Lab 4 pH and Titration Bio 110 Mira Costa College PDF

Intro. Bio.: Prep. for Pre-Heath Professions Name: Prateek Devulpally pH and Titration Objectives: 1. Describe the term molarity. 2. Describe the term pH and the scale used to measure it. 3. Describe...

Intro. Bio.: Prep. for Pre-Heath Professions Name: Prateek Devulpally pH and Titration Objectives: 1. Describe the term molarity. 2. Describe the term pH and the scale used to measure it. 3. Describe how pH indicators are used in a titration. 4. Describe how the titration technique is used to determine the relative pH of solutions. 5. Develop an experimental protocol to determine the relative pH of solutions. (SLO) 6. Graph, analyze, and interpret data collected (SLO). Introduction Molarity: A solution is a liquid composed of a homogeneous mixture of two or more substances. The solute is the substance dissolved in the solution and the solvent is the substance that acts as the dissolving agent. One of the unique properties of H2O is that it is an excellent solvent and can dissolve both ionic compounds and polar molecules. When water is the solvent in a solution it is referred to as an aqueous solution. Molarity is used to express the concentration of the solute in a solution. It is the number of moles of solute dissolved in one liter of solution (equation shown below). Molarity has a unit of moles/liter, which can be abbreviated as M (read as molar). Molarity = moles solute liter of solution It is important to be able to distinguish between moles and molarity. A mole is a scientific unit of measurement; it is 6.02x1023 units of anything – typically atoms, molecules, or ions. For example, one mole of glucose contains 6.02x1023 molecules of glucose. In contrast, as mentioned previously, molarity would be used to indicate the concentration of glucose in a solution (moles solute/liter of solution). So, if you have a 1 M glucose solution, you know it contains 1 mole of glucose (6.02 x 1023 glucose molecules) in one liter of total solution. It is important to maintain an optimal concentration of substances in our body fluids for our cells to function properly. This is especially important when it comes to maintaining an appropriate concentration of hydrogen ions (H+) in our body fluids. Changes in the concentration of H+ can inhibit the function of proteins and other biological molecules within our cells. Next, we will review how altering the concentration of H+ in a solution affects the pH. 1 | Page  Intro. Bio.: Prep. for Pre-Heath Professions Name: Prateek Devulpally pH, acids, and bases: pH is a measure of H+ concentration in a solution and is defined as pH = - log[H+]. Pure H2O has a pH of 7 and contains an equal concentration of H+ and OH-. The concentration of H+ in a solution is inversely related to pH. Increasing the concentration of H+ decreases the pH of the solution, whereas decreasing the concentration of H+ increases pH. A pH scale measures how acidic or basic a solution is. Solutions that have a pH below 7 are considered acidic, solutions that have a pH above 7 are considered basic, and a pH of 7 is neutral (see Figure 1). The pH scale ranges from 0 to 14. It is a logarithmic scale, meaning each unit on the scale represents a ten-fold change in H+ concentration. So, a solution of pH 8 has 10 times more H+ than pH 9 and 100 time more H+ than pH 10. Figure 1. pH scale Various chemical compounds can alter the concentration of H+ in a solution, which results in a change of pH. An acid is a substance that increases H+ concentration and reduces pH. In contrast, a base is a substance that decreases H+ concentration and increases pH. Titration: Titration is a method used to determine the relative pH of solutions. The titration procedure requires the use of a pH indicator. The indicator changes color based on the pH of 2 | Page  Intro. Bio.: Prep. for Pre-Heath Professions Name Prateek_Devulpally the solution it is mixed with. There are many different pH indicators, but in today’s lab we will be using phenol red. Phenol red turns yellow/orange in acidic solutions and bright pink in basic solutions. To titrate a solution, you will add an acid (hydrochloric acid; 0.1M HCl) to a basic solution or a base (sodium hydroxide; 0.1M NaOH) to an acidic solution. Which titrant (acid or base) you select will depend on the starting pH of the solution being titrated. You will add the titrant to a solution by using “drops” that have a volume of 100 µl. You will continue to add 100 µl drops, with complete mixing of the titrant and solution between