PAG 12: Research skills Flashcards
What is a prediction using specific knowledge called?
Hypothesis
What is meant by term accuracy?
How close measurement is to the true value
What are variables?
Factors that can affect the outcome of the experiment
What is an independent variabble?
A factor that is changed during the experiment to see the effect it has on another factor
What is a dependent variable?
A factor that is measured or observed in the experiment
What is a control variable?
A factor that is kept constant throughout the experiment
What is oxidation?
The loss of electrons or increase in oxidation state
What is reduction?
The gain of electrons or decrease in oxidation state
What is a redox reaction?
A reaction in which some atoms are oxidised and others are reduced
How can the percentage of iron in iron tablets be found?
- Prepare a standard solution of iron (II) using the tablets and sulfuric acid
- Titrate a set volume of this iron (II) solution against a solution of KMnO4
- Repeat until you obtain concordance results and calculate a mean titre
- Calculate the number of moles of KMnO4 that reacted
- Use the ratio in the chemical equation to calculate number of moles of iron that reacted
- Calculate percentage mass of iron using mass present in standard solution
Describe how to make a standard solution of acidified iron (II) sulfate
- Grind up some iron tablets. Measure total mass of iron tablets in a weighing bottle
- Add powdered tablets to a conical flask and reweigh weighing boat. The difference is the mass of iron tablets in solution
- Add 50cm^3 of sulfuric acid to conical flask to dissolve acid. Stopper the flask and shake well. Leave the flask for residue to settle
- Filter solution into a volumetric flask without disturbing residue. Rinse the filter paper with a small volume of distilled water.
- Fill volumetric flask up to graduation mark with sulfuric acid then stopeer and invert the flask to mix.
Write an equation for redox reaction between iron (II) ions and manganate (VII) ions
5Fe^2+ + MnO4^- + 8H^+ -> 5Fe^3+ + Mn^2+ + 4H2O
When making a standard solution, what method should be used to find mass of solute?
Weighing-by-difference method
Why is an indicator not required in titration between Fe^2+ and MnO4^-?
KMnO4 is self indicating; the end point is when you get the first permanent pale pink colour.
In a titration, what are concordant results?
Titres that are within 0.1cm^3 of each other
Give 3 possible sources of error in this experiment
- The iron may not completely dissolve- warming may help
- Some iron may not be transferred between containers- take washings
- The end point may be hard to see- place a white tile underneath the conical flask to make the colour change easier to observe
