Separate chemistry 1 Study Guide

The concentration of a solution measures how much solute is dissolved in a specific volume of solvent or solution. A common way to express this in chemistry is molar concentration, often called molarity, which quantifies the amount of solute in moles per decimetre cubed (mol dm⁻³). Another way to express concentration is mass concentration, which measures the mass of solute in grams per decimetre cubed (g dm⁻³). To convert between these two units, you need to use the molar mass of the solute. The molar mass ($M_r$) is the sum of the relative atomic masses of all atoms in a chemical formula, expressed in grams per mole (g mol⁻¹). If you have the mass concentration (g dm⁻³) and the molar mass (g mol⁻¹), you can find the molar concentration (mol dm⁻³) by dividing the mass concentration by the molar mass. Conversely, to go from molar concentration to mass concentration, you multiply the molar concentration by the molar mass. This interconversion is crucial for many chemical calculations, including titrations and preparing solutions of specific strengths.

The usefulness of a metal, or its alloy, is directly linked to its chemical and physical properties. For example, aluminium is lightweight and corrosion-resistant, making it ideal for aircraft bodies and food packaging. Its low density (2.7 g/cm³) compared to steel (7.8 g/cm³) significantly reduces fuel consumption in aviation. Copper's excellent electrical conductivity and ductility make it suitable for electrical wiring, while its good thermal conductivity is utilised in plumbing. Gold, being extremely unreactive and malleable, is perfect for jewellery and high-quality electrical contacts where corrosion resistance is paramount. Alloys like magnalium (aluminium and magnesium) inherit aluminium's lightness but gain increased strength, valuable for lightweight structural components. Brass (copper and zinc) is harder and more corrosion-resistant than pure copper, making it suitable for musical instruments, decorative items, and plumbing fittings.