The moles of sodium hydroxide that are needed to prepare 250 ml of a 0.85 m solution is 0.21 Moles ( answer D)
calculation
moles of sodium hydroxide is calculated using moles = molarity x volume in liters formula
where,
molarity = 0.85 M = 0.85 mol/ L
moles = ?
volume = 250 ml convert into Liters
that is 1 L = 1000 Ml
? L= 250 ml
by cross multiplication
=( 250 ml x 1 L) / 1000 ml = 0.25 L
moles is therefore= 0.85 mol/l x 0.25 L = 0.21 moles of sodium hydroxide
Molarity is the ratio of the moles and the volume of solution in L. The number of moles needed for 0.85 M sodium hydroxide is 0.21 moles.
Moles of the solute can be given as the product of the molar concentration of the solution and the volume of the solution in Liters.
The moles can be given by the formula:
[tex]\rm Moles = Molarity \times Volume \; in \; L[/tex]
Given,
Molarity (M) = 0.85 M
Volume in liters = 0.25 L
Substituting values in the equation:
[tex]\begin{aligned}\rm moles &= 0.25 \times 085\\\\&= 0.21\end{aligned}[/tex]
Therefore, option D) 0.21 moles are needed of 0.85 M sodium hydroxide.
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