Why should you dissolve all the solid in a solution before making up to the required volume?

Question

Thanks for your answer Jason T but what if the solid is already in the flask when the volume is made up, just not completely dissolved yet? I'm told that this would make it inaccurate too.

Answer 1

The main reason IS for accuracy....and when a solute dissolves the volume INCREASES, not decreases....
if you make the solution up to the mark without dissolving the solute fully, then when it does dissolve, your volume will increase and your solution will be inaccurate

Answer 2

The main reason is not really because of the accuracy. It is because there will not be enough turbulence to dissolve the solid quickly when the flask is shaken if it filled to the mark. It is much easier to fill the flask up to the neck then dissolve the solid completely before fulling to the mark.

Answer 3

The solid, in it's undissolved form, is probably going to take up more volume than it will when it's uniformly dispersed throughout the solvent. So, if you dilute to volume before it's completely dissolved, the total volume will probably decrease slightly once the remaining solids have dissolved. End result, you will have a solution that's slightly more concentrated than you intend for it to be.

Answer 4

Because the solid itself has volume. If you try to make a 1M sodium chloride solution by adding 58.4g sodium chloride to 1l of water you'll end up with a final volume greater than 1l because of the volume of the sodium chloride you added, hence you will not have the required concentration. So, you dissolve in less than the final volume, then when it's all dissolved you add water to make up to the required volume with the desired concentration.