Required practical 9

Question 1

Why do we calibrate a pH meter

Answer 1

To ensure we get accurate and reliable values

Question 2

Calibration - step 1

Answer 2

Rinse the pH meter thoroughly with distilled water and shake gently to remove excess

Question 3

Calibration - step 2

Answer 3

Place the pH meter into the standard pH 7.00 buffer solution and record the pH

Question 4

What should be checked about the bulb

Answer 4

That it is fully immersed in the solution

Question 5

Calibration - step 3

Answer 5

Repeat this with the standard buffer solutions of pH 4.00 and pH 9.20

Question 6

What should be done between each solution

Answer 6

Thoroughly rinse the pH probe with distilled water

Question 7

Calibration - step 4

Answer 7

Plot graph of pH reading (x axis) against actual pH (y axis)

Question 8

What does calibration graph allow us to do

Answer 8

Concert pH readings into more accurate pH values

Question 9

Practical - step 1

Answer 9

Rinse and fill a burette with 1.0moldm-3 ethanoic acid solution

Question 10

Practical - step 2

Answer 10

use the burette to transfer exactyl 20cm3 ethanoic acid into a clean, dry 100cm3 beaker

Question 11

Practical - step 3

Answer 11

Rinse and fill a second burette with 1.0moldm-3 NaOH solution

Question 12

Practical - step 4

Answer 12

Rinse pH meter with distilled water and clamp it so that the bulb is fully immersed in the ethanoic acid solution in the beaker

Question 13

Practical - step 5

Answer 13

Use a rod to gently stir the solution and record the pH

Question 14

Practical - step 6

Answer 14

Add 2.0cm3 NaOH from the burette at a time, stir and record the pH

Question 15

Practical - step 7

Answer 15

As the equivalence point is being reached, add the NaOH solution 0.2cm3 at a time

Question 16

Practical - step 8

Answer 16

After the equivalence point, continue to add the NaOH 2.0cm3 at a time

Question 17

What does continue to add the NaOH after the equivalence point allow

Answer 17

A pH curve to be plotted

Question 18

Analysis - step 1

Answer 18

Use the calibration graph to adjust the pH reading

Question 19

Analysis - step 2

Answer 19

Plot a graph of the new pH values (y axis) against volume of NaOH (x axis)

Question 20

Analysis - step 3

Answer 20

Join the dots in a curve