Question

In which case of mixing of a strong acid and a strong base each of \(1 \mathrm{~N}\) concentration, temperature increase is highest in(1) \(20 \mathrm{~mL}\) acid \(-30 \mathrm{~mL}\) alkali (2) \(10 \mathrm{~mL}\) acid \(-40 \mathrm{~mL}\) alkali (3) \(25 \mathrm{~mL}\) acid \(-25 \mathrm{~mL}\) alkali (4) \(35 \mathrm{~mL}\) acid \(-15 \mathrm{~mL}\) alkali

Short answer

Case (3) - 25 mL acid and 25 mL alkali increases the temperature the most, producing the most water.

Step-by-step solution

Identify the Reaction Type

Mixing a strong acid with a strong base results in a neutralization reaction, which is exothermic (releases heat). The heat produced is proportional to the number of moles of water formed.

Calculate Moles of Reactants

Since both the acid and the base have a concentration of 1 N (1 mole/L), the number of moles of acid or base can be calculated using the volume in liters. For example, 20 mL of acid is 0.020 L, so it has 0.020 moles of acid.

Determine Limiting Reactant

For each case, calculate the available moles of acid and base. The limiting reactant is the one that is completely consumed in the reaction, determining the number of moles of water produced.

Case-by-Case Analysis

Review each option:1) 20 mL acid (0.020 moles) and 30 mL base (0.030 moles). The limiting reactant is the acid, producing 0.020 moles of water.2) 10 mL acid (0.010 moles) and 40 mL base (0.040 moles). The limiting reactant is the acid, producing 0.010 moles of water.3) 25 mL acid (0.025 moles) and 25 mL base (0.025 moles). Both are completely consumed, producing 0.025 moles of water.4) 35 mL acid (0.035 moles) and 15 mL base (0.015 moles). The limiting reactant is the base, producing 0.015 moles of water.

Determine Highest Temperature Increase

The highest temperature increase corresponds to the reaction producing the most water. From the analysis, case (3) produces the most water (0.025 moles).

Key concepts

exothermic reactions

When mixing a strong acid and a strong base, you initiate a chemical process known as a neutralization reaction. This process releases heat, making it exothermic. The amount of heat released corresponds to the number of moles of water produced during the reaction. This is why understanding mole calculations is crucial; it directly relates to the heat output and temperature change you observe. For example, if you mix hydrochloric acid (HCl) with sodium hydroxide (NaOH), they react to form water (H2O) and a salt (NaCl), releasing energy in the process.

limiting reactant

In any chemical reaction, the limiting reactant is the substance that is completely consumed first, limiting the amount of product formed. In our case, when you mix varying volumes of acid and base, the limiting reactant will determine the number of moles of water produced and consequently, the amount of heat released. For instance, in the given exercises:

• 20 mL acid and 30 mL base: Acid is the limiting reactant.
• 10 mL acid and 40 mL base: Again, acid is the limiting reactant.
• 25 mL acid and 25 mL base: Both are limiting reactants, each completely consumed.
• 35 mL acid and 15 mL base: Base is the limiting reactant.

mole calculations

Understanding mole calculations is key to solving these types of problems. The concentration of a solution in normality (N) tells you how many moles of solute are present in 1 liter of solution. Here, both acid and base are at 1 N (1 mole/L). To find the number of moles in a given volume, convert milliliters (mL) to liters (L) and multiply by the concentration. For example:

• 20 mL of 1 N acid equals 0.020 moles of acid.
• 30 mL of 1 N base equals 0.030 moles of base.

Performing these calculations for each case helps identify the limiting reactant and the total number of moles of water produced.

heat production in chemical reactions

The heat produced in these neutralization reactions depends on the number of moles of water formed. More moles of water mean more heat. By comparing the number of moles of water produced in each case:

• 20 mL acid (0.020 moles) + 30 mL base (0.030 moles) → 0.020 moles water.
• 10 mL acid (0.010 moles) + 40 mL base (0.040 moles) → 0.010 moles water.
• 25 mL acid (0.025 moles) + 25 mL base (0.025 moles) → 0.025 moles water.
• 35 mL acid (0.035 moles) + 15 mL base (0.015 moles) → 0.015 moles water.

Thus, more heat is produced in the case where 25 mL of acid reacts with 25 mL of base, resulting in the highest temperature increase.