Some Basic Concepts of Chemistry

Q. How many grams of NaCl are in 0.5 moles of NaCl? (Molar mass of NaCl = 58.5 g/mol)

A. 29.25 g
B. 58.5 g
C. 87.75 g
D. 14.625 g

Solution

Mass = moles x molar mass = 0.5 moles x 58.5 g/mol = 29.25 g.

Correct Answer: A — 29.25 g

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Q. If 10 grams of NaOH are dissolved in 1 liter of water, what is the molarity of the solution? (Molar mass of NaOH = 40 g/mol)

A. 0.1 M
B. 0.25 M
C. 0.5 M
D. 1 M

Solution

Molarity = moles/volume(L). Moles of NaOH = 10g / 40 g/mol = 0.25 moles. Molarity = 0.25 moles / 1 L = 0.25 M.

Correct Answer: C — 0.5 M

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Q. If 2 moles of sodium (Na) react with chlorine (Cl) to form sodium chloride (NaCl), how many moles of NaCl are produced?

A. 1 mole
B. 2 moles
C. 3 moles
D. 4 moles

Solution

The reaction is 2Na + Cl2 → 2NaCl. Therefore, 2 moles of Na produce 2 moles of NaCl.

Correct Answer: B — 2 moles

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Q. What is the chemical formula for the compound formed between aluminum and oxygen?

A. AlO
B. Al2O3
C. AlO3
D. Al3O2

Solution

Aluminum has a +3 charge and oxygen has a -2 charge. The formula is Al2O3 to balance the charges.

Correct Answer: B — Al2O3

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Q. What is the empirical formula of a compound that contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen?

A. C2H3O
B. C3H4O
C. C1H2O
D. C1H1O

Solution

Convert percentages to grams (assuming 100g): C=40g, H=6.7g, O=53.3g. Moles: C=40/12=3.33, H=6.7/1=6.7, O=53.3/16=3.33. The ratio is 1:2:1, giving the empirical formula C2H3O.

Correct Answer: A — C2H3O

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Q. What is the molar mass of water (H2O)?

A. 16 g/mol
B. 18 g/mol
C. 20 g/mol
D. 22 g/mol

Solution

The molar mass of water is calculated as follows: H (1 g/mol) x 2 + O (16 g/mol) = 2 + 16 = 18 g/mol.

Correct Answer: B — 18 g/mol

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Q. What is the volume of 1 mole of an ideal gas at STP (Standard Temperature and Pressure)?

A. 22.4 L
B. 24.5 L
C. 20.0 L
D. 18.0 L

Solution

At STP, 1 mole of an ideal gas occupies 22.4 liters.

Correct Answer: A — 22.4 L

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Some Basic Concepts of Chemistry

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