Data processing 1
What is the unit of reaction rate in this experiment?
s⁻¹ (per second)
What mole ratio is used in HCl–NaOH titration?
1 : 1 mole ratio
(HCl reacts with NaOH in equal moles.)
What happens when too much NaOH is added into HCl analyte in the flask?
Mixture turns dark purple and the endpoint is not accurate --> inaccurate calculation to determine the concentration of HCl
How does poor mixing affect reaction time?
Reaction appears slower than it actually is
(Reactants are not evenly distributed.)
What chemical process occurs in the identification reactions of aldehyde and ketone?
Oxidation–reduction (redox) reactions
How does doubling concentration affect collision frequency?
Collision frequency doubles
(More particles per unit volume → more frequent effective collisions.)
How is reaction rate calculated from time data?
Reaction rate is calculated as 1 ÷ time taken
What happens if the burette is not rinsed with solution?
The solution in the burette becomes diluted
(This gives an incorrect titre volume.)
How does parallax error affect volume readings?
Volume is read too high or too low
(Due to misalignment of the eye with the meniscus.)
What reaction happens to Tollens' reagent when it reacts with aldehyde?
reduction
Why is 1/t used instead of t?
Because shorter time means faster reaction
(1/t increases as rate increases, making trends clearer.)
Why is volume converted to dm³ in calculations of titration?
Because concentration is defined in mol dm⁻³
Why should heating be gentle in Fehling’s test?
Overheating can cause false positive results
(Cu²⁺ may decompose even without an aldehyde.)
What error occurs if stopwatch is started late?
Measured reaction time is too short
(Rate is incorrectly calculated as too fast.)
One of these:
- Because it is highly unstable and decomposes over time, losing its effectiveness.
- The reagent decomposes to form explosive silver nitride
Calculate the concentration of HCl if 12.50 mL of 0.100 M NaOH is used.
0.125 M
(Moles NaOH = 0.100 × 12.50/1000 = 0.00125 mol; 1:1 ratio; HCl volume = 0.010 L)
Which titration reading should be discarded and why?
The rough or anomalous titre
(It is less accurate or inconsistent with other results.)
Why must total volume remain constant in concentration experiments?
Changing volume changes concentration
(This introduces another variable affecting reaction rate.)
What happens if Tollens’ reagent is old?
It may fail to produce a silver mirror
(Old Tollens’ reagent decomposes or gives false results.)
What is produced in the reduction of Fehling reagent by aldehyde?
Cu2O (copper(I) oxide)
Why is the average titre used instead of a single value?
To reduce random error and improve accuracy
(A single titre may be affected by technique or endpoint judgment.)
How does temperature affect kinetic energy?
Temperature increases kinetic energy
(Particles move faster and collide more energetically.)
Why does excess indicator affect endpoint accuracy?
Indicators are weak acids or bases
(Excess indicator adds extra H⁺ or OH⁻, shifting the endpoint.)
Why must NaOH be kept covered?
Why must NaOH be kept covered?
Complete the following reaction equation of oxidation of aldehyde using Fehling reagent: RCHO + 3OH− → _________ + 2H2O + ______
RCHO + 3OH− → RCOO− + 2H2O + 2e−