<h2>Answer: 105 mL</h2>
<h3>Explanation:</h3>
We can use the formula M₁V₁ = M₂V₂ the total volume of water that will yield 0.800 M HCl. We can then subtract that from the initial volume to get how much water needs to be added.
Since M₁V₁ = M₂V₂ (starting mole× starting volume = end mole × end volume)
⇒ (5 mol)(20 mL) = (0.80 mol) V₂
100 mol/mL = 0.8 mol × V₂
⇒ V₂ = 100 mol/mL ÷ 0.8 mol
= 125 m
Since we began with 20.0 mL of water,
water needed to add = 125 mL - 20 mL = 105 mL
