d. the Kc for the equilibrium will be too high. With the absorbance value concentration of FeSCNZ complex can be determined (Beer&x27;s law).A &. . Concentration = Absorbance / Slope) where the slope, m, is equal to l. There are quite a few ways that you can Convert a Scanned Pdf File To Excel, a PDF to excel. tell Excel not to change certain parts of a cell address. From the slope of the best-fit line together with the absorbance, you can now calculate the concentration for that solution (i.e. Taking this into account, you could even estimate the ratio of \ce H O A c and \ce N a O A c used. For example, ~1.0Au is equal to 10% transmittance, ~2.0Au is equal to 1% transmittance, and so on in a logarithmic trend. The value of the equilibrium constant (K eq. Step 2 Right-click on Chrome application, select Send to Desktop to create a new shortcut Separate instances of the app do not share data between them Since a day or two my Zendesk keeps crashing not responding every few minutes Tutorial mengatasi google chrome not responding, vid1 It is for instance not possible to send. moncon is paywall for journalists who wants to sell their trusted content using AI certificates that demonstrate the veracity. To determine the equilibrium constant for the reaction of iron (III) and thiocyanate to form the. DATA PRIVACY: All user data input into the apps are processed locally within All Pre-Owned Equipment. These results were plotted in Figure 1. The new concentration has been reduced by one half as the volume was doubled. She has over 10 years of biology research experience in academia. What is the concentration? relationship between the concentration of the compound being studied and its absorbance. Use your Vial 7 absorbance and the known FeSCN2 concentration from Trial 7 to construct a calibration curve. line, we can actually calculate the values of that line for each solution Plug in the y value for absorbance to find the x value for concentration. Step 2 Plug values into the Beer-Lambert formula for each known variable value that is given. Ads help to keep molbiotools up, running and evolving. ), albeit the latter is used either without any 22. Absorbance is directly proportional to concentration and length: A = cl. A The invariant point at which the absorbance will be constant even if the reactant concentration is. cell. A Absorbance 0.60 Concentration 0.002 M Path length 10 mm 1 mm 0.1 cm 10 mm 1 cm Now,. 6 In our example, C (10 g) (1,210 g) 0.00826. Welcome to Sharing Culture! The equilibrium of a reaction is the point at which the conversion of reactants into products equals the conversion of products back into. calculations: The following problem was given in another nM To do this, multiply the number by 106. Equilibrium. Calculate the moles of sodium ions and the concentration of sodium ions in the final solution. Transmission is the process of transmitting or passing light. Because the system will be at equilibrium when we measure the absorbance, the concentration we determine will be the equilibrium concentration and can be substituted into the K expression for the chemical system. Explanation: Transmittance is the ratio of the radiant power transmitted by a sample to the radiant power incident on the sample. Seal the tube and invert repeatedly to mix. Use the spectrophotometer to measure the absorbance of a solution. The transmittance, or intensity of transmitted light, is the fraction of original light that passes through. Prepare 40 mL of 5.0 g/mL Methylene Blue Working Solution, Prepare 80% Methylene Blue Working Solution, Prepare 60% Methylene Blue Working Solution, Prepare 40% Methylene Blue Working Solution, Prepare 20% Methylene Blue Working Solution, Complete Data Table 1. based on your results. v/v (see above), present in a certain volume of a solution. We love technology, the challenges it often poses, both technically and philosophically. Next, calculate the equilibrium FeSCN2 for Part II from, concentration is the molar absorption coefficient. (the "y-hat" value) using another formula. Have the computer put the best straight line and the equation of the line on the graph. using flame atomic absorption spectroscopy. Beer's Law Type in [K2CrO4] in the A1 cell (x-axis) and Absorbance in the B1 cell (y-axis). How does Beer's Law convert absorbance to concentration? Police Officer With Engineering Degree, 2019 jon stetson america's master mentalist, loose fit heavyweight long-sleeve pocket henley t-shirt, Beer's Law Tutorial - University of California, Los Angeles. Place 1 mL of DI water into a clean cuvette. However, if we knew K and one of the equilibrium concentrations, we could solve for the missing concentration. Chemical Equilibrium Lab 4. Absorbance of two different compounds p-nitrophenol and its anion. Find a ligand whose absorbance or fluorescence spectra changes when bound to M. Alternatively, monitor a group on M whose absorbance or fluorescence spectra changes when bound to L. ITC - Isothermal Titration Calorimetry - Measure small, incremental heats (q) of reaction during binding titration. Figure 1 shows the absorbance increasing as the wavelength is increased until approximately 650 nm is reached; from this point, the absorbance pattern decreases . Absorbance can be calculated from percent transmittance (%T) using this formula: Absorbance = 2 - log (%T) Transmittance (T) is the fraction of incident light which is transmitted. 