Chemical Formulae for Elements and Compounds
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Which of the following is considered a strong acid?

  • Hydrochloric acid (HCl) (correct)
  • Ammonia (NH3)
  • Carbonic acid (H2CO3)
  • Ethanoic acid (CH3COOH)

    • What is the primary product when an acid reacts with a metal hydroxide?

  • Salt and carbon dioxide
  • Salt and oxygen
  • Salt and water (correct)
  • Water and hydrogen gas

    • Which of the following compounds is classified as a weak base?

  • Potassium hydroxide (KOH)
  • Calcium hydroxide (Ca(OH)2)
  • Sodium hydroxide (NaOH)
  • Ammonia (NH3) (correct)

    • Which statement about buffer solutions is accurate?

    <p>They maintain pH levels despite significant dilution.</p> Signup and view all the answers

    What is the result of mixing sodium hydroxide (NaOH) with hydrochloric acid (HCl)?

    <p>Sodium chloride and water</p> Signup and view all the answers

    What is the correct chemical formula for Calcium Bromide?

    <p>CaBr₂</p> Signup and view all the answers

    Which formula represents Iron(III) fluoride correctly?

    <p>FeF₃</p> Signup and view all the answers

    What is the correct formula for Magnesium Oxide?

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

    Determine the chemical formula for Manganese(IV) oxide.

    <p>MnO₂</p> Signup and view all the answers

    What is the formula for Germanium Oxide?

    <p>GeO₂</p> Signup and view all the answers

    What is the general reaction pattern for a double displacement reaction?

    <p>AB + CD → AC + CB</p> Signup and view all the answers

    What does it mean for a chemical equation to be balanced?

    <p>The same number of each atom must be present on both sides.</p> Signup and view all the answers

    Which of the following statements is true about coefficients in a chemical equation?

    <p>Coefficients indicate the number of molecules involved in the reaction.</p> Signup and view all the answers

    When balancing a chemical equation, which of the following is NOT a step to follow?

    <p>Change the subscripts to balance elements.</p> Signup and view all the answers

    In the reaction BaCl2 + 2 AgNO3 → 2 AgCl + Ba(NO3)2, what is the role of the coefficient '2' before AgNO3?

    <p>It represents the number of molecules of AgNO3 needed for balance.</p> Signup and view all the answers

    What is the best description of subscripts in a chemical formula?

    <p>Subscripts represent the number of atoms of each element in a molecule.</p> Signup and view all the answers

    In a complete chemical equation, which part must remain unchanged during balancing?

    <p>The subscripts in the chemical formulas.</p> Signup and view all the answers

    What happens to the atoms during a chemical reaction?

    <p>Atoms are rearranged but conserved.</p> Signup and view all the answers

    What does a subscript '2' indicate in the chemical formula of a diatomic element?

    <p>Each molecule consists of two atoms joined together.</p> Signup and view all the answers

    Which of the following is NOT one of the seven diatomic elements?

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

    What is the correct name for the compound NaCl?

    <p>Sodium chloride</p> Signup and view all the answers

    Which group contains elements with a valency of 3?

    <p>Group 3</p> Signup and view all the answers

    What is the first step in writing the chemical formula of a compound?

    <p>Write the symbols of elements present in the compound.</p> Signup and view all the answers

    What is the valency of chlorine?

    <p>1</p> Signup and view all the answers

    Which of the following represents a correct example of a diatomic element?

    <p>Oxygen (O2)</p> Signup and view all the answers

    Which ion is correctly named as 'hydroxide'?

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

    What is assumed when no coefficient is written in a chemical equation?

    <p>The coefficient is assumed to be 1.</p> Signup and view all the answers

    Which element should you begin balancing with when writing a chemical equation?

    <p>Elements other than hydrogen and oxygen</p> Signup and view all the answers

    Which of the following is true about changing subscripts in chemical formulas?

    <p>You must NOT attempt to balance by changing subscripts.</p> Signup and view all the answers

    What is necessary after balancing a chemical equation to ensure correctness?

    <p>At least one coefficient must be a prime number.</p> Signup and view all the answers

    What is the role of a catalyst in a chemical reaction?

    <p>Catalysts lower the activation energy required for a reaction.</p> Signup and view all the answers

    Why do we not include catalysts in chemical equations?

    <p>The amount of catalyst remains unchanged throughout the reaction.</p> Signup and view all the answers

    In equilibrium reactions, what usually happens to the reactants and products?

    <p>The products can revert to reactants in a reverse reaction.</p> Signup and view all the answers

    When balancing the chemical equation $N_2O_5 → N_2 + O_2$, what are the coefficients of the balanced equation?

    <p>2, 1, 2</p> Signup and view all the answers

    What occurs at the point of equilibrium in a chemical reaction?

    <p>The rate of product formation equals the rate of reactant formation.</p> Signup and view all the answers

    According to Le Chatelier’s principle, what happens when a disturbance is applied to an equilibrium system?

    <p>The equilibrium position shifts to counteract the disturbance.</p> Signup and view all the answers

    Which statement correctly defines an acid according to the Arrhenius Theory?

    <p>An acid dissociates in water to produce hydrogen ions.</p> Signup and view all the answers

    What is a major limitation of the Arrhenius Theory of acids and bases?

    <p>It does not account for substances that do not contain hydroxide ions.</p> Signup and view all the answers

    Which theory defines an acid as a substance that can donate a hydrogen ion to another substance?

