Name:
Date:
Period:
So I know about Acids and Bases . . . so what?
On Your Desk:
 This packet
 Pen or Pencil
 Eraser
 Computer
Expectations:
 Students will work quietly and respectfully.
 Students will raise their hands before speaking
 Students will not leave their seats without permission
 Teacher will respect and encourage all questions
 Teacher will enforce all rules and expectations
Do Now:
Why Do Cut Apples, Pears, Bananas, and Potatoes Turn Brown?
By Anne Marie Helmenstine, Ph.D.
Question: Why Do Cut Apples, Pears, Bananas and Potatoes Turn Brown?
Answer: Apples and other produce (e.g., pears, bananas, peaches, potatoes) contain an enzyme (called polyphenol
oxidase or tyrosinase) that reacts with oxygen and iron-containing phenols that are also found in the apple. The
oxidation reaction basically forms a sort of rust on the surface of the fruit. You see the browning when the fruit is cut
or bruised because these actions damage the cells in the fruit, allowing oxygen in the air to react with the enzyme and
other chemicals.
The reaction can be slowed or prevented by inactivating the enzyme with heat (cooking), reducing the pH on
the surface of the fruit (by adding lemon juice or another acid; these acids make the enzyme stop working), reducing
the amount of available oxygen (by putting cut fruit under water or vacuum packing it), or by adding certain
preservative chemicals (like sulfur dioxide). On the other hand, using cutlery that has some corrosion (as is seen with
lower quality steel knives) can increase the rate and amount of the browning by making more iron salts available for
the reaction.
a.
Why do cut apples turn brown?
__________________________________________________________________________________________________________________
__________________________________________________________________________________________________________________
b. How does reducing the pH of an apple’s surface affect the rate at which it turns brown?
__________________________________________________________________________________________________________________
__________________________________________________________________________________________________________________
Terminology Take Down:
1.
2.
3.
Today you will be spending 20 minutes at 5 different stations looking at Real-Life Applications of
Acid-Base Chemistry. You’ll earn 5 points during class today.
Here’s what you do to earn your 5 points:
1. All conversations must be on the topic of chemistry. A point
will be lost if non-chemistry conversations are being had.
2. Students must stay at their own lab station for the duration
of the period and conversations should be ONLY with those at your
own table.
3. Voices should be kept at Volume Level 2 – Collaborative.
4. This packet is to be done during this period and then all the
Groups members will meet for a 20 minute Finale to fill in anything
they might have missed, discuss answers, and grade each other.
5. Group Leader will fill out the discussion log.
Group Member
What station did they write?
1
2
3
4
5
Score?
Station 2:
Analysis of Commercial Antacid Tablets
Hydrochloric acid (HCl) is one of the substances found in gastric juices secreted by the lining of the stomach.
HCl is needed by the enzyme pepsin to catalyze the digestion of proteins in the food we eat. Heartburn is a
symptom that results when the stomach produces too much acid (hyperacidity).
Antacids are bases used to neutralize the acid that causes heartburn. Despite the many commercial brands,
almost all antacids act on excess stomach acid by neutralizing it with weak bases. The most common of these
bases are hydroxides, carbonates, or bicarbonates. The following table contains a list of the active ingredients
found in several common commercial antacids, and the reactions by which these antacids neutralize the HCl in
stomach acid.
Compound
Chemical Formula
Chemical Reaction
Aluminum hydroxide
Al(OH)3
Al(OH)3(s) + 3 HCl(aq) -----> AlCl3(aq) + 3 H2O(l)
Calcium carbonate
CaCO3
CaCO3(s) + 2 HCl(aq) -----> CaCl2(aq) + H2O(l) + CO2(g)
Magnesium carbonate
MgCO3
MgCO3(s) + 2 HCl(aq) -----> MgCl2(aq) + H2O(l) + CO2(g)
Magnesium hydroxide
Mg(OH)2
Mg(OH)2(s) + 2 HCl(aq) -----> MgCl2(aq) + 2 H2O(l)
Sodium bicarbonate
NaHCO3
NaHCO3(aq) + HCl(aq) -----> NaCl(aq) + H2O(l) + CO2(g)
Read the information above and answer the following questions:
1.
Look at the ingredients of Tums. What is the active ingredient in Tums?
_______________________________
2. What is the chemical formula for the acid found in the stomach?
___________________________________
3. Find the reaction in the chart that occurs with stomach acid and Tums and write it below.
________________________________________________________________________________________________________________
4.
Put a box around the salt and a triangle around the gas that is produced when Tums reacts
with stomach acid.
5. Pour some Vinegar in a glass cup and place two tums tablets inside. Observe. What
happened?
__________________________________________________________________________________________________________
Station 3: ACID RAIN
Key Concepts
Rain from an unpolluted atmosphere has a pH close to 6.0 (slightly acidic).
This acidity is due to the reaction of water vapour and non-metal oxides in the atmosphere, such as
carbon dioxide and nitrogen oxide, forming dilute acids.
Carbon dioxide reacts with water to form carbonic acid:
CO2(g) + H2O(l) H2CO3(aq)
Since carbonic acid is a weak acid it partially dissociates:
CO2(g) + H2O(l) H+(aq) + HCO3-(aq)
nitrogen dioxide reacts with water to form a mixture of nitrous acid and nitric acid:
2NO2(g) + H2O(l) HNO2(aq) + HNO3(aq)
Acid rain has a pH below 5.6 due mainly to the reaction of water vapour with sulfur dioxide and the
oxides of nitrogen.
