Reactions of acids common mistakes

Common mistakes

• Confusing Acids and Bases

  Students often confuse acids with bases, thinking that both produce salts and water.

  Fix itRemember that acids react with bases to produce salts and water, while bases neutralize acids.

• Confusing Products of Reaction

  Students often state that acids react with carbonates to produce only salts and water, forgetting to include carbon dioxide.

  Fix itRemember that the reaction of acids with carbonates also produces carbon dioxide gas, so always include it in your answer.

• Common Mistake in Predicting Salt Names

  Students often confuse the names of salts produced from different acids, such as thinking that hydrochloric acid and sulfuric acid produce the same salt when reacting with the same metal.

  Fix itTo fix this, remember that the name of the salt depends on both the acid and the positive ion from the base, alkali, or carbonate. Practice identifying salts by pairing the correct acid with its corresponding positive ion.

• Misidentifying the products in acid‑base word equations

  Students often write the products of an acid‑base reaction as the acid and the base instead of the salt and water, e.g. HCl + NaOH → HCl + NaOH

  Fix itIn an acid‑base (or acid‑alkali or acid‑carbonate) reaction the hydrogen ions from the acid combine with the hydroxide ions from the base (or carbonate) to form water, and the remaining ions form a salt. The correct word equation for HCl + NaOH is: acid + alkali → salt + water.

• Common Mistake in Writing Balanced Equations

  Students often forget to balance the number of atoms of each element on both sides of the equation when writing balanced symbol equations for neutralisation reactions.

  Fix itTo fix this, carefully count the number of atoms of each element in the reactants and products, and adjust the coefficients to ensure they are equal on both sides.

• Common Mistake in Testing for Carbon Dioxide

  Students often confuse the test for carbon dioxide with the test for hydrogen gas, thinking that a lighted splint is used for both tests.

  Fix itRemember that the test for carbon dioxide involves bubbling the gas through limewater, which turns milky, while the test for hydrogen gas uses a lighted splint that produces a 'pop' sound.

• Common Mistake in Preparing Soluble Salts

  Students often forget to add the insoluble solid in excess when preparing a soluble salt, leading to incomplete reaction.

  Fix itAlways add the insoluble solid in excess to ensure that all the acid reacts and to prevent any unreacted acid from remaining in the solution.

• Excess Solid Misunderstanding

  Students often think that adding an insoluble solid in excess is to ensure all the acid reacts, rather than to ensure that the solution is saturated and all the acid is neutralised.

  Fix itEmphasize that the excess solid ensures that any unreacted acid is neutralised, and the remaining solid can be filtered out, leaving a pure salt solution.

• Misunderstanding Filtration Purpose

  Students often think that filtration is used to separate the acid from the insoluble solid instead of understanding that it is used to remove the excess insoluble solid from the solution.

  Fix itEmphasize that filtration is specifically for separating the unreacted solid from the solution containing the soluble salt.

• Evaporation and Crystallisation Confusion

  Students often confuse the processes of evaporation and crystallisation, thinking they are the same step in producing a pure dry salt sample.

  Fix itClarify that evaporation is the process of removing the solvent to concentrate the solution, while crystallisation is the formation of solid crystals from the concentrated solution.