1 Answer. . This is the . In Excel, right click on the data series on the chart and select Add Trendline. From the A demonstration will be shown in class for how to use and calibrate the pH meter. 1 Answer. As a solution is diluted, the absorbance, coefficient is used. Describe how you would prepare 100.0 mL of 10X sodium acetate solution. X-block cells. K eq, which depends only upon temperature, it is necessary to determine the molar concentration of each of the three species in solution at equilibrium. Pre-Owned. Thus the absorbance (A) of the material is related to the initial intensity of the light, I0, and the transmitted intensity of the light (what came through on the other end), I. By comparing the absorbance of each equilibrium system, A eq, to the absorbance of a standard solution, A std, you can determine FeSCN 2 eq. Users may opt out of personalized advertising by visiting Ads Settings. It is the extent to which a body or medium passes a light. So, you could calculate the concentration c by measuring the absorbance A and dividing it by the product of the path length L and absorptivity alpha. Our experts have done a research to get accurate and detailed answers for you. To convert a value from percent transmittance (%T) to absorbance, use the following equation: Absorbance = 2 - log (%T) Example: convert 56%T to absorbance: 2 - log Work Space (Show sample calculation for one of the test tubes). Example 1 Given this equation H 2 I 2. After that, we will use spectrometer at 450nm to find the absorbance, from which we will calculate the Kc value. Pipette 5.0 mL of DI water into the tube for a total of 10 mL of solution. M A solvent is a substance that dissolves a solute, resulting in a solution. Step 2. Spreadsheet Activity #8: Linear prepared. of analyte in the form of a confidence interval. [K2CrO4], M Absorbance, A 0.000 0.000 0.100 0.145 0.200 0.255 0.300 0.415 0.400 0.525 A graph of Absorbance (y-axis) versus concentration (x-axis) is then plotted and its slope, y/x, is evaluated. Finding the Rate Constant: Type what is seen in Figure 1a in the appropriate cells. See Using Graphical Analysis 3.1.1 or Graphing in Excel Solve for Concentration: Entering and Formatting the Data in Excel. Step 2 Right-click on Chrome application, select Send to Desktop to create a new shortcut Separate instances of the app do not share data between them Since a day or two my Zendesk keeps crashing not responding every few minutes Tutorial mengatasi google chrome not responding, vid1 It is for instance not possible to send. The observed red-orange color of an aqueous FeNCS2 solution results from the absorption of photons with the energy of the complementary color, bluegreen. Figure 1. KUBOTA OIL , 5 GAL HYD 46 HD (SINGLE PA. image to download Excel file). In Part IIE, we calculated that the equilibrium concentration of Fe 3 was 9.30 X 10-4 M. In Part IIH1 above, we calculated that the equilibrium concentration of SCN-was 4.22 X 10-4 M. This will give you an equation for calculating the concentration (x) from a given absorbance (y) in the range of the standard curve. Turn the wavelength knob of the colorimeter to the 0 T position. The reason is that copying the equation as it was causes the cells Pipette 2.0 mL of 5.0 g/mL methylene blue working solution into a 15 mL conical tube. Example: Suppose the molar absorptivity of Na Cl is 193L mol -1 cm -1 and the length of its light path is 5 cm, calculate the concentration if the absorbance is 200. Absorbance is directly proportional to concentration and length: A = cl. You effectively s, Standard: $4.99 a month (Beginner plan + Standard website builder), Premium: $7.48 a month (Beginner plan + Premium website builder), Connect Domain: $5 a month (not available in the US, unfortunately), Shared Starter: $6.99 a month (1 website), Shared Unlimited: $12.99 a month (unlimited websites). For that, the following formulas will be used: Multiply the initial volume by the ratio of initial and final concentrations diminished by 1: Dilution factor is the ratio of initial and final concentrations. 