[david222hughes]

Hey all,

Im trying to figure out how to make up a solution in water given only the % content of each compound and the serving size.

The serving size is 0.32mls

The compounds are:

Potassium Carbonate 30.18% w/v
Sodium Bicarbonate 6.04% w/v

If I want to make up a solution containing the above percentages of the two compounds together in a 100mls solution of water, how many grams of Potassium carbonate and Sodium bicarbonate would I need to use?

I'm relatively new to chemistry and my understanding is very basic.

Is the following anywhere close?

For the potassium carbonate: 30.18 x 100mls = 3018 / 69.82 (100-30.18=69.82) =  43.23g in 100mls water.
This is 0.43g per 1ml which is around 0.14g per 0.32ml serving.

For the Sodium bicarbonate: 6.04 x 100mls = 604 / 93.96 (100-6.04=93.96) = 6.43g in 100mls water.
This is 0.0643g per 1ml which is around 0.021g per 0.32ml serving.

If I add these two 100mls solutions together I have a total volume of 200mls. So what happens to the % of each compound? Do they remain at 30.18% and 6.04% respectively when combined to 200mls or do the percentages drop by 1/2 to around 15% and 3% respectively?

Thanks for any help.



 

[mjc123]

Are you required to make a solution containing both potassium carbonate and sodium bicarbonate at the stated concentrations, or separate solutions of each which you then mix together? I assume the former, in which case don't make separate solutions at these concentrations and mix them, or you will halve the concentrations.
30.18% w/v means 30.18 g solute in 100 ml of solution. You cannot assume that this contains 69.82 g water, because the density of the solution will be different from 1.

Add 30.18 g potassium carbonate and 6.04 g sodium bicarbonate to a 100 ml volumetric flask. Add enough water to dissolve the salts, but not quite enough to take the volume up to 100 ml (to allow for possible volume change on mixing). If the solution has warmed up or cooled down, allow it to reach room temperature again. Add more water to fill up to the 100 ml mark, and mix thoroughly.

[david222hughes]

Thanks for the reply.

Yeah its a solution containing both potassium carbonate and sodium bicarbonate at the stated concentrations of 30.18% and 6.04%.

Sounds a lot less complicated with your method I wasn't aware you could add the salts together in the same solution by simply using the same percentage concentrations converted directly to grams without having to alter the numbers. Happy days.

I'll follow your advice  on mixing them up adding around 90mls distilled water to the salts in the flask, then popping on a stopper and mixing them up before making the solution up to the 100ml mark.

Thanks for your guidance.

[Borek]

I'll follow your advice  on mixing them up adding around 90mls distilled water to the salts in the flask

I would use even less. Best approach: don't measure amount of water, instead add it to the solids controlling the level to make sure you have less than you aim at.

then popping on a stopper

Better not. If the solution gets warm/hot stopper can pop out. These are reasonably safe salts so it would be more of a nuance than a danger, but it is always better to stick to safe habits.