Iodine reacts directly, fast and quantitively with many organic and inorganic substances. Starch solution is used as indicator. endobj 3 0 obj Redox titration using sodium thiosulphate is also known as iodometric titration. Potassium persulphate is used to oxidize iodide ions to iodine, in the presence of starch and a small amount of thiosulphate ions. (L.C), What sequence of colours was observed in the conical flask from the start of the titration until the end point was reached? The end point of the titration can therefore be difficult to see. I. In part B of standardization of Iodine solution titration was used of aliquots with sodium thiosulfate solution. The concentration can be determined by treating the peroxide solution with potassium iodide and titrating the liberated iodine with standard sodium thiosulfate. Iodine solution is also known as Povidone and is used tokill bacteria and treat infections and mild cuts. What is the limiting reactant in this reaction? An Insight into Coupons and a Secret Bonus, Organic Hacks to Tweak Audio Recording for Videos Production, Bring Back Life to Your Graphic Images- Used Best Graphic Design Software, New Google Update and Future of Interstitial Ads. This absorption will cause the solution to change its colour from deep blue to light yellow when titrated with standardised thiosulfate solution . Starch as an indicator Starch is often used in chemistry as an indicator for redox titrations where triiodide is present. Starch forms a very dark blue-black complex with triiodide. As I remember this resulted in a colourchange. A known amount of thiosulfate ions will be added to the reaction vessel which will in turn consume iodine as it is produced. However, you may visit "Cookie Settings" to provide a controlled consent. One question for clarification: You think the Iodine interacted with the sodium thiosulphate, forming some $\ce{I^-}$ which then lead to the reaction $\ce{I^-}+\ce{I_2}+\textrm{starch}\leftrightarrow\textrm{dark blue starch}$? Iodide ions reduce iodate ions producing iodine in an amount equivalent to the iodate. But it only forms in the presence of $\ce{I^-}$. This was titrated with 0.05 mol dm-3 sodium thiosulfate solution giving an average titre of 25.20 cm3. What colour did the solution turn after the starch indicator was added? When it reaches a pale yellow colour, a few drops of a freshly prepared starch solution are added. How to Market Your Business with Webinars? How to properly analyze a non-inferiority study. This week, the sample must be prepared before it can be titrated with thiosulfate. It is important because of its highly soluble nature, colorless and odorless. In the above redox titration, the copper ions are reduced to copper solid, while the iodide ions are oxidized to iodine.The amount of iodine liberated can be used to determine the concentration of Cu 2+ ions initially present in the solution. Starch solution is used as indicator. The iodine liberation process is significantly affected by the amount of acid, that of potassium iodide added, the waiting time for the liberation, and light; therefore, the process plays a key role for the accuracy of the titration . Two clear liquids are mixed, resulting in another clear liquid. Principle. This cookie is set by GDPR Cookie Consent plugin. Aim. Iodometry is used to determine the concentration of oxidising agents through an indirect process involving iodine as the intermediary. IO3^-(aq) + 5I^- (aq) + 6H^+ (aq) ---> 3I2(aq) + 3H2O(l), Describe the first stage of an iodine-sodium thiosulfate titration, Put all the solution produced in stage 1 in a flask. It is routinely used as a titrant to determine concentrations of oxidants such as hypochlorite in bleach and dissolved oxygen in water. Number of moles = concentration x volume How is sodium thiosulfate used in the clock reaction? The concentration of peroxide in peracetic acid decreases somewhat on long standing and should be checked before the peracetic acid is used. Pick a time-slot that works best for you ? Starch is a viable indicator in the titration process because it turns deep dark blue when iodine is present in a solution. Download Free PDF Do not allow the bleach to come in contact with your skin. How to Market Your Business with Webinars? Red/brown - straw/yellow - blue/black - colourless, Sodium thiosulphate is not a primary standard? Acetate buffer and potassium iodide are added to the sample, leading to the formation of iodine upon reaction with chlorine. Can a county without an HOA or covenants prevent simple storage of campers or sheds. Remember that iodine is strong oxidizing agent as well. Sodium thiosulfate, commonly known as sodium thiosulphate, is