In this lab you will be performing a titration to determine the concentration of an acid solution. It is necessary in this lab to understand the difference between acids and bases. One definition is that acids produce H+ in aqueous solution, and bases produce OH–. Hydrochloric acid and sodium hydroxide combine together in a double displacement reaction to produce a neutral solution. Hydrochloric acid is actually hydrogen chloride gas in aqueous solution. We will also use aqueous sodium hydroxide.
Square brackets are used to indicate concentration: [H+] means “concentration of the hydrogen ion, in moles per liter.”
An indicator is a substance that changes color depending on exactly how acidic a solution is. You may be familiar with litmus paper, but there are more precise ones available. In this lab you will use Phenolphthalein ("FEEN-ul-thay-leen") as your indicator. This indicator is clear in acid solution and turns pink in base solution. An acid solution with phenolphthalein in it will be clear. If base is added a drop at a time, a pink tint will linger longer and longer after each drop, until it finally stays pink starting exactly when the acid is all neutralized.
Finally, the results section contains a category labeled “mmoles.” This is a millimole, or a thousandth of a mole. If a solution is 1.0 M, then it contains one mole in one liter, or one millimole in one mL. As far as units are concerned, [mol/L]x[mL] = mmol.
Data & Results
|1.||Write the balanced equation for the reaction of sodium hydroxide with hydrochloric acid. Include the correct products.|
|4.||Calculate the average concentration of the acid. Part of your grade will be based on how accurate AND precise your results are. [Attach all sample calculations for Trial #1!]|
|5.||Why are aqueous solutions used in this lab?|
|6.||What did you see as you added each drop of base?|
|7.||How many moles of sodium hydroxide would be required to neutralize 1.5 mole of hydrochloric acid?|
|8.||How many millimoles of acid are present in 150 mL of 2.0 M HCl solution?|
|9.||What type of reaction is represented by your answer to #1 (S, D, SD, DD, C)?|
REMINDER - show ALL calculations
for trial #1 on an attached sheet
[Simple Titration score sheet][MHS Chem page]