What volume, in mL, of 4.50 M NaOH is needed to prepare 250. mL of 0.300 M NaOH?

16.7 mL

Explanation:

Convert 250 mL to L.

250 mL = 0.250 L

Calculate the amount of moles of NaOH in 250 mL of 0.300 M NaOH.

0.250 L × 0.300 M = 0.075 mol

Using this amount of moles, you need to find out what volume of 4.50 M will give you that many moles.  You can do this by dividing the amount of moles by the molarity.

(0.075 mol)/(4.50 M) = 0.0167 L

Convert from L to mL.

0.0167 L = 16.7 mL

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