Molality and Molarity worksheet for chemistry students, featuring questions on concentration calculations and units.

Let’s go step by step through each question.

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Question 1: Molality (m) = moles of solute / _______________.

Molality is defined as the number of moles of solute divided by the mass of solvent in kilograms.

So, we’re looking for “kilogram of solvent”.

✔ Correct answer: kilogram of solvent

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Question 2: How many moles of NaCl are present in a solution with a molarity of 8.59 M and a volume of 125 mL?

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

We need to find moles → so rearrange:

→ moles = Molarity × Volume (in liters)

Volume given is 125 mL → convert to liters:
125 mL = 0.125 L

Now calculate:

moles = 8.59 mol/L × 0.125 L = ?

Let’s compute:

8.59 × 0.125
= 8.59 × (1/8)
= 8.59 ÷ 8
= 1.07375 ≈ 1.07 mol

✔ Correct answer: 1.07 mol

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Question 3: What are the units of molarity?

Molarity is moles per liter → unit is mol/L, which is written as M (capital M).

Example: 1 M means 1 mole per liter.

✔ Correct answer: M

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Question 4: What are the units of molality?

Molality is moles per kilogram of solvent → unit is mol/kg, which is written as m (lowercase m).

Don’t confuse it with molarity (M) or milliliters (ml).

✔ Correct answer: m

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Final Answer:
1. kilogram of solvent
2. 1.07 mol
3. M
4. m