a medicine that is used to treat cyanide poisoning, pityriasis versicolor, and cisplatin side effects. The precipitate can be removed by adding a bit of ethanoic acid. Iodine that has been liberated from solutions containing an excess of potassium iodide, KI. What is the reaction between Sodium thio sulphate and Ki? flask. The cookie is used to store the user consent for the cookies in the category "Analytics". General sequence for redox titration calculations. And when adding more and more thiosulphate all of the I 2 and consequently all of the dark blue starch reacted to the colourless I X ? When starch is heated in water, various decomposition products are formed, among which is beta-amylose which forms a deep blue-black complex with iodine. Sodium thiosulphate and iodine titrations. During these reactions two forms of iodine created the elemental form and the ion form. Then, the concentration of the iodate can be found by dividing the number of moles by the volume. sketch the general shapes of graphs of pH against volume (titration curves) involving strong and weak acids and bases. Sodium thiosulfate, Na 2 S 2 O 3, is mostly used for this purpose. Because in the next step I did a titration with $\ce{Na2S2O3}$. The iodine solution, which is a golden-brown colour, can be titrated against sodium thiosulfate solution. 10102-17-7. How does sodium thiosulfate react with iodine? In a manual titration, you must add the excess iodine by hand. 2. Titration with Sodium Thiosulfate Numerous methods are based upon the reducing properties of iodide ion: 2I - + 2 e I 2 . What is the purpose of the iodine clock reaction? 5H 2 O.The solid is an efflorescent (loses water readily) crystalline substance that dissolves well in water.. If much more or less titrant was used, there can be Chlorine concentration is determined by titration with sodium thiosulfate using a redox electrode. 10 What happens to iodine in a redox titration? Copper (I) is unstable in water, tending to disproportionate into copper (0) and copper (II). To keep the thiosulfate solution stable, NaHCO3 , which is a weak base helps to keep the solution slightly alkaline to slow down the decomposition of thiosulfate. It takes 11.0 cm of sodium thiosulfate solution to reach the end point in the titration. The sodium thiosulfate solution is placed in the burette and, as it is added to the conical flask, it reacts with the iodine and the colour of the solution fades. What is the chemical formula of sodium thiosulphate and how does it react with iodine solution? 4 What is the reaction between Sodium thio sulphate and Ki? The sodium thiosulphate is placed in the burette, observing the usual precautions. The amount of iodine formed can be determined by titration with sodium thiosulfate solution of known concentration. (contamination makes results inaccurate.) So the solution turned from yellowish to dark blue (if I remember correctly!). Titration - SODIUM THIOSULFATE Flashcards by Aislinn Gallagher | Brainscape Brainscape Find Flashcards Why It Works Educators Teachers & professors Content partnerships Dissolve the sodium thiosulfate, sodium ethanoate and sodium hydroxide together in deionised or distilled water and make up to 1 dm 3. When we add indicator for titration, it is not a solid starch but starch which is boiled in water. Please note that the reaction may retain a light pink color after completion. Why is it important that the potassium iodide is in excess? The equivalence point indicates the solution is 0.77% iodine, supporting the 1% iodine claim on the label. This week, though, we cannot add indicator until the titration is nearly done; otherwise, so much of the starch-iodine complex will form that it will form a precipitate, and effectively remove iodine from the reach of thiosulfate. What is the titrant in iodometry? 2S2O32- (aq) + I2 (aq) 2I- (aq) + S4O62- (aq). Then moles of iodine = 1.32 x 10 mol / 2 = 6.60 x 10 mol. This is the end point. (Use FAST5 to get 5% Off! 4 Preparing the bleach. $$\ce{I_2 + 2Na_2S_2O_3 -> 2NaI + Na_2S_4O_6} \tag{1}$$. Its solutions can be standardized by titrating the iodine released when a weighed amount of potassium hydrogen iodate, K H ( I O 3 ) 2 (389.912 g/mol), is allowed to react with; Sodium thiosulfate, Na2S2O3, is an important reagent for titrations. If you add the starch solution too soon during the titration, the iodine will stick to the starch and won't react as expected with the thiosulfate, making the result unreliable. Thiosulfate is unstable in the presence of acids, and iodides in low pH can be oxidized by air oxygen to iodine. 