each drop, until your titration reaches the endpoint. The endpoint is detected by the pH indicator undergoing an irreversible color change, which is near pH 7 for phenol red. Analysis of the volume of titrant needed to reach the endpoint will be used to determine the relative pH of different solutions. Exercise 1: Titration of HCl solutions In this exercise, we will use two HCl solutions that have been premixed with phenol red, 0.02 M HCl + phenol red and 0.04 M HCl + phenol red, to practice the titration procedure. Watch this Introduction to Exercise 1 video to view the experimental set-up that includes steps 1 and 2 in the protocol below. Protocol 1. Obtain two glass test tubes from the back bench. Label them 0.02 M and 0.04 M with a sharpie. 2. Measure 5 ml of 0.02 M HCl + phenol red and transfer to the corresponding test tube. Your instructor will discuss how to avoid cross-contamination by using a color-coded system to measure solutions. Question: What titrant will be used to titrate the 0.02 M HCl + phenol red solution? The base will used to titrate the 0.02 M HCL + phenol red solution in order to neutralize it. Question: What color change is expected when the endpoint is reached? The color change that is expected when the endpoint is reached is pink. 3. Use the 100 µl fixed-volume micropipette to titrate the 0.02 M HCl + phenol red solution. IMPORTANT: You MUST mix the contents of the test tube completely after adding each 100 µl drop of titrant. Count the number of 100 µl drops required to reach an irreversible color change (endpoint of titration) and record in Table 1. Watch this video that demonstrates the titration of the 0.02M HCl + phenol red and record the data collected in Table 1. 4. Calculate and record the total volume of titrant required to reach the endpoint in Table 1. 3 | Page Intro. Bio.: Prep. for Pre-Heath Professions Name:Prateek Devulpally Table 1. Titration data for HCl solutions Number of 100 µl drops of titrant required for Total volume of Final Tube irreversible color titrant added color Tube Label Contents (5 ml) change (µl) observed 0.02 M HCl + 1 0.02 phenol red 19 drops 1900 uL Pink 0.04 M HCl + 2 0.04 phenol red 40 drops 4000 uL Pink Question: Based on what you know about molarity, predict how many 100 µl drops of titrant will be required to produce an irreversible color change for the 0.04 M HCl + phenol red solution. Since the 0.04 M HCL solution is double the molarity of the first solution. There will be a higher concentration of HCL in moles per liter for the the 0.04 M HCL solution. We will require about 38 100 uL drops of titrant for there to be a irreversible color change. 5. Repeat the titration protocol using the 0.04 M HCl + phenol red solution. Again, watch this video that demonstrates the titration of the 0.04M HCl + phenol red and record the data collected in Table 1. Question: Is there a relationship between the concentration of HCl and the volume of titrant needed to produce an irreversible color change? Provide evidence to support your answer. Yes there is a relationship between the concentration of HCL and the volume of titrant needed to produce and irreversible change. As seen in the experiment it took more titrant or a greater volume of it to produce a irreversible change for the 0.04 M HCL with phenol red compared to the 0.02 M HCL solution. This is because it had a higher concentration of HCl. Question: Which of the two HCl solutions is more acidic? Provide evidence to support your answer. 4 | Page Intro. Bio.: Prep. for Pre-Heath Professions Name_ Prateek Devulpally The 0.04 M HCL solution is the most acidic because it has 0.04 mole of HCL per liter of water. so this means that the 0.04 M HCL solution had 1.44 grams of HCL in it. This value is greater than the 0.02 M HCL solution because it only has 0.72 grams of HCL in its solution. Also when looking at the data table it took more drops of the 100 uL titrant in order to for there to be irreversible color change for the 0.04 M HCL solution. This means the the 0.04 M HCL solution was more acidic. Exercise 2: Titration of Body Fluids First, watch the Introduction to Titration of Body Fluids video that provides a quick overview of the instruction below. Now we can apply the titration technique to determine the relative pH of the following “body fluids”: artificial urine, artificial gastric juice, artificial pancreatin, and saliva. Each body fluid will be titrated in duplicate to identify any variations in the experimental results. In the space below, develop an experimental protocol