R2.1

Question 1

properties of chemical reactions

Answer 1

• new substances are formed
• bonds in reactants are broken (endothermic change – absorption of energy)
• bonds in products are created (exothermic change – release of energy)
• stoichiometry

Question 2

stoichiometry

Answer 2

• fixed relationship between the particles of the reactants and products ⇒ no overall change in mass
• the simplest ratio of the number of moles of reactants and products in a chemical reaction
• the balancing numbers are known as the coefficients of the reaction

Question 3

types of chemical reactions

Answer 3

• synthesis reaction: A + B → AB
• decomposition reaction: AB → A + B
• single-replacement reaction: A + BC → AC + B
• double-replacement reaction: AB + CD → AD + CB
• neutralization reaction: HA + BOH → BA + H2O (acid + base → salt + H2O)
• combustion: X + O2 → XO
• polymerization
• redox reaction

Question 4

limiting reactant/reagent

Answer 4

= the reactant which will completely react, leaving other reactants unused, which will be left behind and is said to be in excess

Question 5

titration

Answer 5

• = chemical technique in which one solution is used to analyze another solution to find its concentration or amount
• form of volumetric analysis
• analyte = substance that is being analyzed, usually has an unknown concentration
• titrant = solution with a known concentration (in the burette)
• equivalence point ⇒ stoichiometric equivalence of reactants and products; acid is completely neutralized
• endpoint ⇒ color change

Question 6

acid-base indicators

Answer 6

• protonate or deprotonate in acidic/basic conditions ⇒ change their color
• phenolphthalein: acidic → transparent, basic → purple/pink

Question 7

back (indirect) titration

Answer 7

= technique used to determine the amount of a weak acid or base present in an impure sample
the analyte reacts with a strong acid/base, the excess is then titrated against a strong base/acid

Question 8

when is back titration used

Answer 8

one of the reactants is volatile
an acid or base is an insoluble salt
a particular reaction is too slow
direct weak acid against weak base titration