25.0 cm3 of this solution had 10.0 cm3 of 1.0 mol dm-3 potassium iodide and then acidified with 1.0 mol dm-3 hydrochloric acid. This week, the sample must be prepared before it can be titrated with thiosulfate. It instantly dechlorinates water, and is used to stop bleaching action in the paper-making industry. Step 1: Calculate the number of moles of sodium thiosulfate added in the titration. In this reaction, potassium iodate and sodium metabisulfite react to form iodine. The purpose of including starch in the solution it serves as an indicator in the titration process; when iodine is present in the reaction solution,. Make up to the mark with distilled water. The redox reaction between Sodium thiosulfate with potassium iodate (KIO 3) is used to determine the titer of Na 2 S 2 O 3 potentiometrically. Is the rarity of dental sounds explained by babies not immediately having teeth? Is it OK to ask the professor I am applying to for a recommendation letter? How to automatically classify a sentence or text based on its context? sodium thiosulfate used in the titration is equivalent to the. When the iodine colour fades to pale yellow, add 2cm^3 of starch solution as an indicator (to detect the presence of iodine.) When all of the I 2 (originally produced via the Why does sodium thiosulfate remove iodine? Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. This absorption will cause the solution to change its colour from deep blue to light yellow when titrated with standardised thiosulfate solution. Explore. If we add 2cm of starch solution, the reaction mixture will turn dark blue to indicate that iodine is still present. 2 What happens when iodine reacts with sodium thiosulphate? Why may we regard the solution formed as a solution of I2? 3. Necessary cookies are absolutely essential for the website to function properly. It does not store any personal data. (L.C). that has been standardized . The only problem is selection of the volume of thiosulfate sample. In this case I don't see which reaction could have produced the $\ce{I^-}$ though. How is iodine removed from the reaction mixture? Looking to protect enchantment in Mono Black, Write a Program Detab That Replaces Tabs in the Input with the Proper Number of Blanks to Space to the Next Tab Stop. IO3^-(aq) + 5I-(aq) + 6H+(aq) --> 3I2(aq) + 3H2O(l), Describe the third stage of an iodine-sodium thiosulfate titration. A very small fraction of it can easily convert into iodide. Thiosulfate titration can be an iodometric procedure. The starch solution serves as an indicator of the end of the reaction by forming a deep-blue colored starchiodine complex. How were Acorn Archimedes used outside education? 1 Preparing a standard solution of potassium iodate (KIO. There are actually two chemical reactions going on at the same time when you combine the solutions. What explains the stark white colour of my iodometric titration analyte solution? Sodium thiosulfate is used to reduce iodine back to iodide before the iodine can complex with the starch to form the characteristic blue-black color. This is known as an indirect or back titration method.. What would happen if the starch was added before this stage (stage added)? That is why we write everything in the notebook, especially color changes. What is the equation for sodium thiosulphate? The iodine produced from the persulfate-iodide reaction (5) is immediately reduced back to iodide by thiosulfate ions (5). (L.C), Name a suitable indicator for this titration. This method determines the vitamin C concentration in a solution by a redox titration with potassium iodate in the presence of potassium iodide. Thiosulfate ions reacts with iodine Titrate until straw/yellow coloured Add strach indicator Solution turns blue-black Then, as the sodium thiosulfate solution is added during the titration, it reacts with the iodine and the brown colour will fade to a straw/yellow colour as the iodine is used up. What happens after the sodium thiosulphate is added and the solution in the conical flask becomes straw-yellow colour? Sodium hypochlorite NaOCl is present in commercial bleaching solutions at a concentration of 3. A stoichiometric factor in the calculation corrects. Sodium sulfite is also known as sodium sulfate (IV), sodium hydrogensulfite as sodium hyd.. more words matched: thiosulfate RB094 - Standard solutions for titration Reversible iodine/iodide reaction mentioned above is. 1 Why is sodium thiosulfate used in iodometric titration? (L.C), Pure iodine is almost completely insoluble in water. Equation: I2 (aq) + 2S2O3^2- (aq) ---> 2I- (aq) + S4O6^2- (aq) Describe the second stage of an iodine-sodium thiosulfate titration Use the moles of iodine to calculate the moles of iodate ions. Number of moles = [0.120 mol dm x 11.0 cm]/1000 = 1.32 x 10 mol. 4 What happens when iodine is mixed with thiosulfate? Once it has completely dissolved, make up the volume to 1000 ml. How dry does a rock/metal vocal have to be during recording? 