Question 460561
How many milliliters of distilled water must be added to 50 milliliters of a 40% acid solution to reduce it to a 10% acid solution?
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50 ml of 40% = 20 ml of acid and 30 ml of water
If 20 ml is 10%, 90% is water = 180 ml of water total
180 - 30 = 150 ml to add.
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PS  Add the acid to the water, don't pour water into the acid.