Reference no: EM131271634

Assignment: Introduction to Solubility PhET Lab

Part 1

We can express concentrations in terms of moles solute per liters of solution

Introduction

When we cook pasta, we frequently dissolve table salt in water. Is there a limit to how much salt we can get into the water?

When ionic-bonded compounds (like table salt, NaCl) are dissolved in polar solvents (like water), the polarwater molecules act to pull the ions in the compound apart. When this happens (called dissociation), ions are released into the solution. Is there a limit to the number of ions that can exist in solution?

Pre-lab Vocabulary

Please use your textbook, your notes, or the internet to define the following terms:

Saturated: A saturated solution is a chemical solution containing the maximum concentration of a solute dissolved in solvent.

Unsaturated: When in a solution solute can be added and dissolved, the solution is unsaturated.

Supersaturated: A solution with more dissolved solute than solvent would normally dissolve in its current conditions.

Molarity: A unit of concentration measuring the number of moles of a solute per liter of solution.

Cation: A positively charged ion, ex: one that would be attracted to the cathode in electrolysis.

Anion: A negatively charged ion, ex: one that can be attracted to anode in electrolysis.

Dissociation: A general process in which molecules (or ionic compounds) separate or split into smaller particles such as atoms, ions, or radicals, usually in a reversible manner.

Solubility: Amount of substance that dissolves in a unit volume of liquid substance (called solvent) to form a saturated solution under specific conditions of temperature and pressure.

ProcedurePhET Simulations → Play With Sims → Chemistry→Salts and Solubility→ Run Now

Take some time and familiarize yourself with the simulation before answering the below questions:

1. What happens to the bound Na⁺ and Cl^- ions as they enter the water?

They separate into Na⁺ and Cl^- ions because Na⁺ is attracted to oxygen and Cl^- is attracted to hydrogen.

2. Is there a point at which no more sodium and chloride ions will dissolve? How do you know?

Yes, this is the saturation point. For NaCl the saturation concentration in pure water is relatively high and you can dump a lot of salt into water before it will precipitate out as a solid on the bottom of the container.

3. What do we call a solution that has as many ions as it can hold?

A saturated solution.

4. What happens if you add additional, solid NaCl after the maximum has been reached?

If the solution has reached its maximum (is saturated) then as much of NaCl has dissolved in water as possible and if you add more it will just remain as solid.

5. What happens when more water is added to a saturated solution?

More NaCl would be capable of dissolving in additional solvent.

6. What happens to the ions bound together as a solid when the solution's volume is reduced?

Reducing the volume of an entire solution increases its value.

7. How many total Na⁺ ions can you add until no more will dissolve (the maximum amount)?

8. How many moles does this many ions represent? (recall, 1 mole = 6.02 x 10²³ things)

9. What volume(in Liters) did you use to get the saturation point in #7 above?

10. What concentration is this? (In mole/L, use #8 and #9's answers)This is molarity, M.

For each slightly soluble salt...

1. Determine the Chemical Formula
2. Write a Dissociation Equation (Example: NaCl_(s)→ Na⁺_(aq) + Cl^-_(aq))
3. Determine Concentration (mole/L) of the molecule and EACH ION in the compound in a saturated solution.

Remember...to find concentration in Molarity: calculate moles present, divide moles into volume in Liters.

Mercury (II) Bromide

1. Chemical Formula: ___________________________________________
2. Dissociation Equation:_________________________________________
3. Concentration of entire molecule at saturation (M): ___________________
4. Concentration of cation (+) at saturation (M): ________________________
5. Concentration of anion (-) at saturation (M): ________________________

Copper (I) Iodide

6. Chemical Formula: ___________________________________________
7. Dissociation Equation: _________________________________________
8. Concentration of entire molecule at saturation (M): ___________________
9. Concentration of cation (+) at saturation (M): ________________________
10. Concentration of anion (-) at saturation (M): ________________________

