Acid base titration lab answers hcl naoh

Standardization of NaOH: Acid Base Titration Objective: In this lab, you will accurately determine the concentration of a solution of sodium hydroxide (NaOH) using a 0.500M potassium hydrogen phthalate (KHP) standard solution.

Background: Acid–Base Titrations

When an acid reacts with a base, a neutralization reaction occurs. The H+ ions from the acid and the HO– ions from the base combine to form water and are therefore neutralized. The other product of reaction is a salt. For example, hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) Acids and bases are classified according to the degree to which they dissociate into water. Strong acids and bases dissociate completely, whereas weak acids and bases only partially dissociate into ions. A reaction between a strong acid and a strong base results in a neutral solution (pH = 7). A reaction between a weak acid and a strong base results in a basic solution (pH > 7), whereas one between a strong acid and a weak base results in an acidic solution (pH < 7). The change in pH during the titration allows for monitoring using acid–base indicators. In this lab, a weak acid KHP is used to neutralize NaOH. Acid-base indicator phenolphthalein is added in its (colorless) acidic form to a precise volume sample of

KHP. KHP(aq) + NaOH(aq) → NaKP(aq) + H2O(l)

The base NaOH with an estimated ~1M concentration is slowly added to the sample of KHP. Once all the KHP has reacted with the base, the first excess drop of NaOH will cause the indicator to convert to its basic (pink) form. The exact concentration of the NaOH solution can then be calculated. Because the molar ratio of KHP to NaOH is 1:1, the moles of NaOH equals the moles of KHP in the above solution. From the definition of molarity: MNaOH × VNaOH = moles of NaOH MKHP × VKHP = moles of KHP Therefore, the standardized NaOH concentration, MNaOH = (MKHP × VKHP)/VNaOH.

Experimental Procedure: Simulation Link: http://chemcollective.org/vlab/101

1. Workbench setup. Retrieve the 0.500M KHP, ~1M NaOH solution, and the phenolphthalein from the stockroom. Double click on each solution to place it on the workbench. Note the volume and molarity of KHP, which can be found in the Solution Info window. Record them in the report sheet. 2. Retrieve a 50 mL buret. Click on the glassware button on the action bar. Click on the necessary glassware that appears on the drop-down menu. 3. Add a small amount (~0.3 mL) of indicator to the KHP solution. Drag the indicator solution bottle onto the KHP solution and transfer 0.3 mL indicator solution into the KHP solution. 4. Fill the buret with NaOH solution. Drag the flask of NaOH onto the buret so the mouse pointer is inside the edges of the recipient container (the buret). When the flask is tilted above the buret, click and hold down the Pour button in the transfer bar. When you release the mouse button, the Solution Info window will allow you to infer how much has been transferred. Use the detail view to record the initial volume of NaOH in the buret before starting titration. The buret, with 0 mL is on top and 50mL at the bottom, is a top down glassware and should be read differently than a graduated cylinder. Record and report your initial buret reading in report sheet. 5. Choose the “realistic pour” setting to dispense small volumes of NaOH from the buret into the KHP until a slight color change occurs. One short click typically adds 0.05mL of NaOH to the KHP solution. The longer the hold, the larger volume the buret dispenses. Use the pH value on the left to guide how much to add. Larger volume should be added when pH7. Record the final buret reading in the report sheet once the color change occurs. Calculate how much NaOH used in this titration. Volume of NaOH = final buret reading - initial buret reading. This concludes titration 1. 6. Repeat step 3 to 5 twice with a fresh KHP solution and refilled buret each time, but use the volume of NaOH in the first trial to estimate how much to add. Add only 0.05mL aliquot when pH>7 to achieve more accurate end point. Record the initial and final buret readings of each titration.

Standardization of NaOH Lab Report

Experimental Data and Results Table

Titration

1

2

3

Molarity of KHP

(M)

0.500M

Volume of KHP solution (mL)

25.00mL

Volume of KHP in L

Initial buret volume (mL)

0.00mL

0.00mL

0.00mL

Final buret volume

(mL)

38.85mL

Volume of NaOH

(mL)

38.85mL

Volume of NaOH in L

Molairty of NaOH

(M)

Average molarity of NaOH (M)