Chapter 4 Acids and Redox Flashcards
What do all acids contain?
hydrogen -> release H+ ions into the solution when dissolved in water
Strong acid
Releases all its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solution
Weak acid
- Releases a small proportion of its available hydrogen atoms into solution as H+ ions
- Partially dissociates in aqueous solution
Example of a strong acid
hydrochloric acid
Example of a weak acid
Ethanoic acid -> only releases the H on the COOH group
Bases
A substance which readily accepts H+ ions
Examples of bases
- Metal oxide
- Metal hydroxides
- Metal carbonates
Alkali
- A soluble base
- Dissolves in water, releasing OH- ions into the solution
Neutralisation
- When the H+ ions (of an acid) react with a base to form a salt and neutral water
- The H+ ions from the acid are replaced by metal or ammonium ions from the base
Equations
- Metal + acid -> salt + hydrogen
- Alkali + acid -> water + salt
- Base + acid -> water + salt
- Carbonate + acid -> Water + carbon dioxide + salt
Titration
A technique used to accurately measure the volume of 1 solution that reacts exactly with another solution
What can titrations be used for?
- Finding the concentration of a solution
- Identification of unknown chemicals
- Finding the purity of a substance
Volumetric flask
Used to make up a standard solution very accurately
- come in different sizes
Process of preparing a standard solution
- The solid is weighed accurately
- Solid is dissolved in a break using a little distilled water
- This solution is transferred to a volumetric flask
- The last traces of the solution is rinsed with distilled water
- The flask is filled up to the graduation line (bottom of meniscus) on the volumetric flask with distilled water
- The volumetric flask is slowly inverted several times to mix the solution thoroughly
What would happen if you didn’t invert the volumetric flask
- Titration results would be inconsistent
Apparatus for acid-base titrations
- Pipette
- Burette
The acid-base titration procedure
- Add a measured volume of 1 solution to a conical flask using a pipette
- Add the other solution to a burette, and take the initial burette reading
- Add a few drops of an indicator to the conical flask
- Run the solution in the burette into the conical flask, and continuously swirl it to thoroughly mix the 2 solutions
- Continue until indicator changes colour = end point
- Record final burette reading
- Calculate titre = final burette reading - initial burette reading
- Repeat until results are concordant
The mean titre
- Only use concordant results to keep result accurate
Oxidation number
Based on a set of rules that apply to atoms
Oxidation number of elements
0
Oxidation number for compounds and ions
- Has an oxidation number
- The sign is placed before the number
Special cases
- H in metal hydrides
- O in peroxides
- O bonded to F
H in metal hydrides
-1
O in peroxides
-1
O bonded to F
+2
Calculating oxidation numbers
Sum of oxidation numbers = total charge
Oxidation
- Addition of oxygen
- Loss of electrons
- Increase in oxidation number
Reduction
- Loss of oxygen
- Gain of electrons
- Decrease in oxidation number
Oxidising agent
Facilitates oxidation by being reduces itself
Reducing agent
Facilitates reduction by being oxidised itself
Redox reactions
A reaction where both reduction and oxidation occur
What makes a titre more accurate
- Repeat until results are concordant
- Calculate mean titre from results
