Chemical industry:

Question 1

whats the test for nitrates?

Answer 1

nitrate(V):
* warm with
Devarda’s alloy
and NaOH.
* Test fumes with
damp red
litmus paper
* Paper turns blue
(ammonia is
evolved)
* Redox reaction –
Aluminium
reduces the
nitrogen

Question 2

what’s the test for ammonium ions:

Answer 2

NH4+:
* warm with NaOH.
* Test fumes with damp red litmus paper
* Paper turns blue (ammonia is evolved)
* Acid/base reaction
NH4+ + OH- → NH3 +H2O

Question 3

techniques and
procedures for
experiments on
reaction
kinetics – pH

Answer 3

Use a pH meter if there is a change in [H+] during the reaction.

(Not instead of gas collection if a gas is also made)
* Calibrate pH probe using 2 buffers with known pH
* Submerge the probe into the flask/beaker
* Add the other reactant, start timer
* Record pH every x seconds for x minutes

Question 4

techniques and procedures for
experiments on reaction kinetics –
colorimetry

Answer 4

• Select a filter which is the complementary colour to the solution
• Calibrate the colorimeter using the solvent.
• Mix reactants and start timer
• Quickly place a cuvette containing the reaction mixture into the colorimeter
• Measure the absorbance every x seconds for x minutes
• Plot a graph of absorbance/time
• Draw tangent at t=0
• gradient of the tangent will be proportional to the rate of reaction

Question 5

techniques and
procedures for
experiments on
reaction
kinetics –
chemical
analysis

Answer 5

• At regular intervals remove an aliquot of the reaction mixture
• Quench it (add Na2CO3 to neutralise acids, dilute with excess ice cold distilled water for
  alkalis)
• Titrate the aliquot with a known concentration of acid/alkali

this is done when there’s NO colour change, no pH change and no gas produced