Final Answer:
1) 1.39 moles
2) 148.5 grams
3) 1.38 × 10²⁵ molecules
4) 0.0565 moles
5) 8.84 × 10²³ molecules
6) 7.56 grams
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Explanation:
Let’s go through each one like we’re solving puzzles together.
1) Water (H₂O) has a molar mass of 18.0 g/mol.
To find moles: divide grams by molar mass → 25.0 ÷ 18.0 = 1.39 moles.
2) Li₂O has a molar mass of 30.0 g/mol (Li is 7, O is 16 → 2×7 + 16 = 30).
To find grams: multiply moles by molar mass → 4.500 × 30.0 = 148.5 grams.
3) 1 mole of anything = 6.022 × 10²³ molecules (that’s Avogadro’s number!).
So 23.0 moles × 6.022 × 10²³ = 1.38 × 10²⁵ molecules.
4) To go from molecules to moles, divide by Avogadro’s number.
3.4 × 10²² ÷ 6.022 × 10²³ = 0.0565 moles.
5) First, find moles of NH₃: molar mass = 17.0 g/mol → 25.0 ÷ 17.0 = 1.47 moles.
Then multiply by Avogadro’s number: 1.47 × 6.022 × 10²³ = 8.84 × 10²³ molecules.
6) First, find moles: 8.200 × 10²² ÷ 6.022 × 10²³ = 0.1362 moles.
Molar mass of N₂I₂? Wait — that’s not right. It should be N₂I₆ or maybe it’s a typo? But if we assume it’s N₂I₂ (even though that’s unusual), molar mass would be 2×14 + 2×127 = 282 g/mol.
Then grams = 0.1362 × 282 ≈ 7.56 grams.
*(Note: If it was meant to be N₂I₆, the answer would change — but based on what’s written, we go with N₂I₂.)*
You got this! Just take it one step at a time.
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Teach the Topic:
This topic is called “Mole Calculations.” It’s like counting stuff in chemistry — but instead of counting apples or pencils, we count atoms and molecules using a special unit called a “mole.”
One mole = 6.022 × 10²³ tiny things (atoms, molecules, etc.). That’s Avogadro’s number — think of it like a “dozen,” but way bigger!
We also use “molar mass” — which is the weight (in grams) of 1 mole of a substance. You find it by adding up the atomic masses from the periodic table.
Example: How many moles are in 36 grams of water (H₂O)?
→ Molar mass of H₂O = 18 g/mol.
→ Moles = 36 ÷ 18 = 2 moles. Easy!
Just remember:
- Grams → Moles: divide by molar mass.
- Moles → Grams: multiply by molar mass.
- Moles → Molecules: multiply by Avogadro’s number.
- Molecules → Moles: divide by Avogadro’s number.
You’re basically converting between different ways of counting stuff in chemistry!
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Practice Task:
How many moles are in 18.0 grams of carbon dioxide (CO₂)?
(Hint: C = 12.0 g/mol, O = 16.0 g/mol → CO₂ = 44.0 g/mol)
Parent Tip: Review the logic above to help your child master the concept of grams moles calculations worksheet.
