Acids, Bases and Salts practice questions

Flashcards covering the properties of acids and bases, pH scales, chemical reactions of salts, and common industrial chemicals like baking soda and Plaster of Paris.

How do acids and bases change the color of litmus paper?

Acids turn blue litmus red, whereas bases turn red litmus blue.

Where is the natural indicator litmus extracted from?

Litmus is a purple dye extracted from lichen, a plant belonging to the division Thallophyta.

What are olfactory indicators?

Substances whose odour changes in acidic or basic media, such as onion, vanilla essence, and clove oil.

What is the general product when an acid reacts with a metal?

$$\text{Acid} + \text{Metal} \rightarrow \text{Salt} + \text{Hydrogen gas}$$

What is the chemical equation for the reaction of zinc with sodium hydroxide?

$2NaOH(aq) + Zn(s) \rightarrow Na_{2}ZnO_{2}(s) + H_{2}(g)$ (forming Sodium zincate).

What products are formed when metal carbonates or hydrogencarbonates react with acids?

A corresponding salt, carbon dioxide, and water.

What is the chemical reaction for carbon dioxide being passed through lime water?

$Ca(OH)_{2}(aq) + CO_{2}(g) \rightarrow CaCO_{3}(s) + H_{2}O(l)$, forming a white precipitate of calcium carbonate.

What is a neutralisation reaction?

The reaction between an acid and a base to give a salt and water: $\text{Base} + \text{Acid} \rightarrow \text{Salt} + \text{Water}$.

Why are metallic oxides considered basic oxides?

Because metallic oxides react with acids to give salts and water, similar to how a base reacts with an acid.

What ion is produced by all acids in an aqueous solution?

Acids produce hydrogen ions, $H^{+}(aq)$, or hydronium ions, $H_{3}O^{+}$, in water.

What ion do bases generate in water?

Bases generate hydroxide ($OH^{-}$) ions in water.

What is an alkali?

A base that dissolves in water.

Why must acid be added slowly to water rather than water to acid during dilution?

The process is highly exothermic; adding water to concentrated acid can generate enough heat to cause the mixture to splash out or break the glass container.

What does the 'p' in pH stand for?

The 'p' stands for ‘potenz’ in German, meaning power.

What is the pH range of the human body?

The body works within a narrow pH range of $7.0$ to $7.8$.

At what pH level is rain considered 'acid rain'?

When the pH of rain water is less than $5.6$.

What is the cause of tooth decay in terms of pH?

Tooth decay starts when the pH of the mouth is lower than $5.5$, leading to the corrosion of tooth enamel (calcium hydroxyapatite).

Which acid is present in a honey-bee sting and what is a common remedy?

A bee-sting leaves an acid (methanoic acid); using a mild base like baking soda on the area provides relief.

What three products are formed in the chlor-alkali process?

Sodium hydroxide ($NaOH$), chlorine ($Cl_{2}$), and hydrogen ($H_{2}$).

What is the chemical name and formula for bleaching powder?

Calcium oxychloride, represented as $Ca(ClO)_{2}$ (actual composition is complex).

What is the chemical name of baking soda?

Sodium hydrogencarbonate ($NaHCO_{3}$).

How is baking powder different from baking soda?

Baking powder is a mixture of baking soda ($NaHCO_{3}$) and a weak edible acid like tartaric acid.

What is the chemical formula for washing soda?

$Na_{2}CO_{3} \cdot 10H_{2}O$ (Sodium carbonate decahydrate).

What is water of crystallisation?

The fixed number of water molecules present in one formula unit of a salt (e.g., five molecules in $CuSO_{4} \cdot 5H_{2}O$).

What is Plaster of Paris and how is it formed?

Calcium sulphate hemihydrate ($CaSO_{4} \cdot \frac{1}{2}H_{2}O$); it is formed by heating gypsum ($CaSO_{4} \cdot 2H_{2}O$) at $373\,K$.