1. experimental topic: design an experiment to accurately determine the relative molecular weight of a solid dibasic acid (the range is 80~ 100).

Objective: To investigate the basic operations such as acid-base neutralization titration.

Three. Reagents provided:

1, and the relative molecular weight is 80~ 100.

2. 0.40 mol/L sodium hydroxide solution

Experimental report written by students

First, experimental drugs

In addition to an unknown dibasic acid and 0.40 mol/L NaOH provided in the title, phenolphthalein is also needed as an indicator.

Second, the experimental instruments:

1, alkaline burette (25ml) 2, pipette (10ml) or acid burette.

3, conical flask 4, volumetric flask (100 ml)

Third, the experimental process

1, predicting the amount of acid and alkali.

(1) Assuming that the relative molecular weight of acid is 90 and the volume of NaOH used in titration is 20mL, then

The amount of alkaline substance is: 0.40 mol/L× 0.02 L =0.008 mol.

Because acid is a binary acid, the coefficient ratio of acid to base is 1: 2, that is

X+2 sodium hydroxide

1 2

Y 0.008 Y=0.004 mole.

The mass of the acid is 0.004 mol × 90 mol/L = 0.36 g.

(2) Weigh 3.6 grams of acid and prepare a 100 ml solution (in a 100 ml volumetric flask).

2. Titration process

(1) Take 10 ml acid solution with a pipette or acid burette, transfer it to a conical flask, and drop a few drops of phenolphthalein indicator, and the solution should be colorless.

(2) Titrate the acid with 0.40mol/L NaOH until the solution turns red.

(3) Repeat step 1 2 to ensure the accuracy of the experiment.

Fourth, data recording and processing.

The volume of sodium hydroxide (0.05 ml) is 1.23.

Read A 1 B 1 C 1 after titration.

Pre-titration reading A2 B2 C2

The volume of alkali used is a1-a2b1-B2C1-C2.

Average volume of alkali used: v ml.

Calculation process:

X+2 sodium hydroxide

1 2

Z (V/ 1000)×0.400

z =(V/ 1000)×0.400/2 =(V/ 1000)×0.200

The relative molecular weight of acid is 0.48/z = 0.48/[(v/1000) × 0.200].