Question

You dissolve 4.5 mol of potassium hydroxide to make a 2 L solution. What is the molarity of the solution?

Answer 1

Data:
M (molarity) = ? (Mol/L)
m (mass) = ? (in grams)
V (volume) = 2 L 
MM (Molar Mass) of Potassium Hydroxide (KOH)
K = 1*39 = 39 amu
O = 1*16 = 16 amu
H = 1*1 = 1 amu
------------------------------------
MM  of KOH = 39+16+1 = 56 g/mol

***Let's find the mass
Data:
n (number of mols) = 4.5 mols
m (mass) = ? (in grams)
v (volume) = 2 L

Formula:

$n = \frac{m}{V}$
$4.5 = \frac{m}{2}$
$m = 4.5*2$
$\boxed{m = 9.0\:g}$

***Let's find the molarity:

Formula:

$M = \frac{m}{MM*V}$

Solving:
$M = \frac{m}{MM*V}$
$M = \frac{9.0}{56*2}$
$M = \frac{9.0}{112}$
$M = 0.0803...\:\to\:\boxed{\boxed{M \approx 0.08\:Mol/L}}\end{array}}\qquad\quad\checkmark$