Bio A – Basic Chem
Acids, Bases and pH
When studying solutions, chemists are particularly interested in the concentration of two ions: Hydrogen (H+)
and Hydroxide (OH-). The concentration of these to ions in a solution will determine the solution’s pH. One
hydroxide ion will combine with one hydrogen ion to make water:
H+ + OH-  H2O
So any solution that has an equal concentration of H+ and OH- is said to have a neutral pH. A neutral pH falls
in the middle of the pH scale, at pH = 7.
Certain chemicals, when added to water, throw off the balance of H+ and OH- so they are no longer equal.
Chemicals that shift the balance so the concentration of H+ is higher that OH- are called acids. These solutions
have a pH below 7.
Example: HCl + H2O  H+ + Cl- + H2O
- when hydrochloric acid is added to water, it releases a H+. Therefore the balance of ions is shifted so that
there is more H+ than there is OH-.
Chemicals that shift the balance so the concentration of OH- is higher than H+ are called bases. These
solutions have a pH between 7 and 14.
Example: NaOH + H2O  Na+ +OH- + H2O
- when sodium hydroxide is added to water, it releases an OH-. Therefore the balance of ions is shifted so that
there is more OH- than there is H+.
**There are more ways for acids and bases to work than these simple models above, but for our purposes we
are going to stick with these mechanisms**
So what happens when we combine the two?
If we mix an acid and a base we create a neutralization reaction. Simply put, all the extra OH- of the base mix
with the extra H+ of the acid and create water. The rest of the atoms will come together to make a salt.
Example 1: HCl + NaOH  H+ + OH- + Na+ + Cl-  H2O + NaCl
Example 2: H2SO4 + 2 NH4OH  H+ + OH- + 2NH4+ + SO4-2  2H2O + (NH4)2SO4
The end pH of a neutralization reaction will depend on the strength of the acids and bases. If the acid and base
are the same strength all of the H+ will combine with all of the OH- creating water. The end pH will be neutral.
If the base is stronger than the acid, all of the H+ will combine with OH-, but there will be extra OH-. The end
pH will be closer to neutral, but will remain basic because of the extra OH-.
What do you think will happen if the acid is stronger than the base?
Bio A – Basic Chem
What does any of this have to do with Biology?
Homeostasis is the body’s ability to maintain a stable internal environment. Among other things this includes a
stable temperature, chemical composition and pH. Physiological pH, the pH that allows normal body
functions, is usually in the range of 6.5 – 7.5 throughout most of the body. A pH that deviates from this range
can have a negative effect on many necessary functions.
There are always exceptions:
Although most of the body maintains a pH between 6.5 and 7.5, there are a few exceptions. For starters, the
stomach produces hydrochloric acid and usually has a highly acidic pH of 1.2 – 3. A pH this low anywhere else
in the body would be deadly. The stomach however has a special mucus lining that protects it from being
damaged by the acid. This low pH in the stomach allows food to be broken down more easily and kills bacteria
that we might have ingested.
Another place in the body where the pH deviates from the standard range is in the intestines. After the food
mixes with the stomach acid it passes into the intestines for further digestion. Unlike the stomach, the intestines
do not have a protective lining. If the acid were allowed to enter, without being neutralized, it would damage
the intestines. So how do we neutralize an acid? The intestines contain a base that mixes with the acidic food
as soon as it enters. As a result the intestines are always more basic than the rest of the body.
How do we keep the pH where it needs to be:
Obviously we ingest acidic foods and drinks on a daily basis. So how does the pH stay in such a tight range
when we are constantly adding more acids? The body is full of chemicals called buffers. Basically a buffer is
an acid and base pair that adjusts the H+ or OH- concentration as needed to keep the pH where it needs to be.
Example: The blood has a buffer system made of carbonic acid and bicarbonate (base)
-
If the H+ concentration starts to rise, the bicarbonate will kick in and neutralize the excess H+ ions returning
the blood’s pH to where it should be.
-
If the OH- concentration starts to decrease, the carbonic acid will kick in and neutralize the excess OH- ions
returning the blood’s pH to where it should be.
