What is the molarity of a solution of KCl if 1500. mL contains 149.2 grams of KCl? (Atomic mass of K = 39.10 g/mol and Cl = 35.45 g/mol)

The molarity of a solution of KCl is 1.33

Explanation:

The Molarity (M) or Molar Concentration is the number of moles of solute that are dissolved in a given volume. In other words, the molarity is the number of moles of solute per liter of solution.

Molarity is determined by the expression:

Molarity is expressed in units ().

So in this case you need to know the number of moles. For that you must know the molar mass of KCl. You know:

So the molar mass of KCl is: KCl= 39.10 g/mol + 35.45 g/mol=  74.55 g/mol

Then the following rule of three applies: if 74.55 grams of KCl are in 1 mole, 149.2 grams of KCl in how many moles will they be?

moles= 2

So you know:

Replacing in the definition of molarity:

Solving:

Molarity= 1.33

The molarity of a solution of KCl is 1.33

Explanation:

To convert from moles to grams, we must use the molar mass. This is found on the Periodic Table. Look for Phosphorous or P.

We can use this number as a ratio.

Multiply by the given number of grams: 15.62

Flip the fraction so the grams of phosphorus cancel.

Divide.

The original measurement of grams has 4 significant figures, so our answer must have the same.

For the number we calculated, that is the ten thousandth place. The 9 in the hundredth thousandth place tells us to round the 2 to a 3.

There are 0.5043 moles of phosphorus in 15.62 grams.