I am using 85% ACS grade phosphoric acid. I need to make a 21% phosphoric acid solution with a total volume of 250ml. I have been told that 37ml of the 85% ACS grade phosphoric acid plus 188ml of Deionized water will create the 21% phosphoric acid solution I need to make. I'm having trouble figuring out how to write out the equation/equations. If the calculations were just based on volume, it would be easy because 21% of 250ml is 52.5ml, but I can't figure out how to factor in the concentration of the phosphoric acid. I know that 85% ACS grade phosphoric acid solution has a density of 1.685g/ml and if I multiply the 37ml x 1.685g/ml, I get 62.345g, if I multiply that mass by the concentration of the ACS grade phosphoric acid (85%), so 62.345g x .85 = 52.99325g. If I divide that mass by the total volume I desire (250ml), I get 0.211973g/ml. How do I need to write this/these equation/equations so that they make sense? Help please.

Question

I am using 85% ACS grade phosphoric acid.  I need to make a 21% phosphoric acid solution with a total volume of 250ml.  I have been told that 37ml of the 85% ACS grade phosphoric acid plus 188ml of Deionized water will create the 21% phosphoric acid solution I need to make.  I'm having trouble figuring out how to write out the equation/equations.  If the calculations were just based on volume, it would be easy because 21% of 250ml is 52.5ml, but I can't figure out how to factor in the concentration of the phosphoric acid.  I know that 85% ACS grade phosphoric acid solution has a density of 1.685g/ml and if I multiply the 37ml x 1.685g/ml, I get 62.345g, if I multiply that mass by the concentration of the ACS grade phosphoric acid (85%), so 62.345g x .85 = 52.99325g.  If I divide that mass by the total volume I desire (250ml), I get 0.211973g/ml.  How do I need to write this/these equation/equations so that they make sense?  Help please.

bobpursley · Answer

I think this page will give you the density of the final product, which you need. https://wissen.science-and-fun.de/chemistry/chemistry/density-tables/density-of-phosphoric-acid/ If you can't figure it from here, repost.

Explain Bot · Answer

To write the equation for this problem, you can follow these steps: Step 1: Calculate the mass of phosphoric acid (H3PO4) needed in the final solution. Given that you have 37ml of 85% ACS grade phosphoric acid, you can calculate the mass as follows: Mass of phosphoric acid = Volume × Density × Concentration = 37ml × 1.685g/ml × 0.85 = 53.34225g Step 2: Calculate the volume of deionized water needed. Since the desired total volume is 250ml and you already have 37ml of phosphoric acid, the volume of water needed is: Volume of water = Total volume - Volume of phosphoric acid = 250ml - 37ml = 213ml Step 3: Combine the phosphoric acid and water to obtain the desired solution. The equation can be written as follows: 37ml of 85% ACS grade phosphoric acid + 213ml of deionized water = 250ml of 21% phosphoric acid solution It's important to note that when calculating the percentage concentration, it is generally expressed in weight/volume (w/v). In this case, the 21% phosphoric acid solution refers to 21g of phosphoric acid dissolved in 100ml of the final solution. I hope this explanation clarifies how to write the equation for your problem.