7_CHE 105

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Chemistry

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Dec 6, 2023

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Experiment 7: Determining Unknown Concentrations by Using Titrations. Introduction: The purpose of this experiment is to learn how to use titrations and their methods to determine an unknown substance. Along with determining how much of a substance is present in the solution. Using an acid-base titration the concentration of a solution will be determined. Using the analyte, the solution that is unknown, it will be titrated with the standard solution (sodium hydroxide) till they react completely. Since a neutralization titration is occurring the acid reacts with the base to produce salt and water. At the equivalence point in the acid-base titration, H + moles will be equal to OH - moles. The concentration of the acid can later be determined. For this experiment the sodium hydroxide will be provided by a teaching assistant and will be ready for the lab. The use of the pH electrode in this lab will be used to determine the equivalence point of the reaction. Based on the data obtained by the equivalence point, the concentration of the unknown will be able to be determined. The pH and drop counter will be used to determine the equivalence point, since MeasureNet will make a graph using pH vs. volume curve. Methods: The procedure following this experiment, determining unknown concentrations by using titrations, can be found on ppg. 100-103 in the General Chemistry Laboratory Manual 2022- 2023(April French, et al.). No changes were made to the procedure. Discussion:

The purpose of this experiment is to determine unknown concentrations by using an acid-base titration. For the reaction between the sodium hydroxide and potassium hydrogen phthalate the molarity of KHP solution was determined to be 0.178 M. The sodium hydroxide was determined to be 0.902605048 M. For trial one the molarity of analyte, sodium hydroxide was 0.919778 M, and for trial two it was 0.885432. Producing a rounded average of 0.903 M with a standard deviation of 0.02 M. The following trials will be data related to the reaction between citric acid and sodium hydroxide. For trial one the molarity of citric acid solution was found to be 0.303978 M, for trial two it was 0.298740, and for trial three it was 0.293549. The average molarity of citric acid was determined to be 0.298 M with a standard deviation of 0.005 M. The actual molarity given by instructor was 0.75 M. Causing a 297.3% error to be produced. The experimental results did not support the purpose of this experiment since there was such a large percent error that would not be accepted. There are many potential sources of error that occurred in this lab experiment. One was when turning the stopcock for the buret during the titration there was a moment where the beaker of the unknown was not being stirred. This could cause jumps and inconsistency in the graph. This could of easily been prevented if I continuously stirred the beaker during titration instead of pausing at the start to fix the buret. Another error could be the drops being too quick or accidentally turning the stopcock too far on the buret and a consistent stream could come out for a second. This would result in the drops and pH not being recorded properly for the graph. This could have been prevented by asking for help for stirring the beaker or turning the stopcock, not trying to do both at the same time. The final source of error could be the stirring was not quick enough, causing the graph to spike up in some points. Even towards the beginning there was consistent stirring, but it was inconsistent or just light. That error can be

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Part C – Acid–base and solubility equilibria 1. Rinse 4 regular size test tubes and a 10 mL measuring cylinder thoroughly with water. Number the test-tubes from 1 to 4 in a test tube rack. 2. Into each of test tubes 1 – 3 put a small amount of solid benzoic acid (put the same amount – about the size of a pea – in each test tube). 3. Add 2 mL (use the measuring cylinder) of water to tube 1 and shake to mix the contents. 4. Add 2 mL (measuring cylinder) of 2 M HNO3 to tube 2 and shake to mix the contents. 5. Rinse the measuring cylinder with water, then use it to add 2 mL of 2 M NaOH to tube 3 and shake for about 10 seconds to mix the contents. Rinse the measuring cylinder. 6. Pour about half of the solution from tube 3 into tube 4, than add 2 mL of 2 M HNO3 to tube 4. 7. Allow the test tubes to stand for 2 or 3 minutes then record the appearance of the mixtures in each test tube. 8. Answer the questions on the results page relating to this equilibrium system.

In a lab project, a student obtained a colored basic solution whose concentration has to be determined. The student wants to perform a titration but he does not know which indicator he can use. Can he perform a titration without an indicator? Which method can he use to determine the concentration and why?

Can you help me with this?

Exactly 10.66 ml of 0.066 M strong acid is added to a 30.00 ml. sample of a 0.068 M weak base solution. What is the pH at this point in the titration? K for the base is 2.51x10-5. REPORT YOUR ANSWER TO 2 DECIMAL PLACES. DO NOT INCLUDE UNITS. Type your answer....

1) A 45 mL sample of 0.175 M KOH is titrated with 0.200 M HI. a. b. c. d. Find the initial pH of the 0.175 M KOH solution. Find the pH when 18 mL of 0.200 M HI have been added. Find the pH when 63 mL of 0.200 M HI have been added. How many milliliters of 0.200 M HI must be added to reach the equivalence point? e. What is the pH at the equivalence point? f. Draw a titration curve for this titration. g. Which of the following indicators should be used to signal the endpoint of this titration: methyl red (pK₁ = 5.5), litimus (pK₁ = 7.0), or phenolphthalein (pK, = 8.7)? Explain.

A student performs a titration in order to determine the concentration of a hydrochloric acid solution. Early in the procedure, the flask is not placed directly under the buret and a small amount of the titrant, KOH, drains down the outside of the flask. How will this error affect the calculated value of the HCI concentration? O more information is necessary O calculated value = actual value O calculated value > actual value O calculated value < actual value

I need help answering question 1.

Please help me answer this question:

Write out what data and information you plan to collect during the experiment of identification of a weak diprotic acid using titration to answer how can a weak diprotic acid be identified when titrated with a strong base?Then list the equations and formulas you plan to use to manipulate that data.Also list how many trials you plan to do? If it's just one or more?

Can you confidently determine if the molarities are accurate? Explain why or why not.

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