🧪 (chemistry s2)

what is an element?

A pure substance that cannot be broken down into simpler substances by chemical processes, made of only one type of atom.

Compound

A pure substance containing two or more elements chemically combined in a fixed ratio.

Mixture

A substance consisting of two or more elements or compounds that are physically mixed together in any ratio without chemical bonds.

Atom

The smallest component of an element that retains its chemical identity and properties.

Molecule

A neutral particle composed of two or more atoms held together by chemical bonds.

Proton

A positively charged subatomic particle located in the nucleus of an atom.

Neutron

A subatomic particle with no electrical charge located in the nucleus of an atom.

Electron

A negatively charged subatomic particle that moves around the atomic nucleus in shells.

Atomic number

The total number of protons found in the nucleus of an atom.

Mass number

The total number of protons and neutrons combined in an atomic nucleus.

Subatomic particles of an atom

Protons (relative charge $+1$, relative mass $1$), neutrons (relative charge $0$, relative mass $1$), and electrons (relative charge $-1$, relative mass $\frac{1}{1840}$).

Proton number

The number of protons found in the nucleus of an atom.

Nucleon number

The total number of protons and neutrons in the nucleus of an atom.

Acid

A substance that produces hydrogen ions, $H^+$, when dissolved in water, having a pH of less than $7$.

Alkali

A soluble base that produces hydroxide ions, $OH^-$, when dissolved in water, having a pH greater than $7$.

Products of an acid-metal reaction

A salt and hydrogen gas: $\text{Acid} + \text{Metal} \rightarrow \text{Salt} + H_2$.

Products of an acid-carbonate reaction

A salt, water, and carbon dioxide gas: $\text{Acid} + \text{Carbonate} \rightarrow \text{Salt} + H<em>2O + CO</em>2$.

Products of a neutralisation reaction

A salt and water: $\text{Acid} + \text{Base} \rightarrow \text{Salt} + H_2O$.

Test for hydrogen gas

Place a lighted splint at the mouth of the test tube; it extinguishes with a 'pop' sound.

Test for carbon dioxide gas

Bubble the gas into limewater; a white precipitate is formed.

Separation technique for an insoluble solid from a liquid

Filtration.

Separation technique for a pure solvent from a solution

Simple distillation.

Separation technique for miscible liquids with different boiling points

Fractional distillation.

Separation technique for identifying different pigments or dyes

Paper chromatography.