C2 Calculations And Chemical Analysis Flashcards
What is a mole?
The relative formula mass of a substance in grams.
What does Cl have a relative atomic mass of 35.5?
It has more than one stable isotope so the average mass is found.
How much does one mole of iron weigh?
56g . This is the same as the atomic number.
What is the formula used to calculate the number of moles?
Number of moles = mass in g
Relative formula mass
Find the percentage mass of sodium in sodium carbonate (Na”2”CO”3”)
43.4%
What is a empirical formula?
It is the simplest whole number ratio of each type of atom in the compound.
If after calculating the empirical formula and you get a decimal answer, what do you do?
Round off. If you get a .5 , multiply by two.
How is percentage yield calculated?
Percentage yield =. actual yield(grams) X100
Predicted yield (grams)Why are reactions always less than 100%
The reaavrion may be reversable. This means that some of the products are turned back into the reactants.
When a liquid is filtered, some of it is always lost.
Unexpected reactions could use up the reactants.
How is product yield important to sustainability?
As little energy as possible has to be sued to create the highest possible yield so that resources will be saved.
How can artificial colours be separated using paper chromatography?
Extract the colour from the food sample by putting it in a cup with a few drops of solvent.
Put spots of the coloured solution on a pencil baseline on filter paper. Roll up the paper a put it in a beaker with some solvent.
The solvent seeps up the paper taking the dye with it . Dyes will form in different places. The positions of the dyes will determine what it is.
why are machines used to analyse unknown substances ?
They are very sensitive. They can detect very small amounts.
Very fast.
Very accurate.
How does gas chromatography work?
A gas is used to carry a vaporised sample through a column packed with a solid material.
The substances travel through at different times so they’re separated.
The retention time is the time taken for the substances to reach the detector. The substances can be detected.
How is the information from gas chromatography analysed?
A gas chromatograph is drawn. The number of peaks shows the number of different compounds in the sample.
The position of the peaks shows the retention time.
The Gas chromatography column can also be linked to a mass spectrometer. The process is know as GC-MS and can identify the substances leaving the column very accurately.
The Relative molecular mass of each of the substances can be found from the graph.
What are disadvantages of using gas chromatography?
It is expensive.
It needs specialised training to use.
Results have to be conspired to know samples.
