Methods of measuring the rate of reaction

Question 1

the rate of reaction can be expressed either in terms of how the concentration……………………….or………………………..

Answer 1

a decrease or increase in concentration

Question 2

rate =
or
rate=

Answer 2

rate= change in concentration of product / time
or
rate= - change in concentration of reactant / time

Question 3

rate is measured in

Answer 3

mol dm-3 s-1

Question 4

when measuring the rate using the change in concentration of reactant, we have to use a negative sign because

Answer 4

the concentration change value will be negative for the reactant

Question 5

the (overall) rate of reaction is

Answer 5

the change in concentration of a species divided by the time taken for the change to occur. all reaction rates are positive

Question 6

the 6 ways of measuring a rate of reaction is by

Answer 6

• measuring the volume of gas evolved
• measuring the change in mass of a reaction mixture
• monitoring the change in colour intensity of a reaction mixture (colorimetry)
• measuring the change in concentration of a reactant or product using titration
• measuring the change in pH of a solution
• measuring the change in electrical conductivity of a reaction mixture

ALL in a given time

Question 7

the 2 most common techniques for collecting and measuirng the volume of a gas evolved during a reaction are

Answer 7

• collection over water into a measuring cylinder

- collection using a gas syringe

Question 8

when collecting small volumes of gas, it is best to use …………………..to collect it
however, when collecting large volumes of gas………………..can be used because

Answer 8

use a gas syringe which is more precise

either gas syringes or collection over water can be used as the uncertainty becomes so small that both ways are sufficiently precise

Question 9

measuring the change in mass of a reaction in mixture when a gas is released should only be used if the gas released is of relatively……………….density

this is because

Answer 9

high density (high molecular weight)

this is because low density gases will result in a very small change in the mass of the reaction mixture, so will increase uncertainty of the results

Question 10

high density gases include

Answer 10

carbon dioxide

Question 11

low density gases include

Answer 11

hydrogen

Question 12

the advantage of using a colorimeter is that the result is

Answer 12

quantitative rather than subjective

Question 13

small samples are called

Answer 13

aliquots

Question 14

when measuring the change in the mass of a reaction mixture, we place cotton wool in the neck of the flask because

Answer 14

we can prevent the loss of liquid spray due to effervescence

Question 15

the process for analysis by titration is

Answer 15

• prepare the main reaction mixture
• remove aliquots of the reaction mixture at regular intervals
• quench these to stop the reaction or place into an ice bath to slow the reaction to almost zero
• titrate each aliquot
• use this to work out the concentration of one of the reaction components at that given time

Question 16

quenching is when

Answer 16

the reaction is stopped either by placing it in an ice bath to slow it down to nearly zero or by adding a substance to remove a catalyst

Question 17

we can use a conductivity meter to measure a rate of reaction when the

Answer 17

total number or type of ions in the solution changes during a reaction