A 10.1 g sample of NaOH is dissolved in 250.0 g of water in a coffee-cup calorimeter.The temperature increases from 23.0 °C to ________°C.Specific heat of liquid water is 4.18 J/g-K and ΔH for the dissolution of sodium hydroxide in water is 44.4 kJ/mol.
A)35.2
B)24.0
C)33.7
D)33.3
E)40.2

Question

Quizplus · Accepted Answer

First, calculate the moles of NaOH: $ \frac{10.1 \, \text{g}}{40.00 \, \text{g/mol}} = 0.2525 \, \text{mol} $. The heat released is $ 0.2525 \, \text{mol} \times 44.4 \, \text{kJ/mol} = 11.211 \, \text{kJ} $. Convert this to joules: $ 11.211 \, \text{kJ} \times 1000 = 11211 \, \text{J} $. The mass of the solution is approximately the mass of the water, $ 250.0 \, \text{g} $, since the mass of NaOH is relatively small. Use $ q = mc\Delta T $ to find $ \Delta T $: $ \Delta T = \frac{q}{mc} = \frac{11211 \, \text{J}}{250.0 \, \text{g} \times 4.18 \, \text{J/g-K}} = 10.7 \, \text{K} $. The final temperature is $ 23.0 \, \text{°C} + 10.7 \, \text{°C} = 33.7 \, \text{°C} $. However, due to a calculation oversight, the correct final answer should be 33.7 °C, indicating a mistake in the final selection.

A 101 G Sample of NaOH Is Dissolved in 250