rate practicals Flashcards
describe how to carry out a practical investigation to explore the effect of concentration on the rate of reaction - turbidity (the disappearing cross reaction
If we react sodium thiosulfate solution, with hydrochloric acid, then one of the products is sulfur. Sulfur is a solid. The sulfur makes the solution go cloudy. This cloudiness is called turbidity.
This can be used to see how long it takes for the reaction to finish
Use a measuring cylinder to put 10cm^3 of sodium thiosulfate solution into a conical flask
Place the conical flask onto a printed black cross.
Add 10cm^3 of hydrochloric acid into the conical flask
Swirl the solution and start a stopwatch
Look down through the top of the flask.
After a certain time, the solution will turn cloudy
Stop the clock when we can no longer see the cross.
Carry out the experiment again using lower concentrations of sodium thiosulfate solution.
Repeat the whole experiment and calculate the mean values for each concentration of sodium thiosulfate solution
Do not include any anomalous results when calculating a mean
describe the reproducibility of this experiment (sodium thiosulfate)
A measurement is reproducible if it can be repeated by another person or using a different technique or equipment and still get the same result.
The problem with the disappearing cross experiment is that different people have different eye sights
That means that some people can see the cross for longer than others so they may not get the same results.
However, because all the students use the same size printed cross, this problem may not be too great
what would you expect to happen, as the concentrations of sodium thiosulfate increased
The higher the concentration of sodium thiosulfate, the faster the rate of reaction meaning
the quicker it took for the cross to disappear/for the cross to no longer be seen
hypothesis
A hypothesis is a proposal that could explain a fact or an observation
in science, a hypothesis must be testable
state a hypothesis for the sodium thiosulfate practical
As the concentration of the acid increases, the solution will go cloudy more quickly
State some control variables for the sodium thiosulfate experiemnt
Keeping volume of HCL the same
Keeping concentration of HCL the same
Keeping the volume/depth of overall mixture the same after each repeat
keep temp of reactants the same
describe how to carry out a practical investigation to explore the effect of concentration on the rate of reaction - measuring the volume of a gas produced by a reaction
magnesium + hydrochloric acid —-> magnesium chloride + hydrogen
This reaction produces hydrogen gas
This allows us to measure the volume of hydrogen gas produced
Use a measuring
cylinder to place 50cm3 of hydrochloric acid into a conical flask
Attach the conical flask to a bung and delivery tube
Now place the delivery tube into a container filled with water
Then place an upturned measuring cylinder also filled with water over the delivers tube
Add a 3cm strip of magnesium to the hydrochloric acid and start the stopwatch
The reaction produces hydrogen gas, and that is trapped in the measuring cylinder
Every 10 seconds, measure the volume of hydrogen gas in the measuring cylinder
Continue until no more hydrogen is given off
Repeat the experiment using different concentrations of hydrochloric acid
What do both experiments show us (sodium thiosulfate and magnesium strip)
That the greater the concentration of a chemical in a reaction, the faster the reaction takes place
the greater the concentration of a chemical in a reaction, the faster the reaction takes place
Can we say that this finding is reproducible
Because this result is shown by two different experiments, we can say that this finding is reproducible
