C2bL5 Concentrate now!

Key Words

Excess - too much of something

Initial rate of reaction  - how fast a reaction goes when it has just started

 

 

Test Yourself

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Grade E

You will have done this experiment:

Zinc + sulphuric acid  ®  zinc sulphate  + hydrogen

 

Zn (s) + H2SO4 (aq) ®  ZnSO4 (aq)  + H2(g)

 

As hydrogen is a gas, we can measure the gas collected in an upturned measuring cylinder.

We can then draw a graph that will look like this:

 

We find that the higher the concentration of Sulphuric acid, the faster the rate of reaction.

You can do the same experiment using magnesium and hydrochloric acid.

Grade C

This experiment is often used for an investigation.  You need to do a trial experiment (sometimes called a preliminary experiment) so that you can see:

  • How long it takes for the reaction to happen at a particular concentration;
  • What volume the sulphuric acid should be;
  • What the mass of zinc to use;
  • How many points you will take.

You need to consider not just how the test well be fair, but also how you will make sure that the data are accurate and reliable.

The graph above tells us:

  • How much hydrogen is made in the first minute for each concentration.
  • The total volume of the gas is the same, as the mass of the zinc is the same.
  • The gradient gives us the initial rate of reaction. 

Rate of reaction = mass loss ÷ time

The results can be explained by collisions.  If we have a greater concentration, the more particles there are, so there are more successful collisions

The total amount of gas produced in the end is the same.

The reaction is the fastest at the beginning because there are lots of unreacted sulphuric acid particles to collide with the zinc.  As more particles have reacted, there are fewer unreacted particles, so the chances of a successful collision are less.  So the rate is less

The graph is an idealised curve.  It is unlikely that your results will fit exactly.  Instead they will be scattered about the curve, and you will have to draw a line of best fit (not always easy).  You will need to decide if any results are anomalous (don't fit into the pattern).

Grade A

The are no notes at this level.