Which of the following is acidic pH?

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Detailed Description
Sources/Usage
Which pH is most acidic?
What are 3 examples of acidic substances?
Which of the following solution is most acidic a pH 1 B pH 13 C pH 6 d pH 10?
Which is an acidic acid?

Detailed Description

pH is a measure of how acidic/basic water is. The range goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base. pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water. Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is basic. Since pH can be affected by chemicals in the water, pH is an important indicator of water that is changing chemically. pH is reported in "logarithmic units". Each number represents a 10-fold change in the acidity/basicness of the water. Water with a pH of five is ten times more acidic than water having a pH of six.

As this diagram shows, pH ranges from 0 to 14, with 7 being neutral. pHs less than 7 are acidic while pHs greater than 7 are alkaline (basic).

► Learn more about pH

Sources/Usage

Credit: OpenStax College | commons.wikimedia.org

Source

pH Scale

Introduction and Definitions:

Acidic and basic are two extremes that describe a chemical property chemicals. Mixing acids and bases can cancel out or neutralize their extreme effects. A substance that is neither acidic nor basic is neutral.

The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.

The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each of which is ten times more alkaline (another way to say basic) than the next lower whole value. For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8.

Pure water is neutral. But when chemicals are mixed with water, the mixture can become either acidic or basic. Examples of acidic substances are vinegar and lemon juice. Lye, milk of magnesia, and ammonia are examples of basic substances.

Practice:

HNO3 + KOH -->	+
H3PO4 + 3 NaOH -->	+

Ionization of Water:

Water molecules exist in equilibrium with hydrogen ions and hydroxide ions.

H2O <--> H+ + OH-

The water equilibrium constant is written as:

Kw = [H+] [OH-]

Experimentally, it has been found that the concentration of:
H+ = OH- = 10-7

Therefore: Kw = [10-7][ 10-7] = [10-14]
(To multiply exponential numbers - simply add the exponents.)

The values for Kw, H+, OH- concentration all indicate that the equilibrium favors the reactant (water molecules). In other words, only very small amounts of H+ and OH- ions are present.

Effect of Acids and Bases on Water Equilibrium:

If an acid (H+) is added to the water, the equilibrium shifts to the left and the OH- ion concentration decreases.

Water Equilibrium: H2O <--> H+ + OH-

If base ( OH-) is added to water, the equilibrium shifts to left and the H+ concentration decreases.

Water Equilibrium Principle: The multiplication product (addition of exponents) of H+ and OH- ion concentration must always be equal to 10-14.

BOTH H+ and OH- ions are ALWAYS PRESENT in any solution. A solution is acidic if the H+ are in excess. A solution is basic, if the OH- ions are in excess.

Number Representation and Logarithms
Number	Exponent Notation	Log of the Number
1000	103	3
100	102	2
10	101	1
1	100	0
0.1	10-1	-1
0.01	10-2	-2
0.001	10-3	-3
0.0001	10-4	-4

Solve for any of the others given one
H+	OH-	pH	pOH
0.001
	0.00001
		6
			4

Definition of pH, pOH, and pKw:

The concentrations of hydrogen ions and indirectly hydroxide ions are given by a pH number. pH is defined as the negative logarithm of the hydrogen ion concentration. The equation is:

pH = - log [H+]
similarly, pOH = - log [OH-]
and p Kw = - log [Kw] .

Logarithms of numbers that are multiples of ten are merely the exponents of the number including the sign. See the table on the left for a review. The method to find logs of numbers that are not multiples of ten are found by using a calculator. The method is not discussed here.

Example: If an acid has an H+ concentration of 0.0001 M, find the pH.

Solution:
First convert the number to exponential notation, find the log, then solve the pH equation.

H+ = 0.0001M = 10-4; log of 10-4 = -4;

pH = - log [ H+] = - log (10-4) = - (-4) = +4 = pH

The purpose of the negative sign in the log definition is to give a
positive pH value.

Example:
If the base has an OH- concentration of 0.001M, find the pH.

Solution:

First find the pOH, (similar to finding the pH,) then subtract the pOH from 14.
OH- = 0.001M = 10-3;

pOH = -log [OH-] = -log (10-3) = +3 = pOH

pH = 14 - pOH; pH = 14 - 3 = 11 = pH

pH Principle: pH and pOH must always equal pKw (14).

Click for larger image

pH Scale:

The pH scale, (0 - 14), is the full set of pH numbers which indicate the concentration of H+ and OH-ions in water. The diagram on the left gives some relationships which summarizes much of the previous discussion.

pH Scale Principle:
H+ ion concentration and pH relate inversely.
OH- ion concentration and pH relate directly.

The following statements may be made about the pH scale
numbers. Complete some of them.

a. Increasing pH means the H+ ions are decreasing.
b. Decreasing pH means H+ ions are increasing.
c. Increasing pH means OH- ions are
d. Decreasing pH means OH- ions are

Most H+ ions: pH = 4; or pH = 5.
Most OH- ions: pH = 10; or pH = 13.
Least H+ ions: pH = 12; or pH = 13.
Least OH- ions: pH = 8; or pH = 9.
If acid was added to a solution of pH 4, the pH would increase or decrease?
If acid was removed from a solution of pH 3, the pH would inc. or dec.?
If base were added to a solution of pH 9, the pH would inc. or dec.?
If base were added to a solution of pH 2, the pH would inc. or dec.?
If acid were added to a solution of pH 13, the pH would inc. or dec.?
If base were removed from a solution of pH 12, the pH would inc. or dec.?

Which pH is most acidic?

The scale has values ranging from zero (the most acidic) to 14 (the most basic). As you can see from the pH scale above, pure water has a pH value of 7. This value is considered neutral—neither acidic or basic. Normal, clean rain has a pH value of between 5.0 and 5.5, which is slightly acidic.

What are 3 examples of acidic substances?

Examples of acids include the inorganic substances known as the mineral acids—sulfuric, nitric, hydrochloric, and phosphoric acids—and the organic compounds belonging to the carboxylic acid, sulfonic acid, and phenol groups.