Chemical changes

• What do acids produce in aqueous solutions?


  H⁺ ions
• What do alkalis produce in aqueous solutions?


  OH^- ions
• What is the pH of a neutral solution?

  7
• How does the pH scale measure acidity or alkalinity?

  The pH scale ranges from 0 to 14, with lower values being acidic and higher values being alkaline.
• What does a pH of less than 7 indicate?

  It indicates an acidic solution.
• What does a pH of greater than 7 indicate?

  It indicates an alkaline solution.
• What are the effects of acids and alkalis on indicators like litmus, methyl orange, and phenolphthalein?

  • Phenolphthalein:
  • Alkaline = pink
  • Acidic = colourless
  • Methyl orange:
  • Alkaline = yellow
  • Acidic = red
  • Litmus:
  • Alkaline = blue
  • Acidic = red
  • Blue litmus paper goes red in acidic & stays blue in alkaline
  • Red litmus paper goes blue in alkaline & stays red in acidic
• What happens to the pH when the concentration of hydrogen ions in an acidic solution increases?

  The pH decreases.
• What happens to the pH when the concentration of hydroxide ions in an alkaline solution increases?

  The pH increases.
• How does the pH change when the hydrogen ion concentration increases by a factor of 10?

  The pH decreases by 1.
• What is the method to investigate the change in pH when adding powdered calcium hydroxide to dilute hydrochloric acid?

  Add dilute HCl to a beaker, measure pH, add calcium hydroxide, stir, and record pH until no more change occurs.
• What is the analysis method for the pH change experiment with calcium hydroxide and hydrochloric acid?

  • Draw a line graph with mass added on the horizontal axis and pH on the vertical axis.
  • Draw a line of best fit, ignoring any anomalies.
• What do the terms dilute and concentrated refer to in a solution?


  Dilute refers to a lesser amount of substance, while concentrated refers to a larger amount of substance in a given volume.
• How do strong acids differ from weak acids in terms of dissociation?

  Strong acids fully dissociate in aqueous solution, while weak acids partially dissociate.
• Give examples of strong acids.

  Hydrochloric, nitric, and sulfuric acids.
• Give examples of weak acids.

  Ethanoic, citric, and carbonic acids.
• What is the general reaction of an acid with a base?

  Acid + Base → Salt + Water
• What are alkalis?


  Alkalis are soluble bases.
• What is produced when an acid reacts with a metal?

  Salt and hydrogen gas (H₂).
• What is produced when an acid reacts with a metal oxide?


  Salt and water.
• What is produced when an acid reacts with a metal hydroxide?

  Salt and water.
• What is produced when an acid reacts with a metal carbonate?

  Salt, water, and carbon dioxide (CO₂).
• How do you name salts formed from acids and bases?

  The first part is the name of the metal, and the second part comes from the acid used.
• What is the test for hydrogen gas?

  Use a burning splint held at the open end of a test tube of the gas, which creates a 'squeaky pop' sound.
• What is the test for carbon dioxide?

  Bubble the gas through limewater, which will turn milky (cloudy).
• What is a neutralization reaction?

  • A reaction between an acid and a base.
  • Produces salt and water.
• What occurs during an acid-alkali neutralization reaction?


  Hydrogen ions (H⁺) from the acid react with hydroxide ions (OH^-) from the alkali to form water.
• What is the ionic equation for any neutralization reaction with an acid and an alkali?


  H⁺(aq) + OH^-(aq) → H₂O(l)
• What is the process for preparing soluble salts from an acid and an insoluble reactant?

  1. Add excess of the reactant to ensure complete reaction with the acid.

  2. Remove the excess reactant by filtration.

  3. The remaining solution contains only salt and water.
• What do hydrogen ions (H⁺) from an acid react with in a neutralization reaction?

  Hydroxide ions (OH^-) from an alkali
• What is the ionic equation for a neutralization reaction between an acid and an alkali?


  H⁺(aq) + OH^-(aq) → H₂O(l)
• What is the procedure for preparing soluble salts from an acid and an insoluble reactant?

  • Add excess of the insoluble reactant to ensure complete reaction with the acid.
  • Remove the excess reactant by filtration.
  • The remaining solution contains only salt and water.
• Why is an excess of the reactant added when preparing soluble salts from an acid and an insoluble reactant?

  To ensure that the volume of acid reacts completely
• How is the excess reactant removed when preparing soluble salts from an acid and an insoluble reactant?

  By filtration of the insoluble reactant
• What remains in the solution after the excess reactant is removed in the preparation of soluble salts?

  Only salt and water
• Why is the remaining solution only salt and water after the reaction with an acid and an insoluble reactant?

  Because all of the acid has fully reacted and the other reactant has been filtered off
• What happens if a carbonate is used in the preparation of soluble salts?

  Carbon dioxide gas would be given off into the atmosphere
• What is the procedure for preparing soluble salts from an acid and a soluble reactant?

  • Titration must be used to measure exact volumes of reactants.
  • Mix the acid and soluble reactant in the correct proportions.
  • The remaining solution after the reaction contains only salt and water.
• Why must titration be used when preparing soluble salts from an acid and a soluble reactant?


  To measure the exact amount of volumes that react
• What is the result of mixing the exact proportions of acid and soluble reactant in a titration?

  The leftover solution is only salt and water, with no acid or alkali