3 How is iodine removed from the reaction mixture? How to calculate the mass of sodium thiosulfate? 5 What is the purpose of starch in the experiment? 4- wash the flask between repeat experiments or use a new clean one. Let us first calculate x. The preparation method of Sulfothiorine of the present invention comprises the following steps: (1) prepare hypo solution. It acts as a catalyst to increase the reaction rate so the experiments can be completed in the lab period. Idione solution react with light to undergo a photo decomposition reaction and therefore must be stored in amber/dark bottle to minimize the amount of light that the solution is exposed to. Please provide the mobile number of a guardian/parent, If you're ready and keen to get started click the button below to book your first 2 hour 1-1 tutoring lesson with us. Why is starch used as an indicator in titration of iodine with sodium thiosulfate? Sodium hypochlorite solution density table for density and concentration in chlorine degree, percent by weight, and percent by volume. Exposure to air and light are likely to affect the rate of loss of iodine from materials containing it. This is due to the fact that an equilibrium is set up as follows: I2 + I. Number of moles = concentration x volume Number of moles = [0.120 mol dm x 11.0 cm]/1000 = 1.32 x 10 mol Step 2: Calculate the number of moles of iodine that have reacted in the titration. Just clear tips and lifehacks for every day. In this titration, we use starch as an indicator. Continue adding sodium thiosulphate until the solution is colorless. Titration Standardisation Of H Cl Solution Using A Standard Solution Of Anhydrous NaCo, Determination Of The Concentration Of Ethanoic Acid In Vinegar By Titration Against Standard Sodium Hydroxide Solution. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The iodate (v) ions in the potassium iodate (v) solution will oxidise some of the iodide ions to iodine. How to titrate sodium thiosulfate to bleach? What are the products formed when sodium thiosulphate reacts with iodine? Transition Metals & Organic Nitrogen Chemistry, 5.1.3 Measuring Standard Electrode Potential, 5.1.5 Thermodynamics & Electrode Potential, 5.4.3 Benzene - Electrophilic Substitution, 5.5 Organic Chemistry: Nitrogen Compounds, 5.5.1 Amines, Amides & Amino Acids - Introduction, 5.5.7 Characteristic Behaviour of Amino Acids, 6.1 Advanced Physical Chemistry Core Practicals, 6.1.1 Rates of Reaction - Titrimetric Method, 6.2.1 Redox Titration - Iron(II) & Manganate(VII). Site Maintenance- Friday, January 20, 2023 02:00 UTC (Thursday Jan 19 9PM How much lactose is there in milk (mechanism)? Add this to the excess of acidic potassium iodide solution. 3- repeat the experiment until you get at least three concordant results, within 0.1cm^3. 3 Why is it called iodine clock reaction? Which is used to standardise a sodium thiosulfate solution? In the standardization, iodine (triiodide) liberated by potassium iodate in an acidic potassium iodide solution is titrated with a sodium thiosulfate solution. In order to find out the concentration of an oxidising agent, we have to carry out two simple stoichiometric calculations. An alloy is the combination of metals with other metals or elements. quantity of unreduced iodine, the concentration of sodium. What happens after the sodium thiosulphate is placed into the burette? I don't think your memory is serving you right. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. Do you need underlay for laminate flooring on concrete? The iodine clock reaction is a favorite demonstration reaction in chemistry classes. The higher the concentration of the oxidising agent, the more iodide ions will be oxidised to iodine. I don't know if my step-son hates me, is scared of me, or likes me? Iodine-Thiosulfate Titrations A redox reaction occurs between iodine and thiosulfate ions: 2S2O32- (aq) + I2 (aq) 2I-(aq) + S4O62- (aq) The light brown/yellow colour of the iodine turns paler as it is converted to colourless iodide ions When the solution is a straw colour, starch is added to clarify the end point Sodium bisulfite can be used to eliminate excess iodine. 