Chemical Industry 3: Basic ( Intro ) Rates

Question 1

What is required to measure rate of reactions

Answer 1

• rare at which one of the reactants is used up

- rate at which one of the products is formed

Question 2

Rate equation

Answer 2

Rate = change in property / time taken

Question 3

Name 5 experimental methods which can be used to follow rate of reaction

Answer 3

1. Measuring volume of gases
2. Measuring mass changes
3. pH measurement
4. Colorimetry
5. Chemical analysis eg. Titration

Question 4

How would you measure gas volumes

Answer 4

1. Gas syringe
2. Inverted measuring cylinder ( if gas being collected isn’t soluble in water )

Units = volume ( of gas given off ) / time

Question 5

How would u you measure mass changes

Answer 5

Measure at regular time intervals using a balance

Units = mass ( lost or gained ) / time

Question 6

How would you measure pH changes

Answer 6

1. pH meter
2. pH probe

( pH data can be converted into units of concentration using H+ = 10^-pH )

There units = mol dm^-3 / time

Question 7

What does colorimetry measure

Answer 7

Colour change

• colorimeter measures absorbance of solution
• the more concentrated the colour of solution = higher absorbance

Question 8

What makes chemical analysis eg. Titration different to other experimental methods of following rate

Answer 8

Involves taking samples of reaction mixture at regular intervals and stopping the reaction before analysis = quenching ( interfere with reaction )

Question 9

Definition quenching

Answer 9

Interfering with reaction ( slowing down or stopping entirely )

Question 10

How do you workout the rate from a graph

Answer 10

• gradient ( Change in y / change in x ) of tangent at any point

Question 11

When wanting talking about making something a fair test in an experiment what word should you use instead of mass

Answer 11

No. of moles / amount of…

Question 12

What are 3 common variable that often have to be controlled within an experiment to make it a fair test

Answer 12

1. Volume
2. Concentration
3. Temperature

Question 13

( example 6 marker rate experiment) Describe and experiment involving gas collection that can be used to measure the rate of a reaction between group 2 metals ( Ca & Ba ) and water and explain the expected observations

Answer 13

1. Group 2 metal + water = metal hydroxide + hydrogen gas ( give balanced chemical equation for one of the metals )
2. React water with the same number of moles of metal and measure volume of hydrogen gas given off at regular intervals using a gas syringe
3. Faster rate of reaction for Ba ( more hydrogen gas produced in shorter time )
4. Rate of reaction increases as go down group 2 because increase atomic radius = weaker attraction between the nucleus and outer electrons = electrons more easily lost
5. Ca( OH )2 = cloudier than Ba because group 2 hydroxides increase solubility as you go down the group

Question 14

Describe 4 main steps of carrying out a colorimetry experiment

Answer 14

1. Choose an appropriate filter of a complementary colour
2. Zero the colorimeter using distilled water
3. Mix measured volumes of ( 2 solutions using )
4. Take samples of solution at specific time intervals and measure absorbance