5B1 Acids and Bases

Question 1

Define:

acid

Answer 1

A molecule that donates hydrogen ions (H⁺) to a solution.

Acids increase the hydrogen ion concentration in a solution, which decreases the pH.

Question 2

Define:

base

Answer 2

A molecule that accepts hydrogen ions (H⁺) from a solution.

Bases reduce the hydrogen ion concentration in a solution, which increases the pH.

Question 3

Which scientist proposed the first definition of acids and bases?

Answer 3

Svante Arrhenius

Arrhenius defined acids as substances that release H⁺ ions in water and bases as substances that release OH⁻ ions.

Question 4

What is an example of a strong acid?

Answer 4

Hydrogen chloride

(HCl)

Strong acids tend to disassociate completely, and hydrogen chloride dissociates completely into H⁺ and Cl⁻ ions in solution.

Question 5

What does a strong base do in a solution?

Answer 5

It dissociates completely to produce cations and hydroxide ions (OH⁻).

An example is sodium hydroxide (NaOH), which dissociates into Na⁺ and OH⁻ ions.

Question 6

Define:

salt

Answer 6

An ionic compound composed of metal cations and nonmetal anions bonded together through ionic bonds.

They are formed through the complete transfer of electrons from cations to anions and are often products of acid-base neutralization reactions.

Question 7

What is the chemical formula for table salt?

Answer 7

NaCl

Also known as sodium chloride, it is formed from sodium cations (Na⁺) and chloride anions (Cl⁻).

Question 8

True or False:

Salts are polar compounds.

Answer 8

True

Salts are polar because of the ionic bonds between cations and anions, making them highly soluble in water.

Question 9

Fill in the blanks:

The anions in salts are often ______ or ______.

Answer 9

halogens, oxygen

Common anions in salts include halogens (e.g., Cl⁻, Br⁻) and oxygen (e.g., O²⁻, SO₄²⁻).

Question 10

Which periodic table group contains the most common cations in salts?

Answer 10

Group 1 (alkali metals)

Alkali metals, like sodium and potassium, readily form cations by losing one electron.

Question 11

How are salts formed?

Answer 11

Through acid-base neutralization reactions, where acids and bases neutralize each other to form water and salt.

Example: HCl + NaOH → NaCl + H₂O.

Question 12

What is the charge of a magnesium ion in magnesium chloride?

Answer 12

2

Magnesium loses two electrons to form Mg²⁺, which bonds ionically with two chloride ions.

Question 13

True or False:

Salts are crystalline.

Answer 13

True

Salts, such as sodium chloride, typically form crystals due to the regular arrangement of their ionic bonds.

Question 14

What are two properties of salts?

Answer 14

1. High melting/boiling points.
2. Soluble in water.

Salts are strong ionic compounds, making them thermally stable and excellent electrolytes in aqueous solutions.

Question 15

What is the main use of potassium dichromate (K₂Cr₂O₇)?

Answer 15

It is used in strong cleaning solutions.

Potassium dichromate is highly toxic, flammable, and carcinogenic.

Question 16

What is the formula of calcium chloride?

Answer 16

CaCl₂

Calcium transfers two electrons, each to a chloride ion, resulting in a 1:2 ratio of calcium to chlorine in CaCl₂.

Question 17

What is a key property of calcium chloride (CaCl₂)?

Answer 17

It is an excellent water-absorbing agent.

Calcium chloride is often used to melt ice on roads during winter by absorbing water and lowering the freezing point.

Question 18

How do salts conduct electricity in water?

Answer 18

Salts dissociate into ions in water, which allows them to conduct electricity.

Dissociated ions, like Na⁺ and Cl⁻, move freely in the solution, facilitating electrical conductivity.

Question 19

True or False:

Neutral salts are formed when a strong acid reacts with a weak base.

Answer 19

False

Neutral salts are formed only when a strong acid reacts with a strong base or a weak acid reacts with a weak base.

Question 20

What is an amphoteric compound?

Answer 20

A compound that can act as both an acid and a base.

These compounds can donate or accept protons depending on the reaction. Water (H₂O) is a common example of this kind of compound.

Question 21

Define:

an Arrhenius acid

Answer 21

A substance that increases hydronium ion (H₃O⁺) concentration in water by donating hydrogen ions.

Hydrogen ion dissociation is a key aspect of classifying Arrhenius acids.

Question 22

What are three examples of Arrhenius acids?

Answer 22

1. HCl (hydrochloric acid)
2. H₂SO₄ (sulfuric acid)
3. HNO₃ (nitric acid)

Question 23

Define:

an Arrhenius base

Answer 23

A substance that increases hydroxide ion (OH⁻) concentration in water.

The presence of OH⁻ ions is necessary for classification as an Arrhenius base.

Question 24

What are three examples of Arrhenius bases?

Answer 24

1. NaOH (sodium hydroxide)
2. KOH (potassium hydroxide)
3. Mg(OH)₂ (magnesium hydroxide)

Question 25

# True or False: All substances **containing hydrogen** are Arrhenius acids.

Answer 25

False ## Footnote Only substances that produce hydronium ions in water qualify as Arrhenius acids. Hydronium ions are formed when hydrogen ions combine with water molecules.

