3:quantitive chemistry Flashcards
what are chemical amounts measured in?
moles
what is a mole?
One mole of a substance contains an Avogadro number of particles . One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance.
what is the value of the Avogadro constant
6.02 x 10^23
iron has an R.A.M of 56,how much does one mole of iron weigh?
56g
what does the law of conservation of mass state?
during a chemical reaction,no atoms are made or destroyed so the mads lf products is the same as the mass of the reactants
what is the relative formula mass(Mr)?
the Mr of a compound is all the relative atomic masses of the atoms added together
conservation of mass and Mr
Mr of the reactants and Mr of products show how mass is conserved.the Mr of reactants and Mr of the products is the same
why might it seem like mass has increased in a reaction?
most likely because one or more reactants are gas found in air and the products are solids,liquids or aqueous
before the reaction gas is floating around in the air but its not in the reaction vessel so its mass ca’t be accounted for.When the gas reacts to from part of the product,the particles are then contained in the reaction vessel and the total mass of the products increase
why might it seem like mass has decreased in a reaction?
one product is gas and all the reactants are solids ,liquids or aqueous
before the reaction all reactants are contained in the reaction vessel but if the vessel isn’t enclosed then the gas products can escape from as it is formed.Gas expands to fill the container its in so if a vessel isn’t sealed the gas escapes into the air.As it is not in the vessel,its mass can’t be accounted for and the mass of the reactants decrease
what do gas particles try to do in their container?
fill the container its in.
conservation of mass and equations
chemical reactions can be represented by equations which are balanced in terms of number of atoms on both sides
how to work out the balanced symbol equation for a reaction if you know the masses of the reactants and products?[4]
- divide mass of each substance by relative formula mass to find mes
- divide number of moles of each by smallest number of moles in reaction
- multiply all numbers by same amount if one number isn’t whole
- write balanced equation by putting these numbers in front of the symbol
what is a limiting reactant?
in a chemical reaction involving two reactants it is common to use an excess of one reactant to ensure that all of the other reactant is used up.The reactant that is completely used up is the limiting reactant(limits amount of product formed)
limiting reactant and product?
amount of limiting reactant is directly proportional to amount of limiting reactant.(so if in one reaction 3g of the limiting reactant was used but in a different reaction 3x as much of the limiting reactant was used,the amount of product formed would also go up by 3x)
calculating the mass of a product using the mass of the limiting reactant[5]
- write out the balanced equation
- work out the relative formula mass of the limiting reactant and product you want
- work out moles of limiting reactant(using moles equation)
- use balanced symbol equation to work out number of moles for the product (so if the reactant:product was at a 1:2 ratio then the product would have double the number of moles)
- calculate mass(using rearranged moles equation)
how much volume would 2 moles of oxygen take up if chlorine with the same number of moles took up 50dm^3?
50dm^3 because at the same temper and pressure,equal numbers of moles of any gas will occupy the same volume
how would you find the volume of gas from an equation?
look at the molar ration of the gas of the balanced equation(eg reactant:product is 1:2 so multiply the volume of the gas reactant by 2)
what is concentration?
the amount of a substance in a certain volume of a solution
how would you convert cm^3 into dm^3?
divide the dm^3 amount by 1000
mass of solute in a given volume
the greater the mass of a solute,the higher the concentration (so if you dissolve more of a solute into a solution,the concentration will increase but if you increase the volume w/o increasing amount of solute,concentration decreases)
how to calculate uncertainty[3]
- calculate mean volume
- divide range(highest result-lowest result)by 2 to find uncertainty
3.write mean ± uncertainty unit
how would you convert concentration in mol/dm^3 into concentration g/dm^3?
multiply the concentration by the relative formula mass
what is atom economy?
a measure of the amount of starting materials that end up as useful products
what would the atom economy be if you only have one product?
100% because all of the reactants end up in the useful products
what are the economic advantages of a high atom economy?[2]
- reactions with low atom economies produce more waste
- need more raw materials to produce a certain amount of a product which can be expensive to but and expensive to remove
overall,low atom economies usually aren’t profitable
what are the environmental advantages of high atom economy?
- use fewer raw materials,many of which will run out eventually so it’d be better to try and and make them last
- produce less waste which is good as waste chemicals are often harmful
high atom economy processes are more sustainable
what is the theoretical yield?
amount you would get if all reactants formed desired products and none of the products were lost
what is yield?
amount of product you obtain in a reaction
what is the percentage yield?
comparison between theoretical yield and the yield
what does a 0% yield mean?
no reactants were converted into products
why are percentage yield never 100%[3]
- reaction is reversible
- some product is lost when separated from reaction mixture
- some reactants may react in ways different than expected reaction(eg. side reactions such as reactant reacting with gases in the air)
what factors are considered when choosing a particular reaction pathway to produce a specific product to make sure the reaction is economically and sustainable?[5]
- atom economy
- yield
- rate
- equilibrium position
- usefulness of by-products
why is atom economy considered when choosing which reaction to use to make a specific substance an industrial scale?
reactions with higher stomach economies produce less waste and need less raw materials so reactions are cheaper and more sustainable
why is yield considered when choosing which reaction to use to make a specific substance an industrial scale?
high percentage yield means less reactant wasted so reactions are cheaper and more sustainable as less waste is made and less raw materials used
why is rate considered when choosing which reaction to use to make a specific substance an industrial scale?
rate of a reaction measures how quickly reactants reacts to form product.You want products to be made at a reasonable rate
why is equilibrium position considered when choosing which reaction to use to make a specific substance an industrial scale?
being able to control equilibrium position to maximise amount of product is important for making the process profitable.
where should the equilibrium position of a reversible reaction used in industry be?
should have an equilibrium position where amount of products formed is high and amount of reactant left is low
why is usefulness of by-product considered when choosing which reaction to use to make a specific substance an industrial scale?
by choosing reactions that form useful by-products(as well as intended product)reduces waste
