Module 5

How to determine ph? How to calculate concentration (related to ph)

-log ( number) concentration = 10 - the number (press second then log)

Ph scale

0-14 numeric scale. Substances tending to the 0 end of the scale are increasingly acidic, while those tending to the 14 end of the scale are increasingly basic. Neutral solutions have a ph of 7

_____________ studied the conductivity of solutions and proposed that electrolytes break up into charged particles in water.

Arrhenius

According to the ________ theory, acids and bases can only occur in aqueous solutions (water) However the theory does not account for reactions between substances which are acidic and basic but do not have a hydrogen ion or hydroxide ion. Such examples include

Arrhenius - an aqueous solution of basing soda (NaHCo3) which turns litmus blue in water, but has no apparent hydroxide ion - metal ions, such as iron (III) and aluminum which turns litmus red, but have no hydrogen ions.

Calculate the ph for the following b) 4.00x 10-4 mol/L Ba(OH)2

Ba(OH)2----> Ba2+ + 2OH- OH- = 2(4.00x10-4) = 8.0 x 10-4 mol/L H3O+ = kw/oh- = 1.0 x10-14 / 8.0 x 10-4

Ph range Description 0-3 highly acidic 3-6 acidic 7 neutral 8-11 basic 11-14 highly basic

Colours Red Yellow/orange Green Blue Purple

Calculate the ph for the following a) 0.0020 mol/L HCL

HCL + H2O ---> H3O+ Cl- (H3O+) = 0.0020 mol/L ph = -log (0.0020) = 2.7

Provide one explanation as to why NH3 might not be considered a base according to Arrhenius

It does not donate OH ion, bases give OH ion

In general, a strong acid will dissociate close to 100% and have a very large ______________.

Keq

The ____ of a solution is the negative logarithm of the hydroxide ion concentration.

POH

Determine the concentration of OH- ions in the solutions with the following pH values. a) Ph = 1.6

POH = 14-ph - 14-1.6 = 12.4 OH- = 10-poh = 10- 12.40 = 4.0 x 10-13 mol/l OH-

Monoprotic acids have on hydrogen ions available to be donated, such as HCL. _____ acids have two or more hydrogen ions to donate (di- tri- and so on)

Polyprotic

Why is the bronsted lowry definition of acids and bases considered to be more general than Arrhenius definition

The Arrhensius theory of acids and bases was limited to aqueous solution B-Lowry theory is able to explain why substances such as hydrogen carbonate ion can act as an acids and a base and how substances without hydroxids like Nh3 can act as bases. B-Lowry explains acids and bases in terms of proton donor and acceptors.

Of the three acid-base theories. Which one applies to the greatest number of reactions. Explain your answer

The lewis theory applies to the greatest number of reactions as it is so general that any reaction in which a pair of electrons is transferred becomes an acid base reaction. Explains the majority of reaction chemistry

Are there OH- ions in an acidic solution with a ph of 3.25? How do you know?

Yes, there are always some hyrocxide ions in an aqueous solution. This is evident since the product of the hydrogen ion concentration and must always equal kw.

determine the concentration of H+ for each of the following a) ph = 7.0 b) POH = 5.0

a) H3O = 10-ph= 10-7 = 1.0 x 10-7 b) ph = 14 -POh = 14-5.0 = 9.0 H30+ = 10-ph = 10-9 = 1.0 x 10-9

Arrhenius also stated that a ____ is definied as a compound that ionizes to yield hydroxide ions (OH-) in ______ solutions

base and aqueous

All of these are examples of strong acids with the exception of a. HClO4 (perchloric acid) b. HI (hydroiodic acid) c. HBr (hydrobromic acid) d.H2CO3 (carbonic acid)

d

Which of the following is considered a limitation of the Brønsted—Lowry definition of acids and bases? a. The Brønsted—Lowry theory expands the definition of an acid and base to a proton donor or acceptor. b. Even though acids and bases can occur without water, there is still a requirement for the presence of a solvent. c. The Brønsted—Lowry theory cannot explain why some substances without hydroxides, like ammonia, can act as bases. d. The Brønsted—Lowry theory does not explain how substances without protons can act as acids.

d

The Arrhenius Theory was primarily important in establishing the concept of dissociation and explaining the process of ______

neutralization

Determine the poh of the following if ph is given ph = 5.4

ph= 14-5.4

We call the hydrogen ion (H+) a ___ because, as an ion, it has no electron and the nucleus is a single protron

proton

The bronsted lowry theory is able to explain why substances such as the hydrogen carbonate ion can act as an acid and a base and how substances without hydroxides, like ammonia, can act as bases. The theory does not explain however how substances without ____ can act as acids

protons

in 1887, Svante Arrhenius discovered that all ____ and ___ solutions he tested on were electrolytes. He determined that ___ and ____ must be ionic or dissociate in water. This theory was useful when working with compounds whose formulas contain obvious clues about their acidic or basic nature

acidic, basic, acids and bases

substances such as water which can act as both acids and bases are said to be ________

amphoteric

When a base is dissolved in water, the hydroxide ion concentration increases. the equilibrium shifts left to use up some of the added hydroxide and maintain Kw at 1.0 x 10-14. Since equilibrium shifts left, hydronium ion concentration is ___

reduced

The Lewis acid is a substance that can ___ a pair of electrons to form a covalent bond. A Lewis base is a substance that _______ a pair of electrons to form a covalent bond

accept and donates

A conjugate base is what remains after a/an ______________ has donated its proto

acid

Lewis Theory proposed that an ___ accepts a pair of elections during a chemical reaction, while a base donates a pair of electrons.

acid

According to Arrhenius, an ___ is defined as a hydrogen-containing compound that ionizes to the yield hydrogen ions (H+) dissolved in ________ soluion

acid and aqueous

Dissociation

when ionic compounds dissolve to produce ions.

