C3+C8 - Quantitative Chemistry+chemical analysis Flashcards
Compounds have a relative formula mass - mR
All relative atomic masses of all atoms in molecular formula added together E.g MgCl2 has a Mr Look at relative atomic masses Ar Ar of Mg24 Ar of Cl 35.5 Add up 24 +(2x 35.5) = 95
Formular for percentage mass of elements in a compound
Percentage mass of element in a compound = (Ar x number of atoms of that element/ Mr of compound) x 100
What are moles
Name given to an amount of a substance
What’s the Avogadro constant
6.02 x 10^23
What is one mole of any substance
One mole of any substance is just an amount of substance that contains an Avogadro number of particles. Particles could be atoms, molecules, ions or electrons
What will one mole of atoms or molecules of any substance have
One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass for that substance
E.g carbon Ar of 12 - one mole of carbon weighs 12g
Formula for moles
Number of moles = mass in g(of element or compound)/Mr(of element or compound)
What is meant by mass is conserved in a chemical reaction
No atoms destroyed or changed
Means there’s the same number and typed of atom on each side of the equation > no mass loss or gained
Why might mass increase during a chemical reaction
If mass increases it could be because one of the reactants is a gas that’s found it air like oxygen. And all products are solids, liquids or gases.
Before reaction - gas floating in air - not contained in the reaction vessel so you can’t account for its mass
When gas reacts to form part of product, becomes contain inside reaction vessel > total mass inside vessel increases
What happens if mass decreases during a chemical reaction
If mass decreases, one of products is a gas and all reactants are solids, liquids or aqueous
Before reaction - all in contained vessel
If vessel isn’t enclosed, gas can escape from vessel as its formed. No longer contained in vessel > can’t account for mass so mass decreases
What’s the big number in front of formulas
Big number in front of formulas tells you is many moles of each substance takes part or is formed during the reaction
How do you work out the balanced symbol equation if you know the masses of reactants and products
- Divide mass of each substance by RFM to find moles
- Divide no of moles of each substance by smallest number of moles in reaction
- If any numbers aren’t whole, multiply all numbers by same amount so they’re whole
- Write Balanced Symbol equation with numbers
When does a reaction stop
When one reactant is used up
Process of a reaction stopping
- Reaction stops when all of one reactant is used up. Any other reactants are in excess - usually added in excess so the one reactant is used up.
- Reactant that is used up is the limiting reactant. - limits amount of product formed
- Amount of product formed Is directly proportional to the amount of limiting reactant
How to find the mass of product formed by using mass of limiting reactant and the balanced reaction equation
- Write balanced equation
- Work out relative formula masses of reactant and product you want
- Find out how many moles there are in a substance you want to know the mass of
- Use balanced equation to work out moles of other substances - moles of product
- Use moles to calculate mass
What is concentration
A measure of how crowded things are
Amount of substance (mass or moles) in a certain volume of a solution is called a concentration
More solute there is in a given Volume - more concentrated the solution
Concentration measured in g/dm3
Equation for concentration.
Concentration = mass of solute/volume of solvent
What is a pure substances
Something that only contains one compound or element throughout - not mixed with anything else
How does the boiling/melting point tell you how pure a substance is
A chemically pure substance will melt/boil at a specific point
Test purity of sample by measure its point and comparing it to point of pure substances - close the value, the outer the substance
Impurities will Lower the melting point and increase melting range and will increase the boiling point and may result in sample boiling at a range of temperatures
What are formulations
They are mixtures with exact amounts of components
What are made by following a formula
Useful mixtures with precise purpose - each component in a formula is a measured quantitive and contributes to properties of formulation
Example of formulation e.g paint
Paint contains
Pigment - gives paint colour
Solvent - dissolves other components and alters viscosity
Binder(resin) - forms film to hold pigment
Why are formulations important for pills
Make sure it delivers the drug to the right part of the body at the right concentration and has enough shell life
Test for chlorine gas
Bleached damp litmus paper, turning it white
Test for oxygen
Oxygen will relight a glowing splint
Test for carbon dioxide
Bubbling/shaking CO2 through aqueous solution of calcium hydroxide (limewater) will turn it cloudy
Test for hydrogen
Splint will burn with a squeaky pop
Two phases of paper chromatography
Mobile Phase - where molecules can move - liquid or gas
Stationary phase - molecules can’t move - solid or really thick liquid
Constantly move between phases - equilibrium between the two phases
Mobile phase moves through the….
Stationary phase and anything dissolved in the mobile phase moves with it - how quick it moves depends on how it’s distributed between two phases
What happens if solvent spends more time in the mobile phase
Solvent will move further
Components in mixture will normal separate through what phase
Through stationary phase
What’s a pure substance in paper chromatography
Only one spot
In paper chromatography what is each phase
Mobile - the solvent
Stationary - the paper
Time of molecules in each phase depends on…
How soluble they are in solvent
How attracted they are to the paper
Higher solubility and less attracted molecules spend more time I’m mobile phase - travel further up
What is the rf
Ratio between distance travelled by solute and distance travelled by solvent
Further through stationary phase =
Larger Rf
Equation for Rf
Rf = distance travelled by substance/distance travelled by solvent
Substance distance = distance from baseline to colour spot
Solvent distance = distance from baseline to solvent front
Why is paper chromatography carried out
To see if a specific substance is in a mixture
