Properties, Concentrations, and Dilutions

Solute and Solvent Solute is the substance being dissolved. Solvent is the substance doing the dissolving. Example: Salt and Water. We dissolve salt in water. Therefore, the salt is the solute and the water is the solvent. Why is water called the universal solvent? REVIEW

Forming a Solution The composition (what they are made out of) of the solvent and solute determine whether a substance will dissolve. How FAST will the substance dissolve? This depends on three things: 1. Stirring: Increase of decrease rate? 2. Temperature: Increase or decrease rate? 3. Particle Size: The more surface area exposed, the faster it will dissolve. PART 1: PROPERTIES OF SOLUTIONS

What amount of a substance will dissolve? Particles move from a solid into a solution. But how much can be dissolved? Solubility describes the amount of substance that can be dissolved by a certain quantity of a solvent at a certain temp and pressure until the solution becomes saturated. PART 2: SOLUBILITY

Different Types of Solutions: Saturated Solution: The maximum amount of solute that can be dissolved at a specific temp and pressure. Unsaturated Solution: A solution that contains less solute than required to be a saturated solution and a certain temp and pressure. Supersaturated Solution: contains more solute than it can theoretically hold at a given temperature. Miscible Solution: when two liquids will dissolve into one another. There is no separation. Immiscible: liquids that are not soluble in each other. You can tell if it is immiscible by observing layers. SOLUBILITY

Miscible Immiscible Oil and Water Water and Acetone

SOLUTIONS Supersaturated Solution

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What do YOU think? What type of solution is being utilized? How are they making that solution? ROCK CANDY EXPLAINED

1. Temperature: Solubility of MOST substances increases as temperature increases. You can dissolve more solute in the solvent as you increase the temperature. Think about how we made our rock candy. EXCEPTION: Gas solubility increases as temperature decreases. FACTORS THAT AFFECT SOLUBILITY

2. Pressure: Changes in pressure doesn’t affect the solubility of solids and liquids, but it greatly influences the solubility of gases. As pressure increases, the solubility of gases also increases. Use Henry’s Law for calculations. S = solubility P = pressure Directly Proportional FACTORS THAT AFFECT SOLUBILITY

How would I describe solubility in terms of UNITS? Solubility is usually expressed in grams of solute per 100g of solvent. Example: 36g of sodium chloride in 100g of water at 25 degC. Examples in terms of saturation: If 36g of NaCl is added to 100g water, it will dissolve completely, but if I added 1 more gram of NaCl, only 0.2g of that will dissolve. Therefore, 36.2g of NaCl in 100g of water is a SATURATED solution. How would I make it super saturated?? SOLUBILITY OF SOLUTIONS

Concentration: a measure of the amount of solute that is dissolved in a given quantity of solvent. Dilute Solution: a weak concentration. Contains small amount of solute. Concentrated Solution: strong concentration. Contains a large amount of solute. PART 3: CONCENTRATIONS Dilute Concentrated

MOLARITY Moles of solute dissolved in 1 Liter of solution. CONCENTRATIONS

LET’S MAKE A SOLUTION Let’s determine the molarity of a solution that we make. Let’s start with 10 grams of sodium chloride and add it to a 1-L volumetric flask half filled with distilled water.

LETS MAKE A SOLUTION Swirl the flask carefully to dissolve the solute.

LETS MAKE A SOLUTION Fill the flask with water exactly to the 1-L mark. What is the concentration of the solution in molarity?

Answer: 0.171M

This will work with ANY volumetric flask. Big or small. We can then calculate the molarity (concentration) of our solution. LETS MAKE A SOLUTION How do we convert mL to L?

Find the number of moles of solute in a solution… WHAT IF YOU KNOW THE MOLARITY? We can also convert moles to grams.

Diluting a solution reduces the number of moles per unit volume. The number of moles of solute remains unchanged. Dilution equation: DILUTIONS

To prepare 100 ml of MgSO 4 from a stock solution of 0.171M NaCl, a student first measures 10 mL of the stock solution with a 10-mL pipet.

DILUTIONS She then transfers the 10 mL to a 100-mL volumetric flask.

DILUTIONS Finally, she carefully adds water to the mark to make 100 mL of solution. What is the final concentration?

Use M1 x V1 = M2 x V2 Answer:

Some volume measuring devices… Buret Graduated Cylinder Volumetric Flask Glass Pipets TO MEASURE VOLUME

DILUTION CALCULATION

These are not as common as molarity, but are used sometimes. Percent by volume: Percent by mass: PERCENT CONCENTRATIONS OF SOLUTIONS

Percent by volume: (volume/volume) PERCENT CONCENTRATION CALCULATIONS

Percent by mass: (mass/mass) Suppose you want to make a 2000g solution that has a 2.8% (m/m) concentration of glucose in water. How many grams of glucose should you use? PERCENT CONCENTRATION CALCULATIONS

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