Microsoft Word - 10-18a,b Molarity wkst-Key - CHEMISTRY: A Study ... - Free Printable

Let’s go through each problem step by step. We’ll use the molarity formula:

Molarity (M) = moles of solute / liters of solution

We can rearrange this as needed:
- moles = M × L
- grams = moles × molar mass
- liters = moles / M

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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?

Use:
moles = M × L
→ moles = 4.00 mol/L × 12.0 L = 48.0 moles

✔ Final Answer for #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:
250 mL = 0.250 L

Use:
moles = M × L
→ moles = 0.150 mol/L × 0.250 L = 0.0375 moles

✔ Final Answer for #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 molar mass of HNO₃
H = 1.01, N = 14.01, O = 16.00 × 3 = 48.00
→ Molar mass = 1.01 + 14.01 + 48.00 = 63.02 g/mol

Step 2: Convert grams to moles
moles = 12.6 g ÷ 63.02 g/mol ≈ 0.200 moles

Step 3: Molarity = moles / liters = 0.200 mol / 1.0 L = 0.200 M

✔ Final Answer for #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?

Step 1: Find moles needed
moles = M × L = 0.700 mol/L × 0.250 L = 0.175 moles

Step 2: Find molar mass of KNO₃
K = 39.10, N = 14.01, O = 16.00 × 3 = 48.00
→ Molar mass = 39.10 + 14.01 + 48.00 = 101.11 g/mol

Step 3: Convert moles to grams
grams = 0.175 mol × 101.11 g/mol ≈ 17.7 grams

✔ Final Answer for #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