IBDP Chemistry HL - Advanced Concepts & Analysis

Front

Distinguish between the terms "accuracy" and "precision" in experimental measurements.

Back

**Accuracy** refers to the closeness of a measured value to the true or accepted value. **Precision** refers to the closeness of repeated measurements to one another, regardless of their closeness to the true value. High precision implies low random error (small range), while high accuracy implies low systematic error.

Front

Explain the role of the Standard Hydrogen Electrode (SHE) in determining standard electrode potentials.

Back

The SHE serves as the universal reference point with a defined potential of 0.00 V. It consists of H2(g) at 1 atm bubbling through 1.0 mol dm^-3 H+(aq) at 298 K using an inert platinum electrode. By connecting other half-cells to the SHE, the relative tendency of a substance to gain electrons (be reduced) can be measured as Eo.

Front

Calculate the standard enthalpy change of reaction (deltaH) using mean bond enthalpies.

Back

**Formula:** deltaH = sum(bond enthalpies of reactants) - sum(bond enthalpies of products). Energy is required to break bonds (endothermic, positive) and released when forming bonds (exothermic, negative). Note: Mean bond enthalpies are averages from many compounds and differ from specific data in thermochemical cycles, leading to estimation error.

Front

Describe the shape and bond angle of SF4 (sulfur tetrafluoride) using VSEPR theory.

Back

SF4 has a **seesaw** shape. The central Sulfur has 5 electron domains (4 bonding pairs, 1 lone pair). The lone pair occupies an equatorial position to minimize repulsion (90-degree interactions). This results in axial bond angles of 180 degrees and equatorial bond angles of <120 degrees due to the repulsive force of the lone pair.

Front

Compare the consequences of errors in stoichiometric calculations regarding excess reactant vs. limiting reactant.

Back

Identifying the wrong **limiting reactant** leads to a theoretical yield calculation that does not reflect the actual maximum product possible based on the initial masses. If the **excess reactant** is miscalculated, one might incorrectly assume the reaction consumes more mass than available or underestimate the amount of unreacted material left post-reaction.