Unknown Variables
Unknown Variables - Related Videos
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...
01:21
Testing a Claim about Mean: Unknown Population SD
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2023
A complete procedure of testing a hypothesis about a population mean when the population standard deviation is unknown is explained here. Estimating a population mean requires the samples to be approximately normally distributed. The data should be collected from the randomly selected samples having no sampling bias. There is no specific requirement for sample size. But if the sample size is less than 30, and we don't know the population standard deviation, a different approach is used; instead...
FAQs
An equation connects the unknown quantity to measured values, theoretical relationships, or experimental conditions. The solver substitutes the known information and rearranges the relationship so the required quantity is isolated. This procedure turns a physical description into a numerical result while making clear which observations or assumptions control the prediction.
Conservation laws restrict how physical quantities can change, while boundary conditions specify what happens at particular locations, times, or limits of a system. Together, they provide constraints beyond a single equation and can make a solution physically meaningful. They are especially useful when several possible values satisfy an initial mathematical relationship.
Unit consistency provides a practical test of whether an equation has been applied correctly. The units of the calculated quantity must match the physical quantity being sought, and incompatible units can reveal an incorrect substitution, rearrangement, or model choice. This check does not prove the numerical answer is correct, but it can identify important errors before interpretation.
A model can determine an unknown only when the available equations, known values, conservation laws, boundary conditions, and experimental information provide sufficient constraints. If essential information is missing, the result may remain indeterminate or require additional measurements. The structure of the model therefore affects not only the calculation but also whether a unique physical answer is possible.
Begin by identifying the requested quantity and listing the measured or known values. Represent the unknown with a symbol, select the relevant theoretical relationship, conservation law, or boundary condition, and rearrange the equation before inserting values. Finally, check units and compare the result with the experimental conditions to judge whether the calculation is consistent.
An unmeasured property can be estimated when related quantities are available and a physical relationship connects them. Applying that relationship allows the unknown to be inferred from observations or controlled experimental conditions. Such estimates extend what an experiment can reveal, although their usefulness depends on whether the selected model accurately represents the system being studied.
A calculated unknown can be compared with an observed value or with behavior predicted under different conditions. Agreement supports the model's quantitative description, whereas disagreement may indicate inaccurate measurements, unsuitable assumptions, or an incomplete relationship. This comparison makes solving for an unknown part of model evaluation rather than merely an exercise in algebra.
The approach applies across analyses of motion, forces, energy, and circuits, where some relevant quantities may be measured while others must be inferred. In each case, equations and physical constraints connect the available information to the missing value. This supports quantitative predictions and helps translate observations into a description of how a system behaves.