for titration of the body fluids. Your experimental protocol must include enough detail that another student could use it to repeat the experiment. Experimental Protocol Step 1: label each test tube to the corresponding body fluid. Each body fluid will have 2 testubes because each body will have to be tested twice in order see if there is any variation in the experimental results. so in order to label to test tubes for each body fluid category you would write down the number of the test tube and the first letter of the name of the body fluid. For example if you are labeling the test tubes for saliva you would write 1S on the first test tube and 2S on the second test tube then moving on to the 3rd and 4th test tubes which are for the body fluid gastric juice you would 5 | Page Intro. Bio.: Prep. for Pre-Heath Professions Name Prateek Devulpally label them 3G and 4G. You would continue the same procedure of labeling for the rest of test tubes for the different body fluids There should be a total of 8 test tubes because we are measuring 4 different body fluids(Saliva, Gastric juice, pancreatic, and urine). Step 2: Measure 5ml of each body fluid and pour them in to the the correct test tube which has their label. Remember you will have to do this twice for each bodily fluid because we have 2 test tubes for each bodily fluid. Step 3: For each of the test tubes add 5 drops of phenol red from the squeeze bottle and mix it. In order to mix the phenol red properly in each test tube, tap the base of the test tube quickly numerous times. The squeeze bottle is labeled 0.02% phenol red. Step 4: observe the color of the test tubes for each of the body fluid solutions after the phenol red is mixed in for all of them and record them on the data table 2 to their corresponding category. Step 5: Based on the color observed in the test tubes for each bodily fluids determine what titrant will be used. There are two titrants HCL and NaOH. The record the titrant that will be used for each body fluid in table 2. Steps 6: For each of the body fluid solution use the correct titrant (HCl or NaOh) to neutralize/titrate the solution. Record the number of 100 uL drops for each solution that it takes to titrate it in the table 2. Then record the total volume of titrate in each body fluid category by multiplying the number of drops by 100 uL. Record that in table 2 for each body fluid category. 6 | Page Intro. Bio.: Prep. for Pre-Heath Professions Name_ Prateek Devulpally Table 2. Titration of Body Fluids Additio n of phenol Number of red 100 µl (5 Color drops of drops observe titrant Total from d after Titrant required volum squeez addition selecte for e of Final Body e of d irreversible titrant color Tub Labe Fluid bottle) Mix phenol (NaOH color added observe e l (5 mL) (✓) (✓) red or HCl) change (µl) d 100 1 1S Saliva ✓ ✓ Orange NaOH 1 drop uL Pink 100 2 2S Saliva ✓ ✓ Orange NaOH 1 drop uL Pink Gastric 1600 3 3G Juice ✓ ✓ Yellow NaOH 16 drops uL Pink Gastric 1600 4 4G Juice ✓ ✓ Yellow NaOH 16 drops uL Pink Pancreati Bright 500 5 5P n ✓ ✓ pink HCL 5 drops uL Orange 7 | Page Intro. Bio.: Prep. for Pre-Heath Professions Name:Prateek Devulpally Pancreati Bright 500 6 6P n ✓ ✓ pink HCL 5 drops uL Orange 400 7 7U Urine ✓ ✓ Yellow NaOH 4 drops uL Pink 8 8U Urine ✓ ✓ Yellow NaOH 4 drops 400 uL Pink 1st Video: Experimental set-up for titration of body fluids 2nd Video: Experimental Results After you have finished recording titration data, calculate the average number of 100 µl drops and the average volume of titrant required to reach the endpoint for each body fluid. Record the data in Table 3. Table 3. Average number of 100 µl drops and volume to reach the endpoint of titration Average number of 100 µl drops Average volume (µl) Saliva 1 drop 100 uL Gastric juice 16 drops 1600 uL Pancreatin 5 drops 500 uL Urine 4 drops 400 uL Analysis 1. Which body fluid was determined to be most acidic based on analysis of titration data? Provide evidence to support your answer. Gastric juice was the most acidic because it required the highest volume of titirant out of all the other acids in order to titrate it. It took 16 drops for the solution to neutralize. 