Science1 course

Chemistry

Moles, molar mass, stoichiometry, solutions, gas laws and pH.

About Chemistry

Chemistry studies what substances are made of and how they change. A general chemistry course moves from atoms and the periodic table to bonding, the mole, balanced equations and stoichiometry, then on to gases, solutions, acids and bases, and energy changes in reactions.

Much of the course is quantitative. The mole links the mass you can weigh to the number of particles that react, so most calculations follow the same path: grams to moles using molar mass, moles to moles using the balanced equation, then back to grams, litres or concentration. Logarithms appear with pH, where $\text{pH} = -\log[H^+]$ .

Chemistry is used in medicine, nursing, pharmacy, cooking, manufacturing, environmental testing and materials science. Nurses calculate dosages with the same ratio reasoning as stoichiometry, and laboratory work in almost every science depends on preparing solutions of known concentration.

General Chemistry

Quantitative chemistry with dimensional analysis. (High school)

Moles and Molar Mass

Atoms are far too small to count individually, so chemists count them in moles. One mole is $6.022 \times 10^{23}$ particles, Avogadro's number. The molar mass of a substance, in grams per mole, is the sum of the atomic masses on the periodic table, so one mole of water ( $\text{H}_2\text{O}$ ) has a mass of about $2(1.008) + 16.00 = 18.02$ g.

Stoichiometry

Stoichiometry uses a balanced chemical equation as a recipe. The coefficients give mole ratios: in $2\text{H}_2 + \text{O}_2 \to 2\text{H}_2\text{O}$ , two moles of hydrogen react with one mole of oxygen to make two moles of water. Grams do not appear in the ratio, so every calculation goes grams to moles, across the ratio, then back to grams.

Gas Laws

Gases are described by four variables: pressure $P$ , volume $V$ , temperature $T$ and amount $n$ . The ideal gas law $PV = nRT$ ties them together, with $R = 0.08206$ L·atm/(mol·K). Boyle's, Charles's and Gay-Lussac's laws are special cases where some variables are held constant.

Acids, Bases and pH

Acids donate hydrogen ions (protons) and bases accept them, in the Brønsted-Lowry picture. Strength is about how completely a substance ionises in water, not how concentrated it is: hydrochloric acid ionises fully, while acetic acid in vinegar ionises only slightly.

Full General Chemistry course outline

How to study Chemistry

Balance every equation before using it; the coefficients are the mole ratios.
Use dimensional analysis and write units on every number so they cancel visibly.
Learn the patterns of the periodic table instead of memorising isolated facts.
Keep significant figures consistent with the data you were given.

Before you start: Algebra, ratios and scientific notation.
Where it leads: AP Chemistry, organic chemistry or biochemistry. Students heading toward nursing, pharmacy or medicine usually take general chemistry first, so a strong grasp of moles and solutions pays off quickly.

Key terms in Chemistry

Mole: A counting unit equal to $6.022 \times 10^{23}$ particles; molar mass converts between grams and moles.
Balanced equation: A reaction equation with the same number of each kind of atom on both sides, so mass is conserved.
Limiting reactant: The reactant that runs out first and therefore caps how much product can form.
Molarity: Concentration as moles of solute per litre of solution, $M = n/V$ , used in dilution and titration problems.
Equilibrium constant: The ratio $K$ of product to reactant concentrations at equilibrium, each raised to its coefficient; a large $K$ favours products.
pH: A log scale for acidity, $\text{pH} = -\log[\text{H}^+]$ ; each step of one unit is a tenfold change in hydrogen ion concentration.