chem topic 3

• electrolysis of aq solution

  if the metal at the cathode is less reactive then H+ then it's discharged and a solid layer of pure metal is produced
• electrolysis of aq solution

  if the metal at the cathode is more reactive then H+ then H+ is discharged and H+ gas is produced
• What is an acid?

  A substance that produces H+ ions in water and has a pH less than 7.
• How is the acidity measured?

  Using the pH scale.
• What is an alkali?

  A soluble base that produces OH- ions in water and has a pH above 7.
• What pH does a neutral solution have?

  7
• How can the pH of a solution be found?

  By using an indicator.
• What is an indicator?

  A substance that changes colour depending on the pH.
• What is the chemical formula for the common lab acid 'hydrochloric acid'?

  HCl
• What is the chemical formula for the common lab acid 'sulphuric acid'?


  H₂SO₄
• What is the chemical formula for the common lab acid 'nitric acid'?

  HNO₃
• What do all acids contain?

  Hydrogen ions (H+)
• What do all alkalis contain?

  Hydroxide ions (OH-)
• What is the chemical formula for the common lab alkali 'sodium hydroxide'?


  NaOH
• What is the chemical formula for the common lab alkali 'potassium hyrdoxide'?


  KOH
• What is the chemical formula for the common lab alkali 'calcium hydroxide'?

  Ca(OH)₂
• Name 4 different types of indicators.

  Universal indicator, methyl orange, phenolphthalein, litmus (paper)
• What is the colour range for universal indicator?

  Red for strong acids, orange for weaker acids, green for neutral, blue for weaker alkalis and purple for strong alkalis.
• What colour does litmus paper (blue and red) go in an acid?

  Blue litmus paper: turns red

  Red litmus paper: stays red
• What colour does litmus paper (blue and red) go in a neutral solution?


  Blue litmus paper: stays blue

  Red litmus paper: stays red
• What colour does litmus paper (blue and red) go in an alkali?


  Blue litmus paper: stays blue

  Red litmus paper: turns blue
• What colour does phenolphthalein turn in an acid?

  Colourless
• What colour does phenolphthalein turn in an alkali?

  Pink
• What colour does phenolphthalein turn in a neutral solution?

  Colourless
• What colour does methyl orange turn in an acid?

  Red
• What colour does methyl orange turn in an alkali?

  Yellow
• What colour does methyl orange turn in a neutral solution?

  Orange
• What is an ion?


  An atom that has become electrically charged by gaining or losing electrons.
• What are polyatomic ions?

  Ions that are formed when small groups of atoms, held together by covalent bonds, gain or lose electrons.
• Name three examples of polyatomic ions.


  OH⁻, NO₃⁻, SO₄²⁻
• What do acids produce when they dissolve in water?

  An excess of hydrogen ions
• How is hydrochloric acid formed?

  When hydrogen chloride gas is dissolved in water and splits into H⁺ ions and Cl⁻ ions.
• What do alkalis produce when they dissolve in water? Give an example.

  An excess of hydroxide ions. For example, sodium hydroxide splits into Na⁺ ions and OH⁻ ions in water.
• What is the concentration of a substance?


  How strong a solution is based on the amount of a dissolved substance in a given volume of a solvent.
• What makes a solution higher in concentration?

  The higher the number of hydrogen/hydroxide ions in a solution in a certain volume, the higher the concentration.
• What does a higher concentration mean in an acid?

  The higher the concentration of hydrogen ions, the more acidic the solution is and the lower the pH is.
• What does a higher concentration mean in an alkali?

  The higher the concentration of hydroxide ions, the more alkaline the solution is and the higher the pH is.
• What concentration do neutral solutions have?

  They contain low, equal concentrations of hydrogen and hydroxide ions.
• What does dilute mean?

  To reduce the concentration of a solute in a solution, usually by mixing in more solvent.
• Complete the sentence: A concentrated solution contains...

  A lot of dissolved solute per unit volume.