Objective: To determine the unknown solution (to be measured) by using the solution with known concentration (standard solution) and hydrochloric acid as the standard solution of this experiment.

Solution)? Concentration sodium hydroxide is the solution to be tested in this experiment.

2. Experimental instruments: acid burette, alkaline burette, conical flask, iron frame (including burette clamp).

Experimental drug:? 0. 1000mol/L hydrochloric acid (standard solution), NaOH solution with unknown concentration (solution to be tested), acid-base indicator.

Indicator: phenolphthalein (discoloration range 8~ 10) or methyl orange (3. 1~4.4).

Three: experimental principle:? C (standard) ×V (standard)? =? The stoichiometric ratio of C (to be) ×V (to be) hypothetical reaction is 1: 1.

The experiment is as follows: c(H+)×V (acid)? =? C(OH-)×V (alkali)

Four: experimental process:?

(A) the preparation stage before titration

1, leak detection: check whether the burette leaks water (specific method:? Acid burette, add water to burette and close the piston. Stop 5

Min, see if there is any water leakage. If there is leakage, vaseline must be applied to the piston. Be careful not to smear too much, so as not to block the piston mouth. ? The leak detection method of alkaline burette is to add water to the burette and close the piston. Let it stand for 5 minutes to see if there is any water leakage. If there is leakage, the rubber tube must be replaced. )

2. Rinse: rinse the burette with distilled water first, and then wet it with the liquid to be filled for 2-3 times.

Conical bottles can be cleaned with distilled water and are not allowed to be wet or dry.

3. Measurement: Measure a certain volume (e.g. 20.00ml) of NaOH solution with unknown concentration with an alkaline burette (note, adjust the initial scale.

Below 0 or 0 scale) into the conical flask.

Measure the hydrochloric acid standard solution with an acid burette, remove all bubbles, adjust the liquid level so that the liquid level is just at or below the 0 scale, and record the reading.

V 1, read the second place after the decimal point? .

(2) titration stage

1. Put the conical flask under the acid burette and add 1-2 drops of phenolphthalein (if the color is not obvious, put the conical flask on a white porcelain plate or white paper). Drop the solution in the burette into the conical flask drop by drop. During titration, the right hand keeps shaking the conical flask, the left hand controls the burette piston, and the eyes observe the color change of the solution in the conical flask until the solution becomes colorless after dropping a drop of hydrochloric acid, and the original color does not return within half a minute. At this point, sodium hydroxide is completely neutralized by hydrochloric acid, reaching the titration end point. Record the level gauge V2 after titration.

2. Pour the solution in the conical flask into the waste liquid tank, clean the conical flask with distilled water, and repeat the above operation for 2~3 times.

(3) experimental records?

experimental procedure

Experimental phenomenon

Interpretation and conclusion

(4). Experimental data record:?

Titration time

Acid solution to be measured mL

Volume of standard alkali solution

V 1

After titration

v2

Volume ml (v2-v 1)

first time

second time

the third time

Verb (abbreviation of verb) experimental result processing: c (to be) =c (standard) ×V (standard) /V (to be).

Pay attention to taking several averages.

Experimental evaluation and improvement of intransitive verbs: [according to: c(H+)×V (acid)? =? C(OH-)×V (alkali) analysis]?

Operation and reading?

What is the cause of the mistake?

Resulting in the concentration error of the solution to be measured.

The standard solution leaked out of the conical flask 1 drop.

The standard liquid volume reading is too large.

too large

Check the burette reading before titration and after dripping.

The reading of standard liquid volume is too small.

small

Look up before the drop, look up after the drop.

The standard liquid volume reading is too large.

too large

There are bubbles before the burette drops, but there are no bubbles after the burette drops.

The standard liquid volume reading is too large.

too large

Wet washing of conical bottles

The standard liquid volume reading is too large.

too large

Error analysis method: c (to be) =c (standard) ×V (standard) /V (to be). Taking C (standard) as a fixed value and V (to be measured) as an accurate measurement value, all the causes of errors are transferred to the influence on V (standard) reading. If the volume reading of the standard solution is too large, the concentration of the solution to be tested is too large. When the volume reading of the standard solution is small, the concentration of the solution to be measured is also small. (See the analysis example above. Wet washing of conical flask leads to too much alkali and consumes more standard acid volume. Therefore, if the V (acid) reading is too large, the calculation result of the liquid concentration to be measured will be too large. After understanding, error analysis is a piece of cake)

Suggestions on experimental improvement and understanding;

References:

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