Unit 7 Flashcards
Heterogeneous mixture
A mixture with non uniform composition
Homogenous mixture
Mixture with uniform composition
What are Ions
Charged particles due to the loss/gain of electrons. Positively charged ions are cations and negatively charged ions are anions
What are atoms
Neutral particles
What is a salt
A salt is a chemical compound consisting of an ionic assembly of positive ions and negative ions
Double displacement reaction
two reactants exchange ions to form two new compounds
Typically result in the formation of a product that is a precipitate.
What are halogens
The halogens are the elements in Group 7 of the periodic table. Chlorine, bromine and iodine are halogens.
What are halide ions
Ions of halogens ( elements in group 7) are called halide ions
How are halide ions detected
Halide ions in solutions are detected using silver nitrate solutions. The test solution is acidified using a few drops of dilute nitric acid, and then a few drops of silver nitrate solution are added. Different coloured silver halide precipitates form, depending on the halide ions present.
For example : chloride ions give a white precipitate of silver chloride,
bromide ions give a cream precipitate of silver bromide,
iodide ions give a yellow precipitate of silver iodide
Why is nitric acid added when testing halide ions
The nitric acid is added first to remove any carbonate ions that might be present – they would produce a white precipitate of silver carbonate, giving a false positive result for chloride ions
Trend in color of the halide salt as you move down group 7
The silver halide precipitates become a darker color
Solute
The solid substance to be dissolved
Solvent
Teh liquid into which teh solute will dissolve
Solution
The resulting combination of solvent and solute ( combined in a single phase )
Electronegativity
The tendency of an atom to attract a pair of electrons in a chemical bond
What makes a molecule polar
An unequal share of electrons in a chemical bond. One atom being more electronegative. This causes an imbalance or charge.
Why is hydrogen non-polar
Same atom involved and no electronegative atoms ( bonding electrons are shared equally between teh two atoms )
Polar solvents and solutes ( 3 points :
- polar solvents will dissolve polar solutes
- non-polar solvents will dissolve non-polar solutes
- polar solvents will NOT dissolve non-polar solutes
Why are some molecules polar and others non-polar
In polar molecules, there is an electronegative atom which causes an unequal share of electrons in the chemical bond. This causes an imbalance of charge within the molecule. Non polar molecules do not have electronegative atoms so have an equal share of electrons
Why do polar solvents dissolve polar solutes
The slightly positive atoms are attracted to the negative ions. The slightly negative atoms are attracted to the positive ions.
Why do polar and non-polar molecules not mix
No attractions between the atoms in each molecule
What are the two phases involved in chromatography
Stationary ( the paper) and Mobile ( liquid or gas )
What does separations depend on in chromatography
Depends on the distribution of substances between phases
How does paper chromatography work ? ( 3 points )
- A solvent moves through paper ( teh mobile phase flows through teh stationary phase and Carrie’s the substance under test with it )
- Carries different compounds different distances
- Distances travelled depends on their attraction (solubility) for the paper and the solvent
How to calculate the Rf value
Distance moved by a substance/component divided by the distance moved by solvent
Different compounds have different Rf values in different solvents
What is chromatography
Process used to separate mixtures of gases and liquids
Mole ( definition )
A mole of any substance always contains the same number of particles - 6.022*10^23 particles of atoms, molecules, ions or electrons.
Value of mole is equal to ?
Number of atoms in exactly 12 grams of pure carbon-12
Ideal gas law
Equal volume of all gases, when measured at the same temperature and pressure contain an equal number of particles
Molar volume (definition)
The volume occupied by one mole of a gas at a given temprature and pressure
Isotope
Different number of neutrons ( mass number )
Same atomic number but different mass number
Realative atomic mass
Relative atomic mass takes into consideration all the isotopes of the element and their %abundance
What is a mass spectrometer used for ?
Measures the mass of charged particles ( ions) and shows the frequency of ions for each isotope
How does a mass spectrometer work ? ( 3 points )
• A sample of atoms is ionised and passed along a magnet as a vapour
• The magnet interacts with the ions and deflects them according to mass/charge ratio.
• Vaporization, Ionization, Accelleration, Deflection and Detection
Molar mass and Rf value
As the molar mass increases so the does Rf value. This means that compounds/colors with more molar mass are more soluble and will travel longer distances
Dissasociation and ions
When an ionic compound is dissolved in a polar solvent like water the ions in teh solid separate and disassociate into ions uniformly throughout teh solution.
Ion dipole attraction
The electrostatic attraction between an ion and a molecule with a dipole is called an ion dipole attraction
Concentration
Number of atoms in a given volume of a substance
What is mass spectrometry
Mass spectrometry accurately measures the mass of different molecules within a sample
How are ionic compounds formed
Generally Formed from the electrostatic attraction between a cation ( typically a metal ) and an anion ( typically a non-metal)
Solubility rules ( 5 )
- All nitrates are soluble
- Most sulphates expect lead and barium sulphate are soluble
- Most chlorides, bromides and iodides ( except silver and lead chlorides, bromides and iodides )
- sodium carbonate and potassium carbonates are soluble ( most other carbonates are insoluble )
- Sodium hydroxide and potassium hydroxide are soluble most otehr hydroxides aren’t
What is covalent bonding
In covalent bonding atoms share electrons
Why is a water molecule polar
Ina water molecule, oxygen shares electrons with each of teh hydrogen atoms. The oxygen has a much greater attraction for these shared electrons than teh hydrogen atoms, resulting in an uneven distribution of the bonding electrons in Teh covalent bond.
When is gel permeation chromatography used
To analyse very lareg molecules or polymers
Law of definite propotions
A chemical compound always contains a fixed ratio of elemnst by mass
A more attracted color/solute will travel less or more distance ?
Less
Molar mass - solubility and retention factor
More molar mass = more soluble = higher Rf value = further distance travelled
Why can metals conduct electricity
Metals have a sea of delocalized electrons. Metals conduct electricity by allowing free electrons to move between the atoms. Electrons can carry charge
Solute and soLvent ( chromatography specific )
Teh mobile phase passes through teh stationary phase.
Solute is teh mixture being soersted
Solvent is teh mobile phase
In chromatography distance traveled depends on ?
Distance travelled depends on tehir attraction ( solubility )to the paper and solvent
Molar mass is teh
Mass of 1 mol of any elemnt/compund
Iodine - 131
Used to treat thyroid cancer.
