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Detection of Ions in Solutions Using Acid/Base Paper

Words: 2338, Paragraphs: 15, Pages: 8

Paper type: Essay, Subject: Solutions

You will then conduct quality control testers and determine if the label on a bottle of over-the-counter product actually contains the percentage of compound that it advertises. What is a Titration? A titration is an analytical procedure used to determine the concentration of a sample by reacting it With a standard solution. One type Of titration uses a naturalization reaction, in which an acid and a base react to produce a salt and water. In equation 1, the acid is HCI (called hydrochloric acid) and the base is Noah (called sodium hydroxide), When the acid and base react, they form NCAA sodium chloride), which is also known as table salt.

The titration proceeds until the equivalence point is reached, Where the number of moles of acid is equal to the number of moles of base. This point is usually marked by observing a color change in an added indicator. In a titration, the standard solution goes in a burette, which is a piece of glassware used to measure the volume of solvent to approximately 0. 1 ml of accuracy. The solution that you are titrating goes in an Erlenmeyer flask, which should be large enough to accommodate both your sample and the standard solution you are adding.

What is an Indicator and What is it used For? An indicator is any substance in solution that changes its color as it reacts with either an acid or a base. Selecting the proper indicator is important because each indicator changes its color over a particular range Of pH values. Indicators are either weak acids or weak bases. For example, phenolphthalein is a weak acid (Which we Will represent as Hal). In aqueous solution, the phenolphthalein dissociates slightly, forming an equilibrium. An equilibrium occurs when the amount of reactants and the amount of products are constant.

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When a system is in equilibrium, it Will stay there until something changes the conditions. A famous French chemist, named El Chatterer, developed a way to predict how changes in equilibrium affect the system. El Chatterer’s principle states that when an equilibrium is disturbed by applying stress, the equilibrium will shift to relieve the stress, In an acidic solution, there is an excess of HUH+ ions so the equilibrium will shift to the left and favor the for-nation of Hal, thus we observe a clear solution. In basic solution, there is an excess of OH- ions that react with the HUH* ions to form eater.

This shifts the equilibrium to the right because water is being formed and HUHВ± ions are being removed, thus eve observe a pink solution. We can use this color change to determine when the end of the titration has been achieved. Table I lists common indicators and the pH range over Which they change colors. Measuring pH: How to Calibrate a pH Meter pH is a measure of acidity or basilica. An acid has a pH less than 7, a neutral compound (like water) has a pH near 7, and a base has a pH from 7-14 pH can be measured using either litmus (or indicator) paper, which changes color eased on the acidity of a solution, or by using a pH meter.

A pH meter is a more accurate means Of measuring pH because it can be calibrated to measure one tenth of a pH unit, overhears the indicator paper only measures to one pH unit. A pH meter uses an electrode to measure the pH of a solution. The electrode is stored in distilled water in order to keep it at a neutral PH. To calibrate the pH meter: 1. Remove the electrode from the distilled water and place in pH 4 buffer, Which is pink. Make sure the electrode is completely covered in buffer and swirl the solution around. 2. Set the pH meter to pH a and then rinse the electrode With distilled water to remove any excess solution. . Place the electrode in pH 10 buffer (which is blue) and swirl it around in the solution. 4. Set the pH meter to pH 10 and rinse the electrode, returning it to the distilled water once you are finished. The pH meter should now be calibrated to measure any pH accurately. Standardizing a Sodium Hydroxide (Noah) Solution In a titration, it is critical to know the exact concentration of the iterant (the solution in the burette which will be added to the unknown) in order to determine he concentration of the solution being tested. We will standardize the -?0. M Noah solution (the iterant) with potassium hydrogen phthalate (KIP, KC8H404H) using phenolphthalein as the indicator, KIP is a weak acid and reacts with base in the following way: To Standardize: I _ Weigh -?0. 8 g of dried KIP (MM = 204 23 g/mol) into an Erlenmeyer flask and dissolve in 50-75 ml of distilled water. Record the amount of KIP and water used. 2. Add 4 drops Of indicator into the flask and titrate to the first permanent appearance of pink. Near the endpoint, add the Noah drowses to determine the total volume most accurately. Calculate the concentration Of Noah in the following way: Calculate Concentration of KIP: Calculate Concentration of Noah: Remember: There are 1000 ml in a Land 1000 MGM in a gram. 4. Report the concentration of Noah to the class. An average number will be determined to give the most reliable value of Noah concentration. Do not discard the remaining Noah – you will use this for the rest of these experiments. Standardizing an HCI Solution the concentration of solutions being tested. We will standardize the -?0. 1 M HCI solution (the iterant) with sodium carbonate (Niacin) using phenolphthalein as the indicator.

Niacin is a base and reacts with the strong acid HCI in the I _ Weigh -?0. 2 g Niacin into an Erlenmeyer flask and dissolve it in 50 ml of boiled, cooled distilled water. Record the exact amount of Niacin used in your notebook. (The water is boiled to expel CA from the solution. ) 2. Add 4 drops Of phenolphthalein to the solution and record the color. 3. Titrate with the HCI until just before the endpoint (when the solution is very light pink) and then gently boil the solution to expel the CA from solution that has been produced during the reaction (see CEQ 4). . Cool the solution to room temperature and then wash he sides of the flask with a small amount of H2O to get all of the sample back into solution. S. Finish the titration (this will take VERY little HCI so go slow! ) 6. Record the color of the solution and the volume of HCI used. 7. Calculate the concentration of HCI in the following way: Determination to Magnesium Hydroxide [MGM(OH)2] Content in Milk of Magnesia Milk of magnesia is a viscous, mildly basic mixture that is used to treat upset stomach and occasionally to prevent constipation.