'B12' in the equation represents y (the absorbance of the unknown). to obtain concentrations from instrumental signals when determining unknown solutions. She currently teaches classes in biochemistry, biology, biophysics, astrobiology, as well as high school AP Biology and Chemistry test prep. In your description, include a calculation and step by step procedures including glassware. Apr 20, 2017. This plot allows the rapid determination of solution concentration from solution absorbance. 5. a, can be determined (Beer&x27;s law).A &. Label the bottle with the solution with the following information: The name of the solution (include concentrations), Write a fraction for the concentration \[5\:\%\: ( \frac{w}{v} )\: =\: \dfrac{5\: g\: sucrose}{100\: mL\: solution} \nonumber\], Set up a proportion \[\dfrac{5\: g\: sucrose}{100\: mL\: solution} \:=\: \dfrac{?\: g\: sucrose}{500\: mL\: solution} \nonumber\], Solve for g sucrose \[\dfrac{5\: g\: sucrose}{100\: mL\: solution} \: \times \: 500 \: mL \: solution \: = \: 25 \: g \: sucrose \nonumber\]. (relative cell addresses). c is the concentration of the solution. concentration Absorbance at 280, Equilibrium. CAS GIFs of my Mass Effect conversions. Chapter 4 Lesson 5. When multiplying c, l and , all the units cancel. This equation provides all the information you will need to calculate the equilibrium concentrations of, Knowing the initial concentration values and equilibrium constant we were able to calculate the equilibrium concentrations for N 2, O 2 and NO. The concentration factor is the initial volume divided by the final solution volume. Learn. This experiment outlines the techniques necessary to determine the equilibrium constant for the formation of an iron (III) thiocyanate complex ion (FeSCN 2) from Fe 3 and SCN - . This process is much faster than re-calculating the absorbance for every Molar concentration (also called molarity) is the number of molecules of a substance, expressed in mole units loaded from files, the files should be plain text files (no formatting) containing one item per each line or The linear relationship between absorbance and concentration displays that absorbance depends on the concentration. lists. Service. Find the change in concentration of FeSCN2. Determine the equilibrium Fe3 and SCN- from the ICE table. UnderstandingEvil.com describes how to tell if you're "under assault" by reptilians; "Protector of Mankind" writes at While Icke doesn't describe how to spot someone who has been manipulated bymerged with a reptilian probably to protect his lucrative speaking circuit revenuesothers have. Secure the cap on the tube and invert repeatedly to thoroughly mix the solution. FeSCN2 absorbance - 0.0018 9.9EE3 . How would you calculate the concentration of dye in the solution? One method of determining the concentration of FeSCN2 is by absorbance measured at 468 nm. reactants are known and the product concentration is related to its absorbance, the method of spectophotometry can be used to determine the equilibrium constant for this reaction. g/ml Concentration (c) has a concentration of M or moles per liter (mol L-1). Measure the pH of the test buffer solution using a calibrated pH meter. slope and intercept values, calculate the concentration of the three unknown FeSCN 2 test tube 1 Absorbance test tube 1 FeSCN 2 standard Absorbance standard. If H is negative, reaction is exothermic, then. Pipette exactly 5.0 mL of 1M acetic acid solution into your conical tube (or 25 mL glass test tube). Calculate the amount of sodium acetate needed to make 30 mL of 13.6% sodium acetate solution. nM Concentration (c) has a concentration of M or moles per liter (mol L-1). Select the data values with your mouse. Plot the best-fit line (trendline) and give the equation and R2. One point is earned for the correct substitutions and the calculated value. Explain in words and clearly show (either by drawing on the plot or calculating from the slope and intercept) how these values are obtained. Concentration of known solutions. The author of the software bears no responsibility for any loss or damage that may arise from its use This relationship is described by the Beer-Lambert law which states A ElC where A is absorbance, E is the molar extinction coefficient, l is the path length is cm, and C is molar concentration. In the following boxes, always fill all but one field and click Just in case you are not sure, the subscripted zero, as in H 2 o, means the initial concentration. 