6.4 – The pH Scale Unit 6 – Acids and Bases.

Slides:



Advertisements
Similar presentations
Intro to Acids & Bases.
Advertisements

Hydrogen Ions and Acidity
Section 18.3 Hydrogen Ions and pH
PH worksheet (#1).
Measuring pH and pOH.
Measuring pH and pOH Also Known As…
Chemistry Chapter Acids and Bases. (Self-Ionization of Water) H 2 O + H 2 O  H 3 O + + OH -  Two water molecules collide to form Hydronium and.
PH.
Mr. Chapman Chemistry 30.  We are ready to use what we know about acids and bases to calculate the pH of various solutions.  Before we do this, however,
Ways to measure Acidity/Basicity What is pH? What is pOH?
Ch.15: Acid-Base and pH Part 1.
Acids and Bases. Ionization of Water H 2 O + H 2 O H 3 O + + OH - K w = [H 3 O + ][OH - ] = 1.0 
PH.
Continuing into the world of acids and bases….  pH of a solution is the negative logarithm of the hydrogen ion concentration  pH = -log [H + ]  This.
How is pH defined? The pH of a solution is the negative logarithm of the hydrogen-ion concentration. The pH may be represented mathematically, using the.
Acids & Bases How We Measure Acids and Bases pH Blue Base.
pH and pOH Ionization of water Experiments have shown that pure water ionizes very slightly: 2H 2 O  H 3 O + + OH - Measurements show that: [H 3 O +
Ka and Kb Calculations. For Weak Acid Reactions: HA + H 2 O  H 3 O + + A - K a = [H 3 O + ][A - ] K a < 1 [HA]
TOPIC: pH 1. NaCl 2. C 2 H 5 OH 3. H 2 SO 4 4. NaOH 5. C 12 H 22 O CaI 2 7. HF 8. Mg(OH) 2 9. NH 3 10.CH 3 COOH Do Now: Identify as acid, base, salt,
Acids and Bases pH Calculations
1 Chapter 14 Acids and Bases 14.6 The pH Scale Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings.
WHAT IS PH? Concentration and hydrogen ions and hydroxide ions are a measure of The acidity and alkalinity of a solution.
Unit: Acids, Bases, and Solutions
Hydrogen Ions and Acidity The Ionization of Water and pH.
Hydrogen Ions and Acidity The Ionization of Water and pH.
Chapter 10 Acids and Bases
Wake-up Write down each equation below. Identify the base (B), acid (A), conjugate acid (CA), and conjugate base (CB). 1.NH 3 + HCN  NH 4 + CN 1.HSO 4.
Calculating pH and pOH. pH pH = - log [H + ] [H + ] = the hydrogen ion concentration pH: “potential of hydrogen” - A way of expressing the hydrogen ion.
AP Chemistry Acids Part II – The Calculations. Molarity This is actually “old business” as we covered Molarity in our lessons involving solutions. The.
Here’s another example calculation question involving these quantities [H 3 O + ], [OH – ], pH, and pOH Calculations Example 2.
Section 6.2 pg pH and pOH Calculations.
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.
PH Chapter Vocabulary Word hydronium ion: H 3 O + hydroxide ion: OH -
A C I D - B A S E T I T R A T I O N A N D p H
Hydrogen Ions and Acidity. Hydrogen Ions from Water Water is highly polar – what does that mean? Water particles are in continuous motion If they possess.
Unit 5- Acids and bases Strong acids and bases
We can perform calculations involving pH, pOH, and other quantities for pure water when we’re not at 25°C. We’ll do one example here. Calculations Involving.
Section 6.3—Acidity, pH Objectives
pH and Hydronium Ion Concentration
PH. In any solution the H 3 O + and OH - concentration is always very small. pH- method of representing the H 3 O + concentration in a solution. pH =
Yesterday’s Homework. The concentration of either the H + ion or the OH - ion is given for three aqueous solutions at 298 o K. For each solution, calculate.
Ch. 18: Acids & Bases Sec. 18.3: What is pH?. Objectives n Explain the meaning of pH and pOH. n Relate pH and pOH to the ion product constant for water.
* Name the following acids: * HI * HNO 3 * HCl * Write the formula for the following acids: * Hydrofluoric Acid * Nitrous Acid * Hydrobromic acid.
1 Acids and Bases Chapter Properties of Acids Sour taste Change color of vegetable dyes React with “active” metals –Like Al, Zn, Fe, but not Cu,
Acids and Bases pH and Associated Calculations
Pg  Amphoteric substance: can act as an acid or as a base ◦ Water is the most common amphoteric substance  Self-ionization of water: H 2.
PH ( power of hydronium ion). The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the.
NOTES: 19.2 – Hydrogen Ions & Acidity (pH and pOH)
Acids & Bases pH. Ionization of Water H 2 O + H 2 O H 3 O + + OH - K w = [H 3 O + ][OH - ] = 1.0  Kw=ionization constant for H2O.
 pH: The negative of the common logarithm of the hydronium ion concentration [H 3 O + ] ◦ pH stands for the French words pouvoir hydrogene, meaning “hydrogen.
Aqueous Solutions and the Concept of pH Section 15.1.
Helpful hints To make it simple:  For this unit, all acids/bases are going to be aqueous (except for water = pure liquid) General equations:  Strong.
ION CONCENTRATIONS pH and pOH Calculations.  The pH scale is used to identify a substance as an acid or a base due to the pH value.  This scale is a.
Power of hydrogen. pH scale logarithmic scale expresses H +1 concentration, [H +1 ] pH = -log[H +1 ]pH = -log[H +1 ] If pH changes by factor of 1, [H.
Acids and Bases. Chapter 15 Acids and Bases 15.2 the Acids and Bases properties of water 15.3 PH- a measure of acidity.
Chapter 16 (sections 3-4). © 2009, Prentice-Hall, Inc. Autoionization of Water As we have seen, water is amphoteric. In pure water, a few molecules act.
PH. Ionization of Water  When compounds dissociate/ionize in an aqueous solution, they produce ions - hydronium (H 3 O + ) and hydroxide (OH - )  These.
Acids and Bases Bundle 4: Water.
Calculating pH SCH3U/4C Ms. richardson.
Acids and Bases Bundle 4: Water.
Acids and Bases Bundle 4: Water.
Can you calculate for acids and bases?
pH Scale Definition of Acids and Bases
Calculating pH and pOH.
PH and pOH.
Calculating pH (and pOH)
PH and pOH Acid Neutral Base.
DO NOW Pick up notes. You need a calculator today.
Unit 5- lecture 5 Using the pH scale to characterize acids and bases.
Presentation transcript:

