Chapter 5: Acids and Bases

Comprehensive practice questions covering acid-base definitions, dissociation, chemical reactions, soil pH treatment, and oxide classification based on the provided chemistry lecture notes.

How is an acid defined in terms of its behavior in water?

An acid is a molecule which, when dissolved in water, dissociates to form hydrogen ions ($H^+$).

What is the chemical name and formula of the acid found in vinegar?

Ethanoic acid, with the chemical formula $CH_3CO_2H$.

According to the transcript, what does the dissociation of an acid molecule refer to?

The breakage of the covalent bond linking a hydrogen atom to another atom (such as $N$, $O$, $F$, or $Cl$), where the other atom retains both bonding electrons and the hydrogen atom becomes an ion.

What are the chemical formulas for hydrochloric acid, nitric acid, and sulfuric acid?

Hydrochloric acid: $HCl$; Nitric acid: $HNO_3$; Sulfuric acid: $H_2SO_4$.

Why are acid solutions able to conduct electricity?

Acids are unique because they have a simple molecular structure yet can give mobile ions in solution to act as charge carriers.

What is the difference between a strong acid and a weak acid in terms of dissociation?

A strong acid dissociates completely in water to produce hydrogen ions ($H^+$), whereas a weak acid dissociates only partially.

What is the importance of water for the acidity of molecules?

Acid molecules are only acidic when dissolved in water because dissociation into hydrogen ions does not occur when they are pure or dissolved in organic solvents like ethanol.

How is 'acid basicity' defined?

Basicity is dependent on the maximum number of hydrogen ions ($H^+$) formed per acid molecule dissociated in water.

Provide examples of monobasic, dibasic, and tribasic acids.

Monobasic: Hydrochloric acid ($HCl$); Dibasic: Sulfuric acid ($H_2SO_4$); Tribasic: Phosphoric acid ($H_3PO_4$).

In ethanoic acid ($CH_3CO_2H$), why is only one of the four hydrogen atoms able to form a hydrogen ion?

Only the hydrogen atom covalently bonded to the oxygen atom may break away; the other three are too strongly bonded to the carbon atom.

What are the common products of a reaction between an acid and a metal?

Salt and hydrogen gas ($H_2$).

How is the presence of hydrogen gas tested in a laboratory setting?

A lighted wooden splint is used; hydrogen gas will extinguish the splint with a 'pop' sound.

What components generally make up a salt?

A salt is generally made up of a cation (originating from a base) and an anion (originating from an acid).

What is the product of the reaction between an acid and a carbonate?

Salt, carbon dioxide gas ($CO_2$), and water ($H_2O$).

How is pure neutralisation described as an ionic equation?

$$H^+_{(aq)} + OH^-_{(aq)} \rightarrow H_2O_{(l)}$$

What is the definition of a base and an alkali?

Bases are metal oxides or hydroxides that react with an acid to form salt and water; an alkali is a base that is soluble in water and dissociates to form hydroxide ions ($OH^-$).

Explain the pH scale in terms of ion concentration.

Low pH ($< 7$) means higher hydrogen ion concentration than hydroxide ions; high pH ($> 7$) means lower hydrogen ion concentration; pH $7$ is neutral where concentrations are equal.

What are the color changes for Methyl Orange and Phenolphthalein?

Methyl Orange is red below pH $3.1$ and yellow above pH $4.4$; Phenolphthalein is colourless below pH $8.1$ and pink above pH $10.0$.

Why is calcium carbonate ($CaCO_3$) preferred over calcium hydroxide ($Ca(OH)_2$) for treating soil acidity?

Calcium carbonate is insoluble and does not make the soil too alkaline ($pH > 7$) if added in excess, and it does not react with ammonium salts in fertilisers.

What are the four types of oxides based on their properties?

1. Acidic oxides (non-metal oxides), 2. Basic oxides (metal oxides), 3. Neutral oxides (like $CO$ and $H_2O$), and 4. Amphoteric oxides.

What is an amphoteric oxide?

A metallic oxide that reacts with both acids and bases to form salt and water, such as zinc oxide ($ZnO$) or aluminium oxide ($Al_2O_3$).

What occurs when a strong alkali reacts with an ammonium salt?

They react to produce a salt, ammonia gas ($NH_3$), and water ($H_2O$).

What is a precipitation reaction?

The formation of an insoluble solid (precipitate) when two aqueous solutions are mixed together.

What are two common uses of bases in the home?

Neutralising acids (e.g., magnesium hydroxide in toothpaste or antacids) and cleaning (e.g., sodium hydroxide used to break down grease and dirt in floor cleaners).