Chemistry Molar Calculations Quiz

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Questions and Answers

What is the volume of hydrogen produced when 2 g of zinc reacts completely with hydrochloric acid at standard temperature and pressure?

0.685 dm3 (correct)

0.342 dm3

1.224 dm3

1.414 dm3

What is the molar mass of potassium trioxochlorate (KClO3) used in the reaction?

106.5 g/mol

100 g/mol

122 g/mol (correct)

150 g/mol

In the reaction 2KClO3 → 2KCl + 3O2, how many moles of KClO3 are required to produce 1.37 dm3 of oxygen?

0.5 moles (correct)

0.75 moles

0.25 moles

1.0 moles

Which of the following statements regarding the reaction Zn + 2HCl → ZnCl2 + H2 is true?

2 moles of HCl are required for 1 mole of Zn Signup and view all the answers

If the molar volume of a gas is 22.4 dm3, how much volume will be produced when 5.0 g of KClO3 decomposes completely?

1.37 dm3 Signup and view all the answers

What is the percentage composition of iron in iron (ii) tetraoxosulphate(vi) if Fe = 56, S = 32, and O = 16?

25.6% Signup and view all the answers

Which formula correctly represents the percentage composition of nitrogen in magnesium trioxonitate(v) where Mg = 24, N = 14, and O = 16?

14/54 x 100 = 25.9% Signup and view all the answers

What is the percentage of oxygen in ammonium tetraoxosulphate(vi) if N = 14, H = 1, S = 32, and O = 16?

72.4% Signup and view all the answers

Calculate the percentage of oxygen in sodium trioxocarbonate (IV) monohydrate where O = 16, Na = 23, C = 12, and H = 1.

60.0% Signup and view all the answers

How many moles of a substance are contained in 24 grams of carbon-12?

1 mole Signup and view all the answers

What is the total number of particles in 2 moles of a substance?

1.2046 x 10^24 particles Signup and view all the answers

Which reaction type would describe the combination of oxygen gas and hydrogen gas to form water?

Combination reaction Signup and view all the answers

If the molarity of a solution is defined as moles of solute per liter of solution, what would be the molarity of a solution containing 0.5 moles of sodium chloride in 2 liters of water?

0.25 M Signup and view all the answers

What is the number of moles in 20.0g of nitrogen (N2) where the molar mass is 28 g/mol?

0.500 mol Signup and view all the answers

How many liters of diatomic oxygen (O2) at standard temperature and pressure (s.t.p.) are needed to obtain 0.50 moles?

22.4 L Signup and view all the answers

What is the concentration in mol/dm³ of a solution containing 2 moles of solute in 500 cm³ of solution?

0.8 mol/dm³ Signup and view all the answers

If 1 mole of hydrogen gas reacts with 1 mole of oxygen gas, how many moles of water will be produced?

2 mol Signup and view all the answers

What is the molar mass of diatomic chlorine (Cl2)?

70.90 g/mol Signup and view all the answers

Which of the following is NOT a condition for conducting a stoichiometric calculation?

Absolute temperature Signup and view all the answers

Which of the following represents the correct relationship for calculating the moles of a gas at standard temperature and pressure (s.t.p.)?

n = V/Vm Signup and view all the answers

If the concentration of a solution is 2 mol/dm³ and its volume is 2dm³, how many moles of solute does it contain?

4 mol Signup and view all the answers

Study Notes

Mole Calculations

Number of moles (n) can be calculated via different methods:
- n1 = m/M (mass over molar mass)
- n2 = V/Vm (volume over molar volume)
- n3 = N/NA (number of particles over Avogadro's number)
- n4 = CV(cm³)/1000 (conversion from cm³ to moles)
- n5 = CV(dm³) (volume in dm³ directly as moles)
Molar volume at standard temperature and pressure (s.t.p) is 22.4 dm³ (or 22400 cm³).
Avogadro's number (NA) is approximately 6.02 x 10²³, representing the number of particles in one mole.

Example Calculations

Chlorine Mole Calculation: For 10.65g of Cl (Molar mass = 35.5):
- n = 10.65/35.5 = 0.300 moles.
Oxygen Mole Calculation: For 8.96 dm³ of O₂ (Molar volume = 22.4 dm³):
- n = 8.96/22.4 = 0.400 moles.
Hydroxide Ions Calculation: For 60.23 x 10²² OH⁻ ions:
- n = 60.23 x 10²²/6.02 x 10²³ = 1.00 mole.

Diatomic Gases Molar Mass

Hydrogen (H₂): Molar mass = 2 g/mol
Oxygen (O₂): Molar mass = 32 g/mol
Nitrogen (N₂): Molar mass = 28 g/mol
Other diatomic gases include Fluorine (F₂), Bromine (Br₂), Chlorine (Cl₂), and Iodine (I₂).

Writing and Balancing Chemical Equations

A chemical equation summarizes a chemical reaction's ingredients and outcomes.
Procedure:
- List reactants on the left, products on the right, separated by an arrow.
- Ensure the number of atoms for each element on both sides is equal.
- Example: Lead (II) oxide can be represented as Pb₃O₄ with a molar mass calculation of 685 g/mol.

Percentage Composition

Percentage composition formula:
- % Composition = (mass of atom / molar mass of compound) x 100
Sodium in Sodium Hydroxide (NaOH):
- Molar mass = 40 g/mol, % Na = (23/40) x 100 = 57.5%.
Water in Magnesium Tetraoxosulphate (VI) Heptahydrate:
- Molar mass = 246 g/mol, mass of water = 126g, % water = (126/246) x 100 = 51.2%.
Oxygen in Magnesium Tetraoxosulphate (VI):
- Mass of O = 176g, % O = (176/246) x 100 = 71.5%.

Mole Concept

A mole contains as many elementary units as there are atoms in 12 g of carbon-12, equivalent to Avogadro's number (6.023 x 10²³).
Reaction example:
- Zn + 2HCl → ZnCl₂ + H₂ with a mole ratio of 1:2:1:1.

Gas Volume Calculations

The volume of gas can be calculated from moles:
- Example for Zn and H₂: For 0.0306 moles of Zn, producing H₂:
  - Volume of H₂ produced = 0.0306 x 22.4 dm³ = 0.685 dm³.

Decomposition of Potassium Trioxochlorate (V)

Reaction: 2KClO₃ → 2KCl + 3O₂.
Molar mass of KClO₃ = 122.5 g/mol, meaning 2 moles yield 3 x 22.4 dm³ of O₂.
For 5g KClO₃:
- Calculated volumes of oxygen = 1.37 dm³ based on proportion.

Practice Problems

Calculate percentage compositions for:
- Iron in iron (II) tetraoxosulphate (VI).
- Nitrogen in Magnesium trioxonitrate (V).
- Oxygen in ammonium tetraoxosulphate (VI).
- Oxygen in sodium trioxocarbonate (IV) monohydrate.

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Description

Test your understanding of molar calculations in chemistry. This quiz covers essential formulas and concepts such as mole calculations, molar volume, and Avogadro's number. Perfect for students studying chemistry and preparing for exams.