Below is a lab with a procedure listed as well as my questions for the lab on th

Question

Below is a lab with a procedure listed as well as my questions for the lab on the very end. Please answer the ones with a blank box the best you can. Thank you!!

Procedure:

Coarse Titration

1. Move your mouse cursor over the hydrochloric acid (HCl) and sodium hydroxide (NaOH) on the Materials shelf. You will see that the sodium hydroxide is labeled as 0.1 M while the concentration of hydrochloric acid is unknown. Please assume that NaOH concentration is known more precisely to four significant figures as 0.1000 M, which is usually the case in a real lab.

2. Take a burette from the Containers shelf and place it on the workbench.

3. Fill the burette with 50.00 mL of sodium hydroxide (NaOH) titrant.

4. Take a clean Erlenmeyer flask from the Containers shelf and place it on the workbench.

5. Add 10.00 mL of hydrochloric acid (HCl), unknown concentration, to the Erlenmeyer flask.

6. Add 10.00 mL of water to the Erlenmeyer flask. This increases the total volume in the flask, making it easier to see the color change, but note that the value to use for the volume of hydrochloric acid (HCl) when calculating its concentration is still 10.00 mL.

7. Add 2 drops of phenolphthalein solution to the Erlenmeyer flask.

8. Drag the Erlenmeyer flask and place it anywhere on the base of the burette. The Erlenmeyer flask is placed under the burette so that liquid will drip from the burette into the Erlenmeyer Flask.

9. Addition of titrant from the burette is controlled by the black knob at the bottom of the burette glass tube. You can deliver one drop of titrant with each short click of the black knob, and you can deliver a stream of titrant from the burette by clicking-and-holding the black knob - the longer you hold the knob, the more titrant will be delivered all at once.

10. You are now ready to start the coarse titration. Try to find the length of time required to click and hold the burette knob so that you deliver approximately 2 mL of sodium hydroxide (NaOH) from the burette to the Erlenmeyer flask. After each addition, move the mouse cursor over the burette - this will enable you to see its current volume. To determine the amount of titrant delivered from the beginning until now, subtract the amount of liquid currently in the burette from the starting volume of 50.00 mL. Your volume readings should have 2 decimal places.

11. Continue to add the sodium hydroxide (NaOH) titrant in 2 mL increments. Each time, note the burette volume level - when the end point is passed (when the color of your solution changes) you will have recorded the last volume level before it was passed. For example, if a volume reading of 34.40 mL was in the burette before the end point, but a reading of 32.10 mL was past the endpoint, you know that the FINE TITRATION can begin after adding 15.60 mL (50.00 mL - 34.40 mL = 15.60 mL).

12. Remove the Erlenmeyer flask from the burette and place it in the Recycle Bin.

Fine Titration

13. Refill the existing burrette with 0.1000 M NaOH so that the volume is 50.00 mL.

14. Take a clean Erlenmeyer flask from the Containers shelf and place it on the workbench.

15. Add 10.00 mL of hydrochloric acid (HCl), 10.00 mL of Water, and 2 drops of phenolphthalein to the Erlenmeyer flask.

16. Place the Erlenmeyer flask at the base of a new burette.

17. Add the initial large quantity of titrant, determined performing the coarse titration, so that you can begin with the fine titration. The solution in the Erlenmeyer flask should still be colorless.

18. Once you are close to the end point, add sodium hydroxide (NaOH) from the burette DROP-WISE. This means adding a single drop at time which is done with single, short clicks on the black knob. You may decide to click and hold for short times, but in doing so you may miss the exact endpoint of the titration.

19. When the solution in the Erlenmeyer flask changes color, stop adding titrant. Record the starting volume of the burette and the volume left in the burette when the endpoint was reached. Subtract the second value from the first to obtain the total amount of sodium hydroxide (NaOH) that was delivered to complete the titration.

20. Repeat the fine titration (steps 13-19) at least one more time to ensure you have precise results.

Titration Tutorial

Introductory Questions

Refer to Background and to Section 4.6 in your textbook.

Define equivalence point.

    The point to where both reactants have reacted completely. For this experiment it is when the acid and base reactants are completely neutralized and there is no excess of either one.
  

Define end point.

  This is when the equivalence point has been reached and the indicator changes color.
  

During a titration of HCl with NaOH in aqueous solution, what is the composition of the solution at the equivalence point?

What color is the base form of phenolphthalein indicator?

  Purple/violet
  

Why is the H2O usually a product during an acid-base neutralization reaction?

The Experiment

Complete this assignment using what you think was your most accurate two titrations:

6. Record the following data for what you think were your two most precise titrations. Be sure to report your answers with the number of significant figures you measured.

Fine Titration Data

Trial 1

Trial 2

a
  

Volume of NaOH solution in the burette at the start (mL):

50.00

50.00

b
  

Volume of NaOH solution in the burette at the end (mL):

38.00

38.75
  

c
  

Volume of NaOH solution delivered to the flask (mL):
  

12.00

11.25
  

d
  

Volume of HCl solution added to the flask (before adding water) (mL)

10.00

10.00
  

e

Moles of NaOH added to the HCl solution (mol)

f

Moles of HCl in unknown solution prior to titration (mol)

g

Molarity of HCl in unknown solution prior to titration (M)

    The point to where both reactants have reacted completely. For this experiment it is when the acid and base reactants are completely neutralized and there is no excess of either one.
  

Explanation / Answer

Q. 1) During a titration of HCl with NaOH in aqueous solution, what is the composition of the solution at the equivalence point?

At equivalance point number of moles of acid and base both are reacted completely. and the solution has salt as a solute and water as a solvent.

Q 2 )

Why is the H2O usually a product during an acid-base neutralization reaction?

we know in solution acid gives a proton and base gives OH- . When OH- and H+ reacts then there is formation of H2O (l). Lets explain this by using following general reaction

HA is acid and BOH is water.

when HA reacts with BOH the reaction is

HA(aq) + BOH (aq) -----> AB (aq) + H2O (l)

Experiment :

Calculation of moles of NaOH :

for Trial 1 :

Moels of NaOH = Molarity * volume in L

now we know molarity = 0.100 M

volume = 12.00 mL = 0.012 L

mol NaOH = 0.1000 M * 0.012 L = 0.0012 mol NaOH

For trial 2 : volume of NaOH = 11.25 mL

mol NaOH = 0.1000 L * 0.01125 L

= 0.001125 mol

We know the reaction of HCl and NaOH

HCl (aq) + NaOH (aq) ---------> H2O (l) + NaCl (aq)

From this reaction we say that mole ratio between NaOH and HCl is1 : 1

By using this we calcuate moles of HCl :

for a) Volume of NaOH = 12.00mL , molarity of NaOH = 0.1000 M

For trial 1 :

mol HCl = mol NaOH * 1mol HCl / 1 mol NaOH ...( mol ratio 1: 1 )

= 0.0012 mol NaOH * 1mol HCl / 1 mol NaOH = 0.0012 mol HCl

For trial 2

volume of NaOH = 11.25 mL

mol HCl = 0.001125 mol NaOH * 1mol HCl / 1 mol NaOH = 0.001125 mol HCl

Lets calcualte molarity of HCl in two separate solution :

molarity for trial 1

[HCl ] = no. mol / Volume in L = 0.0012 mol / 0.010 = 0.12 M

for trial 2 :

[HCl ] = 0.001125 mol / 0.010 L = 0.1125 M

Now lets take average of both

[HCl ] = (0.12 M + 0.1125 M )/ 2 = 0.1163 M

Molarity of HCl = 0.1163 M

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