AQA AS Chemistry 1.2 Formulae & Calculations
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Questions and Answers

What is the symbol for the unified atomic mass unit?

u

What is the relative atomic mass of an element?

The ratio of the average mass of the atoms of an element to the unified atomic mass unit.

What is the relative molecular mass (Mr) of a molecular compound?

The ratio of the weighted average mass of a molecule of a molecular compound to the unified atomic mass unit.

What is the empirical formula?

<p>The simplest whole number ratio of the elements present in one molecule or formula unit of the compound.</p> Signup and view all the answers

What is the molecular formula?

<p>The formula that shows the number and type of each atom in a molecule.</p> Signup and view all the answers

What is the atom economy of a reaction?

<p>A measure of how many of the atoms used in the reaction become the desired product.</p> Signup and view all the answers

In a chemical reaction, atoms can be created or destroyed.

<p>False</p> Signup and view all the answers

What is a symbol equation?

<p>A shorthand way of describing a chemical reaction using chemical symbols to show the number and type of each atom in the reactants and products.</p> Signup and view all the answers

What is a word equation?

<p>A longer way of describing a chemical reaction using only words to show the reactants and products.</p> Signup and view all the answers

What is a spectator ion?

<p>An ion that does not take part in a reaction.</p> Signup and view all the answers

What is a hydrated compound?

<p>A compound that contains water of crystallisation as part of its structure.</p> Signup and view all the answers

What is an anhydrous compound?

<p>A compound that does not contain water of crystallisation.</p> Signup and view all the answers

What is a polyatomic ion?

<p>An ion that contains more than one type of element.</p> Signup and view all the answers

What are the steps involved in balancing a chemical equation?

<ol> <li>Write the formulae of the reactants and products. 2. Count the numbers of atoms in each reactant and product. 3. Balance the atoms one at a time until all the atoms are balanced by adding coefficients in front of the formulas. 4. Use appropriate state symbols in the equation.</li> </ol> Signup and view all the answers

Why is it important to understand the concept of limiting and excess reagents?

<p>To determine the maximum amount of product that can be formed in a chemical reaction and to predict the amount of reactants that will be left over after the reaction is complete.</p> Signup and view all the answers

What are some factors that can affect the percentage yield of a reaction?

<p>Some factors that can affect the percentage yield of a reaction include: 1. The reaction may not go to completion. 2. Side reactions may occur, consuming some of the reactants or products. 3. Reactants or products may be lost to the atmosphere, for example, due to evaporation or sublimation. 4. It may be difficult to isolate and purify the desired product from the reaction mixture.</p> Signup and view all the answers

Which of the following is an example of a hydrated compound?

<p>Copper(II) sulfate pentahydrate (CuSO4.5H2O)</p> Signup and view all the answers

What is the empirical formula for glucose (C6H12O6)?

<p>CH2O</p> Signup and view all the answers

Which of the following reactions has the highest atom economy?

<p>The addition of bromine to ethene (CH2=CH2 + Br2 → CH2BrCH2Br)</p> Signup and view all the answers

What is the formula for ammonium sulfate?

<p>(NH4)2SO4</p> Signup and view all the answers

What is the formula for zinc chloride?

<p>ZnCl2</p> Signup and view all the answers

Which of the following is a polyatomic ion?

<p>SO42-</p> Signup and view all the answers

What is the formula for potassium carbonate?

<p>K2CO3</p> Signup and view all the answers

Study Notes

AQA AS Chemistry 1.2 Formulae, Equations & Calculations

  • This section covers relative atomic mass, relative molecular mass, empirical and molecular formulas, balanced equations, reaction yields, atom economy, and hydrated salts.

1.2.1 Relative Atomic Mass & Relative Molecular Mass

  • Relative Atomic Mass (Ar): The average mass of an element's atoms relative to one-twelfth of the mass of a carbon-12 atom. It's a ratio, so it has no units.
  • Relative Molecular Mass (Mr): The average mass of a molecule relative to one-twelfth of the mass of a carbon-12 atom. Also a ratio, so it has no units. Calculated by adding the relative atomic masses of all the atoms in the molecule.
  • Isotopes: Atoms of the same element with different numbers of neutrons. The relative atomic mass of an element is the weighted average of the masses of its isotopes, taking their abundance into account.
  • There exists a mathematical formula for average relative atomic mass

1.2.2 Empirical & Molecular Formulae

  • Empirical Formula: The simplest whole number ratio of atoms in a compound.
  • Molecular Formula: The actual number and type of atoms in a molecule.
  • Empirical and molecular formulas can be different for organic compounds.

1.2.3 Balanced Equations

  • Balanced Chemical Equations: Equations where the number of atoms of each element is the same on both sides of the equation.
  • Chemical reactions involve the rearrangement of atoms, not the creation or destruction of them.

1.2.4 Reaction Yields

  • Percentage Yield: The percentage of the theoretical yield of a product actually obtained in an experiment.
  • Theoretical Yield: The maximum amount of product that could be obtained in a reaction.
  • Actual Yield: The amount of product actually obtained in an experiment.

1.2.5 Atom Economy

  • Atom Economy: A measure of how many atoms of the reactants are used to make the desired product (instead of becoming waste products). It is calculated as the ratio of the molecular mass of the desired product to the total molecular mass of all reactants, then multiplied by 100.

1.2.6 Hydrated Salts

  • Hydrated Salts: Compounds that contain water molecules within their crystal structure.
  • Anhydrous Salts: Salts without water of crystallization.
  • Water of Crystallisation: The water molecules present in the crystal lattice of a hydrated salt.
  • There exists a method of determining the formula of hydrated salts from laboratory data with appropriate equations

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AQA AS Chemistry 1.2 Formulae, Equations & Calculations PDF

Description

Explore the crucial concepts of relative atomic mass, relative molecular mass, and the importance of empirical and molecular formulas in chemistry. This quiz also delves into balanced equations, atom economy, and the calculations involving hydrated salts, providing a comprehensive overview of these fundamental topics.

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