Chem practical Flashcards
titration table final —, initial —
READING!!!!!
Gas evolved format 4/5
- Effervescence is observed
- Moist R/B litmus paper turned B/R
- Gas is [colour] and [smell]
Colour: colourless, yellow (chlorine)
Smell: odorless? (Co2, H2, O2),
pungent (ammonia NH3, SO2) - Gas evolved is (name)
- If CO2: forms white ppt when bubbled into limewater
air hole for solids and liquids
Heating solids: air-hole fully opened. Heating liquids: air-hole half-opened.
test for oxidation agent
add reducing agent KI
ki is colourless and when added to an oxidizing agent, the solution turns brown as I- ion in KI is oxidised to I2 which is brown in colour
alternative: starch-iodine paper
test for reducing agent
solutions: add acidified KMnO4 which is an oxidising agent
gas: piece of filter paper soaked with acidified KMnO4
result: the purple acidified potassium manganate (vii) solution turns colourless because the purple mno4- ions are reduced to colourless mn2+
add acid, test for gases : 3
prepare to test for gases hydrogen, oxygen or carbon dioxide.
Acid is introduced: Expect effervescence and be prepared to test for CO₂ or H₂.
Only test for H₂ if an acid is added to a metallic solid. Hydrogen is unlikely a product of a reaction between two solutions. Possible, but unlikely. So test for other gases (probably CO₂) first.
planning steps 5
Ensure all apparatus are clearly stated
Steps
Observations
Conclusion based on results
include amount (mass/volume) of reagents used
insoluble chlorides
lead, silver
insoluble hydroxides
all expect grp1, first 2 of grp2, ammonium salts
insoluble nitrates
theyre ALL soluble bitch
insoluble sulfates
barium, calcium, lead
insoluble carbonates
all except grp 1 and ammonium
use decimals in calculation
DONT ANS IN FRACTIONS
dps for recording data
according to apparatus.
If calculated (eg.conc), 3sf.
If some data given, follow the dp
graph drawing axis reminders
label all the way on both axes
Remember sf/dp on axis numbers !!
Solid added to smt to form solution
state that solid DISSOLVES to give (colour) solution
solution colour change
Solution turns (original colour) to (new colour)
solution colour change
Solution turns (original colour) to (new colour)
ppt formed format 3
- (Colour) ppt formed
- Ppt is soluble/insoluble in excess
- (If any) solution turns (colour)
qa colours reminder
Colour dependent on QA notes- state clearly eg reddish-brown, light/dark blue. White, not cloudy white
experimental error colour change
subjective to observer
use colourimeter, compare to standards, use black or white tile to improve contrast
Paper chromatography steps 7
- using a pencil, draw a baseline on a rectangular strip of chroatography paper
- Sample spotted onto the baseline
- Entire paper inserted upright into a beaker containing a suitable solvent, ensuring baseline is above solvent level
- Once solvent is near paper edge, remove paper and mark out solvent front
- Measure dist between initial spot and final developed spot in the chromatogram
- Calc Rf value using dist travelled by solute/dist travelled by solvent
- Match unknown spot Rf value with database of Rf values of the sample
How to determine salt prep method
Soluble? No: precipitation
Both og mats sol in water? No: excess Yes: titration
Salts: Precipitation steps 4
- Add excess sol with anion to sol with cation (metal nitrate)
- Filter to obtain ppt (insol salt)
- Wash with distilled water to remove contaminants
- Leave ppt in cool dry place to dry
Salts: titration steps 8
A
1. Fill burearte with dilute acid. Note initial reading (V1)
2. Pipe the 25.0cm3 of alkali into con. flask
3. Add 1-2 drops of indicator eg methyl orange, sol turns yellow
4. Slowly add dilute acid until one drop causes the solution to change colour (end pt)
5. Stop adding hcl, record final reading (V2)
B
1. Pipette 25.0cm3 of alkali into con. flask
2. Add vol of acid req (V2-V1)
3. Allow salt sol to cool and crystallise
(NaCl: heat to dryness)
Salts: Reacting dilute acid w excess steps 7
- React excess metal with dilute acid. Stir until no more dissolved, effervescence stops
- Filter to remove excess unreacted metal. Filtrate is salt solution
- Heat salt solution to half vol to obtain sat. solution (glass rod test)
- Allow sat. solution to cool and crystallise
- Filter to obtain crystals
- Wash with distilled water (remove contaminants)
- Pat dry with filter paper
Heating sample for (time) may not suffice
not all decomposed … explain bow it affects calculations
If its the graph that intersects like ^
finding vol to neutralise is literally use the total minus whatever the other one is. They literally add up to like 50cm3 whats wrong with you
Used too little/ too much of a solution, describe effect
just sub into calc lower/higher and see where it goes
Why add EXCESS acid
ensure whole sample dissolves to form a solution AND ensure other ions eg… are reacted and removed from from the solution → wont affect final ppt
Why nitric acid and not hcl or h2so4
intro Cl and SO4 ions → may affect ppt result
Tests for purity
lower mp raise bp, paper chromatography
Too short heating time
heat for longer until constant mass obtained. Cool and weigh sample
more accurate
Use burette instead of measuring cylinder
thermometer but more accurate/ wont miss highest temp
Use temperature sensor with data logger
