I. Research Question:
How does increasing the temperature (40 – 80°C) of borate buffer solution (made up of 0.5 mol dm-3 boric acid and 0.5mol dm-3 sodium borate) affect the pH readings?
II. Background Information:
A buffer solution is one whose pH hardly changes with an addition of small amounts of an acid or base. A temperature change in the buffer solution will affect the Ka, Kb and Kw values; therefore it will affect the pH level as well. However each buffer is influenced in a different way.
A buffer is mixing an aqueous solution of a weak acid with a solution of its salt of a strong alkali, in this case:
H3BO3 (aq) with Na2B4O7·10H2O (aq)
An increase in the temperature of a borate buffer solution will cause the pH of the solution to decrease, which means that the buffer will become more acidic. Therefore, by changing the temperature of 0.5mol dm-3 sodium borate (salt of a strong alkali), the results may show a decrease in the pH if there is an increase in the temperature of the buffer solution.
III. Variables:
Independent
Variable
Units, range, uncertainty
Measured
Temperature of 25cm3 of 0.5 mol dm-3 sodium borate
°C
Boiling tubes containing 50cm3 of both boric acid and sodium borate will be placed in a water bath of specific temperature
20, 30, 40, 50, 60°C
±0.5°C
Dependent
Variable
Units, uncertainty
Measured
The pH calculated
pH
After the buffer solution has reached the desired temperature, the pH probe will be inserted into the boiling tube, which contains the buffer solution, and the pH is then noted down.
±0.01
Controlled Variables
Variable
How it will be controlled
Volume of boric acid and sodium borate used during the experiment will be 25cm3 each
The volume will be measured using a 50cm3-measuring cylinder (which has an uncertainty of ±0.1cm3) to measure out 25cm3 of boric acid and sodium borate each.
Concentration of boric acid and sodium borate are both at 0.5 mol...