1. How to Tell if Copper is Pure
(1) Visual and Surface Inspections
Color and Luster: Pure copper has a distinct, bright salmon-pink to reddish-orange luster when freshly cleaned or polished. Impure copper (e.g., brass, which is copper-zinc alloy) often appears more yellowish or silvery; bronze (copper-tin) may have a duller gold or brown tint. Over time, pure copper develops a dark brown or greenish patina (verdigris) from oxidation, but the underlying metal (if scratched lightly) should still show the characteristic reddish color.
Surface Uniformity: Pure copper typically has a consistent surface texture. Alloys like brass or bronze may have subtle variations in color or grain structure, especially if cast or machined.
(2) Physical Property Tests
Density Check: Pure copper has a well-defined density of ~8.96 g/cm³. To approximate this:
Measure the copper's mass using a scale.
Calculate its volume (e.g., for a solid piece, use water displacement: submerge it in a graduated cylinder and measure the water rise).
Compute density (mass/volume). A value significantly lower than 8.96 g/cm³ indicates impurities (e.g., aluminum-copper alloys have lower density).
Hardness Test: Pure copper is relatively soft (Mohs hardness of 2.5–3, softer than a penny, which is copper-plated zinc). Scratching it with a sharp steel nail will leave a clear, deep mark; alloys like brass or bronze are harder and will resist scratching more.
Malleability and Ductility: Pure copper is highly malleable (can be hammered into thin sheets) and ductile (can be drawn into thin wires) without cracking. Impure copper or alloys may be brittle, especially if they contain iron or lead.
Thermal and Electrical Conductivity: Pure copper is one of the best conductors of heat and electricity. A simple test: touch a heated metal object to the copper-pure copper will quickly transfer heat to your hand. For electricity, use a multimeter to measure resistance: pure copper will have very low resistance (e.g., ~1.72×10⁻⁸ Ω·m at 20°C); higher resistance suggests impurities.
(3) Chemical Tests
Magnet Test: Pure copper is non-magnetic. If a magnet sticks to the metal, it likely contains iron, nickel, or cobalt impurities (e.g., some copper-nickel alloys are magnetic). Note: This only rules out magnetic impurities, not non-magnetic ones like zinc or tin.
Nitric Acid Reaction: (Caution: Nitric acid is corrosive-wear gloves and goggles.) Pure copper reacts with concentrated nitric acid to produce a blue-green solution (copper nitrate) and brown fumes (nitrogen dioxide). Alloys may produce different colors: brass (copper-zinc) may yield a paler solution, while bronze (copper-tin) could form a milky precipitate.
Lead Acetate Test: To check for lead impurities (common in low-grade copper), rub the copper with a cotton swab dipped in lead acetate solution. If lead is present, the swab will turn black; pure copper leaves no color change.
(4) Advanced Analytical Methods (Laboratory)
Atomic Absorption Spectroscopy (AAS) or Inductively Coupled Plasma (ICP): These techniques quantify trace impurities with high precision, determining the exact percentage of copper (pure copper should be ≥99.9% copper).
X-ray Fluorescence (XRF): A non-destructive method that identifies elements in the copper by analyzing emitted X-rays, quickly detecting alloying elements like zinc, tin, or nickel.
2. What Do We Use Copper and Nickel For?
Uses of Copper
Electrical and Electronics Industry:
The single largest use of copper-its exceptional electrical conductivity (second only to silver) makes it ideal for:
Electrical wires and cables (power transmission lines, household wiring, Ethernet cables).
Circuit boards (copper traces connect components).
Motors, generators, and transformers (copper windings efficiently transfer electricity).
Plumbing and HVAC:
Copper's corrosion resistance (to freshwater) and malleability make it a standard for:
Plumbing pipes and fittings (resistant to rust and scale buildup).
Heat exchangers in air conditioners, refrigerators, and water heaters (excellent thermal conductivity transfers heat efficiently).
Construction:
Roofing and cladding (develops a protective green patina over time, durable for decades).
Architectural details (e.g., statues, domes-malleable for intricate designs).
Transportation:
Automotive: Copper wiring in engines, radiators (heat transfer), and EV batteries (current collectors).
Aerospace: Electrical systems and heat exchangers in aircraft.
Industrial Machinery:
Pumps, valves, and gaskets (corrosion resistance for fluid handling).
Bearings and bushings (low friction when lubricated).
Uses of Nickel
Stainless Steel Production:
~60–70% of global nickel is used to make stainless steel (e.g., 304 stainless steel contains 8–10% nickel). Nickel enhances corrosion resistance, ductility, and high-temperature strength-critical for:
Kitchen appliances (sinks, ovens), cutlery, and food processing equipment.
Construction (building facades, pipelines) and automotive parts (exhaust systems).
Batteries:
Nickel-metal hydride (NiMH) batteries (hybrid cars, portable electronics).
Lithium-nickel-cobalt-aluminum (NCA) and lithium-nickel-manganese-cobalt (NCM) batteries (electric vehicles, smartphones)-nickel boosts energy density.
Superalloys:
Nickel-based superalloys (50–80% nickel, plus chromium, cobalt, etc.) retain strength at 800–1200°C, used in:
Jet engine turbines and gas turbines (power plants).
Aerospace components (rocket engines, aircraft structural parts).
Plating and Coatings:
Electroless nickel plating (EN plating) on metals (e.g., steel, aluminum) to improve wear resistance, corrosion resistance, and solderability-used in electronics, automotive parts, and medical devices.
Alloys with Copper (Cupronickel):
Cupronickel (e.g., 70% copper, 30% nickel) is used for:
Marine hardware (ship hulls, propellers) and seawater pipes (resists saltwater corrosion).
Coinage (e.g., U.S. nickels are 75% copper, 25% nickel; Euro coins contain cupronickel).
Joint Uses (Copper-Nickel Alloys)
Heat exchangers for desalination plants (resists seawater corrosion and biofouling).
Electrical connectors in harsh environments (e.g., oil rigs, industrial settings)-combines copper's conductivity with nickel's corrosion resistance.