According to the ________ definition, an acid is a proton (H+) donor. A base is defined as proton (H+) acceptor

Bronsted-Lowry

What is a natural universal indicator? This indicator will produce different coloured solutions at different ph ranges. Good indicator of ph because it contains flavin, a pigment molecule that changes color acoording to the concentration of the hydrogen ions in a solution. ranges from red, purple, bluish purple, bluish green, greenish yellow

Red Cabbage Juice

will dissociate close to 100% and have a very large keq. This means that the reaction goes to completion with very little, if any of the reactant left. higher H3O+ HClO4 (perchloric acid HI (hydroiodic acid) HBr (hydrobromic acid) HNO3 (nitric acid) H2SO4 (sulfuric acid)

Strong acid

____ is one that completely dissociates into ions. higher (OH-) NAOH (sodium hydroxide) KOH (potassium hydroxide) LiOH (lithium hydroxide) Ca (OH)2 (calcium hydroxide) RbOH (rubdium hydroxide) Ba(OH)2 (barium hydroxide

Strong base

10. Which of these descriptions is not a characteristic of the Lewis theory? a. This theory limits the number of compounds called acids, since any compound that has one or more valence shell orbitals cannot act as an acid. b. The Lewis definition is so general that any reaction in which a pair of electrons is transferred becomes an acid-base reaction. c. Lewis acid-base reactions include many reactions that would not be included with the Brønsted—Lowry definition. d. The Lewis acid-base theory does not affect Brønsted—Lowry bases because any Brønsted—Lowry base must have a pair of non-bonding electrons in order to accept a proton.

a

Which statement regarding indicators is false? a. They are strong, organic acids that change colour when the hydronium or hydroxide ion concentration is changed. b. Indicators change colour over a given pH range (the colour of each indicator can be coordinated with the pH). c. The colour of the indicator can be compared to a standard to determine the pH of the solution. d. Using an indicator is not as accurate as a pH metre.

a

The conjugate acid is what remains after a ___ accepted a proton and the conjugate base is what remains after the ___ has donated its prton

base and acid

______________ salts result from the reaction of a strong base with a weak acid

basic

Which of the following statements does not support Arrhenius' work with acids and bases? a. Arrhenius discovered that all acidic and basic solutions he tested were electrolytes. b. He determined that acids and bases must ionize or dissociate in water. c. According to Arrhenius, an acid is defined as a hydrogen-containing compound that ionizes to yield hydrogen ions (H+) dissolved in aqueous solution. d. According to Arrhenius, an acid is defined as a compound that ionizes to yield hydroxide ions (OH-) in aqueous solution

d

An ______________ is defined as a compound that conducts an electric current when it is in an aqueous state.

electrolyte

Arrhenius proposed that _____ break up into charged particles in water. Knowledge of atomic structure increaed

electrolytes

A neutral solution occurs when the hydronium ion concentration is ______________ to the hydroxide ion concentration.

equal

For strong acids and strong bases - the reaction is so far to the right that there is essentially no reactant left and so there is no _____

equilibirum

Robert Boyle also described the properties of bases or alkalies ( base)

having a slippery feel, able to change litmus blue, becoming less alkali when mixed with acids

Adding an acid to water increases the ______ ion concentration and reduces the hydroxide ion concentration

hydronium

At equivalence, the______________ion and hydroxide ion concentrations are equal.

hydronium

When water acts as the base, accepting the proton, the result is the H3O+ ion called the ______________ ion.

hydronium

Acids are substances that inscrease the ______ (H3o+) ion concentration

hydronium ion

Adding a base to water increases the _____ ion concentration and reduces the hydronium concentration is reduced

hydroxide

Bases are substances that increase the ______ (OH-) ion concentration

hydroxide

When an acid is dissolved in water, the acid produces a large mount of H3O+ ions. IF the H3O+ ion concentration increases the equilibrium will shift to teh rleft to use up some of the added hydronium and maintain kw at 1x10-14. Since equilibrium shifts left the _____ ion concentration is reduced

hydroxide

______ are weak, organic acids that change colour when hydronium or hydroxide ion concentration is changed. Indicators change colour over a given ph range.

indicator

When molecular compounds dissolve in water to produce ions, the process is typically called

ionization

Acids and bases were initially defined based on observable properties, also called operational definitions. In 1661 Robert Boyle described acids as

sour tasting, able to change colour of vegetable litmus dye red, corrosive, becoming less acidic when mixed with alkaline basic substances

Hydration

water molecules then surround the positive cations and negative anions.

According to the Bronsted Lowry theory, substances like ____ can act as both an acid and base. These types of substances are referred ti as

water, amphoteric

_______ dissociate only slightly into ions; therefore, these dissociation equations use a reversible arrow, unlike reactions involving strong acids and bases. lower h3O+ keq <<<<<<1

weak acids

____ dissociates only slightly into ions. An important weak base is ammonia. kb for equlibrium constant for base. lower oh- C6H6NH2 ( aniline) CH3NH2 (methylamine) c5h5N (pyridine

weak base