# What is the concentration of my starch?

1. Jan 16, 2016

### Cyrus the great

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I weight 7 gram of starch and added 3 gram of ethylen glycol and mixed it with 220 gram water. What is the final concentraion of my starch?

2. Jan 16, 2016

### insightful

3.043 wt%.

3. Jan 16, 2016

### Cyrus the great

So for the final volume of the solution we need to sum up everything we added in the solution (starch, ethylen glycol + water). Then divide amount of starch to the total volume (starch+ethylen glycol+water).Am i right? I got confused because It thought presense of ethylen glycol would interfer the concentration of starch and we will not get 3.043 wt %.

4. Jan 16, 2016

### insightful

Be careful using the word "volume" unless you really mean it. Keeping it on a weight basis is foolproof. Volumes can combine in unknown ways.

5. Jan 16, 2016

### Cyrus the great

Sure. So for the final weight we need to sum up (starch+ethylen glycol+water) then divide starch to the final weight. The reason i got confused is in another experiment to the 7 gram of starch i added 223 gram of water and concentration becomes the same 3.043 wt%. So my question is if adding the ethylen glycol would interfere with the concentration of starch?

6. Jan 16, 2016

### insightful

Nope; your method of getting wt% is correct.

7. Jan 16, 2016

### Cyrus the great

Is density of ethylen glycol effect the concentration of starch?

8. Jan 16, 2016

### insightful

Nope; as long as it is all on a weight basis, there is no density effect.

9. Jan 17, 2016

### Cyrus the great

I forgot to tell you about something. My starch has 10 % water content. So basically I weight 7.77 to compensate the water and then i mixed with 3 gram of ethylen glycol and 219.23 gram of water. So my question is now the concentration wt % of starch is 7.77/230=3.37 % or we should consider 7/230=3 %? Because I weight 7.7 gram but it is not only starch but also water is presented together with starch. I took 7.7 gram to compensate the water inside the starch. So, may I ask you what is the concentration wt % of starch in this situation?

10. Jan 17, 2016

### insightful

Yes, wt% is 3% "dry basis." My experience in the starch handling industries is that "dry basis" or "dry solids basis" is used to prevent any confusion.