Strontium Phosphate

11. Chemical Formula: ___________________________________________
12. Dissociation Equation: _________________________________________
13. Concentration of entire molecule at saturation (M): ___________________
14. Concentration of cation (+) at saturation (M): ________________________
15. Concentration of anion (-) at saturation (M): ________________________

Thallium Sulfide

16. Chemical Formula: ___________________________________________
17. Dissociation Equation: _________________________________________
18. Concentration of entire molecule at saturation (M): ___________________
19. Concentration of cation (+) at saturation (M): ________________________
20. Concentration of anion (-) at saturation (M): ________________________

Post-Lab Conclusion Questions and Calculations

1. Adding water to a solution of ions increases / decreases / doesn't change concentration.

2. Reducing volume of an entire solutionincreases / decreases / doesn't change concentration.

3. Adding more solid compound to an unsaturated solution increases / decreases / doesn't change concentration.

4. Adding more solid compound to a saturated solution increases / decreases / doesn't change concentration.

5. The bound ions of a solid compound at the bottom of a saturated solution stay bound / dissolve and are rebound. (watch carefully)

6. Determine the concentration of a solution of 2.4 moles of sugar (no dissociation) in 3.5 L of water

7. How many moles of NaCl would be required to produce .95 L of a .58 M NaCl solution?

8. What volume of water would be required to dissolve 67 grams of Lithium Fluoride (LiF) to a concentration of 2.6 M?

9. What is the concentration of a solution of 3.5 x10²² molecules of sugar in 25 mL of water?

10. How many moles of FeCl3 (compound) are present in 2.1 L of a .85 M solution?

11. How many moles of Fe³⁺ ions are present in this solution?

12. How many moles of Cl^- are present in this solution?

13. What is the concentration of a solution made from 130 grams of Cu₃(PO₄)₂ in 3.9 L of water?

14. What is the concentration of Copper (II) ions in the above solution?

15. What is the concentration of Phosphate ions in the above solution?

Part 2

Learning Goals: Students will be able to:

• Calculate Q.
• Predict what would be observed on a macroscopic level to a solution by comparing Q to Ksp.
• Use microscopic illustrations, to help explain the predictions.
• Use LeChatelier's Principle to predict how changing the amount of water will affect the solution.
• Relate thermodynamic properties to LeChatelier's principle and the solubility of salts.

1. Review your results for how many Strontium and Phosphate ions can be dissolved in 1x10-16liters of water. Predict what would happen if you started with 1x10-16liters of water and shook in 150 Strontium and 100 Phosphate.

a. Write down your prediction. Test it and explain your results. In your explanations, be sure to discuss which components of the solution represent reactants and which represent products. For this example, which direction does this equilibrium shift when you add these many ions (towards the products or reactants)?

b. Calculate the value of Q for 150 Strontium and 100 Phosphate; show your work. (See https://www.chem.purdue.edu/gchelp/howtosolveit/Equilibrium/Reaction_Quotient.htm for sample calculations)

c. Write the Ksp for 150 Strontium and 100 Phosphate (See Solubility Equilibrium for examples)

d. Summarize how comparing the values for Q and Ksp can help predict what will happen when you put salts in water. Illustrate your summary with "test tube" size drawings and "close-up" views to show the ions and crystals.

2. Write LeChatelier's Principle in your own words. (Review LeChatelier Principle for examples and definitions)

a. If you had a saturated solution, what should happen if you add water? Explain your reasoning using LeChatelier's Principle and then test your ideas using the simulation.

b. Predict how your answer would change for an unsaturated solution and then test your ideas.

c. Test to see how letting out water affect saturated and unsaturated solutions.

d. Explain using LeChatelier's Principle what happens to saturated and unsaturated solutions when the amount of water is varied. How does temperature affect equilibrium of a solution? In your discussion, explain the directional shifts that result when a reaction is endothermic versus exothermic and relate these shifts in equilibrium to the salts in your simulations.