Friday, May 20, 2022

How Do You Identify An Unknown Substance In Chemistry

Don't Miss

Introduce The Challenge Of Identifying An Unknown Liquid

How to Identify an Unknown Substance (Chemistry)

Show students the four liquids they will be working with: water, salt water, alcohol, and detergent solution. Tell students that since the liquids are different, they should look and act differently when placed on a surface like plastic, paper, or something else. Explain that you will also give them an unknown liquid that is the same as one of the knowns. Their job is to test the known liquids and the unknown on different surfaces to figure out what the unknown liquid is.;

Give each student an Activity Sheet .Students will record their observations and answer questions about the activity on the activity sheet.

Give Each Student An Activity Sheet

Students will record their observations and answer questions about the activity on the activity sheet. The Explain It with Atoms & Molecules and Take It Further sections of the activity sheet will either be completed as a class, in groups, or individually, depending on your instructions. Look at the teacher version of the activity sheet to find the questions and answers.

Discuss Student Observations And The Possible Identity Of The Unknown

Ask students:

Are there any crystals that you could rule out as probably not the unknown?
Based on their observations, students are most likely to eliminate sugar and Epsom salt as the unknown.
Which cup or cups seem to have about the same amount of crystal left undissolved as the unknown?
The unknown, salt, and MSG appear to have similar amounts of crystal that did not dissolve.
What do you think is the identity of the unknown?
Students might conclude that the unknown is salt, but in some cases might think it could also be MSG.
What evidence do you have to support your conclusion?
Students should cite the amount of crystal left behind in each cup as evidence that the unknown is either salt or MSG.
If someone in the class had a very different conclusion and had very different observations, what do you think may have led to these differences?
Students should mention possible errors in weighing the crystals, in measuring the amount of water used, stirring in a different way, or accidentally pouring the crystals into the wrong cups.

Recommended Reading: Exponential Growth And Decay Worksheet Algebra 1

Lab Techniques For Semi

It’s easy to contaminate the sample through poor laboratory technique, so it’s important to adhere to certain rules:

  • Do not use tap water. Rather, use distilled water or deionized water.
  • Glassware must be clean prior to use. It’s not essential that it be dried.
  • Don’t put a reagent dropper tip into the mouth of a test tube. Dispense reagent from above the test tube lip to avoid contamination.
  • Mix solutions by flicking the test tube. Never cover the test tube with a finger and shake the tube. Avoid exposing yourself to the sample.

Contaminants In Process Quality Control

How do you determine if a substance is an ionic compound ...

Unknown substances such as impurities or adulterants can not only affect your product, but may pose potential health risks. Analysis of unknown substances found during the quality control process must be identified and their source located so corrective action can be determined.

How Do We Approach an Unknown Substance

Substances can be differentiated from one another by examining their physical and chemical properties. Our first step is to gather as much information as possible as to the source and history of the substance and the reasons for the analysis. This gives us a basis for not only determining what it might be, but also what it might not be. We then consider the physical properties which do not change during the analysis and then the chemical properties which react when analyzed. Whether you need to identify an unknown substance, provide confirmation of a substance, determine source, compare properties or uncover a counterfeit product, our experts have the combination of in-depth knowledge and preferred instrumentation to provide the answers you need. Some methods and technologies we use include:

  • Gas Chromatography
  • Gas Chromatography Mass Spectroscopy
  • Ion Chromatography
  • High Performance Liquid Chromatography
  • Dispersive Raman Spectroscopy
  • Fourier Transfer Infrared Spectroscopy
  • Crystallography: X-Ray Fluorescence and X-Ray Diffraction
  • Thermogravimetric Analysis / Differential Scanning Calorimetry

Recommended Reading: Algebra 1 Eoc Answers 2015

Unknown Substances In The Workplace

An unknown substances could be a container with a label that has fallen off or faded so much you cant read it. Alternately it could be a liquid in a plastic cup with a strange smell. It could be a by-product from a chemical reaction gone wrong. If you do encounter an unknown substance in the workplace youll need to take steps to either identify and correctly label the substance, or dispose of it safely.

Take the following steps:

  • Attach a label to the substance with the following statement: Caution – Do Not Use – Unknown Substance.
  • Take reasonable steps to identify the chemical. This could be asking staff about the origin of the container, or calling a chemical supplier
  • Isolate the chemical from work areas and most especially flammable materials and Dangerous Goods.
  • Consult your relevant waste management authority for assistance with safe disposal.
  • Remember: If you dont know what a substance definitely is, its unlikely youll be able to dispose of it safely.

    Have Students Dissolve The Four Known Crystals And The Unknown In Room

    The amount of water used in the procedure is specific and should be used because it gives clear results. Swirling the crystals in water is a good way of mixing them to help them dissolve. Lead the class so that all groups pour their crystal samples into the water at the same time. Also tell students when to swirl the water and crystals and when to stop and observe. There will be three 20-second intervals.

