Chapter 4 Flashcards
Acids and Redox
What is ionic equation ? What does it show ? How do you write one ?
When solutions of different ionic substances are mixed, precipitation sometimes occurs.
An ionic equation shows how ionic substances react as independent ions in solutions.
Separate all ionic aqueous substances into ions
Identify spectator ions ( those present on both sides ) and remove them.
What happens when ionic solids dissolve in water ?
The ions become surrounded by water molecules and
become hydrated (or ‘solvated’).
- O atoms in water molecules are attracted to the
cation.
+ H atoms in water molecules are attracted to the
anion.
The ions are separated and behave independently:
NaCl (s) → Na + (aq) + Cl - (aq)
Ionic solids dissolve in water when the attraction between the polar
water molecules and the ions is sufficient to overcome the attraction
between the ions in the solid lattice.
In solution the individual ions are surrounded by water molecules and are independent of each other.
Are all alkali metals and nitrates ( examples of ionic solids ) soluble or insoluble ?
Soluble
Formula for common acids : Hydrochloric, sulphuric, nitric and ethanoic acids
HCl, H2SO4, HNO3 and CH3COOH
Formula for common alkalis : sodium hydroxide, potassium hydroxide and ammonia
NaOH, KOH, NH3
What do acids release in aqueous solution ?
H+ ions. All acids contain a hydrogen atom which can be lost from the molecule as H+ ions.
What do alkalis release in aqueous solution ?
OH- ions.
Acid definition
Substance that produces hydrogen ions in solution. H+ donors
Base definition
Substance that neutralises an acid to produce a salt. H+ acceptors.
Alkali definition
A soluble base that dissolves in water to form hydroxide ions. H+ acceptors
What are the 4 different types of bases ?
Hydroxides, oxides, carbonates and ammonia.
What is a strong acid ?
Good donors of H+ ions, fully dissociate in aqueous solution ( water )
What is a weak acid ?
Bad donors of H+ ions, partially dissociate in aqueous solution ( water )
Salt definition
It is the product of a reaction where by H+ ions are replaced by metal or ammonium ions.
Neutralisation definition
A chemical reaction in which an acid and a base react together to produce a salt
Neutralisation equation
Reaction of H+ and OH– to form H2O
Name the products when an acid reacts with :
Base
Alkali
Metal
Carbonate
Salt + Water
Salt + Water
Salt + Hydrogen
Salt + Water + Carbon dioxide
How to calculate percentage error ?
( uncertainty in measurement / actual measurement ) x 100
How do you make a standard solution and carry out a titration ?
1) Calculate the amount of solid required and weigh it out
2) Place solid in beaker and dissolve in small volume of solvent
3) Transfer solution to volumetric flask using funnel
4) Rinse breaker and rod into volumetric flask
5) Fill volumetric flask to just below the graduation mark using a wash bottle
6) Use teat pipette to carefully add solvent to bring level up to the mark
7) Stopper the flask and invert to ensure thorough mixing
Using a burette : rinse equipment with solution you are using
Always use funnel to fill burette but remove it afterwards
After taking initial reading run the solution into the conical flask whilst swirling it until colour appears to be changing then add drop wise until one more makes the colour change permanently.
Read burette from bottom of miniscus quoting to 2dp
Need at least 2 concordant results ( within 0.10cm3 of each other )
Indicators used in titrations : phenolphthalein and methyl orange
phenolphthalein = titrating weak acid and strong base
methyl orange = titrating strong acid and weak base
Titration calculations method
Write balanced equation
Calculate moles of one substance using info in question
Calculate moles of other substance using ratio
Calculate concentration using c = n/v
Oxidation number rules
1) Oxidation number of atoms in elements is always zero
2) Group 1 = +1, Group 2 = +2
3) Zn = +2, Al = +3, F = -1
4) H = +1 ( except when in groups 1, 2 or with Al )
5) Oxygen = -2 ( except with F and in peroxides )
6) Chlorine = -1 ( except when with O and F )
Oxidation numbers in a compound
Have to add up to zero
Oxidation numbers in an ion
The sum of all the oxidation numbers is equal to the charge on the ion.
Naming compounds using oxidation numbers
Roman numerals are used to indicate the magnitude of the oxidation number when an element may have compounds/ions with different oxidation numbers
Using oxidation number to decide whether oxidation or reduction has taken place
If element becomes more positive during reaction, it has been oxidised so it has lost electrons.
If element becomes less positive during reaction, it has been reduced so it has gained electrons.
Oxidation and Reduction in terms of electrons
OILRIG
Oxidation is loss of electrons
Reduction is gain of electrons
How you work out oxidation numbers and how they change in reactions
i). Ignore the multipliers in the equation (equations don’t even need to be balanced!!!)
ii). Use what you know to work out what you don’t know.
iii). Use total oxidation numbers to help you work out unknown oxidation numbers
iv). Clearly state what the starting and finishing oxidation numbers are.
