It is often necessary to prepare a dilute solution from a more concentrated solution rather than starting from a solid and just dissolving it then adding water. This technique is called serial dilution. Give all the steps necessary to obtain 100 mL of a 1.7 x 10-5 M solution using a solution prepared by dissolving 0.3 grams of a Red dye (molar mass of 869 g/mol) dissolved in water in a 100 mL capacity volumetric flask. Assume you have access to deionized water, 1.0mL pipette, 5.0 mL pipette, 10.0 mL pipette, and 100.0 mL volumetric flasks.

Take 10.0mL of your original solution and dilute it to 100.0mL and then, take 5.0mL of this solution and dilute it in another flask to 100.0mL

Explanation:

The initial solution of 0.3g of Red dye in 100mL has a concentration of:

0.3g Red dye × (1mol / 869g) = 3.4x10⁻⁴ mol Red Dye in 100mL = 0.100L:

3.4x10⁻⁴ mol / 0.1L = 3.4x10⁻³M

As you want a 1.7x10⁻⁵M solution, you need to dilute your solution:

3.4x10⁻³M / 1.7x10⁻⁵M = 200 times

Having this in mind, you must find the dilutions you must make to achieve the 200 of dilution factor (Dilution factor is how many times you dilute a solution from a concetrated form).

If you dilute the original solution taking 10.0mL to 100.0mL you dilute the solution: 100.0mL / 10.0mL = 10 times.

Now, you need to dilute this solution another 20 times to achieve the 10*20 = 200 times of dilution.

If you take 5.0mL of the last solution and dilute it to 100.0mL you are diluting the solution 100.0mL / 5.0mL = 20 times.

The dilution is:

3.4x10⁻³M × (10.0mL / 100.0mL) × (5.0mL / 100.0mL) = 1.7x10⁻⁵M

Thus, to obtain the 1.7x10⁻⁵M solutionyou need to:

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%