Chemistry Revision (Week 1)

A physical change can be reversed as the particles don’t change, just their arrangement or energy.

A chemical change is permanent and new substances are made.

Writing Equations

Reactants are the chemicals added together

(arrows mean changed)

Products are the chemicals made.

E.g Magnesium + Oxygen → Magnesium Oxide

Lead Ioxide → Lead + Iodine

Calcium Carbonate + Hyrdochloric Acid → Calcium Chloride + Carbon Dioxide

Conservation of Mass

  • The law of conservation of mass states that the mass of the reactant is equal to the total mass of the product + MASS CANNOT BE CREATED OR DESTROYED

If one of the reactant is air, the mass will appear to increase and if one is gas it may appear to decrease as some gas may float away.

Acids + Alkalis

An acid is a substance with a pH less than 7 (hyrdrochloric acid)

An alkali is a soluble base with a pH greater than 7 (sodium hyrdoxide)

Neutral is a substance with a pH of 7 (water)

(a base is a substance that can react with acids and neutralise them, most don’t dissolve (insoluble) but alkalis do.

  • Indicators are substances that change colour depending whether the solution is acidic or basic e.g. litmus paper, universal indicator.

Neutralisation

Neutralisation occurs when the same amount of acid and alkali are added together.

Acid + alkali → Salt + Water

Hydrochloric acids → Chloride salts

Nitric acids → Nitrate salts

Sulfuric acids → Sulfate salts

Example equation

Acid Alkali Salt

Nitric Acid + Calcium Hydroxide → Calcium Nitrate

Acids, bases and salts

  • Bases usually have metals at the start of their names like Calcium Carbonate, Aluminium Oxide.

Bases that dissolve in water are called alkalis + alkalis are usually hydroxide like Lithium Hydroxide, Sodium Hydroxide.

Notes

  • The pH scale goes from 0-14

  • Strongest alkalis have pH of 14. Strongest acids have a pH of 0.

  • A disadvantage of litmus paper is that it only tells you whether it is acidic or alkaline not how strong it is.

    Key Terms

INDEPENDENT VARIABLE = THE VARIBLE THAT IS CHANGED

DEPENDENT VARIABLE = THE VARIABLE THAT IS MEASURED

CONTOL VARIABLE = THE VARIABLE THAT STAYS THE SAME SO THE EXPERIMENT IS FAIR.