Chapter 6 Acids & Bases

Question 1

Svante Arrhenius’ first useful definition of acids and bases

Answer 1

Acids are substances that ionize in aqueous solutions to form hydrogen ions, and bases are substances that dissociate to form hydroxide ions in aqueous solution. This theory has drawbacks

Question 2

Why might a hydrogen ion be too small to exist on its own in an aqueous solution

Answer 2

A hydrogen ion is a tiny proton with a high charge to size ratio and is likely to bond strongly to polar water molecules.

Question 3

Hydronium ion

Answer 3

The simplest representation of a hydrated proton H3O+ (aq). These ions are responsible for acidic properties: high conductivity, high reaction rate, and low pH are all indicative of high concentrations of this ion.

Question 4

Hydroxide ions

Answer 4

OH- ions, form in basic solutions. These ions responsible for the properties of basic solutions.

Question 5

Concentration of hydronium and hydroxide ions in pure water

Answer 5

Neutral water contains trace amounts of both hydronium ions and hydroxide ions due to a very slight ionization. In pure water at SATP, the hydronium ion concentration is very low: 1 x 10^-7 mol/L.

Question 6

pH

Answer 6

Power of hydrogen. defined as the negative exponent to the base ten of the hydronium ion concentration (expressed as moles per litre). A definition that includes non integer numbers: pH is the negative of the logarithm to the base ten of the hydronium ion concentration.

Question 7

pOH

Answer 7

The negative of the logarithm to the base 10 of the hydroxide ion concentration.

Question 8

Acid-base indicators

Answer 8

Substances that change colour when the acidity of a solution changes. Ex. Bromothymol blue, phenolphthalein, litmus

Question 9

The two forms of any indicator depend on

Answer 9

whether a particular hydrogen atom is present in the indicator’s molecule. In general, lower pH form- “HIn(aq)”, higher pH form- “In- (aq)”. Because the chemical structure of each indicator is different, the pH at which the indicator changes from the HIn(aq) form, with one colour, to the In- (aq) form, with another colour, is different for each indicator.

Question 10

Between what pH values does litmus paper change colour?

Answer 10

between a pH of 6.0 and 8.0

Question 11

Arrhenius’ original theory on dissociation and ionization

Answer 11

Ionic compounds- dissociate into separate cations and anions
Bases- soluble ionic compounds that dissociate into cations and hydroxide anions
Acids- ionize in water to produce hydrogen ions plus an anion

Question 12

Revision on Arrhenius’ definitions

Answer 12

Original compound reacts with water molecule. Acids: substances that react with water to produce hydronium ions. Bases: substances that react with water to produce hydroxide ions.

Question 13

Neutralization

Answer 13

the reaction between hydronium and hydroxide ions to produce water

Question 14

Strong acid

Answer 14

Reacts completely with water (over 99%) to produce hydronium ions. The high concentration of the ions gives the properties of high conductivity, high rate of reaction with active metals and carbonates., and low pH

Question 15

Weak acid

Answer 15

Reacts incompletely with water to form relatively few hydronium ions. Most weak acids react much less than 50%

Question 16

Strong base

Answer 16

Dissociate completely in solution to produce hydrogen ions (commonly ionic hydroxides)

Question 17

Weak base

Answer 17

reacts partially (usually much less than 50%) with water to produce relatively few hydroxide ions compared to a similar amount of a strong base. Most bases other than soluble ionic hydroxides are weak bases. Weak bases may be ionic or molecular in their pure state.

Question 18

Monoprotic acid

Answer 18

Have only one hydrogen atom in their compound formula (HA) and can only react once with water to produce hydronium ions. Most strong acids as well as many weak ones are monoprotic.

Question 19

Polyprotic acid

Answer 19

Acids that contain more than one acidic hydrogen in their compound formulas (HxA) and can react more than once with water. In general, polyprotic acids are weak whose reaction with water decreases with each successive step

Question 20

Monoprotic bases

Answer 20

They can react with water only once to produce hydroxide ions.

Question 21

Polyprotic bases

Answer 21

They can react with water more than once with water, but all reactions with water are much less than 50%