Amount of substance Flashcards
What is a mole?
The amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon 12.
What is relative atomic mass?
The average mass of one atom compared to one twelfth of the mass of one atom of carbon 12
What is relative molecular mass?
The average mass of a molecule compared to one twelfth of the mass of one atom of carbon 12
How can you use the Avogadro’s constant to calculate the number of particles?
Number of particles = Number of moles * Avogadro’s constant
What is the Avogadro constant?
One mole contains 6.022*10^23 particles
How do you calculate the number of moles?
Moles = mass/relative molecular mass
What is the Ideal Gas equation?
pV = nRT
How do you convert temperature to Kelvin?
Kelvin = degrees centigrade + 273
How do you convert from cm^3 to dm^3?
cm^3 = dm^3 /1000
How do you convert from cm^3 to m^3?
cm^3 = m^3 /1000000
How do you convert from dm^3 to m^3?
dm^3 = m^3 /1000
What is the concentration of a solution?
The number of moles dissolved per 1dm^3.
How do you calculate the number of mole using the concentration and volume of the solution?
Number of moles = concentration * volume/1000
What are the units for the concentration of a solution?
mol dm^3
What is the empirical formula?
The simplest ratio of atoms of each element in a compound
What is the molecular formula?
The actual number of atom of each element in a compound
Made up of a whole number of empirical units
What is the theoretical yield?
The mass of product that should be formed in a chemical reaction
What is the actual yield?
The mass of product formed after the reaction and is always less than the theoretical yield
Why is the actual yield always less than the theoretical yield?
Not all the starting chemicals react fully
Some chemicals are lost
How do you calculate the percentage yield?
Percentage yield = Actual yield/theoretical yield * 100
What does the percentage yield tell us?
Percentage yield tells us how wasteful a process is as it is based on how much product is lost during the process
What is the atom economy?
Atom economy is a measure of the efficiency of a reaction
How do you calculate the atom economy?
%Atom economy = molecular mass of desired product/sum of molecular masses of all reactants * 100
Why do companies in the chemical industry try to use high atom economies?
High atom economy processses are better for the environment as there is less waste
Why are high atom economy processes more sustainable?
They make more efficient use of raw materials
Why are high atom economy processes less expensive?
Companies will spend less money on separating the desired product from the waste products
What do titrations allow you to do?
Titrations allow you to work out the concentration of an acid or alkali
Describe how you would find the concentration of an alkali or acid from a titration.
-Accurately pipette 25cm^3 of alkali into conical flask
-Touch the surface of the alkali with pipette
-Add a few drops of the appropriate indicator
-Fill a burette with a standard solution of acid using a funnel at eye level
-add the acid into the alkali whilst swirling the mixture
add the acid dropwise at the endpoint
-Repeat the experiment to get 2-3 concordant results
What is a standard solution?
A solution that has a known concentration
What are the two main indicators for acid/alkali?
Methyl orange
Phenolphthalein
What colour does methyl orange become in acid/alkali?
Red in acid
Yellow in alkali
What colour does phenolphthalein become in acid/alkali?
Colourless in acid
Pink in alkali
How do you calculate the apparatus uncertainty?
Apparatus uncertainty = (error /measurement) * 100
Describe how you would find the relative molecular mass of a substance in a titration.
- Calculate the moles of the acid in the solution
- Find the ratio of acid/alkali to substance
- Use the ratio to calculate the number of moles of the substance
- Calculate the relative molecular mass(mass = Mr * moles)
What happens when you increase the amount of equipment being used?
The total apparatus uncertainty increases
How would you calculate the total apparatus uncertainty?
Add all the uncertainties of the equipment together
How could you do to decrease the apparatus uncertainty?
- taking a large reading using the equipment
- using more sensitive equipment
What factors affect volume?
temperature
pressure
number of moles
Describe a method for making a solution
- Weigh a beaker using a top pan balance
- Add the solid into the beaker and weigh them
- Record the difference in mass
- Add distilled water into the beaker
- Stir with a glass rod until all has dissolved
- Transfer the solution into a volumetric flask with washings using a funnel
- Add water up to 250cm^3
- Place a lid on top
- Shake the flask for the solution to mix
Suggest a reason why repeating a titration makes the value for the average titre more reliable
- Anomalies can be eliminated
- Concordant results can be collected
- An average can be calculated
What effect would an air bubble have on the value of the first titre?
The value would be higher than the true value
What effect would an air bubble have on the average titre?
- No effect
- The titre value can be discarded
Suggest ideas on how the overall technique can be improved when making a solution
- weigh by difference
- wash the stirring rod/beaker after use
- shake the final solution
- make the sure the bottom of the meniscus touches the mark
What are the potential errors in using a gas syringe?
gas escapes before bung is inserted
syringe sticks
some gases like carbon dioxide and sodium dioxide are soluble in water
