Method:
- A 250 mL volumetric flask was weighed with it’s mass recorded
- A 10mL measuring cylinder was used to pour 5mL brick cleaner into the volumetric flask. The flask was stoppered straight after all the brick cleaner was in the flask.
- The flask was then reweighed
- De-ionised water was added until the flask was about half full. The flask was stoppered and shaken carefully upside down several times.
- More water was added to the flask about a cm below the graduation line. A dropper was used to accurately drop the right amount of water to the flask so the bottom of the meniscus was on the graduation line.
- A 20mL pipette was used to put 20mL of sodium carbonate solution into each of the four 100mL conical flask. 3 drops of methyl orange indicator was added to each.
- The burette was filled with the solution of brick cleaner.
- The sodium carbonate solution was titrated with the solution of brick cleaner until there was a clear permanent colour change.
- Steps 7 and 8 were repeated until 3 concordant results were
Results:
Calculations:
On page attached.
Discussion:
The weight for the brick cleaner may not be 6.00g as the volumetric flask was not weighed again with the brick cleaner in it because that step was forgotten. So the result above was taken from another student that did the prac. This will affect the results as the mass of the brick cleaner is used to determine the percentage by mass of HCL in brick cleaner. All 3 titres show that they are only within 0.1 of each other. The hypothesis has been disproved because it was suggested the 30% of HCL would be in brick cleaner and there’s only 2.4% although it’s not certain that those steps were done correctly. There were no problems encountered during this prac.
Focus Questions:
8)a) the manufacturer says that brick cleaner is made up of around 35% HCL, which is a massive difference to the answer that was got in this prac but again question 7 was not done correctly.
b) differences in class results occur because not everybody would have done the exact volume of brick cleaner, sodium carbonate etc as each other therefore the difference in results obtained.
9) To correctly clean up a spill of 20mL brick cleaner you would mop it up immediately, washing it away with massive amounts of water
10)a) volumetric flask= once with water twice with brick cleaner
b) Burette= once with water twice with diluted solution of brick cleaner
c)pipette= once with water twice with diluted brick cleaner
d) conical flask=once with water twice with sodium carbonate solution
Conclusion: To conclude, there should be 35% HCL in brick cleaner although it was found that there was only 2.4%