Core practical - Making salts from acids and alkalis

Question 1

Making salts from acids and alkalis process: (3)

Answer 1

1- Carry out a titration. This is to determine the volumes of acid and alkali that must be mixed to obtain a solution containing only salt and water.
2- Mix the acid and alkali in the correct proportions, as determined in step 1.
3- Allow the water in the solution to evaporate (by heating and/or leaving for a few days) to obtain pure dry crystals of the salt.

Question 2

apparatus needed to carry out a titration: (3)

Answer 2

• A pipette to accurately measure the volume of a reactant before transferring it to a conical flask.
• A burette to add small, measured volumes of one reactant to the other reactant.
• A suitable indicator.

Question 3

Method: (6)

Answer 3

1- Use the pipette and pipette filler to add a measured volume of alkali to a clean conical flask.
2- Add a few drops of indicator and put the conical flask on a white tile.
3- Fill the burette with acid and note the starting volume.
4- Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
5- Stop adding the acid when the end-point is reached (when the indicator first permanently changes colour). Note the final volume reading.
6- Repeat steps 1 to 5 until you get concordant titres. More accurate results are obtained if acid is added drop by drop near to the end-point.

Question 4

what is a titre?

-what are concordant titres?

Answer 4

Volume of one reactant needed to react completely with the other reactant in a titration.

-Titres within 0.20 cm³ (or sometimes 0.10 cm³) of each other.

Question 5

why must titrations only be used to obtain a solution of a salt and water, when using an acid and an alkali?

Answer 5

because there is no insoluble excess reactant that could be removed by filtration.