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Solutions

Properties and counting particles in solutions

SolutionsProperties and counting particles in solutions
https://youtu.be/HOQH0kge30o
https://youtu.be/Kwgo9kJ-5kw
Stop at 5:40 in the video above. The rest of the material has been removed from the CHM 101 course.
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Reviewing Mixtures (aka solutions)

Mixtures can be classified as homogeneous or heterogeneous depending on how well mixed the mixture is at the particle level. This is mainly a visual distinction. Homogeneous mixtures look like one substance like sugar dissolved completely in water (we usually call these solutions) or brass (a metal mixture called an alloy).
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Effects of temp on solids dissolving in water

In general, the solubility of solids in water increases with increasing temperature. The solubility represents the maximum amount a given solute will dissolve in a set volume of the solvent (water in this case) at a particular temperature. If a point (amount added to water AND temperature) lies on or above the curve for a particular substance, we call the solution saturated. If the point is above, the solution will be a heterogeneous mixture since there will be solid at the bottom. If a point lies below the curve, the solution is unsaturated.

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Effects of temp for gas solubility in water

An exception to the general increase in solubility of solutes with increasing temperature is the solubility of gases. Gases tend to decrease in solubility with increasing temperature. The effect is why lakes become starved for oxygen in the summer. The reason is that gases are generally nonpolar and do not dissolve well in water anyway. With increasing temperature, the particles all move faster and the interaction between water and the gas molecules weakens.

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Gas solubility decreases with increasing temp in WATER

The reason was covered above but the important thing to note is the difference between this graph and the one for solids above which shows the opposite trend.
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Gas solubility vs temp can increase if it isn't water!

When the solvent is changed to something more non polar as opposed to water, gas solubility increases with increasing temperature just as it does for many solids.
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The solubility of gases increases with pressure

The pssst sound from a carbonated beverage is the result of exploiting Henry's Law: gas solubility increases in a liquid with increasing pressure. The psst is the pressure release which then makes the gas "come out of solution" resulting in the pleasing bubbles.

Solutions: Crash Course Chemistry #27

Practice

1. Identify the solute and solvent in each solution.

(a) 80-proof vodka (40% ethyl alcohol)

(b) oxygenated water

(c) antifreeze (ethylene glycol and water)


2. What are the dissolved particles in a solution containing a molecular solute? What is the name for this kind of solution.


3. A KNO3 solution containing 110 g KNO3 per 100 g of water is cooled from 60 °C to 0 °C. What happens during cooling? Does all of the solute stay dissolved? If not, how much is not dissolved?

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Concentrated vs dilute vs strong vs weak

Strong and weak electrolytes differ in the degree of ionization but concentrated and dilute solutions differ in the amount of solute dissolved. So strong electrolytes like HCl are always strong even in dilute solutions. By contrast, weak electrolytes are always weak even when you have a fairly concentrated solution (like 10M).

Concentration-counting particles

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Mass percentage (w/v)

This kind of concentration is often used for solid solutes dissolved in a solvent to make a certain volume of solution.


Mass of solute/volume of solution x 100


The important thing to recognize here is the word solution is the volume of the solute + solvent (you may need to use density to convert mass to volume).

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Mass percentage (v/v)

This kind of concentration is often used for liquid solutes dissolved in a solvent to make a certain volume of solution.


Volume of solute/volume of solution x 100


The important thing to recognize here is the word solution is the volume of the solute + solvent (you may need to use density to convert mass to volume).

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Molarity

You knew it would come back to moles!


M = moles solute/L of solution

Practice

4. A soft drink contains 32 mg of sodium in 309 g of H2O. What is the concentration of sodium in the soft drink in mass percent?


5. Calculate the molarity of each solution.

(a) 1.54 mol LiCl in 22.2 L of solution

(b) 0.101 mol of LiNO3 in 3000 mL of solution

(c) 0.30 g of glucose (C6H12O6) in 76.2 mL of solution


6. How many grams of solute are present in 355 mL of 0.210 M KNO3?


7. Calculate the volume needed to make the following solutions.

(a) 0.40 M Mg(NO3)2 solution containing 96 g of Mg(NO3)2?


(b) What volume (L) of 0.750 M KCl solution contains 25.0 g of KCl?

https://www.youtube.com/watch?v=pVNpFP2Wmlc
https://www.youtube.com/watch?v=vOwdQRBENJQ
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Solution dilution

You have already done this but this is a technique and a handy formula for diluting a more concentrated solution to make a more dilute solution.

Practice

1. We can think of stoichiometry also when it comes to just dissolving solutes. Back to a question from the previous day: How many particles are generated when the following dissolve? KNO3, MgCl2, NaC2H3O2 What is the concentration of each ion if 0.1M of the solute dissolves?


2. Describe how you would make 500.0 mL of a 0.200 M NaOH solution from a 15.0 M stock NaOH solution.


3. How much of a 5.0 M sucrose solution should you use to make 85.0 mL of a 0.040 M solution?


4. Mg(OH)2 is a strong electrolyte. Determine the concentration of each of the individual ions in a 0.700 M Mg(OH)2 solution.


[Mg2+] = [OH-] =


5. Determine the concentration of Cl- in each aqueous solution. (Assume complete dissociation of each compound.) (a) 0.20 M NaCl

(b) 0.2 M CuCl2 (c) 0.2 M AlCl3

https://www.youtube.com/watch?v=C_Nu0CvC97k

What can you do to help your understanding?

Chemistry is a subject that must be practiced everyday if possible. Work through the lecture examples stopping the video clips and then restarting to check yourself. Take advantage of the practice in Mastering Chemistry to give you the practice you need to be successful. DO NOT PROCRASTINATE! Check announcements on Sakai (USA) everyday. Keep a printed copy of the most recent course calendar (included in syllabus) next to your work area. Email me with questions!!