Concentration Calculations

A solution is prepared by dissolving 15 grams of NaCl in 250 mL of water. Calculate the molarity of the solution. (Molar mass of NaCl = 58.5 g/mol)

• M

• 2 M

• 0.5 M

• 1.5 M

Answer explanation

To find molarity, use the formula: M = moles of solute / liters of solution. First, calculate moles of NaCl: 15 g / 58.5 g/mol = 0.2564 moles. Then, convert 250 mL to liters (0.250 L). M = 0.2564 moles / 0.250 L = 1.0256 M, approximately 1.5 M.

Determine the concentration in ppm of a solution with 0.005 grams of solute in 250 mL of water.

• 20 ppm

• 10 ppm

• 40 ppm

• 30 ppm

Answer explanation

To find ppm, use the formula: ppm = (mass of solute in grams / volume of solution in liters) x 1,000,000. Here, 0.005 g in 0.250 L gives 20 ppm, making the correct answer 20 ppm.

A solution is made by dissolving 0.5 moles of solute in 1 litre of water. What is the molarity of the solution?

• 0.5 M

• 1 M

• 1.5 M

• 2 M

Answer explanation

Molarity (M) is calculated as moles of solute per liter of solution. Here, 0.5 moles of solute in 1 liter of water gives a molarity of 0.5 M. Therefore, the correct answer is 0.5 M.

A solution contains 0.005 grams of solute in 1 litre of water. What is the concentration in parts per million (ppm)?

• 5 ppm

• 50 ppm

• 500 ppm

• 5000 ppm

Answer explanation

To find ppm, use the formula: ppm = (mass of solute in grams / volume of solution in liters) x 1,000,000. Here, (0.005 g / 1 L) x 1,000,000 = 5 ppm. Thus, the concentration is 5 ppm.

What is the percent by mass of ammonium nitrate when 35 grams of ammonium nitrate is added to 250 grams of water?

• 12.28%

• 14.0%

• 13.33%

• 12.5%

A solution for making tea contains 20 g of sugar in 150 ml of water. Find the concentration of solution.

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What is the molarity of a solution prepared by diluting 1 litre of a 6 M solution to a final volume of 3 litres?

• 1 M

• 2 M

• 3 M

• 4 M

Answer explanation

To find the molarity after dilution, use the formula M1V1 = M2V2. Here, M1 = 6 M, V1 = 1 L, and V2 = 3 L. Rearranging gives M2 = (M1V1)/V2 = (6 M * 1 L) / 3 L = 2 M. Thus, the molarity is 2 M.

Convert a concentration of 100 ppm to molarity, given that the molar mass of the solute is 50 g/mol.

• 0.002 M

• 0.02 M

• 0.0002 M

• 0.2 M

Answer explanation

To convert 100 ppm to molarity, use the formula: M = (ppm / molar mass) x 10^-6. Thus, M = (100 / 50) x 10^-6 = 0.0002 M. Therefore, the correct answer is 0.0002 M.

A solution is made by dissolving 0.2 moles of solute in 500 mL of water. What is the molarity of the solution?

• 0.2 M

• 0.4 M

• 0.6 M

• 0.8 M

Answer explanation

Molarity (M) is calculated as moles of solute divided by liters of solution. Here, 0.2 moles in 0.5 L (500 mL) gives 0.2 / 0.5 = 0.4 M. Thus, the correct answer is 0.4 M.

If 2 grams of a solute is dissolved in 1 litre of water, what is the concentration in ppm?

• 2000 ppm

• 1000 ppm

• 500 ppm

• 250 ppm

Answer explanation

To find the concentration in ppm, use the formula: ppm = (mass of solute in grams / volume of solution in liters) x 1,000,000. Here, (2g / 1L) x 1,000,000 = 2,000 ppm, making the correct answer 2000 ppm.