HW: Molarity Practice

Molarity is measured in

• moles per kg

• mols per L

• moles per kJ

• moles per mL

Answer explanation

Molarity is measured in moles per liter, denoted as mol/L. It represents the concentration of a solute in a solution.

What is the molarity of 4 g of NaCl (MM=58.45) in 3,800 mL of solution?

• 0.018 M

• 0.0011 M

• 1.052 M

• 0.062 M

Answer explanation

To find molarity, first calculate moles of NaCl: 4g / 58.45 g/mol = 0.0684 mol. Then, divide moles by liters: 0.0684 mol / 3.8 L = 0.018 M.

How many grams of solute are dissolved in 125.0 mL of 5.00 M NaCl (MM = 58.45)?

• 0.625 g NaCl

• 625 g NaCl

• 36.5 g NaCl

• 0.04 mol NaCl

Answer explanation

To calculate the grams of solute, use the formula: grams = moles x molar mass. Moles = Molarity x Volume (L) = 5.00 mol/L x 0.125 L = 0.625 mol. Grams = 0.625 mol x 58.45 g/mol = 36.5 g NaCl.

Find the molarity of 186.55 g of sucrose, C₁₂H₂₂O₁₁ (MM = 342) that is dissolved in enough water to make 250. mL of solution.

• 2.18 M

• 0.746 M

• 1.18 M

• 0.545 M

Answer explanation

To find the molarity, first calculate the number of moles of sucrose: 186.55 g / 342 g/mol = 0.545 mol. Then, divide moles by liters: 0.545 mol / 0.25 L = 2.18 M.

How many moles of NaCl are present in a solution with a molarity of 8.59 M and a volume of 125 mL?

• 1074 mol

• 0.069 mol

• 1.07 mol

• 62.7 mol

Answer explanation

To find the moles of NaCl, use the formula: moles = molarity * volume (in L). Convert 125 mL to L (0.125 L) and calculate: 8.59 M * 0.125 L = 1.07 mol. Therefore, there are 1.07 mol of NaCl in the solution.

How many grams of AgNO₃ (MM = 169.87) are needed to prepare 0.125M solution with a total solution volume of 250 mL? 

• .03g

• 0.5g

• 5.3g

• 84.9g

Answer explanation

To calculate the grams needed, use the formula: grams = Molarity x Volume x Molar Mass. Therefore, 0.125 x 0.25 x 169.87 = 5.3g, which is the correct choice.

Which of the following has the most NaCl (MM = 58.44)?

• 100 mL of a 1.8 M solution

• 50 mL of a 4.1 M solution

• 9.35 grams

• 1 mole

Answer explanation

1 mole has the most NaCl (MM = 58.44) because it represents Avogadro's number of NaCl molecules, ensuring the highest amount of NaCl.

What is the molarity of a 650. ml solution that contains 63 grams of sodium chloride?

• 2.4 M

• 0.86 M

• 1.7 M

• 0.54 M

Answer explanation

To find the molarity, first calculate the moles of NaCl: 63g / 58.44 g/mol = 1.08 mol. Then, divide moles by liters: 1.08 mol / 0.65 L = 1.7 M.

If you have 0.045 L of 0.465 M potassium bromide, how many moles of potassium bromide are present?

• 20.9 mol

• 0.021 mol

• 0.42 mol

• 10. mol

Answer explanation

To find the moles of potassium bromide, use the formula Moles = Volume (L) x Concentration (M). Moles = 0.045 L x 0.465 M = 0.021 mol, so the correct answer is 0.021 mol.

How many moles of NaCl are present in a solution with a molarity of 8.59M and 125 mL of solution?

• 1.17 gram

• 62.7 mol

• 1.07 mol

• 62.7 grams

Answer explanation

To calculate the moles of NaCl, use the formula Moles = Molarity x Volume (L). Convert 125mL to L (0.125L) and multiply by 8.59M to get 1.07 mol.