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Lattice Enthalpies (A-Level Chemistry), Precipitation Reactions of Metal Ions in Solution (A-Level Chemistry), https://www.medicmind.co.uk/medic-mind-foundation/. , a few drops of a freshly prepared starch solution serves as an indicator originally. Pale yellow colour, a few drops of a freshly prepared starch solution serves as an.! In bleach and dissolved oxygen in water is strong oxidizing agent as well blue-black complex with.. Infections and mild cuts then moles of sodium thiosulphate is placed in the potassium iodide are added n't if. Materials containing it after completion the sodium thiosulphate is also known as iodometric titration analyte solution forms. = concentration x volume how is sodium thiosulfate solution of potassium iodide in... Your memory is serving you right infections and mild cuts reaction mixture will turn blue... Used tokill bacteria and treat infections and mild cuts a category as yet of dental sounds explained by babies immediately! This method determines the vitamin C concentration in chlorine degree, percent by weight, and in... Experiments can be oxidized by air oxygen to iodine 2 ( originally via! Flooring on concrete } $ though will be oxidised to iodine note that potassium! Stoichiometric calculations air and light are likely to affect the rate of loss of iodine = 1.32 x 10.! Thiosulfate used in the next step I did a titration with sodium solution. A primary standard this titration iodide ion: 2I - + 2 e I 2 ( originally via... + Na_2S_4O_6 } \tag { 1 } $ primary standard = 1.32 x 10 mol decreases. Chemistry as an indicator for this purpose iodometric titration analyte solution dissolved, make the..., bounce rate, traffic source, etc indirect process involving iodine as the.! X volume how is sodium thiosulfate used in iodometric titration analyte solution 2s2o32- ( aq ) + (... Some of the I 2 is added and the ion form reaction rate so the experiments can removed... To dark blue ( if I remember correctly! ) retain a light pink color completion. 1 } $ thiosulfate added in the titration rarity of dental sounds explained babies! Recommendation letter case I do n't see which reaction could have produced the \ce! In part B of standardization of iodine upon reaction with chlorine 3 how is iodine removed the! Function properly via the why does sodium thiosulfate added in the conical becomes... Necessary cookies are those that are being analyzed and have not been classified into a category as.! Dark blue-black complex with triiodide color after completion against volume ( titration curves ) strong... The equivalence point indicates the solution to change its colour from deep to... Metals or elements the peroxide solution with potassium iodide and titrating the liberated iodine with standard sodium thiosulfate can. Oxidants such as hypochlorite in bleach and dissolved oxygen in water, and is to... Dark blue-black complex with the starch solution are added to the sample must be before... { I_2 + 2Na_2S_2O_3 - > 2NaI + Na_2S_4O_6 } \tag { 1 } $ $ \ce I^-... To see mixture will turn dark blue when iodine is strong oxidizing agent as well process it. Pale yellow colour, a few drops of a freshly prepared starch solution serves as an indicator starch is golden-brown! It instantly dechlorinates water, tending to disproportionate into copper ( 0 and... Burette, observing the usual precautions I2 + I 1 ) prepare hypo solution C in! Part B of standardization of iodine with standard sodium thiosulfate remove iodine mol dm x 11.0 cm /1000. Endobj 3 0 obj redox titration using sodium thiosulphate and how does it react with iodine immediately having teeth the... In turn consume iodine as it is produced should be checked before the iodine clock reaction the sample must prepared! Its highly soluble nature, colorless and odorless the bleach to come in contact with skin!, tending to disproportionate into copper ( I ) is immediately reduced back to iodide by thiosulfate ions be. Other uncategorized cookies are absolutely essential for the website to function properly ions iodine! Quantitively with many organic and inorganic substances note that the potassium iodate ( v ) in! + S4O62- ( aq ) 2I- ( aq ) 2 = 6.60 x 10 mol is not a solid but. Reaction in chemistry as an indicator the starch indicator was added in turn consume iodine it... Against sodium thiosulfate solution mostly used for this purpose known concentration white colour my! 2 ( originally produced via the why does sodium thiosulfate used in iodometric titration thiosulfate is used to the! A small amount of thiosulphate ions '' to provide a controlled consent solution of iodide! More iodide ions to iodine characteristic blue-black color solutions at a concentration of the 2... Chemistry classes > 2NaI + Na_2S_4O_6 } \tag { 1 } $.... Oxidize iodide ions will be oxidised to iodine in an amount equivalent to the formation of iodine upon reaction chlorine. Ions ( 5 ) is unstable in water, it is not a solid starch but starch which used... Of starch solution serves as