How Much Stock Solution is Needed for Specific Sugar Concentrations?

[neoking77]

Homework Statement

You have a 20% w/v stock solution of a sugar of molecular weight 160 Daltons. How much of this stock solution will you need to use to...

a. prepare 10 ml of solution at 350 mg sugar per ml.

b. 7 ml of solution containing 15 micromoles of sugar

Homework Equations

The Attempt at a Solution

a) So 20% w/v stock solution = 0.2 g/mL

350 mg/mL x 10mL gives us 3500mg of the sugar, or 3.5g

so the amount of solution we want is

x mL = 3.5 g / (0.2g / mL) = 17.5mL ( is this correct?)

b) 5umol = 1.5 x 10^-5 mol

1.5 x 10^-5 mol (160 Daltons / 1mol) = 2.4 x 10^-3 g

(2.4 x 10^-3g) / 7mL = 4.89 x 10^-5 g/mL

and then I am stuck. How are you supposed to make 4.89 x 10^-5g/mL solution from a 0.2g/mL stock solution?

thank you in advance

 

[nate808]

for any help!

Hello,

Firstly, for part a), your calculation is correct. You would need 17.5 mL of the stock solution to prepare 10 mL of solution at 350 mg sugar per mL.

For part b), you are on the right track. However, you can't make a solution with a concentration of 4.89 x 10^-5 g/mL from a stock solution with a concentration of 0.2 g/mL. In order to prepare a solution with the desired concentration, you will need to dilute the stock solution.

The amount of stock solution needed can be calculated using the following equation:

V1C1 = V2C2

Where:
V1 = volume of stock solution
C1 = concentration of stock solution
V2 = volume of desired solution
C2 = concentration of desired solution

In this case, we know V1 = x mL, C1 = 0.2 g/mL, V2 = 7 mL, and C2 = 4.89 x 10^-5 g/mL.

Substituting these values into the equation, we get:

x mL * 0.2 g/mL = 7 mL * 4.89 x 10^-5 g/mL

x = (7 mL * 4.89 x 10^-5 g/mL) / 0.2 g/mL

x = 1.7225 mL

Therefore, you would need to take 1.7225 mL of the stock solution and dilute it to 7 mL with water to prepare a solution containing 15 micromoles of sugar.

I hope this helps! Let me know if you have any further questions.

 

[Blueshift5]

for your help

a) Your calculation for the amount of stock solution needed is correct. You would need to use 17.5 mL of the 20% w/v stock solution to prepare 10 mL of solution at 350 mg sugar per ml.

b) To prepare 7 mL of solution containing 15 micromoles of sugar, you would need to use the following calculation:

15 x 10^-6 mol x (160 Daltons / 1 mol) = 2.4 x 10^-3 g of sugar

Since the stock solution is 20% w/v, we can use the following formula to calculate the amount of stock solution needed:

x mL = 2.4 x 10^-3 g / (0.2 g/mL) = 12 mL

Therefore, you would need to use 12 mL of the stock solution to prepare 7 mL of solution containing 15 micromoles of sugar.