0 0, Absorbance is directly proportional to concentration and length. Note In reality, molar absorptivity. Beer&x27;s law expresses the relationship between light intensity and the concentration of a substance through a formula. This value is far beyond the range of spectrophotometers, but still can be used to determine the concentration of dilute solutions. The percent concentration of a solution can be expressed as mass per mass (m/m or w/w), mass per volume (w/v), Manufacturer part number 70000-15605 98.68. curve to be constructed between absorbance and known concentrations of the product. Absorbance = c x L x = > Concentration = / Lambert - Beer Law describes dependence of absorbance on concentration of sample, optical path length as well as dependence on sample - specific extinction coefficient, which pertains to specific substance at specific wavelength. First type in the formula in the proper cell: Next you can copy this formula so that the Plug the known values (A, and l) into Beer's Law and then solve for concentration: Talking about such a tiny molarity is a bit cumbersome. From the slope of the best-fit line together with the absorbance, you can now calculate the concentration for that solution (i.e. AI, decentralization, privacyall of these pose paradigm shifts, we want to be there to help define the path. Concentration (M) Absorbance. To convert units, use these relationships Mg proteinml protein divided by 10 molarity divided by protein molecular weight. Step 1 Read through the given information and record all known values. The solution for x (Concentration) is then displayed in cell 'C12'. You will be applying Beer&x27;s law to calculate the concentration. It is also important to be able to calculate concentration in order to determine how much of a reactant has been used up in a reaction or how much product has been made. posed: what is the copper concentration in the sample solution? For your sample, absorption values can, coefficient for the sample at this wavelength, consistent with the stoichiometry of the reaction. 3. Place your first sample into spec and record the absorbance reading. Understand the Beer-Lambert law for absorbance, A x l x c. The standard equation for absorbance is A x l x c, where A is the amount of light absorbed by the sample for a given wavelength, is the molar absorptivity, l is the distance that the light travels through the solution, and c is the concentration of the absorbing species per unit volume.. Give the room temperature equilibrium constants (determined by the two methods), the higher temperature equilibrium constant and the concentration of the unknown Fe3 solution. Quantitatively it can be characterized by the equilibrium constant, called dissociation constant K a, which for dilute solutions of the weak acid is expressed by the formula. This calculation is most readily carried out by completing the following tables as. How many grams of dry NaCl should be used to make 100 mL of 15% (W/V) NaCl solution? Write the procedures you used to make the solutions in your lab notebook. where is the molar absorptivity, b is the path length, and c is the concentration in M. and b are CONSTANTS for the same substance . moldm3. Work Space (Show sample calculation for one of the test tubes). Using the remainder of your 5.0 g/mL methylene blue working solution from part 2, perform a set of 1:2 serial dilutions to make the following concentrations of the solution (50.0 %, 25.0 %, 12.5 %, 6.25 %, 3.125 %, and 1.5625 %). Transfer all of the solution back into your 50 mL conical tube and secure the cap. The data is now good to create a standard curve in Excel. In addition, you should construct your own Excel plot in which you plot absorbance vs concentration. Understand the Beer-Lambert law for absorbance, A x l x c. The standard equation for absorbance is A x l x c, where A is the amount of light absorbed by the sample for a given wavelength, is the molar absorptivity, l is the distance that the light travels through the solution, and c is the concentration of the absorbing species per unit volume.. So the equation is where A is absorbance, is the absorbtivity constant, b is the path length of light, and c is the concentration of the solution. Stock 1% (w/v) methylene blue solution (500 microliter (L) aliquots in 1.5 mL microcentrifuge tubes), 15 mL plastic conical tubes with screw-top caps, 50 mL plastic conical tubes with screw-top caps. 4. Two useful Excel functions are slope() and intercept(), I am trying convert an absorbance level to the concentration of zinc in ppm. Whatever light does not pass through to the other side is absorbed. concentration increases, the absorbance increases by a factor.When checked using excel (linear regression bestfit line), the high r^2 value (0.99743) indicates that the data is almost the perfect For example to convert 56% T to absorbance calculate 2 - log(56) = 0.252 absorbance units. In the system we evaluated, at equilibrium we would expect to find that O 2 eq N 2 eq 0.086 M and NO eq 0.028 M. Note that we could have solved for the amount of NO produced rather than for. The absorbance (a measure of the amount of. Beer&x27;s Law is considered to be most reliable for absorbance values between 0.1 and 1. In this equation, e is the molar extinction coefficient. pg/ml The absorbance of a protein is a physical. The equilibrium concentration for the FeNSC2 would be too high because the higher the absorbance the higher equilibrium concentration value. In your notebook, draw a diagram showing the serial dilutions for the 6 methylene blue solutions you are preparing. The Equilibrium Concentration of the product will be measured using Absorbance Spectroscopy. Fill a second cuvette with the same amount of distilled water to be used as a blank. has units of L mol - 1 cm - 1. Our team has collected thousands of questions that people keep asking in forums, blogs and in Google questions. 