Lab question: Based on HH equation, I used 40mL 0.15M dibasic phosphate solution and 60mL 0.15M monobasic phosphate solution to prepare targeted pH 6.7 buffer. But when I used pH meter to measure the pH of my buffer, pH was 6.51. I was confused about the difference. One reason I think is that when I prepared the stock solution: dibasic phosphate solution, I overshot water, so that the solution was diluted. Another reason may be the temperature? Because the room temperature was lower than the standard temperature(25degree I guess), the reaction favors reagent(monobasic phospate), the buffer had a lower pH than targeted? Is there any other reason accounted for that?