Q1. What is the molar mass of oxygen (O2)?

Background

Topic: Molar Mass Calculation

This question tests your ability to calculate the molar mass of a diatomic molecule using atomic masses from the periodic table.

Key Terms and Formulas

• Molar mass: The mass of one mole of a substance, usually in grams per mole (g/mol).

• Atomic mass of oxygen (O): 16.0 g/mol

Step-by-Step Guidance

1. Identify that O2 is a diatomic molecule, so it contains two oxygen atoms.

2. Find the atomic mass of oxygen from the periodic table.

3. Multiply the atomic mass by the number of atoms in the molecule:

Try solving on your own before revealing the answer!

Q2. A sample of gas has a volume of 7.5 L at STP. How many moles are present?

Background

Topic: Mole Conversions (Gas at STP)

This question tests your ability to use the molar volume of a gas at standard temperature and pressure (STP) to convert between volume and moles.

Key Terms and Formulas

• STP: Standard Temperature and Pressure (0°C, 1 atm)

• Molar volume at STP: 22.4 L/mol

• Formula:

Step-by-Step Guidance

1. Write down the volume of the gas: 7.5 L.

2. Recall that at STP, 1 mole of any gas occupies 22.4 L.

3. Set up the conversion:

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Q3. A hydrate of sodium sulfate has a mass of 5.32 g. The sample is heated until water is driven off, leaving 3.76 g of anhydrous sodium sulfate. What is the formula of the hydrate?

Background

Topic: Hydrate Formula Determination

This question tests your ability to determine the formula of a hydrate by calculating the ratio of water to anhydrous salt.

Key Terms and Formulas

• Hydrate: A compound containing water molecules within its crystal structure.

• Anhydrous: The compound after water is removed.

• Formula:

Step-by-Step Guidance

1. Calculate the mass of water lost:

2. Convert the mass of water and anhydrous salt to moles using their molar masses.

3. Find the ratio of moles of water to moles of sodium sulfate.

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Q4. Find the empirical formula for a compound with 88.8% copper and 11.2% oxygen.

Background

Topic: Empirical Formula Determination

This question tests your ability to convert percent composition to the simplest whole-number ratio of atoms in a compound.

Key Terms and Formulas

• Empirical formula: The simplest ratio of elements in a compound.

• Percent composition: The mass percent of each element in the compound.

• Formula:

Step-by-Step Guidance

1. Assume 100 g of the compound, so you have 88.8 g Cu and 11.2 g O.

2. Convert each mass to moles using their molar masses.

3. Divide each by the smallest number of moles to get the simplest ratio.

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Q5. What is the percent by mass/volume of a solution made from 7.5 g of NaCl dissolved in 250 mL of water?

Background

Topic: Solution Concentration (Percent by Mass/Volume)

This question tests your ability to calculate the percent concentration of a solution using mass of solute and volume of solvent.

Key Terms and Formulas

• Percent by mass/volume:

Step-by-Step Guidance

1. Write down the mass of NaCl (solute): 7.5 g.

2. Write down the volume of water (solvent): 250 mL.

3. Set up the formula:

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Q6. A stock solution of sodium nitrate, NaNO3, has a concentration of 1.00 M. The volume of the solution is 50.0 mL. How many moles of NaNO3 are present?

Background

Topic: Solution Molarity

This question tests your ability to use molarity to calculate the number of moles of solute in a given volume of solution.

Key Terms and Formulas

• Molarity (M):

• Formula:

Step-by-Step Guidance

1. Write down the molarity: 1.00 M.

2. Convert the volume from mL to L:

3. Set up the formula:

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Q7. A gold coin contains 1.5 x 1023 atoms of gold. How many moles of gold are present?

Background

Topic: Mole Conversions (Atoms to Moles)

This question tests your ability to convert between number of atoms and moles using Avogadro's number.

Key Terms and Formulas

• Avogadro's number: atoms/mol

• Formula:

Step-by-Step Guidance

1. Write down the number of atoms: .

2. Set up the formula:

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Q8. Which salt on the solubility curve graph has the lowest solubility at 0°C?

Background

Topic: Solubility Curves

This question tests your ability to interpret solubility curves and compare the solubility of different salts at a specific temperature.

Key Terms and Formulas

• Solubility: The maximum amount of solute that can dissolve in a solvent at a given temperature.

• Solubility curve: A graph showing how solubility changes with temperature.

Step-by-Step Guidance

1. Locate 0°C on the x-axis of the solubility curve graph.

2. Find the solubility values for each salt at 0°C.

3. Compare the values to determine which salt has the lowest solubility.

Try solving on your own before revealing the answer!