25.1 Properties of Stars.pdf, HSP3U- U3A1- introduction to Psychology Kassidyhaggar.docx, pts Question 6 12121 1119 PM Stacy Williamss Quiz History Quiz 11 Week 1214 wk, Keywords models ICT use agriculture developing countries 1 Introduction A number, Poetic devices in Thomas Wyatts poem The long love, that in my thought doth harbor.docx, When you create an item on the heap by using new you always delete that item and, 9 According to Japanese folklore what is the favorite food of the Kappa a Soba b, The Lottery - Predicting and Inferencing.docx, including if necessary purchasing them for cash at fair market value Human, Final test_ Ingls IV-VIRT-2022-3-SEP-[3-B].pdf. It is common for solutions that are used often in a lab (or which are time consuming to prepare) to be intentionally prepared to be many times more concentrated than needed. The absolute rate of substrate consumption by microorganisms depends on its concentration in environment and is measured from the rate of s decline over time (ds dt), while the specific rate of substrate consumption, q is calculated by normalizing the absolute rate to the instant cell mass concentration, x (3) q - 1 x d s d t Q s K. Its concentration could then be found by a spectrophotometer set at a wavelength of 447 m. Through the calculated concentrations and the absorbance found through the spectrophotometers, the calibration curve could be created with this data. Beer-Lambert Law The Beer-Lambert law describes the relation of absorbance, path length and concentration of an absorbing substance: A=c*d* Changed to c: c=A/ (d*) To this end, scientists use the Beer-Lambert Law (which can also be called "Beer's Law") in order to calculate concentration from absorbance. image to download Excel file). Position the sensor in the light path after the sample. SCN)2, you do know the absorbance at 455 nm from Fe(SCN)2 and the constant to relate absorbance to concentration. As a solution is diluted, the absorbance of the solution is decreased. Calculate K. To nd the initial concentration of Fe3, use the dilution equation (M 1V 1)V 2 M 2, where V 2 10 mL. Example The absorbance of a sample with a known concentration of 1.00 x 10-3 M in a 1.00 cm cuvette is 0.395. When multiplying c, l and , all the units cancel. In case of infrared spectra you can convert transmittance by 2 - log 10 (%T) to "apparent absorbance". This law relates the attenuation of light as it traverses a material to the physical properties of that material. The absorbance of a protein is a physical. known molecular weight. A chart will appear containing the data points from the two columns. Background Information. 2.) Step 3: Set Page Options and Output Path Set the page size and the orientation in the Page Size and Page Orientation options, and set the output path by clicking on the "Browse" button. The standard curve will be used in part 3 of the lab to determine the concentrations of unknown solutions of methylene blue. b. c, The equilibrium concentration of FeSCN 2 will be. We want to change the formula w/v comma-separated items. Advanced Search Options. 785-456 . (Keep this quantity in mind; practically speaking, it's what you're the most interested in!). The methods described here all relate absorption at a certain wavelength to concentration of protein. what Excel calls absolute cell addresses) rather than variable 2 K. eq Fe. Calculate the final enzyme concentration in each test tube in g/mL. Asking for help, clarification, or responding to other answers. Repeat with each sample and record into lab notebook. These quantities can be related by the following equation. Once you have that you can compare the absorbance value of an unknown sample to figure out its concentration. polished ak bolt; car radiator dimensions. Protecting the excel sheet so you can validate it in the future. Example Calculate the equilibrium constant if the concentrations of Hydrogen gas, carbon (i) oxide, water and carbon (iv) oxide are is 0.040 M, 0.005 M, 0.006 M, 0.080 respectively in the following equation. Because all of the product was formed from the 11 reaction of Fe 3 and SCN-, the equilibrium concentration of Fe(SCN) 2 corresponds to the decrease in concentration of the reactants. Cut the arbor, leaving about &194;&188; of arbor sticking out. Heater Current Calculator, nM You can set this up as an equation and solve for the unknown "x" 12 g iron 100 g sample x g iron 250 g sample. Scientists will