Reactions of acids common mistakes

Common mistakes

• Misunderstanding Acid Reactions

  Students often think that all metals react with acids to produce hydrogen gas, not realizing that only certain metals do.

  Fix itFocus on learning which specific metals react with acids and remember that metals like copper do not react with dilute acids.

• Common Mistake in Predicting Salts

  Students often confuse the metal used in the reaction with the salt produced, predicting the wrong salt name.

  Fix itTo fix this, remember that the salt produced from hydrochloric acid will always be named after the metal and will be a chloride. For example, if zinc reacts with hydrochloric acid, the salt produced is zinc chloride.

• Common Mistake in Predicting Salts

  Students often confuse the names of the salts produced from sulfuric acid reactions, mistakenly predicting salts like sodium sulfate instead of the correct salt, such as copper(II) sulfate.

  Fix itTo fix this, students should remember that the salt name is derived from the metal used in the reaction combined with the acid name. For sulfuric acid, the salt will always end in 'sulfate'.

• Misidentifying the salt from nitric acid reactions

  Students often think the salt formed is a nitrate of the metal’s oxidation state, e.g. writing Fe(NO3)3 for iron reacting with nitric acid, instead of the correct iron(III) nitrate Fe(NO3)3, or confusing with Fe(NO3)2

  Fix itRemind that nitric acid is a strong acid that donates H+ and the metal gives up its positive ions; the salt is the metal nitrate with the metal’s actual oxidation state. For example, Fe + 3HNO3 → Fe(NO3)3 + 3/2 H2. Use the metal’s oxidation state to write the correct nitrate salt.

• Incorrect Word Equation Formation

  Students often write incomplete or incorrect word equations for acid-metal reactions, such as omitting the product or using incorrect terms.

  Fix itEnsure to include both reactants and products in the equation. For example, when hydrochloric acid reacts with zinc, the correct equation is 'hydrochloric acid + zinc → zinc chloride + hydrogen'.

• Incorrect balancing of metal‑acid equations

  Students often write the metal on the left and the acid on the right, or they forget to balance hydrogen gas and salt ions, leading to unbalanced equations such as HCl + Zn → ZnCl₂ + H₂

  Fix itEnsure the metal is on the left, the acid on the right, and that the equation is balanced for all atoms and charge. For example, Zn + 2 HCl → ZnCl₂ + H₂

• Hydrogen Test Confusion

  Students often state that hydrogen gas can be identified by its color or smell.

  Fix itEmphasize that hydrogen gas is colorless and odorless, and the test involves using a lighted splint to produce a 'pop' sound.

• Misunderstanding reactivity series relevance

  Students think all metals will react with dilute acids, ignoring the reactivity series and the fact that metals below hydrogen (e.g., zinc, iron) may not react readily with dilute acids.

  Fix itExplain that only metals higher than hydrogen in the reactivity series (e.g., magnesium, zinc, iron) will displace hydrogen from dilute acids; metals below hydrogen (e.g., copper, silver) do not react with dilute acids because they are less reactive.

• Confusing Neutralisation

  Students often think that neutralisation only involves acids and bases, forgetting that it can also include acids reacting with alkalis.

  Fix itRemember that neutralisation is the reaction between an acid and a base or alkali, and be sure to include both types in your explanations.

• Confusing Products of Neutralisation

  Students often state that acids react with alkalis to produce only salts, forgetting to include water as a product.

  Fix itRemember that the reaction of an acid with an alkali produces both a salt and water. Always include both products when describing neutralisation.