Question

What is the molarity of a solution made by mixing 3.50 g of potassium chromate in enough water to make 100.00 ml of this solution?

Answer 1

Answer:

.18 M

Explanation:

1st

The molarity of an aqueous solution (a solution that has water as the solvent) can be found just by remember this one formula = $\frac{mol}{liters}$.

[moles of solute / volume of solution in L]

So, what do we have? From a glance we have the number of solute (Potassium Chromate), that tells us that we need to convert that value that is in grams (g) into...Moles or (mol), we can do that like this

$\frac{3.50 g}{ } \frac{1 mol}{194.19 g}$

After we cross multiply 3.50 times 1 and then divide by 194.19 - we get this value ⇒ .018 mol (the g cancels, and we keep mol)

(We get the 194.19 from adding up the molecular weight of Potassium Chromate, which is about 194.19 g/mol. In the above equation though, we flipped this, so that 1 mol is in the numerator and the 194.19 is in the denominator; this helps us convert the 3.50 g to moles).

2nd

Now, we just have to remember that 1 liter = 1000 ml. Because its easier for us to use a L instead of "ml" in the molarity formula. So...

100.00 ml = .1 L         ....

(because $\frac{100 ml}{ } \frac{1 L}{1000 ml} = .1L$

Finally, we just add our (.018 mol and .1 L) into one nice equation (plug the numbers we converted to back in)

$\frac{.018 mol}{.1L} = .18 M$

Is it clear now?