| What is an acid? | A substance that produces hydrogen, H⁺, when dissolved in water. |
| What is a strong acid? | An acid that ionises fully in solution. This means that all ions will separate. |
| What is a weak acid? | An acid that partially ionises in solution. This means that some ions will still be bonded. |
| What is a concentrated acid? | A solution that has a larger number of acid particles per volume of water. |
| What is a dilute acid? | A solution that has a smaller number of acid per volume of water. |
| What happens to the pH value if you increase the hydrogen concentration? | It decreases.
E.g.
10 → 100
pH 3 → pH 2 |
| What does 'pH scale' stand for? | Power of hydrogen ions. |
| What is the formula of hydrochloric acid? | HCl. |
| What is the formula of sulphuric acid? | H₂SO₄. |
| What is the formula of nitric acid? | HNO₃. |
| What is an alkali? | A substance that produces hydroxide ions, OH⁻, when dissolved in water.
It's also a soluble base. |
| What is a base? | A substance that can neutralise acids and form salts. |
| What type of salt does hydrochloric acid make? | Chloirde. |
| What type of salt does sulphuric acid make? | Sulphate. |
| What type of salt does nitric acid make? | Nitrate. |
| What are the products of the reaction;
Metal + Acid → | Metal + Acid → Salt + Hydrogen. |
| What are the products of the reaction;
Metal Oxide + Acid → | Metal Oxide + Acid → Salt + Water. |
| What are the products of the reaction;
Metal Hydroxide + Acid → | Metal Hydroxide + Acid → Salt + Water. |
| What are the products of the reaction;
Metal Carbonate + Acid → | Metal Carbonate + Acid → Salt + Water + Carbon Dioxide. |
| What is electrolysis? | The breakdown of ionic compounds with electricity. |
| What type of current is used for electrodes? | Direct current. |
| What are the two electrodes? | Cathode and anode. |
| What is the charge of the cathode? | Negative. |
| What is the charge of the anode? | Positive. |
| What charged ions does the cathode attract? | Positive. So metals form here. |
| What charged ions does the anode attract? | Negative. So non-metals form here. |
| What is the electrolyte? | The ionic compound that's either molten (l) or dissolved in a solution (aq). |
| Why does the electrolyte need to me (l) or (aq)? | So that the ions are free to move and can carry the charge. |
| What forms at the electrodes of NaCl? | Anode = Cl.
Cathode = Na. |
| What forms at the electrodes of MgBr₂? | Anode = Br.
Cathode = Mg. |
| What are half equations? | Equations that show the movement of electrons in atoms or ions. |
| Write a half life equation for NaCl. | Anode = chlorine
Cl → Cl₂ + e⁻
= 2Cl⁻ → Cl₂ + 2e⁻
We have 'Cl₂' because the neutral chlorine atom is a diatomic molecule.
We then have to balance the equation. Two electrons are lost because there are two chlorine atoms that lose an electron.
In half equations, minus signs aren't used, to show electrons being lost, you put them on the product side.
Cathode = sodium.
= Na⁺ + e⁻ → Na
The product is just Na because sodium has to gain an electron to become a neutral atom. |
| What is oxidation? | The gaining of oxygen, and the loss of electrons. |
| What is reduction? | The losing of oxygen, and the gain of electrons. |
| What forms at the anode of an aqueous solution? | If there are halogens present, they will form at the anode instead of OH⁻ ions.
If there are no halogens present, then the OH- from the water will be discharged and oxygen will form. |
| What forms at the cathode of an aqueous solution? | If the metal formed is more reactive than hydrogen, the hydrogen will form at the cathode.
If the metal formed is less reactive than hydrogen, the metal will form at the cathode. |
| Why can different products be formed at the cathode or anode when using electrolysis on aqueous solutions? | There will be hydrogen and hydroxide ions from the water and the ions from the compound.
This means that when the ions are discharged, the ones that form at the electrodes will depend completely on the relative reactivity of the ions in the solution. |
| What forms at the anode and cathode of the electrolysis of a copper sulphate solution? | Copper is less reactive than hydrogen, so the copper will form at the cathode.
There are no halogens present, so that means oxygen will form at the anode. |
| What forms at the anode and cathode of the electrolysis of a sodium chloride solution? | Sodium is more reactive than hydrogen, so the hydrogen will form at the cathode.
Chlorine is a halogen, so that means the chlorine will form at the anode. |
