2a.5 - Percentage Yield and Chemical Analysis Flashcards
How do you calculate percentage yield?
(actual yield (grams) % predicted yield (grams)) x 100
What does a 100% yield mean?
You got all the product you were expecting
What does a 0% yield mean?
No products were made
Why can’t yields be 100%? (3)
- The reaction is reversible
- Filtration
- Unexpected reactions
Why do reversible reactions not give 100% yield?
The reactants will never be completely be converted to products because the products are always reacting together
Why does filtration never give 100% yield?
When a liquid is filtered, you nearly always lose a bit of liquid or or solid
Why does unexpected reactions mean the yield cannot reach 100%?
There is sometimes other unexpectant reactions which use the reactants so then there isn’t as much reactant to make the product you want
What is percentage yield important for?
Sustainable development
What is sustainable development?
Making sure that we don’t use resources faster than we can replace them
How can you separate artificial coloured by paper chromatography?
- Put spots of the coloured solution on a pencil baseline
- Roll up the sheet and put it in a beaker with some solvent but make sure the baseline is above the solvent
- The solvent carries the colours up the paper, separating them
What are the advantages to using machine chromatography?
- Very sensitive
- Faster
- Accurate
How does machine chromatography work?
- A gas carries substances through a column packed with a solid material
- The substances travel through at different speeds
- The time they take to reach the detector is the retention time. This is what identifies a substance
What is retention time?
The amount of time it takes for different substances to reach the detector in gas chromatography
