Q1. Explain why acids conduct electricity in water, while glucose and alcohol do not. Use the nail-and-bulb activity to support your answer.
Answer:
In water, acids produce ions like H⁺ and their anions (Cl⁻, SO₄²⁻, CH₃COO⁻).
Ions carry electric current through the solution.
In the activity, the bulb glows with dilute HCl and dilute H₂SO₄.
This shows that these acids dissociate and make the solution conductive.
Glucose and alcohol do not form ions in water.
So, no charge carriers are present, and the bulb does not glow.
Q2. How do bases behave in water? Explain using examples of NaOH, KOH, and Mg(OH)₂.
Answer:
In water, bases release hydroxide ions (OH⁻).
This makes the solution alkaline and conductive.
NaOH forms Na⁺ and OH⁻ ions in water.
KOH forms K⁺ and OH⁻ ions in water.
Mg(OH)₂ gives Mg²⁺ and OH⁻ ions, though it is less soluble.
These ions help the solution conduct electricity.
Q3. Describe the neutralization reaction. Write the general reactions and give suitable examples.
Answer:
A neutralization reaction occurs when an acid reacts with a base.
It forms salt and water as products.
The key ionic step is: H⁺(aq) + OH⁻(aq) → H₂O(l).
Example: HCl + NaOH → NaCl + H₂O.
Example: H₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O.
Example: CH₃COOH + KOH → CH₃COOK + H₂O.
Q4. Why does HCl show acidic behavior only in the presence of water? Explain with the litmus test.
Answer:
Dry HCl gas does not produce H⁺ ions.
Without water, HCl cannot ionize, so it does not behave as an acid.
Hence, it does not change the color of dry litmus paper.
In the presence of water, HCl releases H⁺ and Cl⁻.
Wet blue litmus turns red, showing acidity.
So, water is essential for acidic behavior of HCl.
Q5. Explain why we must always add acid to water and not water to acid. Give the reason with observations.
Answer:
Mixing acid and water releases a lot of heat (exothermic).
If we add water to acid, the heat can cause violent splashes.
This may lead to burns and accidents.
If we add acid to water slowly, heat spreads in the larger volume.
This makes the process safer and more controlled.
With H₂SO₄, you can feel the temperature rise in the mixture.
High Complexity (Analysis & Scenario-Based)
Q6. A student says, “Dry HCl gas is an acid because it is HCl.” Do you agree? Justify with a test and scientific reason.
Answer:
I do not agree. Dry HCl does not behave like an acid.
An acid must produce H⁺ ions to show acidity.
Dry HCl does not ionize without water.
Test: Hold dry and wet blue litmus in HCl gas.
Only the wet litmus turns red because water allows ionization.
Thus, water is needed for acidic behavior.
Q7. You have four beakers: dilute HCl, dilute H₂SO₄, glucose solution, and alcohol solution. Design a conductivity test and predict observations.
Answer:
Set up a simple circuit with a battery, switch, and bulb.
Dip the electrodes into each solution one by one.
With dilute HCl, the bulb glows (ions: H⁺, Cl⁻).
With dilute H₂SO₄, the bulb glows (ions: H⁺, SO₄²⁻).
With glucose and alcohol, the bulb does not glow.
They do not make ions, so no current flows.
Q8. In a lab, NaCl is mixed with concentrated H₂SO₄ and a gas is produced. Wet blue litmus turns red, but dry litmus does not change. Explain the observations.
Answer:
The reaction produces HCl gas from NaCl and conc. H₂SO₄.
Wet blue litmus turns red due to H⁺ in moist conditions.
Water in the wet litmus allows HCl to form H⁺ and Cl⁻.
Dry litmus does not change because there is no water.
Without water, HCl does not ionize to give H⁺.
Thus, acidity is shown only in the presence of water.
Q9. Compare the neutralization of a strong acid (HCl) with NaOH and a weak acid (CH₃COOH) with KOH. What differences do you observe in ionization and conductivity?
Answer:
HCl is a strong acid. It gives H⁺ and Cl⁻ fully in water.
NaOH is a strong base, giving Na⁺ and OH⁻ fully.
Their solutions are highly conductive, and the bulb glows bright.
CH₃COOH is a weak acid. It only partly ionizes in water.
With KOH (strong base), neutralization still makes salt + water.
But the initial conductivity of acetic acid solution is lower.
Q10. A lab spill of concentrated H₂SO₄ occurs. Explain step-by-step how to dilute and handle it safely, using the rule for mixing acid and water.
Answer:
Keep calm and inform the teacher. Wear gloves and goggles.
Do not pour water on the spill directly. It can splash.
First, contain it with suitable neutralizing agent if available.
For dilution in a beaker, always add acid to water, slowly.
Stir gently so the heat spreads in the larger volume of water.
This follows the safety rule and reduces burn risk.
