Estonian Basic-School Chemistry Exam flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Density formula

Density equals mass divided by volume, ρ = m/V, typically in g/cm³. It lets you compare substances and predict whether an object floats or sinks in water.

Pure substance vs mixture

A pure substance has a fixed composition and sharp melting and boiling points. A mixture contains two or more substances that keep their own properties and can be separated physically.

Solubility of gases

The solubility of gases in water decreases as temperature rises and increases with pressure. This is why warm fizzy drinks go flat and why fish need cooler, oxygen-rich water.

Atomic number and mass number

Atomic number Z is the number of protons and fixes the element's identity. Mass number A is protons plus neutrons; the number of neutrons equals A minus Z.

Isotopes

Isotopes are atoms of the same element with the same proton number but different neutron numbers. They have identical chemical behaviour but slightly different masses.

Ionic versus covalent bonding

Ionic bonding transfers electrons from a metal to a non-metal, forming oppositely charged ions in a lattice. Covalent bonding shares an electron pair between non-metal atoms.

Group and period meaning

In the periodic table, the period number gives the number of electron shells and the main-group number gives the outer-shell electron count, which determines reactivity.

Balancing equations rule

Because mass is conserved, every element must appear with equal atom counts on both sides. Balance by changing coefficients only, never by altering chemical formulas.

Exothermic and endothermic reactions

Exothermic reactions release energy to the surroundings, raising the temperature, as in combustion and neutralisation. Endothermic reactions absorb energy, lowering the temperature, as in thermal decomposition.

Catalyst

A catalyst speeds up a reaction by providing an alternative pathway with lower activation energy. It is not consumed in the overall process and does not change the reaction's equilibrium position.

Combustion of hydrocarbons

Hydrocarbons burning in sufficient oxygen produce carbon dioxide and water. In limited oxygen, incomplete combustion also forms toxic carbon monoxide and soot.

Acidic and basic oxides

Non-metal oxides such as CO₂ and SO₂ are acidic and react with bases. Metal oxides such as CaO and Na₂O are basic and react with acids.

Metal activity series

Metals are ranked by reactivity, for example K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au. A more active metal displaces a less active one from its salt solution.

Acid and carbonate reaction

An acid reacting with a carbonate produces a salt, water and carbon dioxide gas. The gas turns limewater milky, which is the standard test for carbon dioxide.

Amphoteric oxide

An amphoteric oxide such as aluminium oxide or zinc oxide reacts with both acids and bases, forming a salt and water in each case.

Molar concentration

Concentration c equals the amount of solute in moles divided by the solution volume in cubic decimetres, c = n/V, expressed in mol/dm³.

Dilution equation

When a solution is diluted, the amount of solute stays constant, so c₁V₁ = c₂V₂. Adding solvent lowers the concentration while the moles of solute remain unchanged.

pH scale

pH measures acidity on a scale from 0 to 14 at 25 °C. Values below 7 are acidic, 7 is neutral, and above 7 is basic; each unit means a tenfold change in hydrogen-ion concentration.

Neutralisation reaction

An acid and a base react to form a salt and water. In ionic form the essential change is hydrogen ions combining with hydroxide ions to form water molecules.

Titration endpoint

The endpoint is where the indicator changes colour, ideally matching the equivalence point where acid and base have reacted in the mole ratio given by the balanced equation.

Alkanes and alkenes

Alkanes are saturated hydrocarbons with only single bonds and formula CₙH₂ₙ₊₂. Alkenes contain a carbon-carbon double bond and have formula CₙH₂ₙ.

Functional group

A functional group is the atom or group of atoms that determines a compound's characteristic reactions, such as hydroxyl in alcohols and carboxyl in carboxylic acids.

Ethanol oxidation

Ethanol can be oxidised to ethanoic acid, for example by air with bacteria or by oxidising agents. This is why opened wine turns sour over time.

Addition polymerisation

In addition polymerisation, unsaturated monomers such as ethene join without losing any atoms, forming a long-chain polymer like polyethene whose backbone repeats the monomer unit.

Fossil fuel fractions

Crude oil is separated by fractional distillation, based on differing boiling points, into petrol, kerosene, diesel and heavy residues used as fuels and raw materials.

Amount of substance formula

The amount in moles equals mass in grams divided by molar mass in grams per mole, n = m/M. Molar mass is the sum of relative atomic masses in the formula.

Molar volume of gas

At standard temperature and pressure, one mole of any gas occupies about 22.4 dm³, so n = V/22.4 when V is measured in cubic decimetres under those conditions.

Stoichiometric calculation steps

Balance the equation, convert the known quantity into moles, multiply by the mole ratio from the coefficients, then convert the result into the requested unit.

Limiting reactant

The limiting reactant is the reagent consumed first and therefore fixes the maximum amount of product. Product calculations must start from its amount, not from the excess reagent.

Haber-Bosch process

Nitrogen and hydrogen combine reversibly over an iron catalyst at high pressure and moderate temperature to make ammonia, the key feedstock for nitrogen fertilisers.

Hard water

Hard water contains dissolved calcium and magnesium ions. It forms scale in kettles and pipes and produces little lather with soap, but can be softened by ion exchange.

Eutrophication

Excess nitrate and phosphate from fertiliser runoff enter water, causing algal blooms. Their decomposition uses up dissolved oxygen, killing fish and other aquatic organisms.