Term
| What are the five steps in most analyses? |
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Definition
- Obtain a representative specimen of the material you want to analyze.
- Transform the specimen into a form suitable for analysis, which usually means dissolving the substance.
- Remove or mask species that will interfere with the chemical analysis.
- Carry out the analysis.
- Interpret your results.
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Term
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Definition
| - total material from which samples are taken, e.g., truckload of reagents, a batch of pills, or a bovine liver. |
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Term
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Definition
| -Taken from the lot for analysis or archiving. |
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Term
[Sampling] Laboratory sample- |
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Definition
| - formed from the bulk sample and must have the sample composition as the larger sample. This can be accomplished, for example, by grinding an entire solid bulk sample to a fine, powder, mixing thoroughly , and keeping a small portion of powder for testing. |
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Term
[Sampling] Test portions (aliquots)- |
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Definition
| - of the laboratory sample are then used for individual analyses. |
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Term
| Preparing Samples for analysis: |
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Definition
- If a bulk sample is a liquid, a fine powder, or a suspension, it may be homogeneous enough to provide a laboratory sample.
- Solids can be ground in a mortar and pestle.
- Steel mortar is a hardened steel tool into which the steel sleeve and steel pestle fit snugly.
- Ball mill is another grinding device in which sample mixed with balls made of a hard ceramic are rotated in a ceramic drum to crush the sample to a fine powder.
- Shatterbox Mill- a puck and a ring spin inside a container at high speed to grind up to 100 mL of sample to a fine powder.
- Solids typically dried at 110°C at atmospheric pressure hoever heating may cause volatile components of the sample to evaporate or can cause decomposition.
- Once laboratory sample obtained, it is dissolved. If the sample does not dissolve under mild conditions, acid digestion or fusion may be used. Organic material may be destroyed by combustion or wet ashing to place inorganic elements in suitable form for analysis.
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Term
| Dissolving Inorganic Materials with Acids: |
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Definition
- The nonoxidizing acids HCl, HBr, HF, H3PO4, dilute H2SO4 and dilute HClO4 dissolve metals by redox rxn: M + nH+ → Mn+ + n/2 H2
- Substances that do not dissolve in nonoxidizing acids may dissolve in the oxidizing acids HNO3, hot concentrated H2SO4, or hot concentrated HClO4.
- Substances that will not dissolve in acids can usually be dissolved by a hot, molten inorganic flux.The finely powdered unknown mixed with 5-20 times its mass of solid flux, and fusion (melting) carried out in a platinum crucible at 300-1200°C in a furnace or over a burner. The sample dissolves and the melt is allowed to cool. The solid mass then dissolved in solvent, usually dilute aqueous acid. Fusion is a last resort, b/c the flux can introduce impurities.
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Term
| Aqua Regia (water of the king- royal water): |
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Definition
- A 3:1 (vol/vol) mixture of HCl:HNO3 will dissolve Au and Pt.
- Mixture produces free chlorine, i.e., Cl2 and ClNO
- Can dissolve gold b/c each of its two component acids carries out a different function. he nitric acid is a good oxidizing agent. Chloride ions from the hydrochloric acid form coordination complexes with the gold ions, removing them from solution. Reducing the concentration of the Au3+ ions shifts the equilibrium towards the oxidized form.
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Term
| Decomposition of Organic Substances: |
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Definition
- Analysis of elements in organic material usually begins with chemical destruction of the organic compounds. Procedures
- Dry ashing- dont involve liquids for the destructio.
- Wet ashing- liquid used. Accomplished with acids either alone or in combination.
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