Today is Monday,September 21st, 2015

Pre-Class:You may answer either the big question or the little

question, but must pick one.Little Question:Draw (using those circular orbitals) the atomic structure of an H+ ion.

Big Question:What do lemons, apples, and grapefruit all have in common when it comes to taste?

In This Lesson:Solutions and pH

(Lesson 6 of 9)

Today’s Agenda

• Review polarity.• Solutions and pH Challenge Questions.• Learn solutions.• Explore a new(ish) water property.• pH• Da pH Lab (soon).

• Where is this in my book?– Academic: P. 41 and following…– Honors: P. 27 and following…

By the end of this lesson…

• You should be able to distinguish between solutes, solvents, solutions, and suspensions.

• You should be able to identify the properties of acids and bases as they relate to the pH scale.

Solutions

• Today we’re going to be talking about solutions.

• A solution is a mixture in which one or more substances is evenly distributed in another.

– Imagine Crystal Light in water, for example.

– “Crystal Light water” (or lemonade or whatever flavor) is the solution.

• On a molecular level, water is actually surrounding and H-bonding with the substance.

Solutions

• A solute is the substance dissolved (remember that word?) in the solution.

– In our example, Crystal Light is the solute.

• A solvent is the substance in which the solute is dissolved.

– In our example, water is the solvent.

– For most of our examples, water will be the solvent.

One More…

• There’s also suspensions and mixtures.

• These are not true solutions, just like van derWaals forces are not true bonds.

– Suspensions are when a liquid solute does not actually dissolve into water but is instead just kind of…hanging out in it.

• It’ll settle to the bottom if not stirred.

– Mixtures are similar, but can be gases, liquids, or solids. Suspensions are just liquids.

Solutions and Suspensions Example

• Blood is actually both a solution and a suspension.

– Your blood is mostly water.

– Lots of small compounds are dissolved in the water, making it a solution. We call this solution serum.

– However, not included in serum are your red blood cells and white blood cells. These cells are just suspended in the serum, not dissolved in it.

Hemophobia Warning

• The next slide has photos of blood and plasma.

• Consider yourselves warned…

Blood and Plasma

http://newsimg.bbc.co.uk/media/images/45497000/jpg/_45497505_c0013438-frozen_blood_plasma-spl-1.jpghttp://www.heart-valve-surgery.com/Images/Blood-Bag-Image.jpg

Notice that once you take out the red blood cells (and white too, but they don’t have much color), your blood serum is really just yellow. The red blood cells give it the color you see.

Polarity

• Remember that polar molecules (like water) dissolve in water.

• Non-polar molecules (like oil) do not dissolve in water.

• We refer to polar, or water-liking molecules, as hydrophilic.

• Non-polar, or water-fearing molecules, are referred to as hydrophobic.

Polarity

• Another way to think about this is that polar molecules are sticky.

– Water molecules physically stick to and surround other polar substances that are dissolved in them.

– Van der Waals forces!

http://www.chemistryland.com/CHM107/Water/WaterTableSalt.jpg

Water’s Other Property

• Not mentioned recently was one more of water’s essential life-supporting properties.

– Water is pH neutral.

• What exactly do we mean by pH?

– Anyone?

pH

• pH refers to how much of an acid or a base a solution is.

• The scale ranges from 0-14*.

– 7 is neutral. Water is 7.

– Below 7 is acidic (acids)

– Above 7 is basic (bases)

• Basicity is more technically called “alkalinity.”

pH Scale

http://www.epa.gov/acidrain/education/site_students/images/phscale.gif

Other pH levels…

• Normal rain:

• 5.7

• Acid rain:

• 5.2

• White bread:

• 5-6

• Battery Acid:

• < 1

Other pH levels…

• Apple juice:• 2.9-3.3

• Baking Soda:• 8

• Grapefruit Juice:• 3-3.3

• Your blood:– Somewhere between 7.35 and 7.45

– Below: Acidemia [Acidosis] – Confusion, CNS depression/death

– Above: Alkalemia [Alkalosis] – Confusion, CNS excitement/death• These conditions are typically symptomatic of a larger issue, often

respiratory or metabolic.

Question Session!

• Turn to your partner and come up with one question you have about what we’ve done today.

• We’ll go around the room afterward and answer those questions.

Acids and Bases

• So how’re they made?

– Dissociation!

• P.S. This is the Arrhenius acid/base definition.

• Dissociation is when a molecule breaks apart.

• Let’s take water for example:

– Water breaks down into a hydrogen ion (H+) and a hydroxide ion (OH-).

– H2O = H+ and OH-

Dissociation of Water

• [Start drawing]

Dissociation of Water

• Basically (haha), when water dissociates, you’re left with both hydrogen ions and hydroxide ions.

– Wait a second…isn’t…H+ just a…?

• Yep, H+ is just a proton. It’s a free proton moving around the substance, and its presence makes it acidic.

• However, the equal presence of OH- (hydroxide) makes the solution basic/alkaline.

• Thus, water is a neutral 7.

Dissociation of Acids

• When other things dissociate, it may not often be so nice:

• HCl (Hydrochloric Acid) is a good example:

– HCl dissociates into H+ and Cl-.

– Now you have lots of H+ but no OH- to counteract it.

– You’re left with just hydrogen ions (protons, or H+) and that makes the solution acidic.

Dissociation of Bases

• Here’s what happens when alkalinesdissociate:

• NaOH (Sodium Hydroxide) is a good example:

– NaOH dissociates into Na+ and OH-

– Now you have lots of OH- but no H+ to counteract it.

– You’re left with just hydroxide ions (OH-) and that makes the solution basic.

Quia Practice!

• Solution and pH Activities

If the number of HYDROGEN

IONS is greater than the number of

hydroxide ions, the solution is

an . . .

H+ > OH-

If the number of HYDROXIDE

IONS is greater than hydrogen

ions, the solution is a . . . .

OH- > H+

So let’s summarize…

• The pH scale measures acidity or basicity.• Under 7 is acidic (lower numbers = more acidic)• Over 7 is basic/alkaline (higher numbers = more

basic)• Acids have higher proportions of hydrogen ions

(protons)• H+ > OH-

• Bases have higher proportions of hydroxide ions• OH- > H+

• Pure water is a neutral 7.• H+ = OH-

So what does pH stand for, anyway?

• pH stands for “power of Hydrogen,” (as in, mathematical power) but you can best think of it as “parts Hydrogen.”

• That should now make sense to you.

• The more “parts hydrogen [ions]” there are, the more acidic.

One more thing…

• Remember how we said that blood needs to stay in a small range of pH?

• It turns out that physical exercise produces a lot of H+, making a lot of acid.

• How come you don’t get sick?

– Your body naturally buffers pH changes.

Buffers

• A buffer is a substance that minimizes the impact of additional acids or bases to a solution.

– For blood, our body has certain substances that counteract the addition of H+ and/or OH-.

– Body Buffers: Carbonic Acid/Bicarbonate

• Buffers often work by reacting with the H+ or OH- ions and forming other compounds.

Buffers

• Example:

• Bicarbonate is shown by the formula HCO3-.

– What atoms and how many of each make up bicarbonate?

• When you add H+ to the solution, bicarbonate “intercepts” it and forms carbonic acid (H2CO3) with it.• HCO3

- + H+ ↔ H2CO3

• Let’s draw this…

Video Review and Summary

• [well, go ahead and hit play!]