Sulfur dioxide reacts with water to form sulfurous acid (H2SO3):
SO2(g) + H2O(l) H2SO3(aq)
Sulfur dioxide (SO2) can be oxidised gradually to sulfur trioxide (SO3):
2SO2(g) + O2(g) -----> 2SO3(g)
Sulfur trioxide (SO3) reacts with water to form sulfuric acid (H2SO4):
SO3(g) + H2O(l) -----> H2SO4(aq)
Oxides of nitrogen, particularly nitrogen dioxide (NO2) react with water to form nitrous acid
(HNO2) and nitric acid (HNO3):
2NO2(g) + H2O(l) -----> HNO2(aq) + HNO3(aq)
Effects of Acid Rain
Acid rain is a form of environmental pollution that damages buildings and marble statues by
reacting with the calcium carbonate to form soluble calcium hydrogen carbonate (calcium
bicarbonate, Ca(HCO3)2)
CaCO3 + acid rain -----> Ca(HCO3)2(aq)
Acid rain can leach aluminium from the soil into ground water, lakes and rivers, poisoning fish
and plant roots. The sulfates and hydrogen sulfates in acid rain can leach essential plant
nutrients such as calcium and magnesium from the soil. Acid rain disrupts the process of
photosynthesis resulting in damage to plant life. At low concentrations it retards the
production of chlorophyll and at high concentrations it forms sulfuric acid which kills the plant.
Some organisms are sensitive to changes of acidity in water which can affect their ability to
reproduce and in some cases may kill them.
http://www.ausetute.com.au/acidrain.html
1. Look up a food web on the internet and write a brief paragraph on how acid rain would affect the food
web/ecosystem. Be sure to include these terms: Consumer, Producer, Energy
Station 4: Chemistry and Cooking
What makes breads, muffins, cakes, and cookies rise? The gas CO2 is released by various processes, and it
is this gas that makes the bubbles you see in bread. Take a moment to examine the piece of bread at this
station.
1.
Draw a portion of bread below, making sure you show the ‘bubbles’ that were formed in the bread.
2.
What gas formed those bubbles? _____________
Read the following excerpt to learn more about where that CO2 came from . . .
Many recipes use no yeast. Things like muffins, biscuits, cakes and cookies usually use baking powder instead
[to produce CO2]. Baking powder is normally made of three different parts:
 An acid
 A base
 A filler of some sort
All three need to be dry powders that can be mixed together. For example, baking soda (a base), cream of
tartar (an acid) and corn starch (the filler) are three common ingredients.
In school, you may have done the experiment where you mix baking soda (a base) and vinegar (an acid) and get
a bubbling reaction. Baking powder works the same way. When you add water to baking powder, the dry acid
and base go into solution and start reacting to produce carbon dioxide bubbles.
 Single-acting baking powder produces all of its bubbles when it gets wet.
 Double-acting baking powder produces bubbles again when it gets hot.
If you want to prove to yourself that this is how baking powder works, simply try mixing a teaspoon of baking
powder into a cup of hot water. As long as the baking powder is fresh, you will definitely see the reaction!
1. Do It! Add a small scoop of soda to the beaker, then add ~100mL warm water. What do you
see? What gas is produced?
_____________________________________________________________
Pour your mixture down the drain and clean up the space.
Baking soda, also known as sodium bicarbonate, has the chemical formula NaHCO3. Cream of tartar, also
known as tartrate salt, has the formula KHC4H4O6.
The reaction is:
NaHCO3 + KHC4H4O6 ----> KNaC4H4O6 + H2O + CO2
2. Look at the above equation. Draw a box around the salt that is produced. Draw a triangle
around the gas that is produced. LABEL the base and the acid (you may have to reread the
paragraph above to figure out which is the base and which is the acid. It’s there!).
Some baking powders contain sodium aluminum sulfate: NaAl(SO4)2. The reaction there is:
NaAl(SO4)2 + 3 NaHCO3 ----> Al(OH)3 + 2 Na2SO4 + 3 CO2
3.
Look at the above equation. Draw a box around the salt that is produced. Draw a triangle
around the gas that is produced. LABEL the base and the acid (you may have to reread the
paragraph above to figure out which is the base and which is the acid. It’s there!).
Many recipes call simply for baking soda rather than baking powder. Usually these recipes use some kind of
liquid acid like buttermilk or yogurt to react with the baking soda to produce the bubbles.
The reason why people often prefer baking powder to yeast is because yeast takes so long -- usually two to three
hours -- to produce its bubbles. Baking powder is instant, so you can mix up a batch of biscuits and eat them 15
minutes later.
Now that you understand how baking powder works, you can understand two things you often see in recipes:


Many recipes instruct you to mix all of the dry ingredients together and then add the liquid. That
keeps the baking powder from reacting until the end of the mixing process.
Many recipes tell you to mix only briefly -- just until the ingredients are moistened. That minimizes
the escape of the gas from the batter. If you were to stir for a long time, the reaction would end and
the stirring would have allowed the bubbles to escape.
4.
Why add liquids at the last minute when making muffins or cakes?
__________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________
Questions and adaptation to lab LJC 2011. Article from http://recipes.howstuffworks.com/tools-and-techniques/baking-powder.htm
Station 5: What is an Alkaline Battery?
The word “alkaline” means base! What is a base doing in an alkaline battery?
Look at the website http://www.energizer.com/learning-center/Pages/how-batteries-work.aspx
Spend your time at this station looking at the Battery Parts, Constructing the Battery, and Powering the Battery
sections of this website(no other website, please). Take notes on what you learn below. There is one question for
you to answer (plus a writing portion t):
1. What is the base in an alkaline battery? It is NOT explicitly labeled a base, but it is a base that you have
worked with a fair amount the past week.
_______________________________________________
2. Summarize the process required to create and power a battery. Be sure to include these terms: cathode,
anode, zinc, manganese dioxide, positive, negative, charge, electrode, and collector. This will be graded.
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________
_______________________________________________________________________________________________________________________