Concentrations Practice

What is the equation for molarity?

• moles of solute / liters of solution

• grams of solute / liters of solute

• liters of solution / moles of solution

• moles of solution / grams of solute

What is the equation for dilutions?

• initial molarity; x initial volume = final molarity x final volume

• final mass - initial molarity = final volume - initial molarity

• final molarity x initial molarity = final volume x initial volume

• initial mass + final molarity = initial volume + final molarity

A solution contains 0.5 mol of C₆H₁₂O₆ in 1.5L of solution

Calculate the molarity

• 0.503 M

• 0.333 M

• 3 M

• 0.75 M

Answer explanation

The molarity is calculated by dividing the moles of solute (0.5 mol) by the volume of solution in liters (1.5 L), resulting in 0.333 M

A solution contains 45.0g NaOH in 250mL of solution

Calculate the moles of solute

• 1.125 mol

• 0.889 mol

• 0.180 mol

• 0.161 mol

Answer explanation

To find moles of solute, we need to go from grams to moles by taking the grams provided (45g) and dividing by the molecular weight of NaOH (39.997 g/mol) which results in 1.125 moles of solute

A solution contains 55g of BaCl₂ in 500mL of solution

Calculate the molarity

• 0.001 M

• 0.264 M

• 0.132 M

• 0.528 M

Answer explanation

The molarity is calculated by dividing the moles of solute by the volume of solution in liters

~

To find moles of solute, we need to go from grams to moles by taking the grams provided (55g) and dividing by the molecular weight of BaCl₂ (208.23 g/mol) which results in 0.264 moles of solute

~

To find the liters, we need to go from milliliters to liters by dividing by 1,000. 500/1,000 results in 0.5L

~

Now we can divide the moles of solute (0.264) by the volume of solution in liters (0.5) which results in 0.528 M

What concentration would you get if you diluted 12mL of 2.5M KNO₃ down to a 45mL solution?

• 0.67 M

• 4.8 M

• 1.5 M

• 2.7M

Answer explanation

To calculate the concentration needed, use the formula M₁V₁ = M₂V₂

~

where M₁ is the initial concentration (2.5), where V₁ is the initial volume (12), where M₂ is the final concentration, and where V₂ is the final volume (45)

~

2.5 x 12 = M₂ x 45

~

divide the right side by 45 to isolate M₂ which results in 2.7M

A solution contains 0.5 mol CaCl₂ in 500mL solution

Calculate the molarity

• 1 M

• 0.500 M

• 0.010 M

• 0.050 M

Answer explanation

The molarity is calculated by dividing the moles of solute (0.5) by the volume of solution in liters

~

To find the liters, we need to go from milliliters to liters by dividing by 1,000. 500/1,000 results in 0.5L

~

Now we can divide the moles of solute (0.5) by the volume of solution in liters (0.5) which results in 1 M

A solution contains 40g of C₁₂H₂₂O₁₁ in 500mL of solution

Calculate the moles of solute

• 8.55 mol

• 0.117 mol

• 0.017 mol

• 0.081 mol

Answer explanation

To find moles of solute, we need to go from grams to moles by taking the grams provided (40g) and dividing by the molecular weight of C₁₂H₂₂O₁₁ (342.3 g/mol) which results in 0.117 moles of solute

What volume in mL of 6.0M HCL would be needed to make 250mL of 0.20M HCl?

• 0.26mL

• 1.2mL

• 8.3mL

• 15.2mL

Answer explanation

To calculate the volume needed, use the formula M₁V₁ = M₂V₂

~

where M₁ is the initial concentration (6.0), where V₁ is the initial volume, where M₂ is the final concentration (0.20), and where V₂ is the final volume (250)

~

6.0 x V₁ = 0.20 x 250

~

divide the left side by 6.0 to isolate V₁ which results in 8.3mL

A solution contains 40g of NaCl in 2.0L of solution

Calculate the molarity

• 0.684 M

• 0.050 M

• 0.057 M

• 0.342 M

Answer explanation

The molarity is calculated by dividing the moles of solute by the volume of solution in liters (2.0)

~

To find moles of solute, we need to go from grams to moles by taking the grams provided (40g) and dividing by the molecular weight of NaCl (58.44 g/mol) which results in 0.684 moles of solute

~

Now we can divide the moles of solute (0.684) by the volume of solution in liters (2.0) which results in 0.342 M