1.2 - Amounts of Substance Flashcards
What is Avogadro’s Constant?
6.02 x 10^23
What is the formula that links together the number of particles, Avogadro’s Constant and the number of moles?
Number of Particles = Number of Moles x Avogadro’s Constant
How heavy is one mole of a substance?
One mole of a substance is equal to its relative molecular mass
What is the formula that links together the number of moles, relative molecular mass and the mass of a substance?
Number of Moles = Mass of a Substance / Relative Molecular Mass
How many moles of Al2O3 are present in 5.10 grams?
Relative Molecular Mass = (2x27) + (3 x 16) = 102
5.10 / 102 = 0.05 moles
What is the formula that links together the number of moles, volume and concentration?
Number of Moles = Concentration x Volume (dm3)
How many moles of lithium chloride is present in 25cm3 of a 1.2 mol / dm3 solution of LiCl?
Moles = 1.2 x (25 / 1000) = 0.03
What is the formula for the Ideal Gas Equation?
pV = nRT
p = pressure (Pa) V = volume (m3) n = number of moles R = gas constant (8.31) T = temperature (K)
How many moles are there in 0.06 m3 of hydrogen gas, at 283K and 50,000 Pa?
n = (pV) / (RT) n = (50,000 x 0.06) / (8.31 x 283) n = 1.28 moles
What is 1 kPa in Pa?
1,000 Pascals
How do you convert between degrees and K?
Add 273
How many cm3 is in an m3?
1,000,000 cm3
How many dm3 is in an m3?
1,000 dm3
What are the three steps in writing an ionic equation?
1) Write a full balanced equation for the reaction
2) Split any dissolved ionic species into ions
3) Take out any ions that appear on both sides of the equation
What are the four steps to calculate the reaction to work out how much product you will get from a certain mass of the reactant?
1) Write out the balanced equation for the reaction
2) Work out how many moles of the reactant you have
3) Use the molar ratio from the balanced equation to work out the number of moles of product that will be formed from this much reactant
4) Calculate the mass of that many moles of product
What reaction happens when an acid reacts with an alkali to produce salt and water?
A neutralisation reaction
What is a standard solution?
A standard solution is any solution that you know the exact concentration of. Making a standard solution involves dissolving a known amount of solid in a known amount of water to create a known concentration
How do you work out how much solid needs to be used to make a standard solution?
1) Work out the number of moles needed using the formula moles = concentration x volume
2) Work out how many grams are needed using the formula mass = moles x relative molecular mass
How is the exact mass of solid measured?
1) Place a weighing bottle on a digital balance. Weight out the required mass of solid approximately and tip it into a beaker
2) Weigh the weighting bottle (which may contain traces of the solid). Subtract the mass of the bottle from the mass and the bottle together to find the precise mass of solid you have weighed out
How do you make sure no solute is on the rod, beaker and funnel?
They are all rinsed with distilled water and added to the standard solution
How is the correct amount of water measured?
The bottom of the meniscus has to reach the line. When you get close to the line, add the water dropwise
How do you make the standard solution well mixed?
Stopper the flask and turn it upside down a few times
What is the purpose of titration?
Titrations allow you to work out exactly how much acid is needed to neutralise a measured quantity of alkali (or the other way around)
What are concordant results?
For titrations, concordant results are results within 0.1 cm3 of each other
What is the empirical formula?
The empirical formula gives the smallest whole-number ratio of atoms of each element present in a compound
What is the molecular formula?
The molecular formula gives the actual numbers of atoms in a molecule
How are empirical formulas calculated?
1) Assume you have 100g of the compound - you can turn the percentages straight into masses.
2) Work out how many moles of each element are in 100g of the compound
3) Divide each number of moles by the smallest number of moles. This gives you the ratio of the elements in the compound
4) Apply these numbers from the ratio in the formula
What is ‘theoretical yield’?
Theoretical yield is the mass of product that should be formed in a chemical reaction - it assumes no chemicals are ‘lost’ in the process
How is the theoretical yield calculated?
1) Work out how many moles of the reactant you have
2) Use the equation to work out how many moles of product you would expect that that much reactant to make
3) Calculate the mass of that many moles of product
Why is the actual yield always less than the theoretical yield?
Sometimes all of the starting chemicals don’t react fully
Some chemicals are ‘lost’ e.g. some solution gets left on the filter paper
Some are lost during transfers between containers
Other products are formed in side reactions
What is the equation that links together percentage yield, actual yield and theoretical yield?
Percentage Yield = (Actual Yield / Theoretical Yield) x 100
What is atom economy?
Atom economy is the measure of the proportion of reactant atoms that become part of the desired product (rather than by-products) in the balanced chemical equation
What are the advantages of a high atom economy?
More efficient use of raw material
Less waste to deal with (especially if they are toxic)
Less money spent on separation
Better for the environment
Sustainable
Companies can sell the product for cheaper and make it more widespread
What is the equation that links together atom economy, the molecular mass of desired products and the sum of the molecular masses of all the reactants?
Atom Economy = (Molecular Mass of Desired Products / Sum of the Molecular Masses of all the Reactants) x 100
