apparatus and devices. One of them, a desiccator,
is used for drying materials. Ovens, furnaces or kilns serve for generating high temperatures. Where harmful vapors  and  undesirable  odorous  develop  during  the  operation,  a  hood  with  suitable  ventilation  has  to  be provided for their escape.
Of primary importance are glass and porcelain vessels. Glass vessels for chemical processes are made
of special materials. They have to resist sudden changes in temperature, to withstand very high temperature: refractory  glass,  and  be  affected  by  a  few  substances  as  possible.  The  necessary  assortment  of  laboratory glassware includes test tubes, beakers, various flasks, watch glasses, funnels, bottles, and cylinders.
Porcelain articles consist of various kinds of dishes, basins and crucibles of various diameters. A
grinding mortar with a pestle, desiccating dishes and stirrers are also generally made of porcelain.
At  present,  also  plastic  materials  are  finding  increasing  use  in  laboratories,  many  of  them  being chemically  resistant,  unattacked  by  alkalis  or  acids/  acid-or  alkali-proof/,  and  unbreakable.  Containers made of them are especially suitable for storing stock solutions.
The  analytical  balance,  which  is  used  for  accurate  weighing  of  samples,  is  usually  kept  in  a separate room.

Hydrocarbons   are   compounds   containing   only   carbon   and   hydrogen   atoms.   The   simplest hydrocarbon is methane, CH4. Its molecules are tetrahedral, the four hydrogen atoms lying at the corners
of a regular tetrahedron around the carbon atom, and connected with the carbon atom with single bonds.
Methane is a gas, which occurs in natural gas, and is used as a fuel. It is also used in large quantities for
the manufacture of carbon black, by combustion with a limited supply of air. The hydrogen burn to water, and the carbon is deposited as very finely divided carbon, which finds extensive use as filler for rubber
for automobile tires.

Methane is the first member of a series of hydrocarbons having the general formula CnH2n+2, called
the methane series or paraffin series. The compounds of this series are not very reactive chemically. They occur  in  complex  mixtures  called  petroleum.  The  molecules  heavier  than  ethane  are  characterized  by containing carbon atoms attached to one another by single bonds. The lighter members of the paraffin series are gases, the intermediate members are liquids, and the heavier members are solid or semi-solid substances. Gasoline is the heptane-nonane mixture, and kerosene the decane-hexadecane mixture. Heavy fuel oil is a mixture of paraffins containing twenty or more atoms per molecule. The lubricating oils and solid paraffin are mixtures of still larger paraffin molecules.
The substance ethylene, C2H4, consists of molecules in which there is a double bond between the two carbon atoms. This double bond confers upon the molecule the property of much greater chemical reactivity  than  is  possessed  by  the  paraffins.  Because  of  this  property  of  readily  combining  with  other substances, ethylene and related hydrocarbons are said to be unsaturated.
Acetylene  is  the  first  member  of  a  series  of  hydrocarbons  containing  triple  bonds.  Aside  from acetylene, these substances have not found wide use, except for the manufacture of other chemicals.
The  hydrocarbons,  the  molecules  of  which  contain  a  ring  of  carbon  atoms,  are  called  cyclic hydrocarbons.  Cyclohexane,  C6H12,  is  representative  of  this  class  of  substances.  It  is  a  volatile  liquid, closely similar to normal hexane in its properties.
Another  important  hydrocarbon  is  benzene,  having  the  formula  C6H6.  It  is  a  volatile  liquid/  b.p.
800C/,  which  has  an  aromatic  odor.  For  many  years  there  was  discussion  about  the  structure  of  the benzene molecule. August Kekule suggested that the six carbon atoms are in the form of a ring, and this
has  been  verified:  diffraction  studies  have  shown  that  the  six  atoms  form  a  regular  planar  hexagon  in space, the six hydrogen atoms being bonded to the carbon atoms, and forming a larger hexagon. Kekule suggested that, in order for a carbon atom to show its normal quadrivalence, the ring contains three single bonds and three double bonds in alternate positions. Other hydrocarbons, derivatives of benzene, can be obtained  by  replacing  the  hydrogen  atoms  by  methyl  groups  or  similar  groups.  Benzene  and  its derivatives are used in the manufacture of drugs, explosives, photographic developers, plastics, synthetic
dyes, and many other substances.

Every chemical reaction requires some time for its completion, but some reactions are very fast and others  very  slow.  Reactions  between  ions  in  solution  without  change  in  oxidation  state  are  usually extremely  fast.  An  example  is  the  neutralization  of  an  acid  by  a  base,  which  proceeds  as  fast  as  the solutions  can  be  mixed.  Presumable  nearly  every  time  a  hydronium  ion  collides  with  a  hydroxide  ion reaction occurs, and the number of collisions is very great, so that there is little delay in the reaction. The formation of a precipitate, such as that of silver chloride when a solution containing silver ion is mixed with a solution containing chloride ion, may require a few seconds, to permit the ions to diffuse together
to form the crystalline grains of the precipitate. On the other hand, ionic oxidation-reduction reactions are sometimes very slow. An example is the oxidation of stannous ion by ferric ion. This reaction does not occur  every  time  a  stannous  ion  collides  with  one  or  two  ferric  ions.  In  order  for  the  reaction  to  take place, the collision must be of such a nature that electrons can be transferred from one ion to another, and collisions, which permit this electron transfer to occur, may be rare.
The factors, which determine the rate of a reaction, are manifold. The rate depends not only upon
the  composition  of  the  reacting  substances,  but  also  upon  their  physical  form,  the  intimacy  of  their mixture, the temperature and pressure, the concentrations of the reactants, special physical circumstances such as irradiation with visible light, ultraviolet light, X-rays, neutrons, or other waves or particles, and
the presence of other substances which affect the reaction but are not changed by it/catalysts/.
Most actual chemical processes are very complicated, and the analysis of their rate is very difficult.
As reaction proceeds the reacting substances are used up and new ones are formed; the temperature of the system is changed by the heat evolved or absorbed by the reaction; and other effects may occur which influence  the  reaction  in  a  complex  way.  For  example,  when  a  drop  of  a  solution  of  potassium permanganate  is  added  to  a  solution  containing  hydrogen  peroxide  and  sulfuric  acid  no  detectable reaction may occur for several minutes. The reaction speeds up, and finally the rate may become so great
as  to  decolorize  a  steady  steam  of  permanganate  solution  as  rapidly  as  it  is  poured  into  the  reducing
solution.  This  effect  of  the  speeding  up  of  the  reaction  is  due  to  the  vigorous  catalytic  action  of  the products of permanganate ion reduction: the reaction is rapidly accelerated as soon as they are formed.

