Unknown Solutions
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15:03
Identification of Unknown Aldehydes and Ketones - Student Protocol
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2020
Source: Lara Al Hariri and Ahmed Basabrain at the University of Massachusetts Amherst, MA, USA DNPH Test for Aromatic Aldehydes and KetonesExpand In this lab, you'll use the DNPH test, the Tollens' test, and the iodoform test to identify two unknown aldehydes or ketones. You'll use butanone and benzaldehyde as known compounds to confirm that the tests are working as expected. You'll start the lab with the DNPH test, which relies on the reaction between 2,4-dinitrophenylhydrazine, or DNPH,...
06:48
Identification of Unknown Aldehydes and Ketones - Instructor Prep
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2020
Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA Preparation of Test SolutionsExpand Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed. Before you start, put on a lab coat, splash-proof safety glasses, and nitrile gloves. Note: DNPH is a shock explosive, so handle it gently with low friction tools. Phosphoric acid is also toxic and corrosive. Prepare 100 mL of a 0.1 M...
03:09
Identification of Unknown Aldehydes and Ketones - Concepts
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2020
Aldehydes and Ketones Aldehydes and ketones have a carbonyl group (C=O) as a functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon (RCOR’). The simplest ketone is acetone, which has two methyl groups attached to the carbonyl carbon (CH3COCH3). An aldehyde is similar to a ketone, except that instead of two side groups connected to the carbonyl carbon, they have at least one hydrogen (RCOH). The simplest aldehyde is formaldehyde (HCOH), as it has two hydrogens...
08:53
Freezing-Point Depression to Determine an Unknown Compound
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2023
Source: Laboratory of Lynne O' Connell — Boston College When a solid compound is dissolved in a solvent, the freezing point of the resulting solution is lower than that of the pure solvent. This phenomenon is known as freezing-point depression, and the change in temperature is directly related to the molecular weight of the solute. This experiment is designed to find the identity of an unknown compound by using the phenomenon of freezing-point depression to determine its molecular weight. The...
08:04
Viscosity of Propylene Glycol Solutions
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2023
Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA Viscosity is a measure of a fluid's resistance to flow, and it is a useful parameter in the design of efficient product processing and quality control in a wide range of industries. A variety of viscometers are used to obtain the most accurate readings of experimental materials. The standard method of measuring viscosity is through a glass tube viscometer, which...
FAQs
In a titration, the endpoint matters because it marks the point at which the known reagent has reacted with the analyte in the required stoichiometric relationship. The analyst uses the reagent’s known concentration and the measured reaction amount to calculate the analyte quantity. This links an observable endpoint to a quantitative chemical result.
Instrumental analysis connects a measured signal with concentration through standards of known composition or concentration. A calibration curve establishes that relationship, and the unknown sample’s signal can then be compared with it to estimate the corresponding amount. This approach complements titration by replacing a stoichiometric endpoint with an instrument-generated measurement relationship.
Analysis can address two related questions by comparing measured properties with known standards and by applying quantitative relationships. The comparison helps indicate what substances are present, while titration or calibration-based measurements determine how much is present. Together, these approaches connect chemical recognition with concentration or composition measurements.
Uncertainty assessment indicates how much confidence should be placed in a reported measurement. Because analysis depends on solution preparation, quantitative measurement, and interpretation of chemical results, recognizing uncertainty helps distinguish a numerical result from an unquestionable value. It is therefore an essential part of evaluating the quality and meaning of the analysis.
A typical workflow begins with preparing or handling the solution, selecting a suitable analytical approach, and making the required quantitative measurements. The results are then compared with known standards or interpreted through stoichiometry, a calibration curve, or both. Finally, the analyst evaluates the calculated composition or concentration together with its measurement uncertainty.
These methods support quality control, environmental monitoring, clinical testing, and chemical research. In each setting, the central value is quantitative information about sample composition or concentration. The same analytical principles can therefore help evaluate products, characterize environmental samples, support testing of clinical materials, or generate measurements needed for research decisions.