Question 26

What property makes Arrhenius bases **feel slippery**?

Answer 26

The production of **hydroxide ions**. ## Footnote Hydroxide ions react with oils on the skin to create a slippery sensation.

Question 27

Which common **household base** is an Arrhenius base?

Answer 27

Sodium hydroxide | (NaOH) ## Footnote NaOH is often found in cleaning products.

Question 28

Why is **CH₄ not** an Arrhenius acid?

Answer 28

CH₄ **does not contain dissociable hydrogen ions** to form hydronium in water. ## Footnote The absence of dissociable hydrogen ions disqualifies it from being an Arrhenius acid.

Question 29

What is a **limitation** of the Arrhenius model?

Answer 29

It requires water to be present, so it **does not account for acidic or basic behavior in non-aqueous solvents**. ## Footnote This limitation restricts the model's applicability in non-aqueous environments. This limitation is addressed by the Bronsted-Lowry definition that includes acids and bases not in aqueous solutions.

Question 30

# Fill in the blanks: In the **Lewis definition**, acids are electron-pair \_\_\_\_\_\_ and bases are electron-pair \_\_\_\_\_\_.

Answer 30

acceptors, donors ## Footnote Lewis acids and bases form covalent bonds through electron-pair sharing.

Question 31

Which compound is the **Lewis acid** in the reaction Al³⁺ + 6H₂O → [Al(H₂O)6]³⁺?

Answer 31

Al³⁺ ## Footnote Al³⁺ acts as a Lewis acid because it accepts electron pairs from water molecules. Water acts as the Lewis base because it donates electron pairs to form a covalent bond with Al³⁺.

Question 32

Which compound acts as a **Lewis base** in Ag⁺ + 2NH₃ → [Ag(NH₃)₂]⁺?

Answer 32

NH₃ ## Footnote Ammonia donates electron pairs to silver ions, acting as a Lewis base.

Question 33

What is the **difference** between the Arrhenius and Lewis definitions of acids?

Answer 33

* Arrhenius acids: They **release H⁺** in water. * Lewis acids: They **accept electron pairs**. ## Footnote The Lewis definition is broader and not limited to substances containing H⁺.

Question 34

# Define: a Bronsted-Lowry acid

Answer 34

A substance that can **donate a proton** (H⁺). ## Footnote Bronsted and Lowry independently proposed this definition in 1923, focusing on proton donation.

Question 35

# Define: a Bronsted-Lowry base

Answer 35

A substance that can **accept a proton** (H⁺). ## Footnote This definition complements the Bronsted-Lowry acid concept by emphasizing proton acceptance. Bronsted-Lowry bases accept protons from acids.

Question 36

# Fill in the blank: The Bronsted-Lowry theory applies to substances that **may or may not be dissolved in** \_\_\_\_\_\_.

Answer 36

water ## Footnote Bronsted-Lowry acids and bases are not restricted to aqueous solutions. It includes acids and bases in gaseous or non-aqueous systems. For example, HCl can act as a gas-phase Bronsted-Lowry acid.

Question 37

How does the Lewis definition of an acid **differ from the Bronsted-Lowry definition**?

Answer 37

The **Lewis definition is broader** and does not require the presence of hydrogen. ## Footnote Lewis acids can include substances like metal cations (e.g., Al³⁺) that accept electron pairs.

Question 38

# Fill in the blank: In the reaction **NH₃ + H₂O → NH₄⁺ + OH⁻** the Bronsted-Lowry base is \_\_\_\_\_.

Answer 38

NH₃ ## Footnote Ammonia (NH₃) accepts a proton from water, making it a Bronsted-Lowry base.

Question 39

# True or False: All Arrhenius acids are Bronsted-Lowry acids, but **not all Bronsted-Lowry acids are Arrhenius acids**.

Answer 39

True ## Footnote Arrhenius acids are a subset of Bronsted-Lowry acids because they dissociate in water to release H⁺.

Question 40

# Define: conjugate acid

Answer 40

It is the **species formed** when a base accepts a proton. ## Footnote Bases can accept protons to form conjugate acids, which can donate a proton in a reverse reaction.

Question 41

What is the **conjugate acid of ammonia** (NH₃) in the reaction NH₃ + H₂O → NH₄⁺ + OH⁻?

Answer 41

NH4⁺ ## Footnote The conjugate acid forms when the base (NH₃) gains a proton (H⁺).

Question 42

# Define: conjugate base

Answer 42

The **species that remains** after an acid donates a proton. ## Footnote When an acid dissociates, it forms its conjugate base, which can accept a proton in a reverse reaction.

Question 43

What is the **conjugate base of water** (H₂O) in the reaction NH₃ + H₂O → NH₄⁺ + OH⁻?

Answer 43

OH⁻ ## Footnote The conjugate base forms when the acid (H₂O) donates a proton (H⁺).

Question 44

In the reaction HNO₂ + PO₄³⁻ → NO₂⁻ + HPO₄²⁻, identify one **conjugate acid-base pair**.

Answer 44

HNO₂ and NO₂⁻ ## Footnote HNO₂ loses a proton to form NO₂⁻, making them a conjugate acid-base pair.