Practical   chemistry   includes   many   special   techniques   for   the   isolation   and   purification   of substances.  Some  substances  occur  very  nearly  pure in  nature,  but  most  materials  are  mixtures,  which must be separated or purified if pure substances are desired, and most manufactured materials also require purification.
The separation of two different phases is often rather easy. Particles of a solid phase mixed with a liquid phase may be separated from the liquid by filtration. Often the solid is present because it has been produced  from  solution  in  the  liquid  by  a  chemical  reaction  or  by  change  in  conditions/such  as  by cooling/ the solid is then called the precipitate. The precipitate is removed by pouring the mixture on a folded filter paper in a funnel. The liquid/ called the filtrate/ runs through, and the grains of precipitate/
the residue/ are retained, unless they are too small. Ordinary filter paper contains pores about 0.001cm in diameter, and smaller particles pass through.
A precipitate may also be removed by letting the suspension stand quietly until the precipitate has settled to the bottom of the container under the influence of gravity. The supernatant liquid can then be poured off. This process of pouring off is called decantation.
The process of settling can be accelerated by the use of centrifugal force, in a centrifuge. Ordinary centrifuges produce forces of the order of 100 or 1,000 times that of gravity. Supercentrifuges have been built which give forces over 100,000 times as great as that of gravity.
Two liquid phases may be conveniently separated by use of a special device, the separatory funnel.
A dropper may also be used for this purpose.
An impure substance may often be purified by fractional freezing. The impure liquid substance is cooled  until  part  of  it  has  crystallized,  and  the  remaining  liquid,  which  usually  contains  most  of  the impurities, is then poured off, leaving the purified crystals.
A  liquid  can  be  purified  by  distillation  in  a  still.  The  liquid  is  boiled  in  a  flask  or  some  other container, and the vapor is condenser, forming a liquid distillate, which is collected in a receiver. The first portions/fractions/ of the distillate tend to contain the more volatile impurities, and the residue in the flask tends to retain the less volatile ones. Stills so special design have been invented, which are very effective
in separating liquid mixtures into their components.

If sugar and water, two pure substances, are mixed together, a solution result, uniform throughout
in  its  properties,  in  which  the  sugar  can  neither  be  seen  with  a  microscope  nor  filtered  out.  It  is  not distinguishable from a pure substance in appearance.
The experimental distinction between a pure substance and solution is quite simple when the solute
/the dissolved substance/ is not volatile so that it is left behind when the solvent is evaporated. However, when both are volatile the matter is not quite so simple and it is necessary to find out whether any change
in composition and hence in properties occurs during a change in state.
Suppose we wish to determine whether air is a pure substance or a solution. One method would be
to  liquefy  a  certain  amount  and  then  observe  what  happens  to  it  as  it  slowly  evaporates.  As  the evaporation proceeds one may observe that
a- The light blue color gradually becomes deeper
b- The temperature of the liquid slowly rises
c- The densities of both liquid and gas change.
Any  one  of  these  as  well  as  other  possible  observations  show  that  air  must  contain  two  or  more components  whose  relative  amounts  change  during  the  evaporation,  causing  the  observed  changes  in properties due  to differences  between  the  components in  color, volatility, density,  chemical  behavior. Still other properties might have been used.
The term solution is not restricted to liquid solutions. All gases are completely miscible with each other, forming but one phase, so that every mixture of gases is a solution. Alloys of silver and gold, no matter  what  the  relative  amounts  of  the  two  metals,  contain  but  one  kind  of  crystal,/the  properties  of which change continuously with the composition/, thus being a solid solution.
If liquid air is distilled in a scientifically constructed still, it is possible to separate it into two nearly pure constituents. One of these constituents, nitrogen, is found to be slightly lighter than air; it can be condensed to a colorless liquid boiling at -1940C; it is very inert chemically, reacting with but few other substances. The other constituent, oxygen, is slightly heavier than air; it gives, when condensed at low temperatures, a blue liquid boiling at -182.50C, and it reacts readily with many substances.
As another illustration, suppose we have a solid metal, which appears to be perfectly homogeneous under  the  microscope.  We  could  determine  whether  it  is  a  solution  or  a  pure  substance  by  melting  it, dipping  into the  melt  a  suitable  thermometer  and  letting  it  cool  slowly,  taking temperature  readings  at regular intervals, and plotting temperature against time.