Acid-Base Solutions Exploration Worksheet

Acid-Base Solutions Exploration Worksheet University of Colorado PhET Click < Introduction> to begin. Part 1: Procedure 1. The lab has 2 tools that allow you to test for pH values: A probe , and pH paper . Use each one by dipping it into the solution to be tested. Try all the given types of solutions and fill in the Data Chart with the pH value 0-14. 2. The circuit with a battery and bulb is the tool used to test for conduction of a solution. By dipping the wire leads into the solution, the bulb will either remain unlit, be dimly lit, be somewhat bright, or very bright. Test each solution and record your observation for the bulb’s brightness in the chart below. Part 1: Data pH Value from Probe Color & pH Value from pH Paper Observations from Circuit Tool Describe the brightness 3.0 Red (3) Dimly lit 8.5 Blue (8) Bright 7.0 Green (7) Unlit 1.0 Dark red (1) Very dim 12.0 Violet (12) Very bright Part 1: Analysis 1. What pH value range is observed: a. for acids?____0–6 __________b. for bases?__8–14__________ 2. Why are some solutions better conductors of electricity? Solutions with higher concentrations of ions (like H₃O⁺ or OH⁻) conduct electricity better because ions carry electric charge through the solution. Page 1 of 5 © Copyright University of Colorado Acid-Base Solutions Exploration Worksheet University of Colorado PhET Part 2 Procedure, Data & Analysis: Recall: The amount of ionization or dissociation of ions determines the strength of an acid or base. The concentration of [H3O+], hydronium and [OH-], hydroxide ions can be used to calculate pH and pOH as shown on the diagram here: Note: we use [H3O+] and [H+] interchangeably. 1.​ Click on Water Solution, Graph View, Probe Tool. Insert the probe in the water. Notice that the initial concentration of the solution is given before any ionization or dissociation takes place. 2.​ Fill in the missing concentration values for the hydronium and hydroxide ions on the diagram here: Use the concentration value for [H3O⍅] to calculate the pH. Show work: 3. Use the concentration value for [OH-] to calculate the pOH. Show work:[H3O+][H_3O^+][H3​O+] = 1.0×10−71.0 \times 10^{-7}1.0×10−7 M​ [OH−][OH^-][OH−] = 1.0×10−71.0 \times 10^{-7}1.0×10−7 M 4. Did your answer to #2 match the pH given in the simulation? Yes, the calculated pH was 7.0, and the simulation showed pH = 7.0. Page 2 of 5 © Copyright University of Colorado Acid-Base Solutions Exploration Worksheet University of Colorado PhET ​ 5. Is the answer to #3 equal to: (14 - pH)? __Yes_________ Show work: __14−7=7=pOH___________________​ 6. Is the solution an acid, a base or neutral based upon the calculated pH?______Neutral, because the pH is 7. ___________ Part 3 Procedure, Analysis, Conclusion: My Solution At the bottom of the screen, click the button. The default setting shows a weak acid with a concentration of 0.010 M. Insert the pH probe to show an initial pH of 4.50. The beaker is shown below:​ 1. Slide the initial concentration bar to the right to increase the number of solute molecules and then slide it to the left. What effect does changing the concentration have on the pH value? (Be specific)Increasing the concentration of a weak acid lowers the pH (more acidic); decreasing it raises the pH (less acidic). Page 3 of 5 © Copyright University of Colorado Acid-Base Solutions Exploration Worksheet University of Colorado PhET 2. Return to your default setting and insert the probe (you can click reset to return to the default). Now slide the strength to the right to make the acid stronger. a.​ As you increase the strength, describe the change in the number of blue A- ions, orange H3O⍅ ions and the original HA acid:More blue A⁻ ions and orange H₃O⁺ ions appear, and there are fewer un-ionized HA molecules. This means more dissociation happens. ​ b.​ As you increase the strength, describe the change in the concentrations of the ions in the solution? Hint: Click < Graph> to see how the concentrations rise and fall. [H₃O⁺] and [A⁻] go up, while [HA] goes down. Stronger acids dissociate more, even at the same concentration. 3. Does the pH seem to depend upon the concentration of [H3O+] ions? Yes or No? Yes. As [H₃O⁺] increases, pH decreases. 4. We always assume that strong acids will 100% ionize in water. Click reset and move the slider to strength: strong. Insert the probe. Record pH. Observe the number of ions in the beaker and click < Graph> to observe the concentrations.​ a.​ pH Value = _1.00 _____________ ​ b.​ Does the beaker contain particles that have not ionized and have 0% concentration?yes c.​ If so, what particle seems missing? __HA — because strong acids ionize completely. __________________. Why is it likely missing? 5. Click reset and change to a base. Repeat #1-4 above and describe any different results or simply write, “Same results for bases.” #1: Increasing concentration increases the pH (more basic), and decreasing it lowers the pH. #2: Strong bases show more OH⁻ ions and fewer undissociated particles. #3: Yes, pH goes up with higher [OH⁻]. Page 4 of 5 © Copyright University of Colorado Acid-Base Solutions Exploration Worksheet University of Colorado PhET #4: pH is high (13–14), and no un-ionized base particles are seen for strong bases. Conclusions: If the answer is no, explain why not. 6. YES or NO? Can a weak acid be concentrated? 7. YES or NO? Can a strong acid be dilute? 8. YES or NO? For acids, can increasing the initial concentration increase the pH? 9. YES or NO? For Bases, can increasing the initial concentration increase the pH? Page 5 of 5 © Copyright University of Colorado