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Chemistry: Acids and Bases

unit 11: Acids and Bases (Inspire)
by

Valerie Henderson

on 5 May 2016

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Transcript of Chemistry: Acids and Bases

unit:
Acids and bases

designed by Péter Puklus for Prezi
Concentration
Day 2
Quiz 11.1 (review molarity/concentration)
pH lab
pH with indicators
litmus paper:
Neutralization Reactions
Quiz 11.4 - on parts IV and V
Titration technique lab prep
Titration lab
(Molarity)
At the top of this paper, write:
Essential questions:
What does it mean when a juice or other beverage is
"from concentrate"
You must prepare a 50 mL solution of 1M sucrose C H O
12
22
11
Come up with a procedure to perform this task in lab.
2.
1.
Answer these questions on a separate piece of paper. Affix it to your molarity pogil packet.
Molarity pogil packet
Before beginning, define:
solute
solvent
solution
Can write on that separate paper
use your answer to this question to help you answer essential question #2
STOP!
No, not hammer time...collaborate and listen!
Write and answer this question: two solutions of NaCl both contain 0.2 moles NaCL but they have different molarities. How is this possible?
They have different overall volumes
molarity = ?
moles solute
volume of solution
partners. 2 min. sticks.
Complete the Calculations
(remember that equation you wrote down on the previous page...)
unit of Molarity?
moles
liter
0.06 mole CuCl
0.06 L solution
2
=
1 M
sticks.
The ratio of moles to liters of solution is the same.
No. both the # of moles and the volume of solution are needed to determine the concentration.
Molarity is a ratio.
What would affect the molarity of a small volume of solution?
# of moles present
STOP!
Write this question:
A solution that is more concentrated ____________________________________.
a. is darker than a dilute solution
b. has a lower molarity
c. contains more dissolved particles
D. has a greater volume
number of moles
What does number of particles allow you to calculate?
sticks. work under document camera.
In a microscopically small volume of any 3M solution,the # of particles (moles of solute will always be the same.
Be prepared to share your answers to these questions...
sticks. work under document camera.
Essential Question 2.

Prepare 50mL solution of 1M sucrose.
key summative points after answering this question. (write these down)
In making a 1 M solution, do you need to know the amount of water used?
No, the amount of water doesn't need to be known.
Why?
molarity is used when it is important to know how much solute will be present in a given volume.
Now, complete the molarity chemquest
H.W.
outline part I
see video page for help
What is the video page?
molarity pogil packet
answer essential questions
molarity chemquest
Intro to Acids/Bases
What are acids and Bases?
Let's look @ the
basics
of acids and bases...
But first, a puzzle...see if you can solve it by the end of the class...
The answer to this is your exit ticket out of here...
ssh! Don't give it away if you know!
Now, back to the basics...
Complete #1-6 of pogil packet
Arrhenious Acid and Base Re-cap
What is the problem with this theory? - write it on your pogil packet.
stop @ 3 min
1 minute think time. individual.
2 minute partner discussion.
sticks.
What are the problems with the Arrehnius Theory of Acids and Bases?
Remember that the Arrehnius theory says that an acid donates a Hydrogen atom (proton) in the form of an H ion in aqueous solution (water)...
This limits acids to being only aqueous (in water) and doesn't allow for and acid in gaseous form.
Another problem with this theory is that it also doesn't account for substances that can sometimes act as an acid and sometimes act as a base...
stick. check-in.
sticks. work under doc cam.
sticks.
sticks. doc cam - work
sticks. doc cam.
think. partners. sticks.
Yes, in both forward and reverse directions of a reaction, the acid (or conjugate acid) donates a hydrogen ion)
What's for Homework?
Outline part II
and
finish acids and bases pogil packet (if you didn't in class)
SUB - Friday
As usual...papers to pick up will be in stacker.
I'll return @ 2:15 if you have questions.
(I do have a meeting @ 3:30 so be aware if you're asking questions.)
You'll take the quiz, turn it in and work on the papers you pick up during class.
The magic Tea kettle
Acids and Bases Research Project
Group project
This will go in your lab reports category.
max = 3 students
Read paper carefully and be sure to go over the checklist and the rubric.
This project is due on April 16.
Strong vs Weak Acids
What is a strong acid?
when in contact with water, proton transfer occurs with almost every molecule.
complete dissociation of acid.
HA just stands for an acid.
What is pH?
logarithmic measure of Hydrogen ion concentration.
The log is a base-10 logarithm
[H ]
+
=
Hydrogen ion concentration
moles
L of solution
in
"p" stands for the German word for "power", potenz, so pH is an abbreviation for "power of hydrogen"
The pH scale was defined because the enormous range of hydrogen ion concentrations found in aqueous solutions make using H+ molarity awkward. For example, in a typical acid-base titration, [H+] may vary from about 0.01 M to 0.0000000000001 M. It is easier to write "the pH varies from 2 to 13".
Sorta like scientific notation....think of
Danish chemist described pH
While working at the Carlsberg Laboratory he studied the effect of ion concentration on proteins and because the concentration of hydrogen ions was particularly important, he introduced the pH-scale as a simple way of expressing it in 1909
What is pH used for?
it's often used to compare acidities.
One caveat here...
The solutions must use the same solvent.
For example, the concentration of hydrogen ions in pure ethanol is about 1.58 × 10 M, so ethanol is neutral at pH 9.8. A solution with a pH of 8 would be considered acidic in ethanol, but basic in water!
You can't use pH to compare the acidities in different solvents because the neutral pH is different for each solvent.
-10
Now for the lab...
You will be using indicators to determine the pH range of red cabbage juice.
Be sure to use new solution (just take 1 drop max of each of the 7 solutions!) for each different indicator.
So for aspirin, you'll repeat it 7 times
Note that for the litmus paper, you place 1 drop on the litmus paper (throw in trash).
Groups of 4.
What colors indicate what pH for red cabbage?
Day 4
April 8
Day 5
blue litmus paper in base or water:
stays blue
red litmus paper in acid or water:
stays red

