Unit D: Stoichiometry

Dissociation

A chemical compound breaks down into its separate ions

Reaction between ions

Formation of new species through ion exchange either through single/double replacement reaction

Spectator ions

Present in both reactants and products side

Precipitate

Solid product formed after ion exchange in a reaction

Complete Chemical Equation

• shows all reactants and products as if they were intact compounds that has not dissociated in solution

Ionic Equation

• Shows all the high solubility ionic compounds dissociated into ions

Qualitative Analysis

• determined through experiment on what kind of substance is present in a sample

Quantitative Analysis

• calculation that allows you to see how much substance there is in a sample

Ion Colour Solution

• a certain ion is present in solution (adds colour)

Flame Test

• some metal ions react with heat

  Shows a distinct colour

• Ions heated = electrons excited, thus high in energy, occupies highest energy level

Precipitate

• Double replacement reaction forms a solid product

Stoichiometry

• predicting the quantity of a reactant/product by using another quantity of a reactant/product in the same reaction

Gravimetric Stoichiometry

• m=nM

• r/g

Solution Stoichiometry

• concentration

• m = nM

• r/g

• C = n/v

Gas Stoichiometry

• utilize gas formula and charts

Limiting Reactant

• the reactant in the chemical product that is completely consumed

  • can determine the maximum quantity of a product

• reactant = fewer moles of products, produces lowest mass of a product

Oxygen as a limiting reactant

• combustion can go from CO2 to CO

Excess Reageant

• the reactant that remains after a reaction is complete

Predicted Yield

• Expected quantity of a product formed from a reaction

  • Stoichiometry Calculations ( theory )

Actual Yield

• Quantity of a product that was actually used up

Competing Reactions

• some reactants can react to form different products

• experimental yield of any substance will always be less than predicted

Limiting Experimental Yield

• Slow reaction = insufficient time allowed for competition ( yield is less than predicted )

• Collection and Transfer Methods = small losses in products due to transferring & collecting precipitate

  • When rinsing = product lost

  • Solids stick to the surface = lost

• Reactant Purity = Reactants are rarely 100% pure, thus it contains small amounts of contaminants

• Reactions that do not proceed to completion = Reactions reach a point of EQB before all reactants are converted into products

Percent Yield

• Amount of quality product actually obtained as a percentage

Acid-Base Titrations

• Titration is used to find the concentration of a solution by quantitatively observing the reaction with a solution of known concentration ( standard solution )

• Solution that is added in known volume = titrant, and always provided with a concentration

Standardization

• Using a standard solution to determine the concentration if another solution through titration

• Establishing its concentration by analyzing the reaction with a substance with a known purity ( standard )

Equivalence Point

• Reaction is complete

• Moles of Acid = Moles of Base

Standardizing Acids

• Used because the pH changes overtime

• Sodium Carbonate

Standardizing Bases

• Used because they tend to absorb carbon dioxide from the air

• changes concentration of base ( decreases pH, more acidic )

• strong base = potassium hydrogen pnthalale

End point

• Intermediate colour change

Acid-Base Indicators

• Indicate chemical change and colour change over a specific pH range

• Indicators are usually weak monoprotic acids, that do not ionize greatly in acidic solutions, but ionize greatly in basic solutions

Acid-Base Titration Curve

• Strong monoprotic acids have a pH less than 7

• Strong monoprotic bases have a pH greater than 7

Adding base to an acid will increase its equivalence, and pH will increase to the pH of titrant base

*Vise versa with acids

Net Ionic Equation

Shows all the actual chemical change that occurs