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12 Dec 2019

My teacher gives us tables to fill out, and I am really confused about how to go about it. Usually she gives us a few bits of information, but I need to learn how to do the conversions on my own. A table usually looks like this (with some procedure text):

compound mp/bp, C MW (g/mol) equi mmol g density (g/mL) mL
thiamine-HCl mp, 260 (dec) 337.3 (solid) XXX
benzaldehyde bp, 178-179 1.044
NaOH, 10% (w/v) XXX 40.0 XXX

This table is an example for the formation of benzoin. The procedure involves .420 g thiamene HCl, 1.0 mL 10% NaOH, and 1.20 mL of benzaldehyde. I can fill in those things, but I don't know how to fill in the other blanks. For example, how do you calculate equiv (from any of the above)?

From here, how do I calculate theoretical yield? I know that I need to start with the limiting reagent, but how do I determine which one that is?

Thanks!!!! I can usually get help from my friends, but I need to know how to do these calculations (specifically equiv and mmol) on my own.

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Collen Von
Collen VonLv2
13 Dec 2019

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Related questions

So I did a titration lab where were reacted various amounts of Mg with 10mL of HCL and then neutralized the raction with NaOH. I have my table of values for Mass of Mg (g), Initial Volume NaOH (mL), Final Volume NaOH (mL), End Point Volume (mL), Limiting Reagent (Mg or HCL). There is a Titration table I need to fill in that asks for Moles of Mg (mol), Moles of NaOH (mol) and Moles of H+ reacting with Mg (mol). I have the Moles of Mg calculated and I also have Moles of NaOH (mol) calculated but how do I go about finding Moles of H+ reacting with Mg. The manual says I can use: Moles of H+ total - moles of H+ excess = moles H+ reacting with metal. Where could I obtain those numbers.

I had in my notes to take Moles of Mg - Moles of NaOH and that gives the value but the problem with I am getting with that method is that if my limiting reagent is Mg then my Moles of H+ calculation ends up being a negative number.

My formula for calculating Moles of Mg is (Mass of Mg starting) * (1Mol/24.31g) = Moles of Mg

My formula for Calculating Moles of NaOh is: (End Point Volume)*(1L/1000mL)*(.3M HCL/1L) = Moles of NaOH

Thanks!

Some examples of my numbers would be

Moles of Mg = .001, Moles of NaOH = 8.58*10-3 so that gives me a -7.6*10-3 but I don't know if that is correct. Any help?

I am unable to solve these questions due to a time constraint. I received help on part 1 of the unknown acid. Need help with the rest! I really appreciate it!

Lab: ACID-BASE TITRATION

Objective: To use titration to determine in Part 1, the concentration (molarity) of an unknown acid solution and in Part 2, the purity of a sample of KHP acid. Background: Titration is a volumetric technique used to determine the concentrations of solutions, molar masses of solids, and purity of samples. A titration inolves the addition of a titrant (a solution of known concentration) to an analyte ( a solution of unknown concentration), or vice versa, using a piece of glassware called a burette. The titration is carried out until it reaches an equivalence point (the exact point at which the reaction between the two solutions is complete). A chemical indicator is often used to aid in the identification of the equivalence point. An indicator changes color upon reaching the equivalence point of endpoint. Since we will be carrying out an acid-base titration, the indicator must change color upon reaching the endpoint at a specific pH. An example of such an indicator is phenolphthalein, which changes from colorless to pink near the equivalence point when pH approaches 7. It should be noted that the indicator selected is dependent upon a given titration, so that the observed color change is close to the ideal equivalence point. Once the titration is completed, we can use the volumes measured for each solution, as well as the concentration of the titrant, to determine the concentration, molar mass, or purity of the unknown analyte. Procedure Note: During lab, record all measurements and data in a clearly labeled table. Part 1: 1. Obtain ~80mL of ~0.1M of base (sodium hydroxide, NaOH) into a labeled beaker. Make sure to report the actual concentration from the bottle. 2. Obtain ~25mL of unknown acid into a second labeled beaker. Record whether your acid is monoprotic, diprotic, or triprotic. 3. Using a funnel, or carefully pouring, fill the burette with sodium hydroxide NaOH. Make sure a labeled waste beaker is under the buretter to catch any drippings. Rinse your burette by filling it with ~5-10mL of NaOH. Turn the knob to let ~2 mL out the tip into the waste beaker. Make sure your waste beaker is under the burette to catch any drips. Next, turn the Burette upside down and pour the remaining NaOH into your waste beaker while twisting the burette to coat the inside with NaOH. 4. Fill your burette with sodium hydroxide. Turn the knob to fill the tip of the burette with NaOH. Record the initial volume to the correct number of significant figures. 5. Using a volumentric pipette, transfer 10.00 mL of your unknown acid into the Erlenmeyer flask. 6. Add 3 drops of pH indicator and magnetic stirrer to the Erlenmeyer. 7. Under the burette, place the Erlenmeyer on a hot plate and turn on the stir knob. Heat should be off. 8. Titrate the unknown acid until the solution turns pink and remains pink. 9. Record the final volume on the burette to the correct number of significant figures. 10. Repeat (4) to (7). Pre-plan the whole lab and who will do which task. MY RESULTS: PART 1 The actual concentration of NAOH is 0.5939, 80 mL Initial Final 24.9 mL 44.5mL 26.1 mL 45.57mL PART 2 Impure KHP (SAMPLE B ) Only Paper: 0.280 g Impure KHP Mass: 0.526 g Initial volume: 22.30 mL + water +26.10 mL Final Volume: 26.80 mL QUESTIONS: 1. Calculate the concentration (molarity) of your unknown acid. 2. Calculate how many grams in your impure KHP sample was indeed KHP. 3. Calculate the percent (by mass) KHP in the sample. Part 2: 1. What would happen to the final result( state what the final result is ) if the tip of the burette was not filled when reading the initial volume? 2. What would happen to the final answer if you used Ca(OH)2 instead of NaOH and DID NOT know it? 3. What would happen to the final result if the Erlenmeyer flask was contaminated with other types of acid? 4. Recalculate the concentration of your unknown acid if it was given as a diprotic acid. 5. Draw a molecular level picture (showing Na+, H+, OH-, H2O, etc...) of what is in your beaker before, at half point, at equivalent point, and at end point of the titration. Part 3: 1. What would have happened to the final result if the impurity in the sample was also acidic? 2. What would have happend to your final result if you used ~25mL of water to dissolve the solid acid instead of 20mL? Summary data: Create a clearly labeled table of all your final data results for each run, and athe average of multiple runs. Part 1: Unknown #, Vol base, M base, Vol acid, M acid. Part 2: Sample #, % KHP (purity)

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