8 | Page Intro. Bio.: Prep. for Pre-Heath Professions NamePrateek Devulpally 2. Which body fluid was determined to be most basic based on analysis of titration data? Provide evidence to support your answer. Pancreatic body fluid was the most basic because when the phenol red was added to its color was bright pink 3. Which body fluid was determined to be closest to neutral based on analysis of titration data? Provide evidence to support your answer. The saliva was the body fluid that was the closest to the neutral because it needed to lead amount of titirant to neutralize. It only needed 1 drop of the NaOH titrant in order to neutralize Now that you have analyzed titration of body fluid data and answered the questions above, watch this video where we determine the pH of all 4 body fluids by using pH test strips. Record the data from the video in Table 4. Table 4. Results of pH test strips pH Saliva 7 Gastric juice 2 Pancreatin 9 Urine 6 4. How do the results of the titration experiment compare to results from the pH test strips? Include data from each test to support your response. The pH strip shows that gastric juice is very acidic because it has a pH number of 2. In our data table the average number of 100 uL drops of the NaOh titrant was 16 in order to neutralize gastric juice. the gastric juice required the most drops of titirant compared to all 9 | Page Intro. Bio.: Prep. for Pre-Heath Professions NamePrateek Devulpally the other acids in the experiment. A solution is neutral around the pH of 7. The pH strip data shows that saliva got a pH number of 7. So it is the closest to neutral. We can see this in our data because it required the least number of drops(1 drop) to neutralize compared to all the other bodily fluids. Pancreatin was the most basic out of all the solutions because the pH tests strips show that it had the greatest pH number which was 9. This can be proven by the results from our lab. The data table shows that the color observed after phenol red was mixed with pancreatin was pink. The pH strips data show that urine was slightly acidic because it was 1 ph level below the neutral pH value. This can be proven with our data because urine needed less titrant to neutralize compared to Gastric juice but more titirant than saliva. 5. Determine which type of graph will best present the average titration data in Table 3 (drops or volume). Construct the graph using google sheets and paste the graph into the space below. 10 | Page Intro. Bio.: Prep. for Pre-Heath Professions NamePrateek Devulpally Post-lab questions 1. Research each human body fluid tested and write a summary that describes how the pH of the fluid relates to its function. The low pH level(2) of Gastric juice that our body produces helps in digestion by breaking down foods. The high acidity in gastric juice kills bacterias that enter your body when you consume food. it is important for Saliva to be neutral because if it is too acidic then it will cause acid erosion resulting in the decay of ones teeth and a lot of bacterias to form on ones teeth. Urine around the pH of 6 is considered to be normal(it is the same number we got in 11 | Page Intro. Bio.: Prep. for Pre-Heath Professions NamePrateek Devulpally our data). Anything too alkaline indicates that the person has urinary tract infections or anything to acidic means that the person is suffering from dehydration and other health issues. So Urine is our bodies way of telling that we need to take care of our health. Pancreatic juice has a higher pH. The pH strips showed that Pancreatic juice had a pH of 9. the reason why pancreatic juice is more alkaline is because it helps neutralize stomach acid as it enters our small intestine. it is important for it to neutralize the stomach acid in the small intestine because the small intestine is responsible for the absorption of nutrients from our food and our body will not get any nutrients if the stomach acids are high in pH. This is because the acidity will break down the foods till the point where there will be no nutrients left. 2. If the titration technique used in the lab was performed with an unknown body fluid and it was determined that the fluid required an average of 500 µl of 0.1 M NaOH to reach the endpoint, what could you conclude about the unknown body fluid? Is the body fluid acidic or basic? What is the approximate pH based on comparison to the four body fluids (gastric juice, pancreatin, saliva and urine) that were tested in the lab. Include evidence to support your answer. The Body fluid is acidic because NaOH or a base is being used to titrate it. Urine used an average of 400 uL NaOh titrant to reach its endpoint and this unknown body fluid uses an average of 500 uL to reach its endpoint. Urine has a pH number of 6 so the unknown body fluid should have a pH of about 5 because it takes 100 uL of titrant than urine to neutralize which means it is slightly more acidic. 12 | Page