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Acid-Base Titration
Task with Student Directions

Grade 9-12 Performance Task
Developed by: New York State Education Department (NYSED)
University of Buffalo and NORC (1991, revised 1993)

Introduction

This laboratory test presents a problem. Your task in Part A is to plan and design an experiment to solve the problem. You will have 30 minutes to complete Part A. At the end of 30 minutes, your answer sheet will be collected. You will then receive separate directions for Part B. In Part B you will use materials and equipment provided in the laboratory kit to collect experimental data for this problem. You may wish to do your preliminary planning on the sheet labelled "Working Copy." Write this plan on the appropriate answer sheet in your test booklet.

Part A

Problem

Chemists are often required to determine the concentration of unknown acidic or basic solutions. You will be provided with an unknown solution that is either acidic or basic. Your problem is to design an experiment, using the materials (and/or others) listed below, to determine the concentration of the unknown solution provided. Express your concentration of the unknown material in moles of H+ (aq) per liter or moles of OH- (aq) per liter of solution.

a) Under the heading PROCEDURE list in order the steps of the procedure you will use to solve the problem. You may include a diagram to help illustrate your plans for the experiment. Include any safety procedures you would follow.

b) Construt a DATA TABLE or indicate any other method that you could use to record the observations and results that will be obtained.

PLEASE NOTE: In Part A you are NOT to proceed with any part of the actual experiment. You are just to plan and organize a way to investigate the problem.

Materials

  • 2 beakers, 100 ml
  • 1 burette, 50 ml
  • 4 Erlenmeyer flasks, 250 ml
  • 1 filter funnel, small
  • 1 graduated cylinder, 50 ml
  • 1 burette stand
  • safety goggles
  • calculator
  • 1 wash bottle of distilled water
  • 1 white tile
  • hydrochloric acid, 0.1 mol/L
  • sodium hydroxide, 0.1 mol/L
  • phenolphthalein indicator
  • bromothymol blue indicator
  • unknown solution

ANSWER SHEET

PART A - Experiment Design

Organize your experiment design under the following headings:
PROCEDURE and DATA TABLE.
Use the front and back of the sheets if necessary.

PROCEDURE (Include diagram if appropriate)

 

 

 

 

DATA TABLE (For results and observations)

 

 

 

 

Part B

You will have 50 minutes to complete this part. You have been provided with a detailed Procedure (see next page) which you are to follow. Record your work for Part B on the answer sheet under the appropriate headings.

a) Peform the experiment by following the steps outlined in the procedure.

b) Under the heading RESULTS/OBSERVATIONS record the results of the experiment. Use statements, descriptive paragraphs, and tables of data where appropriate.

c) Under the heading CALCULATIONS show all equations and calculations used.

d) Under the heading CONCLUSION give an interpretation of your results. What did you learn from the experiment?

e) You have also been provided with a sheet labelled "Working Copy." Use this scrap sheet for any initial calculations or conclusion. However, be sure to enter your final work on the appropriate answer sheets.

f) At the end of 50 minutes, your answer sheets will be collected.

Safety

Acids and bases are highly corrosive!

(1) Students must wear safety goggles at all times and avoid direct contact with any of the reagents.

(2) If any of the reagents touches skin, the student must wash off immediately with water and inform the instructor of the incident.

 

Materials

  • 2 beakers, 100 ml
  • 1 burette, 50 ml
  • 4 Erlenmeyer flasks, 250 ml
  • 1 filter funnel, small
  • 1 graduated cylinder, 50 ml
  • 1 burette stand
  • safety goggles
  • calculator
  • 1 wash bottle of distilled water
  • 1 white tile
  • hydrochloric acid, 0.1 mol/L
  • sodium hydroxide, 0.1 mol/L
  • phenolphthalein indicator
  • bromothymol blue indicator
  • unknown solution

Procedure

  1. Transfer 25 ml of the unknown to a clean, dry Erlenmeyer flask using a graduated cylinder.

  2. Add three drops of either bromothymol blue OR phenolphthalein indicator to the unknown solution using the dropper. Do either A or B below.

A. BROMOTHYMOL BLUE:

a) If the color of the unknown solution is blue, SLOWLY add HCl solution from a burette. As the HCl solution is added, gently agitate the Erlenmeyer flask until the endpoint is reached (solution turns green). Measure the volume of HCl added to carry out the neutralization. Record your results in the table.

b) If the color of the unknown solution is yellow/green, SLOWLY add NaOH from a burette. As the NaOH is added, gently agitate the Erlenmeyer flask until the endpoint is reached (solution turns blue). Measure the volume of NaOH added. Record your results in the table.

--OR--

B. PHENOLPHTHALEIN:

a) If the unknown solution remains colorless, SLOWLY add NaOH from a burette. As the NaOH is added, gently agitate the Erlenmeyer flask until the endpoint is reached (solution turns pink). MEasure the volume of NaOH added to carry out the neutralization. Record your results in the table.

b) If the color of the unknown solution is pink, SLOWLY add HCl from a burette. As the HCl is added, gently agitate the Erlenmeyer flask until the enpoint is reached (solution becomes colorless). Measure the volume of HCl added. Record your results in the table.

  1. Repeat the titration at least three times to gather more data. Take the average of these readings.

  2. Calculate the number of moles of acid/base used to neutralize 25 ml of the unknown solution. Remember

ANSWER SHEET

PART B - Experiment Report

Organize your experiment report under the following headings:
RESULTS/OBSERVATIONS, CALCULATIONS, and CONCLUSIONS.
Use the front and back of these sheets if necessary.

 

RESULTS/OBSERVATIONS

Indicator: __________________________

 
Volume of Unknown
Volume of Acid/Base Added
Trial 1    
Trial 2    
Trial 3    
Average    

 

 

 

CALCULATIONS

 

 

 

 

CONCLUSIONS

 

 

 

 

 

 

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