Chemistry

Apparatus and measurements Choose apparatus that measures the quantity needed with suitable precision. Quantity Apparatus Use and limitation Time Stopwatch Measures elapsed time; reaction start and stop can be judged inconsistently. Temperature Thermometer Measures temperature; read at eye level and allow the reading to stabilise. Mass Balance Measures mass; zero it before use and avoid drafts or spills. Liquid volume Burette Delivers variable, accurately measured volumes, especially in titrations. Liquid volume Volumetric pipette Transfers one fixed, accurate volume. Liquid volume Measuring cylinder Measures a range of volumes quickly, but less precisely than a pipette or burette. Gas volume Gas syringe Collects and measures gas directly; check connections for leaks. A measuring cylinder is convenient for approximate volumes. Use a pipette and burette when accurate solution volumes matter. Read liquid levels at eye level, using the bottom of the meniscus for colourless liquids. ...

Organic chemistry quiz Duration: 45 minutes Total marks: 22 Answer all questions. Show structural formulae clearly and include reaction conditions where requested. Section A: Multiple choice (5 marks) Q1 (1 mark) Which is the general formula for alkenes? A. $C_nH_{2n+2}$ B. $C_nH_{2n}$ C. $C_nH_{2n+1}OH$ D. $C_nH_{2n+1}COOH$ Q2 (1 mark) Which change occurs from the bottom to the top of a fractional distillation column? A. Chain length increases. B. Boiling point increases. C. Volatility increases. D. Viscosity increases. ...

Organic chemistry marking scheme This is the marking scheme for quiz: C11 - Organic Chemistry Quiz Topic Guide: C11 - Organic Chemistry Total marks: 22 Accept equivalent displayed or structural formulae where bonds and atom connections are unambiguous. Section A: Multiple choice (5 marks) Q1 (1 mark) B — Alkenes have general formula $C_nH_{2n}$. [1] Q2 (1 mark) C — Volatility increases from the bottom to the top of the column. [1] ...

Chemistry of the environment Water tests Anhydrous cobalt(II) chloride is blue. It turns pink when water is present. Anhydrous copper(II) sulfate is white. It turns blue when water is present. Purity A pure substance has a sharp melting point and boiling point. Impurities usually change and broaden these values. Distilled water is used to avoid dissolved impurities interfering with an experiment. Natural water Natural water may contain dissolved oxygen, metal compounds, plastics, sewage, microbes, nitrates, and phosphates. Dissolved oxygen supports aquatic life. ...

Stoichiometry Marking Scheme This is the marking scheme for quiz: C3 - Stoichiometry Quiz Topic Guide: C3 - Stoichiometry Section A: Multiple Choice (5 Marks) B [1] ($\text{Ca}(40) + 2\times\text{O}(16) + 2\times\text{H}(1) = 40 + 32 + 2 = 74$) D [1] ($24\text{ dm}^3 = 24,000\text{ cm}^3$) C [1] (Empirical $M_r$: $12 + 2 = 14$. $56 / 14 = 4$. $\text{C}_4\text{H}_8$) A [1] (Ratio $2:1$. 2 moles $\text{H}_2$ need 1 mole $\text{O}_2$. 2 moles $\text{O}_2$ available $\rightarrow \text{H}_2$ runs out first) A [1] ($M_r \text{ NaCl} = 58.5$. $0.5 \times 58.5 = 29.25$ g) Section B: Short Answer (15 Marks) $2\text{NaOH}(aq) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{Na}_2\text{SO}_4(aq) + 2\text{H}_2\text{O}(l)$ ...