Titration lab gizmos

Unit 5 Culminating Component

 

Scientific Terminology Inventory Probe – Acids & Bases

 

Read through the list of terms on the left-hand side. Place a check mark þ underneath the appropriate column based on your familiarity with that scientific term. If you know the term and can describe it, please write a description/definition in the space provided. At the end of the unit, return to this list and see where you’re at with your understanding of the terms.

 

Scientific Term	I have never heard of this.	I have heard of this but I’m not sure what it means.	I have some idea of what it means.	I clearly know what it means and I can describe it!
volumetric flask
pipet
net ionic equation
acid
base
pH
indicator
salt
Arrhenius definition
strong acid (or base)
weak acid (or base)
neutralization reaction
titration
burette
end point

 

Acid-Base Neutralizations

Label the parts of the Titration apparatus below.  Label the diagram (electronically or hand-written)

 

What should be placed here when titrating?

 

 

Define the following terms:

Titration
Indicator
Burette
Tap (stopcock)
Meniscus
Titrant
Equivalence point
Endpoint

 

 

Prior Knowledge Questions

One way to determine if a solution is acidic or basic is to use

litmus paper, as shown to the right. There are two types of

litmus papers: red and blue.

 

 

How does litmus paper indicate an acid? ___________________________________________

 

How does litmus paper indicate a neutral substance? _________________________________

 

How does litmus paper indicate a base? ____________________________________________

 

 

 

Gizmo Warm-up

Litmus is an example of an indicator, a substance that changes color depending on its pH (pH is a measure of the concentration of protons, or H⁺ ions). In the Titration Gizmo™, you will use indicators to show how acids are neutralized by bases, and vice versa.

 

To begin, check that 1.00 M NaOH is selected for the Burette, Mystery HBr is selected for the Flask, and Bromthymol blue is selected for the Indicator.

 

 

1. Look at the flask. What is the color of the bromthymol blue indicator? __________________

 

2. What does this tell you about the pH of the solution in the flask? ______________________

 

3. Move the slider on the burette to the top to add about 25 mL of NaOH to the flask. What happens, and what does this tell you about the pH of the flask?

 

_________________________________________________________________________

 

 

Activity A:   Acids and bases

Get the Gizmo ready: ·      Click Reset. Select 1.0 mol/L HNO3 for the Burette and Mystery NaOH for the Flask. ·      Select Phenolphthalein for the Indicator. ·      You will need a scientific calculator for this activity.

 

Introduction: When most acids dissolve in water, they dissociate into ions. For example, nitric acid (HNO₃) dissociates into H⁺ and NO₃^– ions.

 

Question: How do acids and bases interact in solution?

 

Measure: A titration can be used to determine the concentration of an acid or base by measuring the amount of a solution with a known concentration, called the titrant, that reacts completely with a solution of unknown concentration, called the analyte. The point at which this occurs is called the equivalence point.

 

Carefully add HNO₃ into the flask until the phenolphthalein begins to lose its color. Stop adding HNO₃ when the color change is permanent.

 

1. How much (HNO₃) was required to cause the indicator to change color? __________

 

1. What can you say about the pH before and after the last drop of HNO₃ was added?

 

___________________________________________________________________

 

 

Explore: Click Reset and change the indicator to Bromthymol blue. Add exactly 8.9 mL of HNO₃ to the flask.

 

1. What does the color of the indicator tell you about the current pH of the flask?

 

___________________________________________________________________

 

3. Add one more drop of HNO₃. What does the color tell you about the pH now?

 

­­­­­­­___________________________________________________________________

 

1. If you combine the results of this question with the results from part B above, what do you know about the total pH change caused by adding the last 0.1 mL of HNO₃?

 

___________________________________________________________________

 

 

 

 

Activity B:   Determining concentration

Get the Gizmo ready: ·      Click Reset. Select 1.00 mol/L NaOH for the Burette and Mystery H2SO4 for the Flask. ·      Select Bromthymol blue for the Indicator.

 

Introduction: By using an appropriate indicator, a chemist can tell when a solution is neutralized by monitoring its color.

 

Question: How is titration used to determine an unknown concentration?

 

1. Measure: Titrate the sulfuric acid analyte (H₂SO₄) with the sodium hydroxide titrant (NaOH).

 

How much 1.00 mol/L NaOH is needed to neutralize the H₂SO₄ solution? _______________

 

Calculate the amount concentration (mol/L) of H₂SO₄ using stoichiometry.  Use the GRASP method as shown in class to generate a complete response.  You may handwrite your response (strongly suggested) and send a copy or type it electronically.

 

2. Calculate: Select the Worksheet This tab helps you calculate the analyte concentration.

• Fill in the first set of boxes (“moles H₂SO₄” and “moles NaOH”) based on the coefficients in the balanced equation. (If there is no coefficient, the value is 1.)
• Record the appropriate volumes in the “mL NaOH” and “mL H₂SO₄” boxes.
• Record the concentration of the titrant in the M NaOH box.

 

Click Calculate. What is the concentration listed? ___________________________

 

Click Check. Is this the correct concentration? ___________________________

 

If you get an error message, revise your work until you get a correct value. (You may have to redo the titration if you do not have the correct volume of titrant.) And compare your answer with #1.

 

 

3. Practice: Perform all of the following titrations and determine the concentrations of the following solutions.

 

In each experiment, write the balanced chemical equation.

 

Complete the table below by listing the volume of titrant needed to neutralize the analyte and then calculate the analyte concentration.

 

 

Use the Worksheet tab of the Gizmo to verify the calculation each analyte concentration. Include all units.

 

Titrant	Analyte	Indicator	Titrant volume	Analyte concentration
0.70 mol/L KOH	HBr	Bromthymol blue
0.50 mol/L HCl	Ca(OH)2	Phenolphthalein
0.80 mol/L H2SO4	NaOH	Methyl orange

 

Balanced Chemical Equations:

 

 

Activity C:   Determining concentration

·      Using the inquiry data collected below, determine the concentration of the acids below.

 

 

1. A student obtained the data below from their titration. Determine the concentration (titre) of the hydrochloric acid.  Assume the student used 20.0 mL of hydrochloric acid for each trial.

 

Table 1 Burette Readings for the Titration of Hydrochloric Acid with 0.1 M Sodium Hydroxide

Reading (mL)	Trial 1	Trial 2	Trial 3
final reading	24.1	50.6	76.0
initial reading	0.0	24.1	50.6
volume added

 

2. If it takes 50.0 mL of 0.5 M KOH solution to completely neutralize 125 mL of sulfuric acid solution (H₂SO₄), what is the concentration of the H₂SO₄ solution?

 

 

Activity D:   Qualitative Analysis of Ions in a Solution

·      Investigate then qualitative properties of the solutions in the scenario below

 

1. Suppose that you are given two test tubes, labeled A and B. Each test tube is filled with a clear, colourless, aqueous solution.  One solution contains calcium chloride, and the other solution contains potassium nitrate.

 

1. Create a procedure for two tests you would perform to identify the contents of each tube.
2. Create and complete a data table with the observations you would expect for each solution.