***Notice we did not say the buffer will neutralize the blood!! Buffers do not neutralize blood, they
neutralize the excess acid or base to keep the blood’s pH from changing***
The pH scale itself:
The numbers of the pH scale range from 1 – 14. As we said before, pH 7 is smack in the middle; acids are
below 7 and bases above. But what do the numbers mean? Until you learn logarithms in math, it is a little
complicated. All you need to know now is that the number refer to the concentration of H+ ions AND that a
difference of 1 on the pH scale means a 10 fold difference in H+ ion concentration.
Example: A solution with a pH of 3 has an H+ concentration that is 10 times MORE than a solution of pH 4.
- A solution with a pH of 8 has an H+ concentration that is 100 times (10 x 10) LESS than a solution of pH 6.
Bio A – Basic Chem
Directions: Read the ENTIRE page, front and back, on acids and bases. Then answer the questions thoroughly.
The information you put on your sheet will serve as your notes for acids, bases and pH. We will go over the
question but we will not be covering these in lecture.
1.
Explain what happens to the balance of hydrogen and hydroxide ions when:
a. An acid is added to water.
b. A base is added to water.
2. If a solution has a pH of 7, what do we know about the concentration of H+ and OH-?
3. An acid is added to a base and the resulting pH was 5.
a. What type of reaction occurred?
b. What are the products of this reaction?
c. Which was stronger, the acid or the base? How do you know?
d. Which were left over, H+ ions or OH- ions? How do you know?
Bio A – Basic Chem
4. Identify a part of the body where the H+ concentration exceeds the OH- concentration? Why is this
necessary?
5. Identify a part of the body where the OH- concentration exceeds the OH+ concentration? Why is this
necessary?
6. Carefully explain the role of a buffer IN YOUR OWN WORDS.
Bio A – Basic Chem
Elements, Compounds & Mixtures Worksheet
Part 1: Read Chapter 2 in your text for information on elements, compounds and mixtures. Fill in the
blanks where necessary.
Elements:
 A pure substance containing only one kind of ____________.
 An element is always uniform all the way through (homogeneous).
 An element _____________ be separated into simpler materials (except during nuclear
reactions).
 Over 100 existing elements are listed and classified on the ____________________.
Compounds:
 A pure substance containing two or more kinds of _______________.
 The atoms are _________________ combined in some way. Often times (but not always) they
come together to form groups of atoms called molecules.
 A compound is always homogeneous (uniform).
 Compounds ___________________ be separated by physical means. Separating a compound
requires a chemical reaction.
 The properties of a compound are usually different than the properties of the elements it
contains.
Mixtures:
 Two or more ________________ or _________________ NOT chemically combined.
 No reaction between substances.
 Mixtures can be uniform (called ________________________) and are known as solutions.
 Mixtures can also be non-uniform (called ________________________).
 Mixtures can be separated into their components by chemical or physical means.
 The properties of a mixture are similar to the properties of its components.
Part 2: Classify each of the following as elements (E), compounds (C) or Mixtures (M). Write the
letter X if it is none of these.
___Diamond (C)
___Sugar (C6H12O6)
___Milk
___Air
___Sulfuric Acid (H2SO4) ___Gasoline
___Krypton (K)
___Bismuth (Bi)
___Uranium (U)
___Water (H2O)
___Alcohol (CH3OH)
___Pail of Garbage
___Ammonia (NH3) ___Salt (NaCl)
___Energy
___Wood
___Bronze
___Ink
___Dry Ice (CO2)
___Baking Soda (NaHCO3) ___Titanium (Ti)
___Iron (Fe)
___Electricity
___Popcorn
___A dog
___Gold (Au)
___Pizza
___Concrete
Part 3: Match each diagram with its correct description. Dots represent an element. Black dots are on
atom of one type of element, White dots represent an atom of a second element. Each diagram is
used only once.
