C5 - Acid Strengths Flashcards
What is the difference between strong and weak acids?
Strong acids and weak acids have different pH values, even
if they are at the same concentration. A strong acid will have a lower pH than a weak acid of the same concentration. Its solution will be more strongly acidic.
Acids ionise in water to produce hydrogen ions, H+. Strong acids such as hydrochloric acid completely ionise in solution. Weak acids such as ethanoic acid only partially ionise in water. Many of their molecules do not release hydrogen ions.
What is the difference in concentration and strength?
The concentration of an acid is a measure of the number of moles of acid in 1 dm3. The higher the concentration, the more moles of acid are dissolved in the same volume of water. The strength of an acid is a measure of how ionised the acid is in water. The stronger the acid, the more ionised it is.
How are acids electrolysed?
Solutions containing ions conduct electricity because the ions are free to move. They carry charge from one electrode to the other. Acids in solution contain hydrogen ions and other ions, so they conduct electricity. Hydrogen gas is made at the negative electrode during the electrolysis of either hydrochloric acid or ethanoic acid. This is because the positively charged hydrogen ions are attracted to the negatively charged electrode, where they gain electrons and become hydrogen gas:
2H+ + 2e– → H2
Why do different acids have different electrical conductivity?
It is more ‘dif cult’ for current to pass through a weak acid than it is through a strong acid at the same concentration. For a given potential difference or voltage, the current will be lower through the weak acid. The electrical conductivity of ethanoic acid is lower than it is for hydrochloric acid at the same concentration, because ethanoic acid solution contains fewer hydrogen ions.
Why is ethanoic acid less conductive than hydrochloric acid?
Ethanoic acid is less conductive than hydrochloric acid at the same concentration because it is a weak acid, whereas hydrochloric acid is a strong acid. There is a lower concentration of hydrogen ions to carry the charge through ethanoic acid than there is in hydrochloric acid.
What is limescale? Why is it bad?
Tap water contains dissolved mineral ions. Over time, particularly in hard water areas, limescale can build up in washing machines, kettles, and irons.
This a deposit of calcium carbonate, which coats the surface of the heating elements in these appliances.
Limescale looks unpleasant and it makes the appliances less efficient, wasting electricity.
How is limescale removed?
Descalers contain a weak acid such as citric acid. This reacts with the limescale without damaging the metal of the heating element.
A strong acid such as hydrochloric acid would remove the limescale. Unfortunately, it would also damage the metal.
Why are there different rates of reaction between ethanoic acid and hydrochloric acid?
The reactions with ethanoic acid are slower than with hydrochloric acid. This is because ethanoic acid is a weak acid, but hydrochloric acid is a strong acid.
At the same concentration, there are fewer hydrogen ions in ethanoic acid. As a result, there are fewer collisions between hydrogen ions and the reactant particles.
How does strength of acid affect product made?
Acid strength does not affect amount , only rate of reaction. The amount of the reactants affects the amount of product.
