# What is the concentration of starch in this example?

1. Jan 17, 2016

### Cyrus the great

1. The problem statement, all variables and given/known data

I had 3 wt % starch concentration in 230 gram of water. During the experiment 100 gram of water was evaporated and gone. Therefore, 130 gram of solution was remained. What is the wt% concentration of the starch after water evaporation? Is my calculation sounds correct to you?

2. Relevant equations

3. The attempt at a solution

230 gram 3 %
130 gram X=1.69+3=4.69 %

2. Jan 17, 2016

### Bystander

No. Try again.

3. Jan 17, 2016

### Staff: Mentor

Can you say a bit more in words what your calculations are?

4. Jan 17, 2016

### Staff: Mentor

In your previous thread you correctly solved slightly different case, and the rules are identical here. After you remove 100 g of solvent, what is the final mass of the mixture? How many grams of starch does it contain?

5. Jan 17, 2016

### Cyrus the great

I calculated if in 230 gram we have 3 wt % of starch so what wt % we have in 130 gram and it becomes 1.69 wt %. Then, I summed up 3 %+1.69 %=4.69 %. May I ask if I calculated correctly?

6. Jan 17, 2016

### Cyrus the great

130 gram multiple to 0.03 =3.9 gram of starch we have got.

7. Jan 17, 2016

### Cyrus the great

8. Jan 17, 2016

### Staff: Mentor

What was the initial amount of starch and why do you think it has changed? Was it removed from the mixture, or was only water removed?

And the most important thing: what is the definition of the % concentration?

9. Jan 17, 2016

### Cyrus the great

Yes it was only water evaporated and removed. The % concentration is based on gram of starch divided to gram of all the materials (Starch+water). In this example 3.9 gram starch remained and the total gram of material left is 130 gram. So, 3.9/130=3 %.

But, I get confused why I get again 3 % concentration. 100 gram of water is removed so I should get above 3 % concentration for starch. Have I done something wrong?

10. Jan 17, 2016

### Cyrus the great

Now I understood. Initial amount of starch was 230 mutiple 0.03=6.9 gram therefore the concentration is 6.9/130=5.3 %

Am i right?

11. Jan 17, 2016

Yes.