CPrac A - General

Titration table

Titration number	1	2
Final burette reading / cm^3
Initial burette reading / cm^3
Volume of _ used / cm^3
Best titration results (✔)

Mass reading recording

Mass of salt used = 2.300g (tared)

Heating (water of crystallisation) table

Temperature change table

Highest / lowest temperature reached / degrees
Initial temperature / degrees
Temperature change / degrees

1. ALL temp related graph , origin is a point 

2. Line : does NOT mean straight line , can be CURVE or STRAIGHT 

• Draw a straight line of best fit

How to find gradient and average rate, which variables on which axis

• Dependent variable : y-axis 

• Independent variable : x-axis

1. Finding gradient : choose 2 points far apart -> reduce % uncertainty in calculation of gradient 

2. Average rate OVER 7 min (find gradient at 7 min DO NOT draw tangent)

Describing error: time taken for reaction (what is measured?) is subjective as it is difficult determining exact movement when insert is obscured NOT it is subjective 

Describe error stopwatch + modification

• Human reaction time (NOT human error) when starting and stopping the stopwatch leading to inaccurate time measurement 

• Modification: repeat -> average -> reduce % of human reaction time error 

Describe error % purity

The impurities inside sodium hydroxide might react with the hydrochloric acid and this will result in higher volume of hydrochloric acid recorded. The percentage purity would have been higher than the expected percentage purity

Describe error Heat loss to surrounding + modification

• To reduce heat loss to the surroundings, the boiling tube can be insulated

• This can be done by wrapping the boiling tube with a towel and holding it using a rubber band (NOT wet towel)

• Use a lid to cover the cup to prevent heat loss from the top -> ∆T measured -> enthalpy change of neutralisation be more accurate

• Switch off the fans and stand the apparatus in a metal shield to reduce heat loss due to draughts

1. Impurities reduce the actual amount of Na2CO3, lowering the concentration of Na2CO3 -> larger volume of FA 3 is required to react with the H2SO4

2. Attach a syringe to the conical flask

H2O2 and ethanoic acid safety hazard

H2O2 and ethanoic acid are corrosive chemicals, so gloves and safety goggles should be worn during the experiment to minimise contact of chemicals with our skin and eyes

Those how this method value is lower than true value 

1 step at a time: lower temperature recorded -> lower heat change -> lower enthalpy

Describe test to find purity of substance 

Heat a small sample of the substance to determine the melting point. If the solid has a fixed melting point , it is pure. If it melts at a temperature lower than melting point or over a range of temperature , it is not pure

Suggest the advantage of using this modified conical flask instead of the original one

The reaction can be started by tipping the flask, thus do not have to replace the bung and no gas escapes -> all H2 gas produced can be accurately collected and measured

Check for purity 

• Solid sample -> check for mp NOT chromatography

• Liquid sample -> check for bp