5B1 Acids and Bases Flashcards
Describe models of acid and bases and their properties, including the Arrhenius, Brønsted-Lowry, and Lewis models.
Define:
acid
A molecule that donates hydrogen ions (H⁺) to a solution.
Acids increase the hydrogen ion concentration in a solution, which decreases the pH.
Define:
base
A molecule that accepts hydrogen ions (H⁺) from a solution.
Bases reduce the hydrogen ion concentration in a solution, which increases the pH.
Which scientist proposed the first definition of acids and bases?
Svante Arrhenius
Arrhenius defined acids as substances that release H⁺ ions in water and bases as substances that release OH⁻ ions.
What is an example of a strong acid?
Hydrogen chloride
(HCl)
Strong acids tend to disassociate completely, and hydrogen chloride dissociates completely into H⁺ and Cl⁻ ions in solution.
What does a strong base do in a solution?
It dissociates completely to produce cations and hydroxide ions (OH⁻).
An example is sodium hydroxide (NaOH), which dissociates into Na⁺ and OH⁻ ions.
Define:
salt
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.
What is the chemical formula for table salt?
NaCl
Also known as sodium chloride, it is formed from sodium cations (Na⁺) and chloride anions (Cl⁻).
True or False:
Salts are polar compounds.
True
Salts are polar because of the ionic bonds between cations and anions, making them highly soluble in water.
Fill in the blanks:
The anions in salts are often ______ or ______.
halogens, oxygen
Common anions in salts include halogens (e.g., Cl⁻, Br⁻) and oxygen (e.g., O²⁻, SO₄²⁻).
Which periodic table group contains the most common cations in salts?
Group 1 (alkali metals)
Alkali metals, like sodium and potassium, readily form cations by losing one electron.
How are salts formed?
Through acid-base neutralization reactions, where acids and bases neutralize each other to form water and salt.
Example: HCl + NaOH → NaCl + H₂O.
What is the charge of a magnesium ion in magnesium chloride?
2
Magnesium loses two electrons to form Mg²⁺, which bonds ionically with two chloride ions.
True or False:
Salts are crystalline.
True
Salts, such as sodium chloride, typically form crystals due to the regular arrangement of their ionic bonds.
What are two properties of salts?
- High melting/boiling points.
- Soluble in water.
Salts are strong ionic compounds, making them thermally stable and excellent electrolytes in aqueous solutions.
What is the main use of potassium dichromate (K₂Cr₂O₇)?
It is used in strong cleaning solutions.
Potassium dichromate is highly toxic, flammable, and carcinogenic.
What is the formula of calcium chloride?
CaCl₂
Calcium transfers two electrons, each to a chloride ion, resulting in a 1:2 ratio of calcium to chlorine in CaCl₂.
What is a key property of calcium chloride (CaCl₂)?
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.
How do salts conduct electricity in water?
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.
True or False:
Neutral salts are formed when a strong acid reacts with a weak base.
False
Neutral salts are formed only when a strong acid reacts with a strong base or a weak acid reacts with a weak base.
What is an amphoteric compound?
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.
Define:
an Arrhenius acid
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.
What are three examples of Arrhenius acids?
- HCl (hydrochloric acid)
- H₂SO₄ (sulfuric acid)
- HNO₃ (nitric acid)
Define:
an Arrhenius base
A substance that increases hydroxide ion (OH⁻) concentration in water.
The presence of OH⁻ ions is necessary for classification as an Arrhenius base.
What are three examples of Arrhenius bases?
- NaOH (sodium hydroxide)
- KOH (potassium hydroxide)
- Mg(OH)₂ (magnesium hydroxide)
True or False:
All substances containing hydrogen are Arrhenius acids.
False
Only substances that produce hydronium ions in water qualify as Arrhenius acids.
Hydronium ions are formed when hydrogen ions combine with water molecules.
What property makes Arrhenius bases feel slippery?
The production of hydroxide ions.
Hydroxide ions react with oils on the skin to create a slippery sensation.
Which common household base is an Arrhenius base?
Sodium hydroxide
(NaOH)
NaOH is often found in cleaning products.
Why is CH₄ not an Arrhenius acid?
CH₄ does not contain dissociable hydrogen ions to form hydronium in water.
The absence of dissociable hydrogen ions disqualifies it from being an Arrhenius acid.
What is a limitation of the Arrhenius model?
It requires water to be present, so it does not account for acidic or basic behavior in non-aqueous solvents.
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.
Fill in the blanks:
In the Lewis definition, acids are electron-pair ______ and bases are electron-pair ______.
acceptors, donors
Lewis acids and bases form covalent bonds through electron-pair sharing.
Which compound is the Lewis acid in the reaction Al³⁺ + 6H₂O → [Al(H₂O)6]³⁺?
Al³⁺
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⁺.
Which compound acts as a Lewis base in Ag⁺ + 2NH₃ → [Ag(NH₃)₂]⁺?
NH₃
Ammonia donates electron pairs to silver ions, acting as a Lewis base.
What is the difference between the Arrhenius and Lewis definitions of acids?
- Arrhenius acids: They release H⁺ in water.
- Lewis acids: They accept electron pairs.
The Lewis definition is broader and not limited to substances containing H⁺.
Define:
a Bronsted-Lowry acid
A substance that can donate a proton (H⁺).
Bronsted and Lowry independently proposed this definition in 1923, focusing on proton donation.
Define:
a Bronsted-Lowry base
A substance that can accept a proton (H⁺).
This definition complements the Bronsted-Lowry acid concept by emphasizing proton acceptance.
Bronsted-Lowry bases accept protons from acids.
Fill in the blank:
The Bronsted-Lowry theory applies to substances that may or may not be dissolved in ______.
water
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.
How does the Lewis definition of an acid differ from the Bronsted-Lowry definition?
The Lewis definition is broader and does not require the presence of hydrogen.
Lewis acids can include substances like metal cations (e.g., Al³⁺) that accept electron pairs.
Fill in the blank:
In the reaction NH₃ + H₂O → NH₄⁺ + OH⁻ the Bronsted-Lowry base is _____.
NH₃
Ammonia (NH₃) accepts a proton from water, making it a Bronsted-Lowry base.
True or False:
All Arrhenius acids are Bronsted-Lowry acids, but not all Bronsted-Lowry acids are Arrhenius acids.
True
Arrhenius acids are a subset of Bronsted-Lowry acids because they dissociate in water to release H⁺.
Define:
conjugate acid
It is the species formed when a base accepts a proton.
Bases can accept protons to form conjugate acids, which can donate a proton in a reverse reaction.
What is the conjugate acid of ammonia (NH₃) in the reaction NH₃ + H₂O → NH₄⁺ + OH⁻?
NH4⁺
The conjugate acid forms when the base (NH₃) gains a proton (H⁺).
Define:
conjugate base
The species that remains after an acid donates a proton.
When an acid dissociates, it forms its conjugate base, which can accept a proton in a reverse reaction.
What is the conjugate base of water (H₂O) in the reaction NH₃ + H₂O → NH₄⁺ + OH⁻?
OH⁻
The conjugate base forms when the acid (H₂O) donates a proton (H⁺).
In the reaction HNO₂ + PO₄³⁻ → NO₂⁻ + HPO₄²⁻, identify one conjugate acid-base pair.
HNO₂ and NO₂⁻
HNO₂ loses a proton to form NO₂⁻, making them a conjugate acid-base pair.
