Find the mass of potassium hydroxide required to prepare 250cm³ of a 0.2 mol dm-³ solution, and how many grams do you need in 1dm³ of the solution?

1. Find the amount of KOH required in the solution: n (KOH) = c x (V ÷ 1000) = 0.2 x (250 ÷ 1000) = 0.05mol. 2. Convert moles to grams: molar mass = 39.1 + 16 +1 = 56.1 g mol-¹. n = m ÷ n. Hence, m = n x M=0.05x56.1=2.805g, and 11.22g or 11.22g dm-³.

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