Flashcards in module 3 Deck (46):
What is reletive formula mass with an example?
MgCl2 Mr (small r) is relative formula mass is just relative atomic masses of all atoms in molecular formula added together.
What is the formula for percentage mass of an element in a compound?
percentage mass of an element in a compound=Ar(small r)*number of atoms of that element/Mr(small r) of the compound.
Where do you find the relative atomic mass Ar(small r)?
Periodic table-same as mass number.
What is the Avogadro constant?
602,000,000,000,000,000,000,000 or 6.02*10 23.
What is one mole?
Amount of substance that contains an Avogadro number of particles. Particles can be atoms, molecules, ions or electrons.
Why is Avogadro's number the number it is?
mass of that number of atoms or molecules of any substance is exactly the same number of grams as relative atomic mass.
What is the formula for moles?
Number of moles=mass in g(of an element or compound)/Mr (small r[of the element or compound]).
What happens during a chemical reaction?
no atoms are destroyed and no atoms are created, means same number and types of atoms on each side of a reaction sequence. No mass is lost or gained-mass is conserved during a reaction.
By adding the relative formula mass of substance on each side of balanced equation what happens?
Can see mass is conserved. Total Mr of all reactants equals total Mr of products.
What happens if the mass increases it's probably because one of the reactants is a gas that's found in air (e.g.oxygen) and all the products are solids, liquids or aqueous in an unsealed reaction vessel?
Before reaction, gas is floating around in air. It's there but it's not contained in the reaction vessel so you can't account for its mass. When gas reacts to form part of product, becomes contained inside reaction vessel, so total mass of stuff inside reaction vessel increases.
What is the example for explanation 1 of an unsealed reaction vessel?
When metal reacts with oxygen in an unsealed container, mass of metal oxide produced equals the total mass of the metal and the oxygen that reacted from air.
What happens in the second explanation of a change in mass of an unsealed reaction vessel if the mass decreases, it's probably because one of the products is a gas and all the reactants are solids, liquids or aqueous?
Before reaction all reactants are contained in the reaction vessel, if vessel isn't enclosed then the gas can escape from reaction vessel, so you can't account for its mass-total mass of the stuff inside reaction vessel decreases.
What is the example for explanation 2 of an unsealed reaction vessel?
when metal carbonate thermally decomposes to form metal oxide and carbon dioxide gas, the mass of reaction vessel will decrease if it isn't sealed. But inn reality mass of metal oxide and carbon dioxide produced will equal mass of metal carbonate that decomposed
What are the equations for each explanation?
1. metal+oxygen=metal oxide 2. metal carbonate=metal oxide+carbon dioxide.
How do you balance a mole equation?
Divide mass of each substance by its relative formula mass to find relative formula mass to find number of moles. Divide number of moles of each substance by smallest number of moles in reaction. If any of numbers aren't whole numbers multiply all numbers. Write balanced symbol equation for reaction by putting numbers in front of chemical formulas.
What happens when some magnesium carbonate is placed into a beaker of hydrochloric acid?
Can tell reaction take place because can see lots of bubbles of gas being given off. After while amount of fizzing slows and reaction eventually stops
When does a reaction stop?
When reactants are used. Any other reactants are in excess. Usually added in excess to make sure that the other reactant is used up
What is the used up reactant called?
Limiting reactant (because limits amount of product that's formed).
What does the product formed being directly proportional to amount of limiting reaction mean?
if half amount of limiting reactant. E.g. halve amount of limiting reactant amount of product formed halve. If double amount of limiting reactant amount of product will double (as long as it's still limiting reactant). Because if add more reactant will be more reactant particles to take part in reaction which means more product particles.
How do you calculate the mass of product formed in a reaction by using the mass of the limiting reactant and the balanced reaction equation?
Write out balanced equation, work out relative formula masses (Mr) of reactant and product you want, find how many moles there are of substance you know the mass of, use balanced equation to work out how many moles there'll be of other substance. In case that's how many moles of product will be made of this may moles of reactant, use number of moles to calculate mass.
