GCSE Chemistry Higher Tier - Paper 1 Summary Notes

Reaction Word Equation: $\text{copper carbonate} + \text{sulfuric acid} \rightarrow \text{copper sulfate} + \text{water} + \text{carbon dioxide}$ .
Observation for Excess: Solid copper carbonate remains at the bottom of the beaker after stirring.
Filtration: Used to remove unreacted solid copper carbonate from the solution.
Crystallisation: Warm the filtrate gently using an evaporating basin or water bath until crystals appear; then leave to cool.
Percentage Yield Calculation: $\text{\% yield} = \frac{\text{mass of salt actually produced}}{\text{maximum theoretical mass}} \times 100$ .
Reactivity Constraints: Copper is not used with sulfuric acid because it is too unreactive; Sodium is not used because it is too reactive (dangerous).

Group 1 (Alkali Metals):
- Similarity: Both sodium ( $Na$ ) and potassium ( $K$ ) have one electron in their outer shell.
- Difference: Potassium has more energy levels (shells) than sodium.
- Reaction with Water: Potassium reacts vigorously, producing a lilac flame and hydrogen gas.
- Alkalinity: Produces potassium hydroxide ( $KOH$ ); universal indicator turns purple/blue (pH 11–14).
Group 0 (Noble Gases): Density increases as atomic number increases down the group (e.g., Helium $0.2\,mg/cm^3$ to Radon $9.1\,mg/cm^3$ ).
Group 7 (Halogens):
- Reactivity decreases down the group; chlorine can displace bromine from potassium bromide.
- Going down the group, both relative molecular mass and boiling point increase.

Model Comparison:
- Model A (Plum Pudding): A ball of positive charge with embedded negative electrons; no empty space or nucleus.
- Modern Model: Contains a central nucleus (protons and neutrons) with electrons in specific energy levels and a large amount of empty space.
Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons.

Zinc and Copper Sulfate: The reaction is exothermic (temperature increases). The temperature rise stops when the copper sulfate reactant is depleted.
Polystyrene Cup: Used because it is a thermal insulator, reducing heat loss to the surroundings for more accurate results.
Ionic Equation: $Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)$ .
Random Errors: May be caused by heat loss to surroundings or variations in stirring speed.

Formation of Calcium Chloride ( $CaCl_2$ ): Calcium atoms lose two electrons to form $Ca^{2+}$ ions; chlorine atoms gain one electron to form $Cl^-$ ions.
Conductivity: Solid ionic compounds do not conduct electricity because ions are in a fixed lattice; they must be molten or aqueous to allow ion movement.
Aqueous Electrolysis ( $CaCl_2$ ):
- Negative Electrode (Cathode): Hydrogen gas ( $H_2$ ) is produced if the metal is more reactive than hydrogen.
- Positive Electrode (Anodic Half-Equation): $2Cl^- \rightarrow Cl_2 + 2e^-$ .
Copper Chromate: In an electric field, blue $Cu^{2+}$ ions move toward the negative electrode, and yellow $CrO_4^{2-}$ ions move toward the positive electrode.

Voltage Production: The potential difference depends on the difference in reactivity between the two metal electrodes and the concentration of the electrolyte.
Reactivity Order (from Table 3): Mg > Zn > Ni > Cu > Ag.
Hydrogen Fuel Cells: Produce a potential difference through the oxidation of hydrogen, creating water as the only byproduct.

Thermal Conduction: Metals conduct heat via the movement of delocalised electrons and lattice vibrations.
Alloys: Harder than pure metals because different-sized atoms distort the regular layer structure, preventing layers from sliding over each other.
Quantitative Analysis: Calculations involve relative atomic masses ( $Ar$ ) and formula masses ( $Mr$ ). Percentage mass of iron in $Fe_3O_4$ is calculated as $\frac{3 \times 56}{(3 \times 56) + (4 \times 16)} \times 100$ .
Gas Volume: At room temperature and pressure (RTP), $1\,mol$ of any gas occupies $24\,dm^3$ .

Propane ( $C_3H_8$ ): Has a low boiling point due to weak intermolecular forces that require little energy to overcome.
Bond Energy Calculation: Total energy change = (energy of bonds broken in reactants) - (energy of bonds formed in products).
Exothermic Profile: Products have lower energy than reactants; overall energy change is negative.

Weak Acids: Only partially ionise in aqueous solutions (e.g., ethanoic acid).
pH and Dilution: As an acid is diluted, the concentration of $H^+$ ions decreases, and the pH increases toward 7.
Titration Requirements: Use a pipette to measure alkali, add an indicator (e.g., phenolphthalein), and place the flask on a white tile to see color changes clearly.
Reactivity of Group 2: Calcium reacts more vigorously than magnesium because its outer electrons are further from the nucleus, resulting in weaker attraction and easier electron loss.