Science: Solution Chemistry: Molarity and Concentration Worksheet

Question 1

A solution contains 2.0 moles of sodium chloride dissolved to make 0.50 liters of solution. What is the molarity of the solution?

Accepted Answer

The molarity is 4.0 M because molarity equals moles divided by liters, so 2.0 mol divided by 0.50 L equals 4.0 mol/L.

Question 2

How many moles of potassium nitrate are present in 250 mL of a 0.80 M solution?

Accepted Answer

There are 0.20 moles of potassium nitrate present because moles equal molarity times volume in liters, so 0.80 mol/L times 0.250 L equals 0.20 mol.

Question 3

A student dissolves 5.85 grams of sodium chloride, NaCl, in water to make 500 mL of solution. What is the molarity of the solution? Use a molar mass of 58.5 g/mol for NaCl.

Accepted Answer

The molarity is 0.20 M. First, convert grams to moles: 5.85 g divided by 58.5 g/mol equals 0.100 mol. Then divide by volume in liters: 0.100 mol divided by 0.500 L equals 0.20 M.

Question 4

What volume in liters is needed to prepare a 0.25 M glucose solution that contains 0.75 moles of glucose?

Accepted Answer

The needed volume is 3.0 L because volume equals moles divided by molarity, so 0.75 mol divided by 0.25 mol/L equals 3.0 L.

Question 5

Which solution is more concentrated: 1.5 M hydrochloric acid or 0.75 M hydrochloric acid? Explain your answer.

Accepted Answer

The 1.5 M hydrochloric acid solution is more concentrated because it contains more moles of solute per liter of solution than the 0.75 M solution.

Question 6

A 2.0 L solution contains 0.10 moles of calcium chloride. What is the concentration in molarity?

Accepted Answer

The concentration is 0.050 M because molarity equals moles divided by liters, so 0.10 mol divided by 2.0 L equals 0.050 mol/L.

Question 7

How many grams of sodium hydroxide, NaOH, are needed to make 400 mL of a 1.5 M solution? Use a molar mass of 40.0 g/mol for NaOH.

Accepted Answer

You need 24.0 grams of NaOH. First find moles: 1.5 mol/L times 0.400 L equals 0.600 mol. Then convert to grams: 0.600 mol times 40.0 g/mol equals 24.0 g.

Question 8

A stock solution has a concentration of 6.0 M. What will the final concentration be if 100 mL of this solution is diluted to 300 mL total volume?

Accepted Answer

The final concentration is 2.0 M because M1V1 = M2V2, so 6.0 M times 100 mL equals M2 times 300 mL, giving M2 = 2.0 M.

Question 9

How much 3.0 M sulfuric acid is needed to prepare 250 mL of a 0.60 M solution?

Accepted Answer

You need 50 mL of the 3.0 M sulfuric acid because M1V1 = M2V2, so 3.0 times V1 equals 0.60 times 250 mL. Solving gives V1 = 50 mL.

Question 10

A laboratory solution is labeled 0.10 M copper sulfate. How many moles of copper sulfate are in 1.20 L of this solution?

Accepted Answer

There are 0.12 moles of copper sulfate because moles equal molarity times volume, so 0.10 mol/L times 1.20 L equals 0.12 mol.

Question 11

A student mixes 0.50 L of a 2.0 M sodium chloride solution with enough water to make 1.0 L of solution. What is the new molarity?

Accepted Answer

The new molarity is 1.0 M because the number of moles stays the same during dilution. Using M1V1 = M2V2, 2.0 M times 0.50 L equals M2 times 1.0 L, so M2 = 1.0 M.

Question 12

Explain in one or two complete sentences what it means when a solution has a molarity of 0.50 M.

Accepted Answer

A molarity of 0.50 M means the solution contains 0.50 moles of dissolved solute in every 1.0 liter of solution. It describes how concentrated the solution is.

Science: Solution Chemistry: Molarity and Concentration

Science: Solution Chemistry: Molarity and Concentration

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