C2- atomic structure, analysis and quantitative chemistry Flashcards
(37 cards)
What will all atoms of a particular element have the same?
The atoms of a particular element will all have the same number of protons. Their atomic number will be the same.
What are isotopes?
Atoms of the same element with different numbers of neutrons are called isotopes. The different isotopes of an element have identical chemical properties. However, some isotopes are radioactive.
What is the symbol for relative formula mass?
Mr (small r)
What is the symbol for relative atomic mass?
Ar (small r)
How do you work out the relative formula mass?
To find the relative formula mass of a substance, you just add together the relative atomic mass values for all the atoms in its formula.
What is one mole of a substance?
The relative formula mass of a substance - shown in grams - is called one mole of that substance. For example, the Mr of carbon monoxide (CO) is 28. This means that one mole of carbon monoxide has a mass of 28 g. You should be able to see that:
14 g of carbon monoxide contains 14 ÷ 28 = 0.5 moles 56 g of carbon monoxide contains 56 ÷ 28 = 2 moles
What is the relative atomic mass?
The relative atomic mass of an element (Ar) is an average value for the isotopes of the element. For example, the Ar for chlorine is 35.5 because it contains two different isotopes.
What do you work out the relative atomic mass (chlorine is provided as an example)?
75 per cent of chlorine atoms are 35Cl and 25 per cent of chlorine atoms are 37Cl.
This means that in 100 chlorine atoms, 75 will be 35Cl and 25 will be 37Cl.
The total Ar for these chlorine atoms will be (75 × 35) + (25 × 37) = 2625 + 925 = 3550.
So the average Ar for chlorine is 3550 ÷ 100 = 35.5.
What is the standard atom?
The mass of the 12C (upper 12) isotope is the ‘standard atom’ that the masses of other atoms are compared to. The Ar of 12C is defined as 12. This is also Avogadro’s number, which is the amount of amounts in 12 grams of carbon-12, which is 6.02x10^23
What is chromatography used for?
Chromatography is used to separate mixtures of substances into their components.
What is paper chromotopraghy used for?
Paper chromatography is used to analyse coloured substances
What is the method of paper chromotography?
Samples of each substances are spotted onto a pencil line drawn on a sheet of chromotography paper. The paper is suspended in a container with a shallow layer of a suitable solvent or mixture of solvents in it. It is important that the solvent level is below the line with the spots on it. The container should be covered. As the solvent slowly travels up the paper, the different components of the ink mixtures travel at different rates and the mixtures are separated into different coloured spots.
Why is it important that the container is covered?
The reason for covering the container is to make sure that the atmosphere in the beaker is saturated with solvent vapour. Saturating the atmosphere in the beaker with vapour stops the solvent from evaporating as it rises up the paper.
Why does paper chromotography work?
Paper chromatography works because some of the coloured substances are better at dissolving in the liquid than they are at bonding with the paper, so they travel further up the paper.
What are instrumental methods of analysis?
Instrumental methods of analysis rely on machines. There are several different types of instrumental analysis.
What are the advantages of instrumental methods of analysis?
Some are suitable for detecting and identifying elements, while others are better suited to compounds. In general, instrumental methods of analysis are:
Fast Accurate (they reliably identify elements and compounds) Sensitive (they can detect very small amounts of a substance in a small amount of sample)
What does Gas chromatography do?
Gas chromatography allows a mixture of compounds to be separated.
What does a gas chromatography machine consist of?
The GC machine consists of a long glass tube packed with a powdered solid material, which is fitted into an oven. The tube is called the column, even though it is usually wound into a coil so that it fits into the oven.
How does gas chromatography work?
The sample is dissolved in a solvent, then injected into one end of the column.
An unreactive gas - usually nitrogen - carries the sample through the column.
Different substances in the sample travel through the column at different speeds and so become separated from each other.
The separated substances leave the column one after the other. As they leave, they are detected by a detector.
What is the retention time?
The time taken for a substance to travel through the column is called its retention time.
What does the graph produced by the detector show?
A detector produces a graph where each substance is represented by a peak:
The number of peaks shows the number of compounds present in the sample The position of each peak shows the retention time for each compound
What does the mass spectrometer do?
The mass spectrometer can be used to identify substances quickly and accurately, and in very small amounts. It can also provide the relative formula mass of the substances separated by gas chromatography. If a GC machine is linked to a mass spectrometer, this combined GC-MS method allows the separated substances leaving the column of the GC machine to be detected.
What is the molecular ion peak?
The peak furthest to the right in a mass spectrum is called the ‘molecular ion peak’. Its relative mass is the relative formula mass of the substance being analysed.
How do you work out the percentage of mass of an element in a compound?
Find the relative atomic mass of the element you want ( if there is more than one atom of the element in the compound, you need to multiply your answer by the number of atoms.) Then divide this number by the relative formula mass of the compound, and then times by 100 to get the percentage.