    <p>Bronsted-Lowry Theory</p> Signup and view all the answers

    What happens when an acid donates a hydrogen ion according to the Bronsted-Lowry Theory?

    <p>It forms its conjugate base.</p> Signup and view all the answers

    In what way do acids and bases behave similarly to temperature extremes?

    <p>Mixing acids and bases can cancel out their extreme effects, like mixing hot and cold temperatures.</p> Signup and view all the answers

    What is the characteristic of a substance that is considered neutral?

    <p>It exhibits neither acidic nor basic properties.</p> Signup and view all the answers

    Study Notes

    Chemical Formulae for Elements

    • Chemical formulas for elements are simply their chemical symbols. (e.g., Mg for Magnesium)
    • Some elements exist as two atoms joined together, called diatomic elements.
    • There are 7 diatomic elements: Iodine, Oxygen, Chlorine, Bromine, Nitrogen, Hydrogen, Fluorine.
    • Diatomic elements have a subscript '2' in their chemical formula (e.g., O₂ for Oxygen). This indicates two atoms are joined together in a molecule.

    Chemical Formulae for Compounds

    • Chemical formulae for compounds are determined using the valency of the composing elements.
    • The names of elements sometimes end in 'ide'. (e.g., Sodium Chloride NaCl)
    • Some ions can also end in 'ide', (e.g., Hydroxide OH⁻)
    • The valency depends on the group number of the element in the periodic table.
    • Rules to write chemical formulae for compounds with two elements:
      • Write symbols of the elements.
      • Write valency above each symbol.
      • Cross valency over (swap and drop).
      • Cancel down ratios if necessary.
      • Write correct chemical formula.

    ###Elements with Multiple Valances

    • Transition metals often have more than one valency.
    • Roman numerals are used to indicate the valency. (e.g., Copper (II) chloride)
    • Follow the rules to determine the correct chemical formula.

    Polyatomic Ions

    • Some compounds contain multiple ions, containing more than one type of atom. (e.g., carbonate CO₃⁻⁻)
    • The valency of a polyatomic ion is equal to its charge.
    • Polyatomic ions are written in brackets in chemical formulas. (e.g., Ammonium Nitrate (NH₄)NO₃)

    Names with Prefixes

    • Prefixes indicate the ratio of atoms in some compounds. (e.g., Mono, Di, Tri, Tetra, Penta, Hexa)
    • If a prefix is used in a compound's name, don't use the cross-valency method.

    Chemical Reactions

    • Chemical reactions involve the rearrangement of atoms, not creation or destruction.
    • Reactants are the substances that undergo change, and products are the newly formed substances.
    • Chemical reactions involve changes in energy, heat content of the reactants and products is never the same.
    • The physical state of reactants and products are indicated by state symbols. (s, l, g, aq)

    How to Detect a Chemical Reaction

    • Colour changes, heat content changes, gas production (bubbles) are indicators of a reaction.

    Types of Chemical Reactions

    • Combination/Synthesis: two or more reactants form a single product. (e.g., S + O₂ → SO₂)
    • Decomposition: a single reactant breaks down into two or more components. (e.g., CaCO₃ → CaO + CO₂)
    • Substitution/Single Replacement: a free element replaces another element in a compound. (e.g., Zn + 2HCl → H₂ + ZnCl₂)
    • Metathesis/Double Displacement: the ions of two compounds swap partners. (e.g., HCl + NaOH → NaCl + H₂O)

    Balancing Chemical Equations

    • Chemical equations must be balanced meaning that the same number of each atom must be present on both sides of the equation.
    • Coefficients are used to balance chemical equations to indicate how many molecules of each substance are involved.
    • Subscripts, part of the formula, cannot be changed to balance the equation.

    Catalysts

    • Catalysts speed up reactions.
    • Catalysts provide a different reaction path.
    • Catalysts don't undergo a change in the chemical reaction themselves.

    Equilibrium Reactions

    • Reactions that proceed simultaneously in both directions (forward and reverse) reach a point of equilibrium.
    • The rates of the forward and reverse reactions become equal.

    Acids and Bases

    • Acids and bases are substances that have different properties.
    • Mixed acids and bases can cancel each other's extreme effects, leading to neutralisation.
    • Definitions of acids and bases exist in different theories, such as Arrhenius and the Brønsted-Lowry theories.
    • Arrhenius: acid release H+ ions in water and base release OH⁻ ions. Brønsted-Lowry: acid donates H+ ions to other substances and base accepts H+ ions.

    pH Scale

    • The pH scale measures the concentration of hydronium ions (H⁺) in a solution.
    • A pH of 7 is neutral.
    • A pH less than 7 is acidic; higher than 7 is basic.
    • Each whole pH unit difference represents a tenfold change in H⁺ concentration.

    Reactions of Acids and Bases

    • When acids react with bases (or metal oxides, or metal hydroxides) the reaction is called neutralisation, producing a salt and water.

    Buffer Solutions

    • Buffer solutions resist changes in pH.
    • Buffer solutions contain a weak acid and one of its salts or a weak base and one of its salts.
    • Buffers resist pH changes when small amounts of acid or base are added to a solution.

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    Chemical Formulae for Elements and Compounds PDF

    Description

    This quiz covers the basic concepts of chemical formulae for both elements and compounds. Learn about the symbols of elements, the characteristics of diatomic elements, and the rules for writing chemical formulae for compounds based on valency. Test your understanding of how these fundamentals interconnect in chemistry.

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