6.4 – The pH Scale Unit 6 – Acids and Bases

What is pH? pH is just another way to express [H+], the hydrogen ion concentration of an acidic or basic solution. Hydrogen acid concentrations are often small numbers, such as 1.3 × 10-3. pH is a method of transforming this number into something that is a little easier to work with. In math class you may have learned about logarithms - log for short. We'll leave the definitions of logs to math and just work with how to find them here. Get your calculators out. Different calculators work in slightly different ways, and it will be VERY IMPORTANT for you to know how to use yours when working with logs.

Logs – Using your Calculator Example: Find the log of 1.0 ×105 Enter the number 1.0 ×105 (don't forget to use the calculator's scientific notation feature!), then press the LOG key. Try that. You should get an answer of "5". If you get a different answer, or an error, try pressing the LOG key before you enter the number 1 ×105. Be sure you get the correct answer of 5 before continuing on. Try the examples shown on the right. Again, be sure you are getting the correct answers - if not, try changing the order than you enter items into your calculator. Number Log 1 ×10-3 -3 2.5 ×1012 12 3.5×10-9 -8.5

Logs & pH pH is defined as the negative log of hydrogen ion concentration. pH = -log[H+] Because hydrogen ion concentration is generally less than one (for example, 1.3 x 10-3), the log of the number will be a negative number. To make pH even easier to work with, pH is defined as the negative log of [H+], which will give a positive value for pH.

pH & Your Calculator - Practice Try the examples shown on the right. Find the pH, given [H+]. Answers are shown, but be sure you are able to arrive at that answer with your calculator! Notice the last example. 1.0 ×10-7 is the [H+] in pure water. Pure water therefore has a pH of 7. [H+] pH 1 ×10-3 3 2.5 ×10-11 11 4.7 ×10-9 8.3 5.8 ×10-4 3.2 1.0×10-7 7.0

What do pH Values Mean? By looking at the [H+] values in the table above, can you determine which solutions would be acidic, and which would be bases? Number 1 and 4 are acids. In those, [H+] is greater than 1.0×10-7 Numbers 2 and 3 are bases. In those solutions, [H+] is less than 1.0×10-7. Working with negative powers of 10 is not easy for many of us, so some of you may be confused by trying to identify acids and bases based on [H+]. But if we use pH values instead we find it much easier to identify acids and bases.

What do pH Values Mean? Acids Bases Neutral solutions pH < 7 The lower the pH, the stronger the acid Bases pH > 7 The higher the pH, the stronger the base Neutral solutions pH = 7

Examples of Calculating pH 1. Calculate the pH of a 0.01M HNO3 solution. 2. Find the pH of a 0.01 M solution of ammonia.

pOH There is a way to simplify the last parts of this operation. In addition to pH, we can also define pOH: pOH = - log [OH-] For bases, once we find [OH-] for a base, we can quickly determine pOH: For example: [OH-] =4.2 × 10-4 pOH = -log [OH-] = -log (4.2×10-4) pOH= 3.4 answer

pH & pOH Next we make use of the following easy-to- memorize relationship: pH + pOH = 14 Does the number 14 ring a bell? Remember Kw = 1.0 × 10-14. The negative log of 1.0 × 10-14 = 14 Once we find pOH, it is a simple matter to find pH: pH = 14 - pOH = 14 - 3.4 pH = 10.6

Finding [H+] when you know pH Sometimes you need to work "backwards" - you know the pH of a solution and need to find [H+], or even the concentration of the acid solution. How do you do that? To convert pH into [H+] involves taking the antilog of the negative value of pH . [H+] = antilog (-pH) As mentioned above, different calculators work slightly differently - make sure you can do the following calculations using your calculator. Practice as we go along . . .

Finding [H+] when you know pH Example 3. We have a solution with a pH = 8.3. What is [H+]? With some calculators you will do things in the following order: Enter 8.3 as a negative number (use the key with both the +/- signs, not the subtraction key) Use your calculator's 2nd or Shift or INV (inverse) key to type in the symbol found above the LOG key. The shifted function should be 10x. You should get the answer 5.0 × 10-9

Finding [H+] when you know pH Example 3. We have a solution with a pH = 8.3. What is [H+]? Other calculators require you to enter keys in the order they appear in the equation. Use the Shift or second function to key in the 10x function. Use the +/- key to type in a negative number, then type in 8.3 You should get the answer 5.0 × 10-9 If neither of these methods work, try rearranging the order in which you type in the keys. Don't give up - you must master your calculator!

Example 4. Find the hydronium ion concentration in a solution with a pH of 12.6. Is this solution an acid or a base? How do you know?

Example 5. A 0.24M solution of the weak acid, H2CO3, has a pH of 3.49. Determine Ka for H2CO3 (carbonic acid). *Assume only the first (or one) H+ ionizes.