Help-Chem. Lab Problem

[DrEaMeRcHiCk]

Hey you guys I know everyone is really busy but I was wondering if any of you can help me out with this assignment. I haven't done titrations in awhile so any help would be greatly appreciated...or maybe recommend a book that might help?

You are given a sample of an HCl solution of unknown concentration (also called analyte). Make and use a solution of NaOH (titrant) to determine the original concentration of the HCl solution. Sodium hydroxide (NaOH) solutions do not keep their concentration over long periods of time bacause NaOH reacts with CO2 in air.
Your available materials are:

-NaOH solid
-acidic solution of potassium hydrogen phthalate (KHP) of known concentration
-buret and other common glassware
-analytical balance
-water
-phenolphthalein as indicator

Describe the titration of a solution of HCl using a solution of standardized NaOH as the titrant.

Here are some questions to help with the assignment:
1. What is a titration? An analyte? A titrant?

2. What glassware is needed to perform a titration?

3. What is a standardization? Why would one need to make a standard solution?

4. What is the equivalence point? What methods can be used to determine the equivalence point?

5. How do you prepare a standard solution?

6. What is an indicator? What is it's role in a titration?

7. What is the laboratory method used to titrate an unknown strong acid solution with a standardized strong base solution?

8. What data should be collected during your titration in order to calculate the concentration of HCl?

9. How do you calculate the molarity/concentration of the unknown HCl solution?

Thanks in advanced! The general idea I have is to do a titration with NaOH and KHP (standard solution) to figure out the conc. of NaOH by testing with an indicator to find equivalence point. Then once conc. of NaOH is known, use it as the titrant in the titration of HCL to figure out the HCL conc. by once again using the phenolphthalein indicator to find e.p. and since moles of acid = moles of base at this point, I can find the conc. of HCL.

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[KUMoose]

The general idea I have is to do a titration with NaOH and KHP (standard solution) to figure out the conc. of NaOH by testing with an indicator to find equivalence point. Then once conc. of NaOH is known, use it as the titrant in the titration of HCL to figure out the HCL conc. by once again using the phenolphthalein indicator to find e.p. and since moles of acid = moles of base at this point, I can find the conc. of HCL.

Well since you have a balance and you have common glassware you don't need to determine the [NaOH], because you will know it. Find the molar mass of NaOH, measure out an amount of NaOH and throw it in a known amount of water. Thus you will know the [NaOH]. Add a Ph indicator to the KPH and titrate to the indicator set point (in my Chem2 class it was ~7, although I've seen it done to 5, 6 and 9). Once you know the [OH-] taken to get to a specific Ph, then you know the [H+]. Bing, bang, boom you're done.

The rest of the questions should be in any titration write-up, google for them.

 

[gimpsd]

Well since you have a balance and you have common glassware you don't need to determine the [NaOH], because you will know it. Find the molar mass of NaOH, measure out an amount of NaOH and throw it in a known amount of water. Thus you will know the [NaOH]. Add a Ph indicator to the KPH and titrate to the indicator set point (in my Chem2 class it was ~7, although I've seen it done to 5, 6 and 9). Once you know the [OH-] taken to get to a specific Ph, then you know the [H+]. Bing, bang, boom you're done.

The rest of the questions should be in any titration write-up, google for them.

Close but no cigar.

Unfortunatly, as much as we would like to think that the balance is super accurate and that nothing gets lost in transfer, that is never the case. In order to determine the true [NaOH], you will first need to do a titration with KHP. First, make a ~1M solution of NaOH (you will find the exact molarity in a sec.), then add one to two drops phenolphthalein indicator to ~10 ml of KHP to turn it a pinkish color and proceed to do a titration with your NaOH solution. From the volume of NaOH that it takes to turn the KHP clear, you will be able to determine the exact [NaOH]. Once you know this, then just run the experiment with HCl with phenolphthalein indicator and figure out how much volume of NaOH is needed to turn the neutralize the HCl. From this volume, you should be able to calculate the exact Molarity of HCl. Let me know if you need help with the calculations.

 

[KUMoose]

Close but no cigar.

Unfortunatly, as much as we would like to think that the balance is super accurate and that nothing gets lost in transfer, that is never the case. In order to determine the true [NaOH], you will first need to do a titration with KHP.

Yea I missed the known KPH concentration line, so I assumed there was no known concentration (remarkably like the final and midterm tests in Chemistry). Mea culpa.

 

[DrEaMeRcHiCk]

Thanks for the help gimpsd and KUMoose! I think I understand it now, I had the general idea, but I just wanted to make sure I was on the right track. Thanks so much =)