Mole Concept

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Q1. How many moles are in 100 grams of NaOH? (2022)

Solution:

Molar mass of NaOH = 23 + 16 + 1 = 40 g/mol. Number of moles = mass/molar mass = 100 g / 40 g/mol = 2.5 moles.

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Q2. If 0.5 moles of a gas occupy 12 liters at STP, what is the molar volume of the gas? (2023)

Solution:

At STP, 1 mole of any gas occupies 22.4 L. Therefore, 0.5 moles occupy 0.5 x 22.4 L = 11.2 L, confirming the molar volume is 22.4 L.

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Q3. How many molecules are in 0.1 moles of oxygen gas (O2)? (2021)

Solution:

Number of molecules = moles x Avogadro's number = 0.1 moles x 6.022 x 10^23 molecules/mole = 6.022 x 10^22 molecules.

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Q4. If 0.5 moles of a gas occupy 12.2 liters at STP, what is the molar volume of the gas? (2023)

Solution:

At STP, 1 mole of gas occupies 22.4 liters. Therefore, the molar volume is 22.4 L.

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Q5. What is the number of moles in 10 grams of H2? (2020)

Solution:

Molar mass of H2 = 2 g/mol. Number of moles = mass/molar mass = 10 g / 2 g/mol = 5 moles.

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Q6. What is the number of moles in 250 mL of a 2 M NaCl solution? (2021)

Solution:

Moles = Molarity x Volume (L) = 2 M x 0.250 L = 0.5 moles.

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Q7. What is the mass of 3 moles of sodium chloride (NaCl)? (2023)

Solution:

The molar mass of NaCl is 58.5 g/mol. Therefore, 3 moles of NaCl weigh 3 x 58.5 g = 175.5 g.

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Q8. How many grams are in 0.5 moles of glucose (C6H12O6)? (2023)

Solution:

Molar mass of C6H12O6 = 6*12 + 12*1 + 6*16 = 180 g/mol. Mass = 0.5 moles x 180 g/mol = 90 g.

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Q9. How many moles are in 32 grams of O2? (2021)

Solution:

Molar mass of O2 = 16*2 = 32 g/mol. Number of moles = mass/molar mass = 32g/32g/mol = 1 mole.

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Q10. How many molecules are present in 2 moles of water (H2O)? (2022) 2022

Solution:

Number of molecules = moles x Avogadro's number = 2 moles x 6.022 x 10^23 molecules/mole = 1.2044 x 10^24 molecules.