Required practicals

Question 1

(1) Outline how to prepare a Standard Solution in a Volumetric Flask (for an acid-base titration).

Answer 1

1. Weigh the sample bottle containing the solid on a (2 dp) balance. (clean+dry)
2. Transfer solid to beaker and reweigh sample bottle.
3. Record the difference in mass.
4. Add 100cm^3 distilled water and stir with a glass rod until all the solid has dissolved.
5. Transfer to a volumetric flask with washings.
6. Make up to the 250cm3 mark with distilled water.
7. place stopper and Shake flask.

Question 2

(1) Outline how to carry out an acid-base titration.

Answer 2

1) Fill the burette with the solution
2) Pipette 25cm^3 of NaOH solution into a conical flask
3) use phenolphthalein as indicator
4) record initial burette reading
5) titrate and swirl solution till it changes colour
6) record burette reading
7) calculate change
8) repeat until two concordant results are obtained

Question 3

(1) Why do we use a white tile?

Answer 3

To see indicator colour change better.

Question 4

(1) Why is swirling necessary?

Answer 4

To ensure that solutions mix and so react completely.

Question 5

(1) Why is a conical flask used?

Answer 5

Can be swirled without losing any solution.

Question 6

(1) How did you eliminate any procedural errors?

Answer 6

1) Added the last 1cm^3 of water dropwise using a pipetter
2) Ensured meniscus was on the line when read at eye level
3) used distilled water to rinse

Question 7

(1) What would you use to rinse the pipette, burette and conical flask? (if dirty)

Answer 7

Sodium hydrogensulfate (burette)
Sodium hydroxide (pipette)
Distilled water (conical flask)

Question 8

(1) what was the main procedural error when carrying out the titartion? And how would you eliminate this error?

Answer 8

Determining the end point

Use a white tile so the colour change can be seen clearly and the endpoint can be determined more accurately.

Question 9

(1) Formula for procedural errors

Answer 9

(uncertainty/reading) x 100

Question 10

(1) why is phenolphthalein a better indicator for this experiment than methyl orange?

Answer 10

P: suitable for weak acid - strong base
MO: suitable for strong acid - strong base /
strong acid - strong base

Question 11

(1) What can be done to minimise any safety risks in this experiment?

Answer 11

• make sure eye protection is worn

- filling burette using a pipette

Question 12

There is a general trend for an increase in ionisation energy across period 3. Give one example of an element that deviates this trend.
explain why this deviation occurs (3)

Answer 12

Al: has an outer shell electron in 3p orbital, whereas Mg has 3S. 3p is further away from the nucleus.

S: Has spin pair repulsion but P there is no paired repulsion.

Question 13

Give an equation,including state symbols, to represent the process that occurs when the third ionisation energy of sodium is measured.

Answer 13

Na 2+(g) —–> Na 2+ (g) + e-

Question 14

The student uses a funnel to fill a burette with sulfuric acid before starting the titration. After filling, the student forgets to remove the funnel from the top of the burette.

suggest why this might affect the titre volume recorded?

Answer 14

A droplet might be stuck at the funnel, filling in the burette later increasing the volume.