Chem Practical

Question 1

Titration table?

Answer 1

Titration number
Initial burette reading /cm3
Final burette raring /cm3
Volume of (titrant) /cm3
Check out

Question 2

Redox Rxctns w/ KMnO4 / KI / H202

Answer 2

** If H2O2 is added
- Test for OXYGEN w/ glowing splint

1. KMnO4. It is OA
   - Test for RA
   - Purpler to colurless ++++
   - KMnO4 is reduced. RA is oxidised
2. KI. It is RA
   - Test for OA
   Colourless to brown +++
   - KI is oxidised. OA is reduced

Question 3

Effect of washing titration conical flask with water, titrant & analyte.

Answer 3

1. Washing with distilled water ONLY:
   - GOOD. No effective on results
   - Does not change number of reactant moles in the conical flask
   - Titration measures the endpoint based on moles, not based on dilution
2. Washing with titrant (solution from the burette)
   - BAD. Adds more moles of titrant than expected
   - Leads to lower than expected volume reading of titrant used
3. Washing with analyte (solution in conical flask)
   - BAD. Increases number of moles of reactant in conical flask
   - Titration reading higher than expected

Question 4

How to wash burette, pipers & conical flask

Answer 4

• Burette:
  Rinse w/ distilled water then titrant

Pipette
Rinse with water then analyte (solution for conical flask)

Conical flask
Rinse with water ONLY

Question 5

Reminder: Always link what Qn asked to titration results (Eg: More or less of solution XX)

Question 6

4/5 Common Sources of Error & Solutions (Them & Bio)

Answer 6

1. Thermometer reading is not accurate
   - Use a thermometer with a higher precision
2. Temperature of solution may changed over time
   - Use a thermostatically-controlled water bath OR Use a insulated beaker
3. Measuring cylinder is not accurate
   - Use burette or pipette
4. Hard to tell colour change of solution
   - Compare against a colour chart
5. (BIO) Cannot start/end experiment at the same time for all variables
   Eg: Can’t remove all potatoes from salt solution at exactly 5 min at the same time
   - Carry out experiments separately

Question 7

When to draw line graph touching origin?

Answer 7

When you are certain that a 0 value for IV will give you a 0 value for the DV

Question 8

Heating/ thermal decomposition table

Answer 8

Mass of empty test tube /g
Initial mass of beaker/container with XX /g
Final mass of beaker/container with XX after heating /g
Loss/gain in mass /g

Question 9

5 Observations for Heating Solids

Answer 9

Write down:
- initial colour of solid
- Gases produced
- final colour of solid
- Whether solid melts/change colour
- Whether condensation droplets form on sides of boiling tube

Question 10

5 Displacement Rxctns Observations

Answer 10

Write down:
- Initial Colour of solution?
- Final colour of solution?
- Formation of coloured ppt ?
- Test tube feels HOT/COLD?
- Any solid deposited onto more reactive metal ? (Metal displacement)

WRITE DOWN EVERYTHING

Question 11

Purpose of Cotton Wool in Acid carbonate rxctns

Answer 11

Allows CO2 gas to escape & prevents acid from splashing out of flask

Question 12

What are catalysts?

Answer 12

Catalyst are a substance that speeds up the ROR by finding an alternative pathway with lower activation energy. They remain chemically unchanged afterwards.

They are specific in action, sensitive to temp, pH and and made of proteins

Question 13

5 Rate of rxctn factors & Exp

Answer 13

1. Concentration (aqueous stuff only) OR Number of Moles of any substance (limiting or not)
   - Conc increase, ROR increase
   - More reactant particles per unit volume
   -Freq of effective collision increase
   - ROR increase
2. Catalyst
   - Increase ROR
   - Find alt pathway with lower act energy
   - More reactant particles ___ possess energy equal to or greater than act energy
   - Freq of effective collision between ___ increase
   - ROR increase
3. Temperature
   - Temp increase ROR increase
   - Reactant particles ___ gain heat and kinetic energy so they move faster
   - More reactant particles ___ possess energy equal to or greater than act energy
   - Freq of effective collision increase
   - ROR increase
4. Particle size (Solids)
   - Particle decrease, ROR increase
   - Lower PS increases SA to Vol ratio of solid reactant ___ in contact with reactant ___
   - Freq of effective collision increase
   - ROR increase
5. Pressure (gases)
   - Higher pressure
   - Reactant Particles ____ closer packed
   - More reactant particles per unit volume
   - Freq of effective collision between ____ increase
   - ROR increase

Question 14

NH3

Answer 14

Pungent, colourless gas turns damp red litmus paper blue

Question 15

O2

Answer 15

Colourless, odourless gas delights glowing splint

Question 16

Cl2

Answer 16

Pungent, greenish-yellow gas turns damp blue litmus paper red then bleached into white

Question 17

CO2

Answer 17

Colourless, odourless gas forms white ppt when bubbled into limewater

Question 18

Why is no indicator needed for titration of KMnO4 & Fe2+

Answer 18

The reactants and almost Colourless. One drop of KMnO4 / Fe2+ turns the solution from ___ to ___