fandomhigh | Biology (2nd Period) / Chemistry (4th Period) / Forensics (5th Period)

"Good morning, everyone. First thing we have today is a quiz. Please don't ~~forget to tell me how you did~~ forget to turn it in."

Once the quiz is complete, Ms. Sidle lectures extensively on DNA.

"Good morning."

The concentration of a solution is the "strength" of a solution. A solution typically refers to the dissolving of some solid substance in a liquid, such as dissolving salt in water. It is also often necessary to figure out how much water to add to a solution to change it to a specific concentration.

The concentration of a solution is typically given in molarity. Molarity is defined as the number of moles of solute (what is actually dissolved in the solution) divided by the liters of solution (the total volume of what is dissolved and what it has been dissolved in).

Molarity is probably the most commonly used term because measuring a volume of liquid is a fairly easy thing to do.

Example: If 5.00 grams of NaOH are dissolved in 5000 mL of water, what is the molarity of the solution?
One of our first steps is to convert the amount of NaOH given in grams into moles:

Now we simply use the definition of molarity: moles/liters to get the answer

So the molarity (M) of the solution is 0.025 mol/L.

Molality is another common measurement of concentration. Molality is defined as moles of solute divided by kilograms of solvent (the substance in which it is dissolved, like water).

Molality is sometimes used in place of molarity at extreme temperatures because the volume can contract or expand.

Example: If the molality of a solution of C2H5OH dissolved in water is 1.5 and the weight of the water is 11.7 kg, figure out how much C2H5OH must have been added in grams to the solution?
Our first step is to substitute what we know into the equation. Then we try to solve for what we don't know: moles of solute. Once we know the moles of solute we can look at the periodic table and figure out the conversion from moles to grams.

It is possible to convert between molarity and molality. The only information needed is density.

Example: If the molarity of a solution is 0.30 M, calculate the molality of the solution knowing that the density is 3.25 g/mL.
To do this problem we can assume one (1) liter of solution to make the numbers easier. We need to get from the molarity units of mols/Liter to the molality units of mols/kg. We work the problem as follows, remembering that there are 1000 mL in a Liter and 1000 grams in a kg. This conversion will only be accurate at small molarities and molalities.

It is also possible to calculate colligative properties, such as boiling point depression, using molality. The equation for temperature depression or expansion is

Change in T= K * m

Where: T is temperature depression (for freezing point) or temperature expansion (for boiling point) (°C)
K is the freezing point constant (kg °C/moles)
m is molality in moles/kg

Example: If the freezing point of the salt water put on roads is -5.2 C, what is the molality of the solution? (The Kf for water is 1.86 C/m.)
This is a simple problem where we just plug in numbers into the equation. One piece of information we do have to know is that water usually freezes at 00C.

T=K * m
T/K= m
m = 5.2/1.86
m = 2.8 mols/kg

In forensics, they continue discussing elements of arsonists.

"I'm dismissing you guys early today. I want you to find a newspaper article relating to arson by Friday and summarize it."

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Honey's tail thumps against Sara's lap. She lurves her daddy.

"It does, if only so you're not in a bad mood later with your students." Her own little smirk and she gives him a quick kiss. "Have a good afternoon, babe."

He steals another quick peck, and a giant smile spreads across his face.

"You too," he says, moving to sign the affectionate nickname he uses for her.

He signs his love as well, and heads out for class prep.

Biology (2nd Period) / Chemistry (4th Period) / Forensics (5th Period)

Re: Lunch

Re: Lunch