Physical & Chemical Changes
Melting wax and dissolving sugar are similar because both are this type of change.
Physical change
Water can be separated into hydrogen and oxygen only by this type of change.
Chemical change (electrolysis)
An atom is neutral because numbers of these particles are equal.
Protons and electrons
Difference between 2H2O and H2O2.
2 water molecules vs hydrogen peroxide
Metals conduct due to these mobile particles.
Copper powder turns black on heating. This indicates formation of this substance.
Copper oxide
Name the type of substance: brass
Mixture (Alloy)
Mass of atom is mainly concentrated in this region.
Nucleus
Formula: 2 Al atoms and 3 O atoms combined.
Al2O3
Why are non-metals not malleable?
Brittle structure
A change produces a gas but no new substance is formed. Give one example.
Boiling water / releasing dissolved gas
Why is air not considered a compound?
Components not chemically combined; variable composition
Electronic configuration of P.
2, 8, 5
Balance: H2 + O2 → H2O
2H2 + O2 → 2H2O
Property where graphite differs from other non-metals.
Conducts electricity
Why is rusting considered a chemical change even though it occurs slowly?
New substance (iron oxide) forms
A substance has fixed melting point and cannot be separated physically. Identify it.
Compound
Why do atoms of same element have identical chemical properties?
Same number of electrons
Balance: Na + Cl2 → NaCl
2Na + Cl2 → 2NaCl
Why copper used for wiring instead of sulphur?
Copper conducts, ductile; sulphur brittle
One similarity and one difference between burning Mg and candle wax.
Both chemical; Mg → solid ash, wax → gases
Mixture: iron filings, sand, salt. First separation step?
Magnetic separation
Atom: 17 protons, 18 neutrons. Element and mass number?
Chlorine, 35
Balance: Al + O2 → Al2O3
4Al + 3O2 → 2Al2O3
A cookware manufacturer must choose between copper and graphite to make the base of cooking pans so that heat spreads quickly and evenly.
Which material is most suitable and why?
Copper, because it has very high thermal conductivity and is a metal suitable for cookware, whereas graphite is brittle and unsuitable structurally.