Chemistry worksheet on molarity with problems and definitions.

Let’s solve each problem step by step.

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Problem 1:
To make a 4.00 M solution, how many moles of solute will be needed if 12.0 liters of solution are required?

We know:
Molarity (M) = moles of solute / liters of solution

So, rearrange to find moles:
moles = Molarity × liters

Plug in the numbers:
moles = 4.00 mol/L × 12.0 L = 48.0 moles

✔ Final Answer for Problem 1: 48.0 moles

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Problem 2:
How many moles of sucrose are dissolved in 250 mL of solution if the solution concentration is 0.150 M?

First, convert mL to L because molarity uses liters:
250 mL = 250 ÷ 1000 = 0.250 L

Now use:
moles = Molarity × liters
moles = 0.150 mol/L × 0.250 L = 0.0375 moles

✔ Final Answer for Problem 2: 0.0375 moles

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Problem 3:
What is the molarity of a solution of HNO₃ that contains 12.6 grams HNO₃ in 1.0 L of solution?

Step 1: Find the molar mass of HNO₃.
H = 1.0 g/mol
N = 14.0 g/mol
O = 16.0 g/mol × 3 = 48.0 g/mol
Total = 1.0 + 14.0 + 48.0 = 63.0 g/mol

Step 2: Convert grams to moles.
moles = mass ÷ molar mass = 12.6 g ÷ 63.0 g/mol = 0.200 moles

Step 3: Use molarity formula.
Molarity = moles ÷ liters = 0.200 mol ÷ 1.0 L = 0.200 M

✔ Final Answer for Problem 3: 0.200 M

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Problem 4:
How many grams of potassium nitrate are required to prepare 0.250 L of a 0.700 M solution?

Potassium nitrate = KNO₃

Step 1: Find moles needed.
moles = Molarity × liters = 0.700 mol/L × 0.250 L = 0.175 moles

Step 2: Find molar mass of KNO₃.
K = 39.1 g/mol
N = 14.0 g/mol
O = 16.0 g/mol × 3 = 48.0 g/mol
Total = 39.1 + 14.0 + 48.0 = 101.1 g/mol

Step 3: Convert moles to grams.
grams = moles × molar mass = 0.175 mol × 101.1 g/mol = 17.6925 grams

Round to 3 significant figures (since 0.700 and 0.250 have 3 sig figs):
→ 17.7 grams

✔ Final Answer for Problem 4: 17.7 grams

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Final Answer:
1. 48.0 moles
2. 0.0375 moles
3. 0.200 M
4. 17.7 grams