A cleaning solution is made up by combining one part phosphoric acid concentrate

Question

A cleaning solution is made up by combining one part phosphoric acid concentrate with eight parts of water. A food technician has 10 L of the cleaning solution already prepared and needs to make more to a total of 25 L.

a.How many liters of acid concentrate and how many liters of water should be added to the existing 10 liters of cleaning solution to obtain 25 liters at the correct dilution?

b.The acid concentrate is a 10% solution (i.e., it is 90% water, 10% acid). What is the acid concentration in diluted solution of 25 L?

Explanation / Answer

A)

In 10 L :
water = 8 parts of 9 = 8*10/9 = 8.89 L
Concentrated acid = 1 part of 9 = 1*10/9 = 1.11 L

In 25 L:
water = 8 parts of 9 = 8*25/9 = 22.22L
Concentrated acid = 1 part of 9 = 1*25/9 = 2.78 L

Amount of water to be added = 22.22 - 8.89 = 13.33 L
Amount of acid to be added = 2.78-1.11 = 1.67 L

B)
Acid is in L = 10% of 25 L = 2.5 L
Assuming its dilute, I am taking density as 1 Kg/L
So mass = 2.5 Kg
Molar mass of phosphoric acid = 98 gm
So, number of moles = mass/molar mass
                              = 2500/98
                               = 25.51 mol

Volume = 25 L

Concentration = 25.51/25 = 1 mol/L = 1M

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