Making salts from acids and alkalis
A Able to dissolve in solvent. For example, sugar is soluble in water because it dissolves to form sugar solution. The substance formed when the hydrogen ion in an acid is replaced by a metal ion. can be prepared by reacting an Substance producing more hydrogen ions than hydroxide ions when dissolved in water. with a dilute Mixture formed by a solute and a solvent. of an Substance producing more hydroxide ions than hydrogen ions when dissolved in water. such as sodium hydroxide or ammonia. The main steps are:
- Carry out a A quantitative procedure in which two solutions react in a known ratio, so if the concentration of one solution is known and the volumes of both are measured, the concentration of the other solution can be determined.. This is to determine the volumes of acid and alkali that must be mixed to obtain a solution containing only salt and water.
- Mix the acid and alkali in the correct proportions, as determined in step 1, but this time without including an A substance that has different colours, depending upon the pH of the solution it is in..
Pure dry A solid containing particles (atoms, molecules or ions) joined together to form a regular arrangement or repeating pattern. can be produced by The process of producing crystals from a solution by evaporating the solvent., followed by drying on a watch glass or in a warm oven.
Carrying out a titration to find out volumes of acid and alkali solutions that react
Apparatus
The apparatus needed includes:
- a A piece of apparatus used to measure accurate and repeatable volumes of liquid. Also called a volumetric pipette. to accurately measure the volume of a reactant before transferring it to a conical flask
- a A piece of apparatus used to add varying but measured volumes of solution during a titration. to add small, measured volumes of one A substance that reacts together with another substance to form products during a chemical reaction. to the other reactant
Method
This is an outline method for carrying out a titration in which an acid is added to an alkali. The method is the same for sulfuric acid, hydrochloric acid and nitric acid.
- Use the pipette and pipette filler to add a measured volume of sodium hydroxide solution to a clean conical flask.
- Add a few drops of indicator and put the conical flask on a white tile.
- Fill the burette with hydrochloric acid and note the starting volume.
- Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
- Stop adding the acid when the In a titration, the point at which the indicator first permanently changes colour. is reached (when the indicator first permanently changes colour). Note the final volume reading.
- Repeat steps 1 to 5 until Titres within 0.10 cm鲁 of each other. are obtained. More accurate results are obtained if acid is added drop by drop near to the end-point.
Results
Record the results in a suitable table. The one here also shows a rough reading.
| Run | End vol | Start vol | Titre |
| Rough | 26.85 cm3 | 1.00 cm3 | 25.85 cm3 |
| 1 | 24.60 cm3 | 0.00 cm3 | 24.60 cm3 鉁 |
| 2 | 24.90 cm3 | 0.60 cm3 | 24.30 cm3 |
| 3 | 24.00 cm3 | 0.30 cm3 | 24.70 cm3 鉁 |
| Run | Rough |
|---|---|
| End vol | 26.85 cm3 |
| Start vol | 1.00 cm3 |
| Titre | 25.85 cm3 |
| Run | 1 |
|---|---|
| End vol | 24.60 cm3 |
| Start vol | 0.00 cm3 |
| Titre | 24.60 cm3 鉁 |
| Run | 2 |
|---|---|
| End vol | 24.90 cm3 |
| Start vol | 0.60 cm3 |
| Titre | 24.30 cm3 |
| Run | 3 |
|---|---|
| End vol | 24.00 cm3 |
| Start vol | 0.30 cm3 |
| Titre | 24.70 cm3 鉁 |
Readings should be recorded to two decimal places, ending in 0 or 5 (where the liquid level is between two graduations on the burette). The Volume of one reactant needed to react completely with the other reactant in a titration. is the volume added (the difference between the end and start readings).
Analysis
At least two concordant titres should be ticked (鉁) in the table above. Concordant titres often lie within 0.10 cm3 or less of each other.
Worked example
Calculate the mean titre from the table above. Ignore the rough run, and run 2 (because they are not concordant):
Mean titre = \(\frac{\textup{(24.60~+~24.70)}}{\textup{2}}\)
= 24.65 cm3