Question

State two reasons for supposing that brass is a mixture and not a compound.

Answer 1

Hint: A metal admixture, or a metal mixed with one or more other components, is known as an alloy. Combining the metals gold and copper, for example, yields red gold, gold and silver yields white gold, and silver mixed with copper yields sterling silver. Steel and silicon steel are alloys made by combining iron with nonmetallic carbon or silicon. The resultant combination has characteristics that are often different from those of pure metals, such as added strength or hardness.

Complete answer:
Brass is a copper-zinc alloy with variable amounts of copper and zinc to produce different mechanical and electrical properties. It's a substitutional alloy, which means the atoms from the two constituents will swap places within the same crystal structure.
Brass's structure, which is usually 66 percent copper and 34 percent zinc, makes it a good choice for copper-based jewellery because it is more corrosion resistant. Brass is often used in conditions where sparks are a concern, such as fittings and instruments used near flammable or explosive materials.
Compounds are substances that can be created by adding two or more elements chemically. Mixtures are compounds that are created by combining two or more substances physically. Covalent compounds, metallic compounds, and ionic compounds are the three groups of compounds.
Since the elements in a compound must be in definite proportions and chemically bonded to each other, brass is a mixture rather than a compound.
In contrast, the two elements Zn and Cu in brass are not in fixed proportions (they can combine in any ratio) and have no chemical bonding.
To summarise, brass is a combination because:
1. Its composition is not set.
2. It demonstrates the characteristics of its constituents.

Note:
Lead is often applied to brass in quantities of about 2% to improve its machinability. Since lead has a lower melting point than the other constituents of brass, when it cools from casting, it continues to move into the grain borders in the shape of globules. The globules' pattern on the brass surface raises the available lead surface area, which influences the degree of leaching. Cutting operations will also smear the lead globules around the soil. These effects can cause substantial lead leaching even in brasses with low lead content.