levo

Experimental Techniques

Rates of reaction and organic preparations

  • 3 things to know
  • AS 1

Overview

Measuring rate with gas syringes and the disappearing cross, initial rate, fair tests, reflux and distillation, percentage yield with a worked example, purity checks and risk assessment.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Key term

How can the rate of a reaction be measured?

Key term

How can a gas syringe be used to follow a reaction rate?

Key term

How is the initial rate found from a graph of product against time?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How can the rate of a reaction be measured?

    Model answer

    The rate can be found by measuring how quickly a reactant is used up or a product forms. Gas volume, mass loss or colour change can be measured over time.

  2. 2

    How can a gas syringe be used to follow a reaction rate?

    Model answer

    The gas syringe collects the gas produced, and its volume is read at regular time intervals. A graph of volume against time shows the rate.

  3. 3

    How is the initial rate found from a graph of product against time?

    Model answer

    A tangent is drawn to the curve at time zero. The gradient of the tangent gives the initial rate.

  4. 4

    A reaction produces 48 cm³ of gas in the first 30 seconds. What is the mean rate over that time?

    Model answer

    The mean rate is 1.6 cm³ per second. The working is 48 ÷ 30 = 1.6 cm³/s.

  5. 5

    How does a disappearing-cross experiment measure rate?

    Model answer

    The time taken for a precipitate to hide a cross under the flask is recorded. A shorter time means a faster rate.

  6. 6

    Why must only one variable be changed in a rate investigation?

    Model answer

    Changing one variable at a time shows its effect alone. Other variables, such as temperature and volume, must be controlled.

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book
2Open book
3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Experimental Techniques
Human Body Systems
Physical Chemistry in Industrial Processes
Brain Science

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

One cubic equals 1000 cm³.
decimetremetrecentimetre

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AThe energy of all bonds broken is added up.
BThe energy of all bonds formed is subtracted.
CA negative answer shows an exothermic reaction.

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Acidosis means blood pH falling below 7.35.
TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Experimental Techniques, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Or £46 a year, about £3.83 a month. Cancel anytime.