Bio A – Basic Chem
A
B
C
D
E
___1. Pure Element – only one type of atom present.
___2. Mixture of two elements – two types of uncombined atoms present.
___3. Pure compound – only one type of compound present.
___4. Mixture of two compounds – two types of compounds present.
___5. Mixture of a compound and an element.
Part 4: Column A lists a substance. In Column B, list whether the substance is an element (E), a
compound (C), a Heterogeneous Mixture (HM), or a Solution (S). (Remember a solution is a
homogeneous mixture.) In Column C, list TWO physical properties of the substance.
Column B
1. Summer Sausage
2. Steam
3. Salt Water
4. Pencil lead (Graphite
(C)
5. Dirt
6. Pepsi
7. Silver (Ag)
8. Toothpaste (Na2HPO4)
9. A burrito
10. Italian Dressing
11. Chicken Soup
12. Lemonade
Column C
Bio A – Basic Chem
Principles of Chemistry Worksheet:
Use chapter 2 of your text (and your notes) to complete the following.
Part 1: Define the following terms IN YOUR OWN WORDS.
1. Atom: ______________________________________________________________________________
2. Compound:__________________________________________________________________________
3. Suspension: _________________________________________________________________________
4. Homogeneous: ______________________________________________________________________
Part 2: Use the following descriptions to identify each substance as a compound or a mixture
1. Substance A: Made up of three different components each of which is chemically bonded to one of the
other components. __________________________
2. Substance B: Made up of component C and D. Requires there to be exactly 3 times as much C as there
is D or another substance is formed. _____________________
3. Substance C: When the components are mixed together, they each still behave like they did before they
were mixed. There is no change in their chemical properties. _________________
Part 3: Identify each chemical reaction as a Synthesis (building), Decomposition (breaking down) or
Displacement (rearranging “partners”) reaction.
1. AgNO3 + NaCl  AgCl + NaNO3
_______________________
2. 2H2 + O2  2H2O
_______________________
3. 8 FeS  8 Fe + S8
___________________________________________________
In All three examples above UNDERLINE the reactants
Part 4: Answer the questions below as they relate to pH
1. Bleach has a high pH of 11. If I add this to a solution explain the concentrations each ion below will
increase or decrease:
a. H+ : _____________________________ b. OH- : ______________________________
2. HCl tastes extremely sour and can corrode metal. If I add this to a solution explain the concentrations each
ion below will increase or decrease:
a. H+ : _____________________________ b. OH- : ______________________________
3. KOH, if you’re silly enough to drink it, would taste very bitter and turns litmus paper blue. If I add this
to a solution explain the concentrations each ion below will increase or decrease:
a. H+ : _____________________________ b. OH- : ______________________________
Bio A – Basic Chem
Part 5 – Chem in the body:
1. What pH range does most of your body fall into?
2. What does your body use to keep this pH from changing greatly?
3. List two places in your body where the pH is NOT in this range.
4. What happens when an acid and a base are mixed together? What are the products of such a reaction?
What happens to the pH?
Part 6: Atomic Structure
1. For each of the following elements, look up or calculate the numbers below:
a. Calcium:
Atomic number _______________ Atomic Mass _________________
Protons_______
Neutrons _________ Electrons _____________
b. Magnesium+2: Atomic number _____________ Atomic Mass ____________
Protons_______
Neutrons _________ Electrons _____________
c. Gold: Atomic number _____________
Protons_______
Atomic Mass ________________
Neutrons _________ Electrons _____________
d. Oxygen-2 : Atomic number _____________
Protons_______
Atomic Mass ____________
Neutrons _________ Electrons _____________
2. Which of the atoms above is a Cation? ______________________
3. Which of the atoms above is an Anion? _____________________
4. Fill in the chart with the proper information:
Bio A – Basic Chem
Location in the atom?
Charge?
Does it contribute to
Is it in constant motion?
Atomic mass?
Protons
Neutrons
Electrons
Part 6: Polarity and Water
1. What does “polar” mean?
2. Draw a picture of a water molecule and put in the proper charges.
3. What is cohesion?
a. Why does cohesion happen? How can it be demonstrated?
4. What is adhesion?
a. Why does adhesion happen? How can it be demonstrated?
5. What happens when water is added to salt? What does polarity have to do with this?