At same temperature and pressure, equal numbers of moles of any gas will what?
Occupy the same volume
What is the formula for volume of any gas at room temperature?
Volume of gas (dm3)=mass of gas (g)/Mr of gas* both 24
The amount of substance (e.g. mass or number of moles) in a certain volume what?
Of a solution is called its concentration. More solute (substance that's dissolved) there is in a given volume, more concentrated the solution.
What is one way to measure concentration?
by calculting the mass of a substance in a given volume of solution. Units will be units of mass/units of volume.
What is the formula for calculating mass of solute in solution?
Concentration (g/dm3)=number of moles of solute (in mol)/volume of solvent (dm3).
What is the formula for concentration in form of mol/dm3?
Concentration (mol/dm3)=number of moles of solute(in mol)/volume of solvent (in dm3).
What are titrations experiments?
let you find out volumes needed for 2 solutions react together completely. If you know concentration of one solutions, can see volumes from titration experiment, along with reaction equation to find concentration of other solution.
What is the triangle formula to find concentration of substance in form of mol/dm3?
No. of moles/conc*volume
What do you do to find concentration in g/dm3?
start by finding concentration in mol/dm3. convert concentration in mol/dm3 using equation mass=moles*Mr.
What is atom economy (atom utilisation)?
Of reaction tells you how much of mass of reactant wasted when manufacturing and how much ends up as useful products. Higher atom economy more 'greener' products.
What is the equation for atom economy?
atom economy=relative formula mass of desired products/ relative formula mass of all reactants * both 100.
What are properties of reactants with low atom economy?
Use up resources quickly. At same time, they make lots of waste materials that have to be disposed of somehow. Tends to make these reactions unsustainable-raw materials will run out and waste has to go somewhere.
what are low atom economy's faults?
aren't profitable. Raw materials expensive to buy waste products can be expensive to remove and dispose of responsibly.
What are problems with waste products?
Better to use waste products rather than just throw them away. Often more than 1 way to make product you want, trick is to come up with reaction that gives useful "by products" rather than useless ones
What are properties of highest atom economy products?
Only have 1 product. Reactions have an atom economy of 100%. More products there are, lower atom economy.
What is yield?
rate of reaction and position of equilibrium for reversible reactions also need to be thought about. Reaction with low atom economy, produces useful by-products, might also be used.
What is yield 2nd card?
more reactants start with, higher actual yield will be. Percentage yield doesn't depend on amount of reactants started with-percentage.
What is the formula for percentage yield?
percentage yield=mass of products actually made(g)/maximum theoretical mass of products [can be calculated by balanced equation](g)* both 100
Where does yield between and what does this mean?
0 and 100% yield. 100% yield means you got all product you expect to get. 0% yield means that no reactants were converted into product i.e. no product at all was made. Industrial processes should have high percentage yield as possible to reduce waste and cost.
Why will you never get 100% yield?
some product or reactant always gets lost along way-and goes for big industrial processes as well as school lab experiments. How this happens depends on what sort of reaction it's and what apparatus is being used. Lots of things can go wrong.
What are the 3 common problems in yield trying to get 100%
Not all reactants react to make a product, might be side reactions, lose some products when separate if from reaction mixture.
What happens when not all reactants react to make product?
In reversible reactions, products can turn back into reactants so yield never be 100%. E.g. Haber process at same time as reaction N2+3H2=2NH3 is taking place, reverse reaction 2NH3=N2+3H2 also happening. Means reacton N2+3h"=2NH3 never goes to completion (reactants don't all get used up.)
What happens if there might be side reactions?
Reactants sometimes react differently to how expect. Might react with gases in air, or impurities in reaction mixture, so end up forming extra products other than ones you want.
What happens if you lose some products when you separate it from the reaction mixture.
When filter a liquid to remove solid particles, nearly always lose a bit of liquid or a bit of solid.
What happens if you want to keep the liquid and solid in percentage yield third problem?
Liquid: You'll lose bit that remains with solid and filter paper (as they always stay a bit wet)
Solid: Some of it'll get left behind when scrape it off filter paper.