Day 5
Titration
Purpose:
To determine the concentration of an unknown solution commonly called the titrand or analyte by adding a volume of a known solution called the titrant.
Sometimes also known as volumetric analysis.
end point
equivalence point
when the indicator changes color
the point where Hydrogen ions = hydroxide ions
determined by stoichiometry
Today's mantras:
NOTHING down the drain!!
You don't need exactly 10 ( see #5)
The buret
0 is on top!
For 2nd titration:
Don't need to refill.
Your last ending point is your new starting point.
The pH range of the indicator we're using is pH 8-10
in general: you want the indicator to change color around the equivalence point
This is strong acid-strong base
titration.
The equivalence point for a strong acid-strong base titration is pH 7
Our endpoint will be pH 8
(indicator doesn't change color until pH 8)
Set-up:
1. rinse buret with small amount of titrant (NaOH)
DO NOT POUR ANY OF THIS RINSE DOWN THE DRAIN!!
It must go in the waste beaker!
Once you have added the NaOH you will use to your buret...
Remember that 0 is on top! so read from top down
remember: strength does not discuss concentration
Let's start with an experiment...
Take 1 seashell.
Place it in the acetic acid carefully.
What is an acid?
What is a base?
Acids
Bases
Some common examples...
acetylsalcylic acid
vitamin C
soda
citric acid
HCl
nitric acid
Bases dissolve organic things (hair, skin, etc) which is basically why household cleaners contain basic substances.
aka: alkaline
Why does my tummy hurt?
stomach acid = HCl
pH = 1.5 -3.5
upset stomach is caused by an overproduction of stomach acid, lowering the pH of the stomach.
Right before you get sick, your breathing rate is shallow and increases.
carbon dioxide is basic.
What happens when an acid and a base are mixed?
acid + base
H O
2
+ salt
Ocean Acidification - The other carbon Dioxide problem
Interactive Map of Ocean Acidication Monitoring Stations around the world and their websites.
http://www.goa-on.org/GOA-ON_Map_FullScreen.html
Ala Wai monitoring station:
http://www.pmel.noaa.gov/co2/story/Ala+Wai
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