required practical 9: Investigating PH changes Flashcards
What do you do in this practical
Investigate how PH changes when a weak acid reacts with a strong base, and when a strong acid reacts with a weak base
How do you calibrate a PH probe
How do you make a graph
. Rinse probe with deionised water and shake gently to remove excess water
. Place probe in standard PH 7 solution provided. Record the PH reading and ensure the bulb is fully immersed
. Repeat process with PH 4 and PH 9.2 buffer solutions. Record PH readings.
Make sure to rinse probe with ionised water between readings
. Then plot a graph of recorded PH reading on x axis against PH of buffer solution on Y axis
If experiment is with ethanoic acid and NaOH, how do you start it off to get one beaker of ethanoic acid, and a burette of NaOH
. First rinse burette with 0.1moldm-3 of ethanoic acid, and then fill burette with this solution. Label the burette.
. Then using the burette, transfer exactly 20cm^3 of it to a clean 100cm^3 beaker
. Then rinse a second burette with 0.1moldm-3 NaOH solution, and fill it up with it. Label this burette.
What precaution should you take when filling up burette
Ensure the jet of burette is filled without any air bubbles
What is the next stage of experiment to set up PH probe
. Rinse PH probe in deionised water and clamp it so the bulb is fully immersed in ethanoic acid solution in beaker
. Use a rod to stir solution gently and record PH reading in suitable table
Describe titration part of experiment
. Add 2cm^3 of NaOH from burette at a time.
Stir solution and record PH alongside each volume of NaOH added
. After this keep adding 2cm^3 of NaOH until it is in excess. Stir solution and keep recording PH alongside volume added.
These results allow a PH curve to be added
How do you analyse the data you have gotten from experiment
. Use PH probe calibration graph to adjust the PH readings obtained from experiment.
These correct PH readings should be entered into a new column in table of results
. Plot a graph of corrected PH values (y axis) against volume of NaOH added
. Join the points in an appropriate way eg a curve
Why does PH probe need to be calibrated
To ensure that all PH values for each PH reading is accurate
What is accuracy
The more accurate the data, the closer it is to the true value
Why do you stir solution whilst adding NaOH
To ensure all acid and alkali mixes so PH doesn’t significantly vary throughout solution as this would give an inaccurate reading
