Quantative Chemistry Flashcards
What is relative formula mass?
The sum of the relative atomic masses of all the atoms in the molecular formula
What is the formula for percentage mass of an element in a compound?
Percentage mass = ((Atomic mass x Number of atoms)/Relative formula mass) x 100
What is the percentage mass of sodium in sodium carbonate Na2CO3?
43%
How much is a mole?
6.02 x 10^23
How does the mole relate to particles in a substance?
One mole of any substance is the amount of that substance that contains 6.02 x 10^23 particles. This could be atoms, molecules, ions or electrons
Why is a mole that number?
One mole of atoms of any substance will have a mass in grams equal to the relative formula mass
What is the formula for the number of moles in a given mass?
Number of moles = mass(g) / Relative formula mass
What is the conservation of mass theory?
Atoms/mass cannot be created or destroyed so there are the same number and type if atoms on each side of a reaction equation
What does it mean if the mass of the products is larger than the mass of the reactants?
One of the reactants is a gas found in the air but all the products are solids, liquids or aqueous because the gas is part of the reaction
What does it mean if the mass of the products is smaller than the mass of the reactants?
One of the products is a gas and all the reactants are solids, liquids or aqueous and the gas escaped during the reaction.
What do the big numbers in front of the chemical formulas of the reactants and products tell you?
How many moles of each substance take part in the reaction
How do you work out a balanced symbol equation using the masses of the products and reactants?
-Divide each substance’s mass by its relative formula mass to find the number of moles
-Divide all of these by the smallest number of moles in the reaction
-(If there are decimals) Multiply everything out so all of the numbers are whole
-Put these numbers in front of the chemical formulas
What is the limiting reactant in a reaction?
The reactant that ends the reaction by being used all the way up. The amount of product formed is normally directly proportional to it
How can you use the limiting reactant and balanced equation to calculate the amount of product formed?
-write out the balanced equation
-work out the relative formula mass of the desired reactant and product
-find out the number of moles of the substance you know the mass of
-use the equation to work out how many moles there will be of the other substance
-use this to calculate the mass
What is the theorectical yield of a reaction?
The mass of product that you calculate (theoretical because you will never get 100% of the product)
At room temperature (20 degrees celsius) and room pressure (1 atm) what volume will one mole of any gas occupy?
24dm^3
What is the formula for finding the volume of a known mass of any gas at room temperature (r.t.p.)?
Volume of gas = (Mass of gas / Relative formula mass of gas) x 24
What is the formula for finding the concentration of a substance in a solution using mass?
Concentration = mass of the solute / volume of the solvent
What is the formula to convert the units of a concentration from mol/dm^3 to g/dm^3?
Mass = moles x Mr
What is the formula for finding the concentration of a substance in a solution using moles?
Concentration = number of moles of solute / volume of solvent
What are the negatives of reactions with low atom economies?
-use up resources
-make waste materials that need disposing
-unsustainable
-not profitable
What does the atom economy of a reaction tell you?
How much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as useful products. 100% atom economy means all the atoms have been turned into useful products
What is the formula for atom economy?
Atom economy = (relative formula mass of desired product / relative formula mass of all reactants) x 100
What is the yield of a reaction?
The amount of product that is made
What are the factors to consider when choosing which reaction to use to make your product?
-atom economy
-yield
-rate of reaction
-position of equilibrium (in reversible reactions)
What is the best way around the negatives of reactions with low atom economies?
Finding a use for the waste products or using an alternative reaction that still makes the product you want but also makes useful by-products instead of waste products
What is the formula for the percentage yield of a reaction?
Percentage yield = (mass of product actually made / maximum theoretical mass of the product) x 100
What are the benefits of a high percentage yield?
-reduced waste
-reduced cost
What are the three most common ways for percentage yield to be decreased in a reaction?
-not all reactants react to make the product (reversible reactions)
-side reactions (reactants may react with gases in the air or impurities in the mixture)
-product lost during separation from the reaction mixture (e.g. during filtration)
Why can you never get 100% yield in real life?
Because some product or reactant will always get lost along the way somehow
