Concentration Pre-Quiz Review

How many L are required to make 3.5 M hydrochloric acid using 1.1 moles? 

• 3.18 L

• 0.31 L

• 3.85 L

• 4.6 L

Answer explanation

To make 3.5 M HCl with 1.1 moles, divide moles by molarity: 1.1 moles / 3.5 M = 0.31 L

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

• 0.02 mol

• 0.0209 mol

Answer explanation

To find the moles of potassium bromide, multiply the volume (0.045 L) by the molarity (0.465 M) to get 0.0209 mol.

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 the molarity, first calculate the moles of NaCl: 4g / 58.45 g/mol = 0.0684 mol. Then, convert mL to L: 3800 mL = 3.8 L. Finally, divide moles by liters: 0.0684 mol / 3.8 L = 0.018 M.

Find the molarity of 186.55 g of sucrose, C₁₂H₂₂O₁₁ (MM = 342) in 250 mL of water.

• 2.18 M

• 0.746 M

• 1.18 M

• 0.545 M

Answer explanation

Calculate moles of sucrose, then divide by volume in liters to get molarity: (186.55 g / 342 g/mol) / (250 mL / 1000 mL/L) = 2.18 M

What is the molality of a solution in which 3.0 moles of NaCl is dissolved in 1.5 Kg of water?

• 2.0 M

• 0.22 m

• 135 m

• 2.0m

Answer explanation

The molality of a solution is calculated by dividing the moles of solute by the mass of the solvent in kg. In this case, 3.0 moles of NaCl in 1.5 kg of water gives a molality of 2.0m.

What is the molality of a solution made by dissolving 2 moles of NaOH in 400 grams of water?

• 5 mol/kg. solvent

• 4 mol/kg solvent

• 3 mol/kg. solvent

• 2.5 moles /kg solvent

Answer explanation

The molality of a solution is calculated by dividing the moles of solute by the mass of the solvent in kg. In this case, 2 moles of NaOH in 400g of water gives a molality of 5 mol/kg solvent.

How many kilograms of H2O must be added to 75.5 g of Ca(NO3)2 to form a 0.500m solution?

• 0.920 Kg

• 0.00662 Kg

• 37.75 Kg

• 0,03775 Kg

Answer explanation

To calculate the amount of H2O needed, use the formula: moles of Ca(NO3)2 = moles of H2O. Convert 75.5g Ca(NO3)2 to moles, then to kg to find 0.920 Kg of H2O.

What is the molality of a solution made from 1.14 mol of CO2 dissolved in 1000 mL of acetone? (Density of acetone = 0.789 g/mL)

• 1.44 m

• 1.34 m

• 1.24 m

• 1.54 m

Answer explanation

The molality of a solution is calculated by dividing the moles of solute by the mass of the solvent in kg. First, convert grams of CO2 to moles, then calculate the mass of acetone in kg. Finally, divide moles of CO2 by kg of acetone to get 1.44 m.

Calculate the molality of a solution that is 10% ethanol by mass.

Ethanol, C₂H₅OH , has a molar mass of 46.068 g/mol

• 2.1 m

• 2.3 m

• 2.4 m

• 2.2 m

Answer explanation

To calculate molality, use the formula: molality = (mass of solute in kg) / (molar mass of solute in g/mol) / (mass of solvent in kg). First, find the mass of ethanol in 100g of solution, then convert to kg. Next, calculate molality using the given density and molar mass of ethanol to get 2.415m.

What is the concentration of solution (in ppm) made up of 0.005 grams of solute in 350 grams of solution?

• 14.3 ppm

• 12.1 ppm

• 1.4 ppm

• 9.8 ppm

Answer explanation

To calculate the concentration in ppm, first convert grams to mg (0.005g = 5mg). Then, divide the mass of solute by the mass of solution and multiply by 1,000,000 to get ppm. (5mg / 350g) * 1,000,000 = 14.3 ppm.