4 (a) (i) Give the name of a carbonate in scale - AQA - GCSE Chemistry - Question 4 - 2014 - Paper 3

The gas produced when acids react with scale is carbon dioxide (CO₂).

The displayed structure of ethanoic acid is:

        H
        |
    H - C - C - OH
        |
        O
        |
        H

Where the COOH group is correctly represented.

Hydrochloric acid reacts faster than ethanoic acid because it is a stronger acid. A stronger acid has a lower pH and produces more hydrogen ions (H⁺) in solution, which increases the reaction rate with scale.

Hydrochloric acid is corrosive and can damage the kettle by reacting with the metal or heating element.

Using the titration data:

1. The moles of NaOH used are calculated as:

   • Volume of NaOH = 28.60 cm³ = 0.02860 dm³
   • Concentration of NaOH = 0.200 mol/dm³
   • Moles of NaOH = Volume × Concentration = 0.02860 × 0.200 = 0.00572 moles

2. Since the reaction ratio is 1:1, moles of HCl = moles of NaOH = 0.00572 moles.

3. The concentration of HCl is found using:

   • Volume of HCl = 25.00 cm³ = 0.02500 dm³
   • Concentration of HCl = Moles / Volume = 0.00572 / 0.02500 = 0.2288 mol/dm³.

Thus, the concentration of hydrochloric acid is approximately 0.2288 mol/dm³.