咖啡杯量热法

用简易量热计测量中和焓

Thermochemistry Intermediate (High School) 40 分钟 ~$8.00

目标

用聚苯乙烯杯量热计测定HCl和NaOH的中和焓。

背景

A polystyrene cup makes an inexpensive but effective calorimeter because it has low thermal conductivity. By mixing known volumes of acid and base and measuring the temperature change, the enthalpy of neutralization can be calculated. The accepted value for strong acid-strong base neutralization is -57.1 kJ/mol.

安全警告

  • HCl and NaOH are corrosive
  • Wear safety goggles
  • The mixture will get hot

所需PPE

goggles gloves lab_coat

材料

  • Hydrochloric acid (HCl) (50 mL)
    1M
  • Sodium hydroxide (NaOH) (50 mL)
    1M
  • Distilled water (100 mL)
    For calibration

设备

Two polystyrene (Styrofoam) cups (nested) Cardboard lid with hole Thermometer (0.1°C resolution) Graduated cylinder (50 mL) Stopwatch

步骤

1

Measure 50 mL of 1M HCl and pour into the nested polystyrene cups. Record the initial temperature every 30 seconds for 3 minutes.

5 分钟 HCl is corrosive
2

Measure 50 mL of 1M NaOH in a separate container. Record its temperature.

2 分钟 NaOH is corrosive
3

Quickly pour the NaOH into the HCl, stir gently, and replace the lid with thermometer.

1 分钟 Exothermic reaction
4

Record the temperature every 30 seconds for 5 minutes. Note the maximum temperature.

5 分钟
5

Plot temperature vs time. Extrapolate the cooling curve back to the mixing time to find the corrected maximum temperature.

5 分钟
6

Calculate ΔT, then q = mcΔT (assume c = 4.18 J/g°C, mass = 100 g). Calculate ΔH per mole of water formed.

8 分钟

预期结果

Temperature should rise by approximately 6-7°C. Calculated ΔH should be approximately -50 to -57 kJ/mol (accepted: -57.1 kJ/mol). Losses to the calorimeter walls typically give lower values.

清理

The neutralized solution is safe to pour down the drain. Rinse and dry the calorimeter cups for reuse.

详情

类别
Thermochemistry
难度
Intermediate (High School)
时长
40 分钟
预估费用
$8.00
步骤数
6
材料
3

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Frequently Asked Questions

What is the objective of 咖啡杯量热法?
用聚苯乙烯杯量热计测定HCl和NaOH的中和焓。
How difficult is 咖啡杯量热法?
This experiment is rated as Intermediate (High School). It takes approximately 40 minutes to complete.
What safety precautions are needed for 咖啡杯量热法?
Key safety precautions include: HCl and NaOH are corrosive; Wear safety goggles; The mixture will get hot.
What materials are needed for 咖啡杯量热法?
The main materials required are: Hydrochloric acid (HCl), Sodium hydroxide (NaOH), Distilled water.
What results should I expect from 咖啡杯量热法?
Temperature should rise by approximately 6-7°C. Calculated ΔH should be approximately -50 to -57 kJ/mol (accepted: -57.1 kJ/mol). Losses to the calorimeter walls typically give lower values.