According to standards set by the pharmaceutical industry, milk of magnesia should contain at least 7% y weight We will be doing detective work to see if the pharmaceutical industry is being truthful in their claim by determining the weight percent of magnesium hydroxide in different bottles of milk of magnesia. An accurate analysis Of milk Of magnesia must measure the total both dissolved and suspended in solution. This is tricky because milk of magnesia exists as a White opaque solution so each sample may not be representative Of the whole bottle. To make the solution as homogeneous as possible, the bottle must be shaken thoroughly.

Direct titration of milk of magnesia is difficult due to the cloudy suspension and he fact that some of the solution may cling to the sides of the flask, preventing complete titration and altering the measurement of the endpoint. The opaque solution may also make it difficult to detect the color change of the endpoint. For this reason, a back titration will be used to measure the weight percent MGM(OH)2 in milk of magnesia. Excess HCI will react with all of the MGM(OH)2 to yield a clear solution and then the excess unrelated acid will be back titrated with standardized Noah.

The reactions in this titration are as tools: Procedure: I _ Obtain a vial filled with between I-I . G milk of magnesia and weigh the vial and sample without the lid on. Record the value. 2. Rinse the contents of the vial into a 250 ml Erlenmeyer flask With distilled water and dilute the solution to 50 ml total volume. Extra water can be used if milk of magnesia remnants remain in the vial. 3. Add a measured amount Of HCI (from a burette) into the beaker until the solution is clear and then add an additional 1-2 ml HCI to ensure there is an excess Of acid. Record the volume of HCI added. For a I g sample Of milk Of magnesia, this should be at least 30 ml HCI. ) Measure the pH of the solution sing a pH meter or pH paper and record the value. 4. Add 4 drops of indicator (what color is the solution? ) and titrate the solution with standardized Noah. The titration will go quickly, with less than 5 ml of Noah required. Record the volume of Noah used and the color of the solution, Measure the pH of the solution again and record the value. 5. Rinse the vial with distilled water and dry in an oven or in a microwave for 1 minute. When dry and cool, weigh the vial to determine the actual weight of the milk to magnesia sample.

Make sure there is no water left in the vial! This will skew your results! Record the weight. 6. Calculate the weight percent to MGM(OH)2 in milk of magnesia using the following equation: Calculate the weight percentage of Milk of Magnesia: 7 _ Repeat with another sample of milk of magnesia from a different bottle to see if the weight percent of MGM(OH)2 is consistent from sample to sample. Questions: 1. Would the weight percentage of MGM(OH)2 be higher or lower if some of the milk Of magnesia sample got stuck on the sides Of the flask and was not titrated? Show the thought process for your answer. . Was there a consistent amount Of MGM(OH)2 in each bottle Of milk Of magnesia, or did the values change? Was the change dramatic or small? 3. How would the weight percentage of MGM(OH)2 change if the weight of the sample was measured incorrectly (for example, the vial was not washed thoroughly or some water remained, changing the weight)? 4. If you determined a different weight percent of MGM(OH)2 other than – 7%, what do you think is the reason? Is there something in your determination that went wrong or are pharmaceutical companies giving us false information?

Standardizing an EDIT (delimitation attractive acid) Solution elution in the burette that will be added to the unknown) in order to determine the concentration of the solutions being tested. We Will standardize a -0. 01 M DE TA solution (the iterant) by adding it to a calcium carbonate (Cacao) solution using hydroxylation blue as the indicator. EDIT is used because it can chalet (bind to a metal atom through many different bonds) so that it captures and surrounds the calcium in solution. EDIT can capture the metal through any Of its six donor atoms, indicated by boxes.

In this experiment, one molecule Of EDIT captures one atom of calcium. EDIT . Weigh -?0. 25 g Cacao into a 250. 0 ml calibrated flask and dissolve it in a minimal amount of concentrated HCI. Then dilute with distilled water to the 250. 0 ml mark, Record the exact amount of Cacao used in your notebook. 2. Calculate the concentration of Cacao in the following way: 3. Transfer 25. 00 ml (measured with a calibrated pipette) into a 250 ml Erlenmeyer flask and dilute with an equal volume of water. 4 Add 1 M Noah to raise the pH to 12 (measure with a pH meter or pH paper). Fifth pH drops below pH 12 during the titration, add additional Noah. . Add 4-8 drops of hydroxylation blue indicator to the solution and record the color _ 6. Begin adding EDIT until the color change is observed. Record the color of the solution and the volume Of DE TA necessary to achieve this change. 7. Calculate the concentration of EDIT in the following way: Determination of Calcium in [email protected] by Back Titration [email protected] is an orange drink that serves as an orange juice substitute, and astronauts drink Tango because it is easy to transport to space! Tang boasts that it is a “good source of calcium” despite containing only a fraction of the minimum daily requirement of Ca*.

To test the manufacturer’s claim, we will determine the amount of calcium in [email protected] the use of a complimentary titration. A complimentary titration is a type of titration verge a complex is formed between an analyze and a iterant. The analyze is the ion you are testing for, here Ca+. The iterant is the EDIT that was previously standardized. During the course Of the titration, the EDIT Will capture one molecule Of Ca+ and bind to it, forming a colored complex. During the forward titration, each molecule of EDIT will capture one molecule Of Ca*.

When all Of the Ca* is compelled, the solution Will change color and o will observe the endpoint. To check yourself, you will add additional EDIT to the solution and perform a back titration. Now there is excess EDIT floating in solution but no Ca* to bind to it. By adding Cacao, the EDIT can bind to the new source of Ca+, which leads to the next color change when all of the Ca+ has found an EDIT molecule. The color change at the endpoint will be hard to see due to the orange nature of the [email protected], so it will be necessary to perform a back titration.

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