Laboratory Procedures

Gravimetric Analysis Precipitation Reactions Examples

The conditions essential to accurate gravimetric analysis have been given. As a rule such estimations come under one of four classes:

Direct Estimations

These are the most usual and accurate methods of gravimetric analysis. The element sought is precipitated and weighed generally as a compound, definite in composition.

Direct Estimation by Loss

Here the element sought is volatile or forms a volatile compound and is driven off, the weight being taken as the volatilisation loss.

Indirect Estimation

When the previous methods are difficult these are used. If, for instance, Na or K are to be determined, unite them to Cl or SO4, say to the latter, and weigh the joint

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By | 2017-03-19T08:44:35+00:00 January 20th, 2017|Categories: Laboratory Procedures|Comments Off on Gravimetric Analysis Precipitation Reactions Examples

Quantitative Chemistry Gravimetric Analysis: PRECIPITATE

WASHING THE PRECIPITATE: A precipitate may be washed directly on the filter, or it may be washed partly by decantation and partly on the filter. If by decantation, the precipitate is allowed to settle, and the supernatant liquid is poured on the filter. Wash water is added to the precipitate, and after settling, the decantation is repeated a few times, and finally the precipitate is transferred to the paper or Gooch crucible.

Whatever method of washing be used, it must be thorough; and that this may be so, both the precipitate and the paper or asbestos must be washed free from all traces of

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Gravimetric Analysis: Substance into Solution

Material of Vessels for Solution

The student must consider the effect of the solvent used on the vessel. In most cases the solvent used is an acid or mixture of acids, and for such solvents glass and porcelain are generally used. Platinum may be used, provided no chlorine or other attacking agent be present. (See notes regarding care and use of platinum crucibles.) For strong alkalies silver or nickel vessels should be used, as glass is attacked sensibly by hot and even cold solutions of caustic potash or soda, and porcelain is also attacked to some extent.

Methods of Solution & Apparatus used

When a substance is soluble in water

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Gravimetric Analysis: Precipitation

After solution, certain minor operations may or may not be necessary, but as a rule the next essential operation is that of precipitation. In his qualitative work the student has already come across many cases of precipitation, and he will find that many of the methods there used are again applied for quantitative purposes. Silver, for instance, is precipitated as the chloride AgCl, copper as the sulphide by H2S, iron as the hydroxide by NH4HO, and so on. He will also find that some methods are introduced which are either not used or are of minor importance in qualitative

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By | 2017-03-17T19:06:35+00:00 January 19th, 2017|Categories: Laboratory Procedures|Tags: |Comments Off on Gravimetric Analysis: Precipitation

Gravimetric Analysis: Precipitate Filtration

When precipitation is complete the precipitate must be separated from the solution. The means of bringing about this separation will be described under this head. Under the next head (Washing) the completeness of this separation will be considered.

Filtering Medium

In quantitative gravimetric analysis the two materials generally used are paper and asbestos, and the student must be familiar with the use of both of these. He has already used paper in his qualitative work, but in quantitative analysis paper of a special quality must be used. This paper in various qualities may be obtained from the dealers. It is

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Quantitative Analysis Chemistry: GRAVIMETRIC METHODS

In the course of work completed, the problem so far met with has been the determination of the various elements (or compounds) present in a substance. In an ore, for instance, there may be present silica, iron, copper, arsenic, and sulphur, and it is the province of qualitative analysis to determine the presence or absence of these and other elements. It is obvious, however, that there still remains an unknown factor, namely, the quantity of each element present in any given substance. Having found that the ore contains the substances mentioned, the student is now asked how much silica, iron

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By | 2017-03-17T19:06:37+00:00 January 18th, 2017|Categories: Laboratory Procedures|Tags: |Comments Off on Quantitative Analysis Chemistry: GRAVIMETRIC METHODS

Analytical Balance

Analytical Balance Principle

In this place it will be sufficient to describe the usual chemical balance, designed to carry in each pan a load up to 100 gms. This balance can be obtained at a reasonable figure, and sensitive to 1/10 of a milligram (0.0001 gm.). In the section on Assaying the student will find two other forms—Pulp Scales and the Assay Balance— mentioned. The pulp

Scales are cheap, and sensitive to about 1/100 gm., and serve well for weighing quantities of 20 gms. and over. The assay balance is more sensitive than the chemical balance, but its range is shorter (from .5 gm. to .00005 gm.). The student who

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Lethal Dose of Cyanide

The chemistry of cyanide solutions is complicated because the cyanide ion forms compounds and complexes with many elements. Some cyanide species are highly toxic whereas others are relatively inert and harmless. Molecular hydrogen cyanide (HCN) is the most toxic form of cyanide. Under most conditions, HCN exists as a gas which readily dissipates or reacts with the environment to form less toxic or nontoxic forms of cyanide. Thus HCN is an ephemeral toxin, and many naturally occurring geochemical processes reduce the HCN concentration of a heap system with time.

As discussed below, free cyanide

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Mineral Identification by Spectroscopy

FIG. 35 gives an idea of the spectroscope and of its different parts. P is a flint glass prism, having a refracting angle of 60° and resting on a brass plate fixed on a brass support, S. The brass plate carries the collimator tube C, in the end of which nearest to the prism is fixed a lens, the other end being closed by a plate in which there is a vertical slit, which can be widened or narrowed as required by means of a small screw

The tube E has also on the end nearest the prism a lens, and at the other end a reduced photographic millimetre scale which can be seen through the telescope T

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By | 2017-03-19T09:19:19+00:00 January 11th, 2017|Categories: Laboratory Procedures, Mineralogy|Tags: |Comments Off on Mineral Identification by Spectroscopy