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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Alex koosha on January 17, 2016, 10:36:41 AM

Title: What is the concentration of starch in this example?
Post by: Alex koosha on January 17, 2016, 10:36:41 AM

I wanted to make 3 wt % of starch. So I calculated I needed 6.9 gram of starch in 230 gram. However my starch had 10 % water content. So, I calculated that I need 7.66 gram of starch to compensate the water.

I also needed to add 30 % of glycerol to starch. So I calculated i needed 2.95 gram of glycerol.

Then I mixed 7.66 gram of starch with 2.95 gram of glycerol and 219.39 gram of water.

P.S: I weight 7.66 gram of starch but in reality this 7.66 gram is not only starch because some water is also presented together with starch.

So my question is what is the concentration of starch wt %? 7.7/230x 100=3.34 % or 7/230x100=3 %?

Title: Re: What is the concentration of starch in this example?
Post by: Alex koosha on January 19, 2016, 02:13:03 AM

Any help?

Title: Re: What is the concentration of starch in this example?
Post by: Borek on January 19, 2016, 02:37:20 AM

Hint: how much pure starch is there in the sample you are dissolving, is it 6.9 g, or 7.66 g?

Title: Re: What is the concentration of starch in this example?
Post by: Alex koosha on January 19, 2016, 02:51:38 PM

Hi,

I meant starch is not dried. It is 90 % starch and 10 % water. I need to weigh 6.9 gram but my sample has 10 % water content. So it is not very pure. I have to weigh 7.66 gram to compensate the water inside my sample.