# Question about solution preparation - (Jun/27/2006 )

hello everybody
i have a really stupied question in preparation of solutions......

do we measure first our dry component and add to the flask then add the amount of water needed?
or can we measure the water first and add it to the flask then add the dry components?
i made an acrylamide solution 30% and first i measure 100 ml water and put it into a flask then add my acrylamide amounts but i noticed the net result was more than 100 ml and the solution wasnot that good in gel making?????

thankx

-spanishflower-

1. Measure the powder
3. then add the required amount of water

because the powder takes up volume.

If you measure the water first, then add powder, the concentration of the solution will be less than required.

Also, 1g of powder roughly equal 1ml of solution when dissolved.

I hope this may help.

-Minnie Mouse-

QUOTE (spanishflower @ Jun 28 2006, 01:26 PM)
hello everybody
i have a really stupied question in preparation of solutions......

do we measure first our dry component and add to the flask then add the amount of water needed?
or can we measure the water first and add it to the flask then add the dry components?
i made an acrylamide solution 30% and first i measure 100 ml water and put it into a flask then add my acrylamide amounts but i noticed the net result was more than 100 ml and the solution wasnot that good in gel making?????

thankx

You can put the water in first and add the dry components as long as you only add ~80% of the liquid volume. You can use the rest of the water to wash off the walls of your beaker, or remove any powder that has stuck on the weighboat. I also rinse the beaker once I transfer into a measuring cylinder, and top up to volume as required.

-swanny-

THANKX A MILLION

-spanishflower-

QUOTE (swanny @ Jun 28 2006, 12:47 AM)
You can put the water in first and add the dry components as long as you only add ~80% of the liquid volume. You can use the rest of the water to wash off the walls of your beaker, or remove any powder that has stuck on the weighboat. I also rinse the beaker once I transfer into a measuring cylinder, and top up to volume as required.

we do it similarly but we start with less water (usually no more than 50%, unless there is a solubility problem).

with acrylamide, by pouring the powder into water you reduce the amount of dust that would get into the air if you were to hit the pile with water.

-mdfenko-