often convert this to micromolar so that it is easier to talk about. You will determine the. A transmittance to absorbance table enables fast conversion from transmittance values to absorbance in the lab or in the field. (MW or M.W., sometimes also called formula weight - FW or F.W. 11. Once the equilibrium concentration of FeSCN2 has been determined, the equilibrium . Convert spectrophotometer absorbance reading to test result (ppm) for all CHEMetrics instrumental test kits. The concept of dilution relates molar concentration and volume. that is linearly proportional to the analyte concentration. g/l (or press Ctrl-C): After copying, you will see a "marquee" surrounding the source Thus, standard solutions that range in concentration from, for example, 0.010 to 0.100 moles per liter will exhibit linearity. The absorbance measurements of the standard solutions are used to determine the concentration of iron in the pill solution, which is used to determine the amount of iron present in the original pill. From the balanced reaction, if 0.0000195 M is gained on the product side, it must have been lost from the reactants. If you were accurate in all of your work, the test buffer should have a pH of 4.75 (+/- 0.06). Spectrophotometry measures how much radiant energy a substance absorbs at varying wavelengths of light. Constants and degree of dissociation The expression for the equilibrium constant has the form HA H A K (1) where HA is the equilibrium concentration of the acid, A- its conjugate base respectively and H the concentration of hydrogen ions in. An unknown amount of HI was placed in a 1 dm3 container. An useful tool in solving equilibrium problems is an ICE chart. Swarovski Rose Gold Tennis Necklace, The light beam has a fixed diameter, so adjusting the length of the sample interface determines how much of the sample is measured. Sedimentation equilibrium (SE) is a thermodynamic method where equilibrium concentration gradients at lower centrifugal fields are analyzed to define molecule. Have the computer put the best straight, with time of collection. The Equilibrium Concentration of the product will be measured using Absorbance Spectroscopy. In this type of problem, there will be one species which we will know the concentration of initially and at equilibrium. This relationship is described by the Beer-Lambert law which states A ElC where A is absorbance, E is the molar extinction coefficient, l is the path length is cm, and C is molar concentration. initial amount of product (the amount before the reaction begins) zero equilibrium concentration of product (FeSCN2 eq) determined spectroscopically FeSCN2 at equilibrium is determined using Beer&x27;s Law; x is the amount of. You can directly copy - paste data from Microsoft Excel or other spreadsheet programs. For example, if you take 1 part of a sample and add 9 parts of water (solvent), then you have made a 1:10 dilution; this has a concentration of 1/10th (0.1) of the original and a dilution factor of 10. See Resources for a tutorial on graphing in Excel. Which comes first prologue or introduction? CO H HO CO . in the graph are A. x . You place 1 mL of the solution in a cuvette with a width of 1 cm. Absorption is the negative logarithm of transmittance. So you put the known DNA concentration into A3, and B3 will calculate the expected absorbance for that concentration. Finding initial concentration by using Kc and equilibrium concentration At a certain temp the Kc for the Equillibrium reaction H 2 I 2 2H I is 51,50. FeSCN . After obtain q, it is necessary make a graph of q versus Ce and interprete the expermental data with langmuir or freundlich model to obtain the isothermss. For that, the following formulas will be used: For w/v percentage, to find the molar concentration, multiply the percent concentration value by 10 to obtain referred to as a working or final concentration, for actual use. Calculate the molar extinction coefficient for the sample at this wavelength. Calculate a volume adjustment to reach a desired final concentration. 2023 Leaf Group Ltd. / Leaf Group Media, All Rights Reserved. The equilibrium constant, K eq, is defined by the equation shown below. On the Insert tab, click on the Scatter icon and select Scatter with Straight Lines and Markers from its drop-down menu to generate the standard curve. Absorbance (A) = C x L x => Concentration (C) = A/(L x ). Manufacturer part number 70000-15605 98.68. Evaluate the quality of the standard curve above by using the R2 value. Open Excel and begin by formatting the spreadsheet cells so the appropriate number of decimal places are displayed (see Figure 1a). 4. of how strongly a chemical species attenuates light at a given wavelength. pg/ml The best way to explain is by example.
Is Police Officers Support Association Legitimate,
Articles H
how to convert absorbance to concentration in excel