4.2 Flashcards
Why is hydrated salts not good as a base for making a standard solution
What does efflorescent mean
This is because they lose a lot of their mass due to being water to the atmosphere as they are efflorescent.
This means their formula mass is VARIABLE
Why is sodium hydroxide NaOH not good for making standard solution
What does deliquescent mean
Sodium hydroxide absorbs moisture from the air (it’s DELIQUESCENT) so it also has variable formula mass, not goof
How to read burette
Get to eye level
- bottom of meniscus avoiding PARALLAX ERROR
- hold vertical
- add white sheet behind
- 0 and 5 second decimal place
Why adding water doesn’t affect titre
X
Read bottom meniscus, swirl, white tile etc
S
What is an acid , strong acid and weak acid
How represent strong and weak
Acid is that releases H+ ions as protons when dissolved in water
Strong acid is one that fully dissociates into H+ ions in aqueous solution
- represent by full arrow
Weak acid is one that partially dissociates into H+ ions in aqueous solution
- THIS REPRESENTED BY DOUBLE HALF ARROW
Examples of weak and strong acids
Weak
- organic are weak so ethanoic acid and other CARBOXYLIC ACIDS ARE WEAK
STRONG
- SHAND ACIDS ARE STRING + HCL
What is a base
What difference between bases and alkalis
Definition of alkali
What are examples of bases and alkalis out of three possible combos
A base is a substance that NEUTRALISES an acid to form a salt
2) alkalis are just bases that can dissolve in water, all alkalis are bases
3) Alkalis are bases dissolved into water that releases HYDROXIDE IONS
4)Metal carbonate, metal hydroxide , metal OXIDE = bases
Metal hydroxide = alkalis
What is a neutralisation reaction
Where a H+ ion from an acid and a OH- ion from a base react to produce water
A salt is also formed when the H+ reacts with the base
Three neutralisation reactions?
What is the state symbol of they are alkali ?
Metal hydroxide + acid = salt + water (this is alkali so always AQUEOUS )
Metal oxide + acid = salt + water (CAN BE SOLID )
Metal carbonate + acid = salt + water + carbon dioxide (CAN BE SOLID )
What did bronsted Lowry say about acids, strong and weak acids?
Acids are PROTON DONNORS
- strong acids FULLY ionise
- weak acid WEAKLY ionise
What is neutralisation reaction for carbonates
H+ + Co32-= Water and co2
What happens in PARTIAL NEUTRALISATION
Why is sodium hydrogen carbonate considered an acid salt? Made from partial neutralisation of carbonic acid and sodium hydroxide
1) Like only one of the Hydrogens are replaced !!!
2) One of the hydrogen from H2Co3 has been replaced with a metal, but still acts as an acid as has one hydrogen left to give
How can hydroxonium ions be made ?
Reactions of likeethanoic acid and water, acids are proton donnors so they will give a H+ to water marketing it H3O + which is dative
Oxidation number for elements and elements like diatomic bonded to themselves?
Compounds?
Ions?
1)0,
Anything like p8 h2 etc = 0
2) 0
3) charge in ion
Oxidation number for special case metal hydride H ?
Metal hydride H = -1
So NaH = -1
Oxidation number for special case O in peroxide’s?
O in peroxide’s = -1
Hydrogen peroxide =H2O2, so o is -1
Special case of oxidation O BONDED TO F
Like F2 O, O would be +2!!
What about oxidation states of transition metals
What a bout chlorine
They have variable oxidation which changes their colours
So like Mn+7 = can gain 5 electrons to become Mn+2
Chlorine can take different ones too
What is the oxidation number
A number representing how many electrons sn atom in a compound has gained or lost
What is a redox reaction
Where both oxidation and reduction happen in the same reaction
What does Roman numerals represent
Oxidation number on the atom that could change its oxidation number
Like nitrate (V) means N= +5
What are full definitions for reduction and oxidation!!!!
Reduction is reduce of oxidation number, or gain of electrons !
Oxidation is increase of oxidation number, or loss of electrons
What to remember when describing change of oxidation state for an atom in a reaction , do you balance!
Don’t have to balance, but later you can
And it’s shown on a SINGLE ATOM OF THAT ELEMENT!
Oxidising agent and reducing agent?
Oxidising agent is the one that gains / accepts electrons
Reducing agent is the one that gives / donates electrons
What happens in halogen displacement reactions?
More reactive one, the one higher, will displace lower reactive
What are titrations used for?
- finding PURITY
- concentration
- identification
How to prepare a standard solution?
FIRST RINSE EQUIPMENT with appropriate solutions
1) weigh the solid accurately (2dp)
2) dissolve in a beaker using less distilled water or other solvent then required for volumetric flask
3) ensure it is dissolved (may need to heat)
4) transfer this solution to the volumetric flask with a funnel. RINSE FUNNEL AND FLASK USING EXTRA SOLUTION (SO WATER HERE
5) invert and swish to mix
6) then fill to graduation line DROP BY DROP for bottom of meniscus
7) mix again
What are the error uncertainties for volumetric flasks 100 and 250 cm3?
Remember!
+- 0.2 cm3 for 100
+- 0.3 for 250 cm3
How to carry out a titration
1) using Pipette and Pipette filler take a known volume of standard solution and put into conical flask
2) fill up Barette attached to clamp stand. Record to nearest 2DP!
3) add a few drops of specific indicator to conical flask!!!
4) place white tile underneath and run a test run, swirling the solution every often . This gives rough titre, stop when colour change (end point)
5) NOW DO ACCURATELY! Add solution drop by drop as close to end point.
() repeat until get two concordant results (within 0.10 cm3 of each other)!
What are error uncertainties for Pipette?
10 and 25
10 = 0.04 25= 0.06
Error uncertainty for brütet 50cm3?
Why?
0.10cm3!
If resolution is 0.1cm3, uncertainty would be half
But because you measure this twice one up and one down, it becomes 0.1 (add)!!
How to accurately measure volume in Barette?
- read values bottom of meniscus
- ensure burette is clamped vertically
- use a WHITE SHEET OF PAPER BEHIND
Why is burette being used make experiment more accurate to compared to something else?!!!
- burette has mich higher resolution than like a measuring cylinder, resolution is 0.1cm3 compared to like 2cm3, so percentage uncertainty is less and so more accurate
Values won’t spread around the mean
How to increase reliability of the results for titration
Do concordant values , as these give a mean which reduces uncertainty and human error and is more accurate
What do you rinse the glassware out with
ONLY WITH THE REAGENT THAT WILL GO IN IT, OR ELSE THE AMOUNT OF MOLES WILL BE LESS AGAIN
Why do you need to remove funnel? What effect does it have?
Funnel will displace water causing it to go higher than it actually is + extra DRIPS STIL IN COUKD GO TO IT .
Thus your titre will actually be slightly lower than the real value !
What to make sure before running the burette
Make sure the air bubble goes so run it through so it goes all the way, otherwise your titre will be higher than it actually should be !
How to make titration more accurate
LEARN ALL
- pre rinsed equipment with high resolution = low percentage uncertainties
- use concordant titres for mean reducing human error
- small amount if indicator so moles aren’t affected
- white tile as background + bottom meniscus for accurate readings
- swirl conical flask so it mixes
- ensure no air bubbles remain
- remove funnels
- TOUCH BURETTE WITH SIDE IF FLASK WHILE EMPTYING TO GET LAST DROP IN!
What error is why you use bottom meniscus?
Parallax error
