Question

How many moles of solute are in 250 mL of 2.0 M CaCl ?

Answer 1

`\boxed {\boxed {\sf 0.5 \ mol \ CaCl}}}`

Step-by-step explanation:

Molarity is a measure of concentration in moles per liter.

`molarity= (moles \ of \ solute)/(liters \ of \ solution)`

We know the molarity is 2.0 M CaCl. However, we can convert the units to make the problem easier. 1 molar (M) is equal to 1 mole per liter. A 2.0 M CaCl molarity is equal to 2.0 moles of CaCl per liter.

We also know there are 250 milliliters of solution. however, we need to find the liters. Remember that 1 liter contains 1000 milliliters.

• 
  `\frac { 1 \ L}{1000 \ ml}`

• 
  `250 \ mL * \frac { 1 \ L}{1000 \ ml}`

• 
  `250 * \frac { 1 \ L}{1000}= 0.250 \ L`

Now we can substitute the values we know into the formula. Since moles of solute are unknown, we can use x.

• molarity= 2.0 mol CaCl/ L
• moles of solute =x
• liters of solution = 0.250 L

`2.0 \ mol \ CaCl/ L= (x)/(0.250 \ L)`

Since we are solving for x (the moles of solute), we need to isolate the variable. It is being divided by 0.250 L. The inverse of division is multiplication, so we multiply both sides by 0.250 L.

`0.250 \ L *2.0 \ mol \ CaCl/ L= (x)/(0.250 \ L) * 0.250 \ L`

`0.250 \ L *2.0 \ mol \ CaCl/ L=x`

The units of liters (L) cancel.

`0.250 * 2.0 \ mol \ CaCl=x`

`0.5 \ mol \ CaCl=x`

There are 0.5 moles of solute in 250 milliliters of a 2.0 M solution.