RP7 - measuring the rate of reaction : by an initial rate method

Question 1

what is the common clock reaction

Answer 1

H2O2 + 2H+ + 2I- => I2 + 2H2O
2S2O3 2- + I2 => 2I- + S4O62-
when I2 produced has reacted with all of the limited amount of thiosulfate ions present , excess I2 remains in solution . Reactions with the starch then suddenly forms a dark blue black colour .

Question 2

what’s the typical method for the continuous monitoring method

Answer 2

• measure 503 of the 1.0 moldm-3 hcl and add to conical flask
• set up gas syringe in stand
• weigh 0.2g of magnesium
• add the magnesium ribbon to the conical flask , place bung firmly into the top of the flask and start the timer .
• record volume of hydrogen gas collected every 15 seconds for 3 mins

Question 3

what are techniques to investigate rate of reaction

Answer 3

-measurement of change in volume of gas
- measurement of change of mass
- titrating samples of reaction mixture with acid , alkali , sodium thiosulfate etc
- colorimetry
- measuring change in electrical conductivity
- measurement of optical activity

Question 4

how do you investigate rate of reaction using measurement of change in volume of a gas

Answer 4

this works if there’s a change in the number of moles of gas in the reaction . Using a bad syringe is a common way of following this

Question 5

how do you investigate rate of reaction using measurement change of mass

Answer 5

this works if there’s a gas produced which is allowed to escape . Works better with heavy gases such as CO2

Question 6

how do you investigate rate of reaction titrating samples of reaction mixture with acid , alkali , sodium thiosulphate

Answer 6

small samples are removed from the reaction mixture , quenched and then titrated with a suitable reagent

Question 7

how do you investigate rate of reaction using colorimetry

Answer 7

if one of the reactants or products is coloured then colorimetry can be used to measure the change in colour of the reacting mixture

Question 8

how do you investigate rate of reaction using measuring change in electrical conductivity

Answer 8

can be used if there is a change in the number of ions in the reaction mixture

Question 9

how do you investigate rate of reaction using optical activity

Answer 9

if there is a change in the optical activity through the reaction this could be follow r in a polarimeter