Science: Solution Chemistry: Molarity and Concentration
Calculating molarity, dilution, and concentration relationships
Science: Solution Chemistry: Molarity and Concentration
Calculating molarity, dilution, and concentration relationships
Chemistry - Grade 9-12
- 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?
Use the formula M = n/V.
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. - 2
How many moles of potassium nitrate are present in 250 mL of a 0.80 M solution?
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. - 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.
Convert grams to moles before using the molarity formula.
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. - 4
What volume in liters is needed to prepare a 0.25 M glucose solution that contains 0.75 moles of glucose?
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. - 5
Which solution is more concentrated: 1.5 M hydrochloric acid or 0.75 M hydrochloric acid? Explain your answer.
A larger molarity means more solute in the same volume.
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. - 6
A 2.0 L solution contains 0.10 moles of calcium chloride. What is the concentration in molarity?
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. - 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.
Find moles first, then convert moles to grams.
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. - 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?
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. - 9
How much 3.0 M sulfuric acid is needed to prepare 250 mL of a 0.60 M solution?
Use the dilution equation M1V1 = M2V2.
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. - 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?
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. - 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?
Dilution changes volume, not the amount of solute.
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. - 12
Explain in one or two complete sentences what it means when a solution has a molarity of 0.50 M.
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.