Mole calculations and numerical skills Flashcards
What is a mole? -> amount within a substance
Why do we need moles?
A simple way of comparing and counting molecules.
The same number of molecules remains in the solution, no matter what shape or size.
The number of molecules in a solution can be compared directly, no matter how big or small these are.
Example:
One enzyme molecule which is very large, reacts with a substrate molecules which is very small.
It is important to have the ability to work out how many molecules of each can be found in a solution.
Structure of atoms
Atoms consist of subatomicle particles (Protons, Neutrons and Electrons).
Protons - have a positive charge
-> 1.67 x 10 (to the power of) - 24 g
Neutrons - electrically neutral, similar mass
Electrons - negative charge
-> only 9.1 x 10 (to the power of) - 28 g
Relative mass scale
Measurement of the subatomic particles due to their small size and light weight.
The Carbon atom is given a mass and all others are measured in comparison to this.
Atomic mass and Dalton
Consists of 6 protons and 6 neutrons.
This represents 12 atomic mass units (amu)
-> 1 amu = 1 / 12 C
This is also called Dalten and is named after John Dalton.
-> 1 Dalton = 1.66 x 10 (to the power of) - 24 g
A proton or neutron therefore have 1 amu
- > Neutrons - 1.0086 amu - > Protons - 1.0073 amu
Examples:
H = 1 Mg = 24
Composition of Atoms
The number of protons makes elements distinguish themselves from one another. This value is known as the element’s atomic number (Z).
Atomic Mass number (A) -> The sum of protons plus neutrons.
The number of electrons is equal to the number of protons.
Periodic Table of Elements
Beginning at the upper left corner of the periodic table, all elements are ordered in increasing atomic number.
The atomic mass number (A) is given in subscript (under the name of the element), whereas the atomic number (Z) in superscript.
Moles
Amu or also known as Dalton is very small.
It is more convenient to express the atomic mass in grams, hence we define 12 g of Carbon as 1 mole. 1 mole of Carbon contains 6.022 x 10 (to the power of) 23 atoms of Carbon.
1 mole in any substance contains 6.022 x 10 (to the power of) 23 of atoms. This is known as the AVOGRADO’S NUMBER.
This also works for compounds, e.g. Water (H2O) :
18 g of Water equals 1 mole, so 18 g of Water contain 6.022 x 10 (to the power of) 23 H2O molecules.
This also works for Glucose (C6H12O6) and ionic compounds such as NaCl.
Molecular mass
The Molar mass is the mass of one mole of a compound in grams.
Example:
Molar mass of glucose - 180 g mole (to the power of) - 1
relative molecular mass of glucose (M subscript r) - 180.
Dalton is used as a unit for ‘atomic mass unit’ by Biologists.
Calculations
Number of moles = mass in grams / Molar mass = m / M
Example: glucose - 180 g mol (to the power of) - 1
Number of moles = 90 / 180 g mole (to the power of) -1 = 0.5 mol
Molarity
A mole measures the amount within a substance.
The molarity i a measure of concentration.
The molarity of a solution measures the number of moles of a substance in a certain volume.
This is the number of moles per litre of solution.
Units of molarity :
mol / l - mol l (to the power of) - 1 - M
A molar solution (1 M) contains one of a substance in 1 litre volume.
Example:
Glucose M = 180 g mole (to the power of) - 1
180 g of glucose in 1 litre (1000 ml) gives us a concentration of 1 M (1 mol / l).
In 1 ml of that solution the concentration would still just be 1 M due to 1 ml only containing 1 / 1000 of a mole - 1 mmol.
Units
In Biology, small units are very common.
Prefixes are being used such as milli (m), micro (μ), nano (n) or even pico (p). These can be put in front of any unit such as Metre (m), litre (l), gram (g) or mole (mol).
These units work in steps of 1000 or 10 (to the power of) 3.
This means that 1 litre contains 1000 ml, 1 000 000 μl, 1 000 000 000 nl.
1 g contains 1000 ml, 1 000 000 μg, 1 000 000 ng.
Scientific notation
This is a convenient way to display a very small or very large number. Written as a product of a number between 1 and 10, times the number by 10 to the power.
Dilution
In order to achieve the required polarity, solution often have to be diluted. This could be achieved through a simple or serial dilution.
Simple dilution - a unit volume of a liquid is combined with an appropriate volume of a solvent.
Serial dilution - This is a series of simple dilutions which amplifies the dilution factor quickly.
Starting off with 10 cm3 of original sample, 10 (tp the power of) -1, 10 (to the power of) -2, 10 (to the power of) -3, 10 (to the power of) -4
Percentage solutions
Percentage means number of parts per hundred.
W / w percentage composition - a certain mass of dry solute and the solvent are given in mass unit (e.g. gram).
20 g of glucose (solute), is combined with 480 g of water (solvent): 20 / 500 = 4 %
W / v Percentage - a certain mass of dry solute is weighed and solvent added in order to reach a certain volume.
10 g NaCL in 100 m; = 10 / 100 x 100 = 10 %
V / v percentage - both the solute and the solvent are given in liquid unit (e.g. ml).
70 ml ethanol in 100 ml liquid is 70 %.
Parts per notation:
- ) Parts per thousand (‰ [the per mille symbol] or ppt)
- ) Parts per million (ppm)
- ) Parts per billion (ppb)
- ) means 1 part of 1000. Roughly equivalent to one drop of ink in a coup of water. This (‰) is often used to record the salinity of seawater.
- ) means 1 part in 10 (to the power of) 6 or 0.0001 %. Roughly equivalent to one drop of ink in 150 litre of water.
- ) means 1 part in 10 (to the power of) 9. Roughly equivalent to one drop of ink in an Olympic-sized swimming pool.
