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Acids_and_Bases_Lab_1 – Physical Science Titrating with HCl and NaOH

Acids_and_Bases_Lab_1 – Physical Science Titrating with HCl and NaOH. Titration is a technique that chemists use to determine the Molarity of a solution of which we know the type of solute dissociated in water, but don’t know its concentration (concentration is in Molarity of course).

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Acids_and_Bases_Lab_1 – Physical Science Titrating with HCl and NaOH

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  1. Acids_and_Bases_Lab_1 – Physical Science Titrating with HCl and NaOH

  2. Titration is a technique that chemists use to determine the Molarity of a solution of which we know the type of solute dissociated in water, but don’t know its concentration (concentration is in Molarity of course). Because we know what the chemical (solute) is, we know how it will react with other chemicals and we can use that reaction to determine the concentration of the solution by measuring the formation of product(s).

  3. In the case of an unknown concentration of acid, we can use a known concentration of hydroxide base. This type of reaction is a neutralization reaction, where salt and water are products of the reaction: Acid + Base  Salt + H2O

  4. Acid + Base  Salt + H2O We can use a pH indicator, a chemical that changes color depending on the pH, to show us when the reaction has completely neutralized. This point, where all acid was consumed and there is a small known excess of base, is called the equivalence point.

  5. Acid + Base  Salt + H2O We can then use this equivalence point to determine the initial concentration of acid using a series of calculations. The goal of the titration is to get as close as possible to the equivalence point by careful addition of the base; this will ensure the calculated acid concentration is as close to the true value as possible.

  6. Acid + Base  Salt + H2O ? M HCl + 0.05 M NaOH  Salt + H2O For this lab, you will use a 0.05 M NaOH solution to titrate a HCl solution of unknown molarity. You will use a small amount (3 drops) of phenolphthalein as an indicator. Phenolphthalein appears clear in an acidic solution but undergoes a chemical reaction when the pH is 8.2 or higher and turns a bright fuchsia.

  7. Cut the top off of a plastic water bottle and throw the top away.

  8. Your teacher will pour approximately 100 mL of the ? M HCl solution into a graduated cylinder for you. Record the volume both precisely and accurately (make sure your measurement has a guesstimate)

  9. Slowly pour the ? M HCl solution into the prepared plastic water bottle. Set the graduated cylinder aside.

  10. Carefully add three drops of phenolphthalein to the mystery solution in the plastic water bottle. The phenolphthalein will be used as the indicator.

  11. Using the syringe provided, carefully pull out 60 mL of solution from the bottle of 0.05 M NaOH solution provided. Make sure your amount is exactly 60 mL.

  12. Carefully add the solution in the syringe to the solution in the plastic water bottle (do this drop by drop) until the solution turns a very light pink and stays that way even with gentle swirling.

  13. If you use all 60 mL of the 0.05 M NaOH solution that you have in the syringe and the mystery solution is still not pink, pull up another 60 mL of the 0.05 M NaOH solution and continue.

  14. When the mystery solution stays light pink, even with gentle swirling, stop adding the 0.05 M NaOH solution. Record how much of the 0.05 M NaOH solution was added to the mystery solution.

  15. If instructed to do the titration again, cut the top off of another plastic water bottle, throw the top away and proceed as before.

  16. When you have done all the titrations that your teacher has asked you to do, follow the instructions on the following slides to clean up.

  17. Step 10 Do not pull the plunger completely out of the syringe when rinsing out the syringe. You will get docked points if you do!!!!!! When completely done with the titration, dump any solution in the plastic water bottles down the drain with running water and then throw the plastic water bottle away. Rinse out the graduated cylinder and syringe (see above) and put them in the drying rack. Cap the bottle of 0.05 M NaOH solution.

  18. For the Lab report that you will hand in, you will need to figure out the molarity of the ? M HCl solution and show all the work required to do that figuring. To figure the molarity, you will have to use Unit Analysis and that requires a given and several ratios. The given you need is the volume of 0.05 M NaOH that you dropped into the mystery solution to make it turn slightly pink. The first ratio needed is the molarity ratio for the 0.05 M NaOH solution 0.05 molNaOH = 1 L solution

  19. The second ratio needed is the ratio of the number of moles of OH- ions produced from the dissociation of one mole of the ionic unit of NaOH 1 mol OH- = 1 molNaOH The third ratio needed is the ratio of the neutralization reaction which proceeds from the basic neutralization reaction equation H+ + OH- H2O or in other words, one H+ neutralizes one OH- So therefore the ratio is: 1 molH+ = 1 molOH- This Unit analysis will get you the number of moles of H+ that were neutralized.

  20. Now set the number of H+ neutralized over the volume that you recorded of the original amount of mystery HCl solution that you used. Simplify this ratio so that it gives you the molarity of the mystery HCl solution.

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