Chemistry Chapter on Moles and Mass

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Questions and Answers

What does the empirical formula represent?

A random arrangement of atoms

The simplest whole number ratio of atoms of each element (correct)

The molecular weight of a substance

The actual number of atoms in a molecule

The molecular formula is derived from the empirical formula and the actual molar mass of the molecule.

True

What is typically calculated using balanced chemical equations?

Reacting masses, percentage yield, and atom economy.

A high atom economy signifies that there is little or no ______ in a chemical reaction.

waste product Signup and view all the answers

Match the terms with their definitions:

Empirical formula = Simplest ratio of elements Molecular formula = Actual number of atoms in a molecule Atom economy = Efficiency of a chemical process Percentage yield = Actual yield compared to theoretical yield Signup and view all the answers

Why is balancing chemical equations important?

To ensure the reacting ratios are correct Signup and view all the answers

An empirical formula can have multiple molecular formulas that correspond to it.

True Signup and view all the answers

What is a benefit of high atom economy?

It uses fewer natural resources and produces less waste. Signup and view all the answers

The multiplier value used to calculate the molecular formula is derived from the ratio of the of the empirical formula to the of the molecule.

Mr / true Mr Signup and view all the answers

Which formula provides the correct ratio of components in a compound?

Empirical formula Signup and view all the answers

What is the relative atomic mass (Ar) defined as?

The mean mass of an atom of an element, divided by one twelfth of the mean mass of an atom of the carbon-12 isotope. Signup and view all the answers

Relative molecular mass (Mr) is applicable to ionic compounds only.

False Signup and view all the answers

What unit of measurement is used for the amount of substance?

mole Signup and view all the answers

The constant that allows for the determination of the number of particles in a mole is called the __________.

Avogadro Constant Signup and view all the answers

Match the following variables with their meanings in the ideal gas equation:

p = Pressure in Pascals V = Volume in m³ T = Temperature in Kelvin n = Moles Signup and view all the answers

What must be the unit of pressure when using the ideal gas equation?

Pascals Signup and view all the answers

The ideal gas constant (R) is equal to 8.31 JK⁻¹mol⁻¹.

True Signup and view all the answers

Under standard conditions, pressure and volume are __________ proportional.

inversely Signup and view all the answers

The ideal gas equation can be represented as PV = nRT, where R is the __________ constant.

ideal gas Signup and view all the answers

The given formula for moles (n) can be written as:

n = PV/RT Signup and view all the answers

Study Notes

Relative Atomic Mass (Ar)

Defined as the mean mass of an atom of an element, divided by one-twelfth the mean mass of a carbon-12 atom.

Relative Molecular Mass (Mr)

Defined as the mean mass of a molecule of a compound, divided by one-twelfth the mean mass of a carbon-12 atom.
For ionic compounds, it's known as relative formula mass.

Moles and the Avogadro Constant

The mole is a unit of measurement for substances, containing a constant number of particles.
Avogadro's constant (L) = 6.022 x 10²³ particles.
The number of particles in a substance can be calculated using the formula: Number of particles = nL (where n = moles and L = Avogadro's constant).
Moles are crucial in various calculations, including those involving mass, concentration, and volume: Moles = mass/Mr = concentration x volume/1000 (where concentration is in mol/dm³).

Ideal Gas Equation

Under standard conditions, gases and volatile liquids follow certain trends: pressure is proportional to temperature, volume is proportional to temperature, and pressure and volume are inversely proportional.
Combining these relationships yields the ideal gas equation: pV = nRT = mRT/Mr, where:
- p = pressure in Pascals
- V = volume in m³
- n = moles
- T = temperature in Kelvin
- m = mass in grams
- R = ideal gas constant (8.31 J K⁻¹ mol⁻¹).

Empirical and Molecular Formulae

Empirical formula: The simplest whole number ratio of atoms of each element in a compound, determined using molar ratios.
Molecular formula: The true number of each atom in a molecule, calculated using the empirical formula's Mr and the molecule's true Mr (which gives a multiplier).

Equations and Calculations

Chemical equations must be balanced for accurate calculations and reflecting reacting proportions.
- Balanced equations allow the calculation of reacting masses, percentage yield, and atom economy.
Percentage yield = (Experimental mass/Theoretical mass) x 100
Atom economy = (Mr of desired product/Mr of reactants) x 100.
High atom economy is desirable in industrial processes as it minimizes waste, reducing environmental impact and cost.

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Description

This quiz covers key concepts in chemistry regarding relative atomic mass, relative molecular mass, moles, and the Avogadro constant. You'll explore the relationships between these concepts and their applications in gas equations and calculations. Test your understanding of fundamental chemical principles and their significance in various calculations.