Quantative Chemistry and Analysis Flashcards
What does the atomic number of an element tell us?
The number of protons in one atom of that element.
What does the mad number of an element tell us?
The total number of protons and neutrons in one atom of that element.
How can we find the number of neutrons in an atom?
Subtract the atomic number from the mass number.
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What term do we use to describe the relative mass of an electron?
Negligible
What is an isotope?
Different atomic forms of the same element which have different numbers of neutrons.
What is the symbol for relative atomic mass?
Ar
What is the relative atomic mass in comparison to?
The mass of an atom of Carbon-12 which scientists have decided has a mass of exactly twelve.
What two things are taken into account when finding the Ar of an element with different isotopes?
- The Ar of each isotope
* The abundance of each isotope
What is the symbol for relative formula mass?
Mr
What is relative formula mass?
The relative atomic masses of all the atoms in a compound added together.
What is a mole?
The relative mass (Mr or Ar) of a substance in grams.
What formula can be used to work out the number of moles in a substance?
Number of moles = Mass (g) / Mr (of substance)
What is percentage mass?
A way of saying what proportion of the mass of a substance is due to a particular element.
How can one find out percentage mass?
Percentage mass = ((Ar x number of atoms) / Mr (of compound))x100
What is an empirical formula?
The simplest number of ratio of atoms of each element in a compound.
What is the empirical formula of glucose (C6H12O6)?
CH2O
How do you work out empirical formulae?
1) List all the elements in a compound.
2) Write their masses or percentages.
3) Divide each mass/percentage by the Ar of the element.
4) Divide all your answers by the smallest answer you get to find the ratio.
5) If you don’t get whole numbers, you need to multiply all the numbers so that you do.
How do you work out the mass of a product?
1) Weite out a balanced equation for the reaction.
2) Find the Mr of the reactant and product you’re interested in.
3) Apply the “divide to get one, multiply to get all” rule:
- Divide both relative masses by the mass of the reactant.
- Multiply the answers by the amount of reactant given in the question.
What is percentage yield?
The percentage yield is a comparison between the amount of product you can expect to get and how much you actually get.
How do you work out percentage yield?
(Actual yield (g) / predicted yield (g)) x100
What are three reasons why percentage yield is never 100%?
1) The reaction is reversible so the backwards reaction is taking place as well.
2) Product is lost when it’s separated from the reactants.
3) Unexpected reactions may be happening.
What are three ways we can make chemical industrial processes more sustainable?
- Use reactions with high percentage yields.
- Use reactions that don’t require much energy.
- Use materials from renewable sources.
How does one carry out paper chromatography?
1) Extract the colour from the food sample by placing it in a cup with solvent.
2) Put a spot of the coloured solution on a pencil baseline on some filter paper.
3) Put the sheet in a beaker with some solvent, being careful to keep the baseline above the solvent.
4) The solvent seeps up the paper, taking the dyes with it which form spots in different places in the paper.
Why must the baseline in paper chromatography be drawn with pencil?
Because ink could dissolve into the solvent as well which would confuse the results.
What is the filter paper you get at the end of paper chromatography called?
A chromatogram
What can we learn from a chromatogram?
- What dyes a colouring contains.
* How many dyes a colouring contains.
What is meant by the term instrumental method?
Methods that use machines
What are tree advantages of using instrumental methods?
- They are very sensitive.
- They are very fast and can be automated.
- They are very accurate.
What is an example of an instrumental method?
Gas chromatography
What does gas chromatography do?
Separate out a mixture of compounds to help us identify the substances present.
How does gas chromatography work?
- A gas carries the mixture through a column packed with solid material.
- The substances travel at different speeds through the column so are separated out.
- The time it takes for each substance to reach the detector at the other end of the column is recorded - this is called the retention time.
- The detector sends information to the recorder which draws a gas chromatogram.
How can we tell how many substances were present in a mixture used in gas chromatography?
Each peak on the chromatogram represents a different substance so you just count the peaks.
What is GC-MS?
Gas Chromatography- Mass Spectrometry is a process that is used to identify substances in a mixture in very small quantities.
How does GC-MS help us identify substances?
It tells us the relative molecular mass of each substance.