    Don’t Miss: What Is Figure Ground Perception Psychology

    Uses For Unknown Substance Testing

    Unknown substance testing is often used if a person believes they have been drugged and would like to identify the suspected drug. We can use either a urine or hair specimen.

    Parents will also request unknown substance testing if they find a strange substance in their child’s room and want it tested. Call us and we will provide instructions to ship the unknown substance via FedEx to our laboratory for testing. We make the process easy so you can get the results you’re looking for.

    Additionally, people will sometimes find unknown substances on their spouse’s clothing and want it tested.

    Introduce The Activity And Ask Students How They Might Test And Compare The Four Different Powders With Four Different Test Solutions

    Using Chemical Change to Identify an Unknown

    Tell students that in this activity they will test four different similar-looking powders with four different test solutions. The four powders are baking soda, baking powder, cream of tartar, and cornstarch. The four test solutions are water, vinegar, iodine solution, and universal indicator. Explain that each powder will react in a certain way with each solution used to test it. Each powder and solution pair is one set of reactants. Let students know that in some cases, no chemical reaction will occur.

    Students will need to observe and record the reactions the liquids have with each powder.

    Have students look at the testing chart. Point out that the names of the four test solutions are on the left and the names of the different powders are on the top.

    There is also one column for an unknown powder. Explain that after testing all four known powders and recording their observations, you will give students an unknown powder to identify.

    Recommended Reading: Eoc Fsa Warm Ups Algebra 1 Answers

    Determination Of Equivalent Weight

    Molecular Weight Determination

    Generally, any acid can be titrated using standard solutions of base . The neutralization equivalent obtained is usually a simple fraction of the molecular weight . In the titration of an acid with standard base, the endpoint is reached when all the acid is neutralized and a drop of excess base is added. If phenolphthalein is used as the indicator, it will turn red at this instant. For a dicarboxylic acid such as malonic acid, the endpoint is reached when the last of the acid is converted to the carboxylate anion. The neutralization equivalent will be one-half its molecular weight.

    CH2 2 + 2 NaOH —– CH2 2 + 2 H2O

    Equivalent weights must be done in duplicate and the values obtained should agree within a few percent. If not, do a third determination.

    Procedure for acids. Into a 125 ml Erlenmeyer flask place approx. 150 mg* of the unknown, accurately weighed to the nearest 1 mg or 0.1 mg for at least three place accuracy. Add approx. 5-10 ml of 95% ethanol to dissolve the unknown and add an equal amount of water. Add a drop or two of phenolphthalein solution, a magnetic stirring bar, and titrate with standardized aqueous base to the first permanent pink color that lasts about 60 seconds.

    The equivalent weight can be calculated as follows:

    V x M = wt /equivalent weight ;

    * larger quantities will be required if 150 mg is less than 1.0 meq since at least 10.0 mL of 0.100 N of solution is required for three place accuracy.

    Relate Student Observations In The Demonstration To The Five Crystals They Will Dissolve In Water

    Tell students to imagine that the large cereal balls represent large crystals and the crushed cereal represents small crystals. Explain that the size and shape of the crystals may be different, but the balance shows that their mass is the same. Remind students that mass is a measure of the amount of matter. Because the large and small crystals have the same mass, both cups contain the same amount of matter. Conclude that, in order to measure equal amounts, it is better to measure the mass of substances than the volume.

    Ask students:

    In the solubility test you will do, you will need to measure equal amounts of the five crystals. How will you measure equal amounts?
    After this demonstration, students should realize that measuring mass for a solubility test is better than measuring by volume.

    Based on what students observed when they looked closely at the different crystals along with evidence from the demonstration, they should realize that different crystals have a slightly different size or shape. This will cause them to pack differently in the spoon so that more granules of one will be in the spoon than the other.

    Don’t Miss: What Is The Molecular Geometry Of Ccl4

    Have Students Conduct Another Test To Confirm The Identity Of The Unknown

    Explain to students that they might be able to get more clues about the identity of the unknown if they allow the solutions of the dissolved crystals to recrystallize. Allowing the substances to recrystallize from their solutions might show similarities and differences that were not as easily seen in the original crystals.

    Materials notes: The recrystallization test should be done immediately after the solubility test with the solutions made during the solubility test. Students will reuse the large clear plastic cups and solutions from the dissolving part of the activity, according to the procedure.

    Incorrect Or Damaged Labels On Hazardous Chemicals

    Properties are used to identify substances.

    You should ensure that all commercially purchased chemicals are received with proper labels, and train your staff not to accept deliveries of chemicals if the labels are obscured or damaged in any way. When purchasing from different suppliers or introducing new chemicals to the workplace youll need to be especially careful.

    Ask yourself as you inspect the label on an imported chemical:

    • Is the label in English?
    • Does it follow GHS protocols?
    • Is the text clear and easy to read

    Over time chemical labels can become damaged or obscured. Train your staff to flag these containers for corrective action and re-labeling. If you dont have approved job procedures for label printing you should contact the supplier to assist you with a replacement label.

