quantitative chemistry Flashcards
(25 cards)
What is the formula for percentage mass of an element in a compound?
(relative atomic mass x no of atoms of that element) /
(relative formula mass of the compound) x 100
What is a mole?
The amount of a substance that contains an Avogadro number of particles
What is the Avogadro constant?
The number of particles in a mole 6.02 x 10^23
Why is the Avogadro constant used?
the mass of that number of particles is equal to the relative atomic mass or relative formula mass. E.g. carbon has a relative atomic mass of 12, meaning that one mole of Carbon weighs twelve grams
What is the formula for moles?
mass/relative formula mass
Why might the mass change in an experiment?
gas may have reacted to form some of the products or some of the reactants may have turned to gas and evaporated
What is the limiting reactant?
The reactant that is used up first in a reaction
How can you calculate the mass of a product formed using the mass of the limiting reactant?
Write out a balanced symbol equation, work out the relative formula masses of the reactant and desired product, calculate the moles of the substance you know the mass of, use the balanced equation to work out how many moles there will be of the other substance, use the moles to calculate mass
What do the numbers used to balance equations mean?
The amount of moles reacting, no number indicated one mole is reacting, a 2 would indicate 2 moles are reacting
How many decimetres cubed does a mole of any gas occupy at room temperature?
24dm^3
What is the formula for the volume of gas?
24 x (mass of gas/relative formula mass of gas)
What is the formula for concentration using mass?
mass of solute/volume of solvent
What is the formula for concentration using moles?
number of moles of solute/volume of solvent
How do you convert mol/dm^3 to g/dm^3?
multiply by relative formula mass
What is atom economy?
the percentage of reactants forming useful products
What is the formula for atom economy?
(relative formula mass of desired product/relative formula mass of all reactants)x100
What is meant by a 75% atom economy?
three quarters of the reactants have been converted into the desired product
Why is a high atom economy favourable?
A higher atom economy means less reactant is wasted and there is a higher yield, requiring less energy and less material, making it more profitable and environmentally friendly
What is percentage yield?
The amount of product made compared to the maximum amount of product possible to make
What is the formula for percentage yield?
(mass of product made/maximum theoretical mass of product)x100
What may cause percentage yield to change?
gases in the air reacting to form unwanted products, losing product when transferring containers or filtering, reversible reactions will have some products turning back
What is the law of conservation of mass?
No atoms are destroyed or created in a reaction therefore the mass of the products should be the same as the mass of the reactants
How can you prevent unwanted factors from affecting the mass in your experiment?
use a closed system to prevent loss or gain of mass from gas, ensure you transfer all the liquid from containers
What is the relationship between the amount of product formed and the amount of limiting reactant?
directly proportional-if you halve the limiting reactant, the amount of product formed will also halve
