Using reagents to identify unknown substances

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SUMMARY

This discussion focuses on the use of reagents such as KOH (aqueous) and H2SO4 (aqueous) to identify unknown substances in a laboratory setting. The example provided illustrates how mixing NaBr and AgNO3 results in the formation of a precipitate, AgBr, indicating the presence of halide ions. Additionally, the discussion highlights that acids like HCl and H2SO4 can indicate the presence of carbonates or sulfites through gas evolution, while KOH can produce precipitates depending on the ionic compounds present. Understanding these reactions is crucial for accurately identifying unknown substances.

PREREQUISITES
  • Basic knowledge of chemical reactions and ionic compounds
  • Familiarity with precipitation reactions and solubility rules
  • Understanding of acid-base reactions and gas evolution
  • Experience with laboratory techniques for mixing and observing reactions
NEXT STEPS
  • Study the solubility chart of ionic compounds for predicting precipitate formation
  • Learn about the specific reactions of halide ions with silver nitrate (AgNO3)
  • Research the gas evolution reactions of carbonates and sulfites with acids
  • Explore the use of KOH in identifying metal hydroxides and their solubility
USEFUL FOR

Chemistry students, laboratory technicians, and educators involved in practical chemistry experiments focused on substance identification and reaction analysis.

wonders
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My group has to design a lab based on the materials and purpose our teacher gave us. The purpose is to identify some unknown substances. One of the tests that we will conduct is the KOH (aq) and H2SO4 (aq) reagents tests. The teacher gave us the following example:

suppose
NaBr (s) --> Na+ (aq) + Br- (aq)
AgNO3 (s) --> Ag+ (aq) + NO6- (aq)

If the solutions are mixed,
Na+ (aq) + Br- (aq) + Ar+ (aq) + NO3- (aq) --> AgBr (s)

AgBr (s) is the precipitate, so what is in the mixture will be:

AgBr (s) + Na+ (aq) + NO3-(aq)


I have no idea how to apply that example to identify substances, and am still a bit unclear on how reagents work. Can someone give me a hand?

Thanks in advance!
 
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certain reagents like AgNO3, when added to a sample that has a halide ion in it like cl-, Br- or I-, it will always give a ppt (solid)

acids like HCl or H2SO4 can tell you if carbonate or sulfites are present because they will give off a gas (fizzing) - what is the reaction?

KOH can also give ppt, depending on what is in solution. there should be a solubility chart of ionic compounds somewhere in your textbook. the things that make ppt or gases will have similar ions

ex hydroxides are mostly insoluble so a rxn of Fe3+ and KOH will give a red ppt (of what?)