    If you find that any container of a hazardous chemical with an incorrect label, attach a product identifier and store it in isolation until it can be correctly labeled.

    Remember: A label for a hazardous workplace chemical is only acceptable if it has been prepared in accordance with the model WHS Regulations.

    Recommended Reading: What Is The Molecular Geometry Of Ccl4

    Identifying Anions And Cations

    • Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
    • B.A., Physics and Mathematics, Hastings College

    Qualitative analysis is used to identify and separate;cations and anions;in a sample substance. Unlike quantitative analysis, which seeks to determine the quantity or amount of sample, qualitative analysis is a descriptive form of analysis. In an educational setting, the concentrations of the ions to be identified are approximately 0.01 M in an aqueous solution. The “semimicro” level of qualitative analysis employs methods used to detect 1-2 mg of an ion in 5 mL of solution.

    While there are qualitative analysis methods used to identify covalent molecules, most covalent compounds can be identified and distinguished from each other using physical properties, such as;refractive index and melting point.

    Responding To Incorrect Or Unlabeled Chemicals

    Walter Ingles

    Business owners and operators have a legal obligation to ensure that their hazardous chemicals held at the workplace are labeled correctly, and in accordance with the model WHS Regulations. This blog explains what to do if you encounter a chemical container that has:

    • A substance you dont recognise.
    • No label at all.
    • A damaged or faded label.
    • Been imported from overseas and the label doesnt follow Australian protocols.

    REMEMBER: In Australia, chemical labels must follow the GHS and clearly display: a product identifier; hazard class pictogram and hazard statement, signal word, relevant precautionary statements, first aid and emergency information.

    Recommended Reading: What Is Mean Median Mode And Range In Math

    Materials For Each Group

  • What is the identity of the unknown?
    Baking powder is the unknown.
    Which observations led you to your conclusion?
    The unknown reacted with each test solution the same way baking powder did.

    Explain that each substance is made up of certain molecules which interact with the molecules in each test liquid in a characteristic way. Some of these interactions result in a chemical reaction and others do not. However, each observation students made is based on the way the molecules of each powder interact with the molecules of each test solution.

  • Extend

    Have Students Test The Water Salt Water And The Unknown On Construction Paper

    Using Dissolving to Identify an Unknown
  • Use a pencil to label the construction paper W and SW for water and salt water and U for the unknown.
  • Use a dropper to get a small amount of each liquid.
  • At the same time, gently squeeze 1 drop of each liquid onto its labeled area of the construction paper.;
  • Expected results

    The water soaked into the construction paper more than the salt water, which stayed on top of the paper in a bead longer than the water. The unknown soaked in similarly to the water.

    Ask students:

    • What did you notice?The water absorbed into the constructionpaper more than the salt water did. The unknown absorbed into the construction paper like the water.
    • What is the identity of the unknown?Water;

    You May Like: Law Of Figure And Ground

    How Do Chemists Determine The Composition Of An Unknown Substance

    Chemists : Suppose it was necessary to determine what a particular, unidentified thing was made of. How is this generally accomplished? Im writing a story of which this is a peripheral element, but Id rather not just have someone say, We analyzed it, and its ______, as that seems to be a sub-comic book turn of phrase.

    Please assume in this case that whatever the substance in question is, it is rather hard to identify, forcing the chemist in question to exhaust many resources in the process.

    There are several tools which are used to analyze samples of unknown substances, such as mass spectrometers, gas chromatographs, absorption photometers and others. If you do searches on these terms, youll find a wealth of information to get you started.

    If I had that sort of lab, I guess Id start with determining the class of compound; in fairly short order, one can distinguish an inorganic compound from an organic compound. Identifying inorganic compounds is done with a series of simple wet chemistry techniques. For organic compounds, Id start with GC-MS .

    The chosen detector in this case is a mass spectrometer; these instruments use a variety of techniques to ionize the incoming molecules. The MS then separates the ions according to the ratio of mass to charge. For organic molecules, this is usually close to the moelcular weight . Destructive MS can resolve the elemental composition of the material.

    Assume it is not pure, then as nametag said, chromatography would be good .

    How Can Density Be Used To Identify Substances

    You can identify an unknown substance by measuring its density and comparing your result to a list of known densities.

    Density = mass/volume. Assume that you have to identify an unknown metal. You can determine the mass of the metal on a scale. You can determine the volume by dropping the object into a graduated cylinder containing a known volume of water and measuring the new volume. You divide the mass by the volume and compare the density to a list of known densities.

    EXAMPLE

    A metal bolt with a mass of 99.7 g is dropped into a graduated cylinder containing 50.0 cm³ of water. The new volume reads72.1 cm³. Identify the metal.

    Solution

    V = 72.1 cm³ – 50.0 cm³ = 22.1 cm³

    D = #m/V = /# = 4.51 g/cm³

    Now you compare your density with a list obtained from your instructor or from an on-line source such as

    Don’t Miss: Geometry Segment Addition Postulate Worksheet

    More articles

    Popular Articles