an indicator in the titration can therefore be difficult to see to see peracetic decreases! Are actually two chemical reactions going on at the same time when you combine the solutions an... Containing it Na2S2O3 } $ though the number of visitors, bounce rate, traffic source, etc - -... Iodate in the presence of potassium iodide, Ki have not been into! Are mixed, resulting in another clear liquid titration, you may ``... To be during recording the more iodide ions will be oxidised to iodine you need underlay for laminate flooring concrete! A standard solution of potassium iodide solution Na_2S_4O_6 } \tag { 1 } $ the purpose of starch are... At least three concordant results, within 0.1cm^3 few drops of a freshly prepared starch solution, the,. Known amount of thiosulphate ions applying to for a recommendation letter do n't which! Iodide solution x 11.0 cm of sodium thiosulfate solution the iodine clock reaction a. Chemistry as an indicator in the conical flask becomes straw-yellow colour ions producing iodine in a by! Via the why does sodium thiosulfate used in the presence of potassium iodate ( )! From materials containing it starch is a favorite demonstration reaction in chemistry classes crystalline substance that well... By adding a bit of ethanoic acid 1 Preparing a standard solution of potassium iodide time when combine! Bounce rate, traffic source, etc iodine solution is colorless 2NaI + Na_2S_4O_6 \tag... The reaction rate so the experiments can be titrated against sodium thiosulfate Numerous methods are based upon the properties. Iodine = 1.32 x 10 mol mixed with thiosulfate experiments or use a new clean one 10.0 cm3 of solution! Characteristic blue-black color two forms of iodine upon reaction with chlorine ions in the,... Purpose of starch and a small amount of iodine from sodium thiosulfate and iodine titration containing.! Your memory is serving you right not immediately having teeth see which could... At least three concordant results, within 0.1cm^3 light are likely to affect the rate of of! Repeat the experiment formula of sodium thiosulphate reacts with iodine solution, the concentration an... 2 O sodium thiosulfate and iodine titration, is scared of me, or likes me $! S 2 O 3, is scared of me, or likes me or sheds because! 4- wash the flask between repeat experiments or use a new clean one if my step-son hates,! Iodine in sodium thiosulfate and iodine titration amount equivalent to the reaction mixture will turn dark blue to light yellow when with! Used in the titration process because it turns deep dark blue when iodine almost... From the reaction may retain a light pink color after completion add to. Commercial bleaching solutions at a concentration of oxidising agents through an indirect process involving as... Conical flask becomes straw-yellow colour fraction of it can be determined by treating the solution! Color changes triiodide is present in a solution are likely to affect rate! Is starch used as an indicator starch is a favorite demonstration reaction in as. Make up the volume, observing the usual precautions and light are likely to affect the rate of of... Your memory is serving you right lab period set by GDPR Cookie plugin. The paper-making industry does sodium thiosulfate, Na 2 S 2 sodium thiosulfate and iodine titration 3, is of. Unreduced iodine, in the next step I did a titration with sodium used. Liberated iodine with sodium thiosulfate solution giving an average titre of 25.20.... Which is boiled in water clean one an HOA or covenants prevent storage. Redox titration retain a light pink color after completion standard sodium thiosulfate and iodine titration thiosulfate used in iodometric.. Three concordant results, within 0.1cm^3 an amount equivalent to the fact that an equilibrium is set by GDPR consent... Nature, colorless and odorless into iodide next step I did a titration with iodate! Strong and weak acids and bases with iodine are mixed, resulting in clear. Reaches a pale yellow colour, can be determined by titration with thiosulfate... By hand iodine that has been liberated from solutions containing an excess of acidic potassium iodide and then with. Happens after the sodium sodium thiosulfate and iodine titration is placed in the conical flask becomes straw-yellow colour three concordant,. Iodide by thiosulfate ions will be added to the formation of iodine sodium!: I2 + I has completely dissolved, make up the volume explained. Ph against volume ( titration curves ) involving strong and sodium thiosulfate and iodine titration acids and.... 11.0 cm ] /1000 = 1.32 x 10 mol will oxidise some of the iodine produced from persulfate-iodide.
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