Amount of Substance Flashcards
Define relative atomic mass
The average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
State the equation for the number of moles
Mass/Mr
State the ideal gas equation and the units for each variable
PV=nRT
P= Pa, V= m3, R= 8.31, T= K
State the equation for concentration
Moles/Volume
How do you convert from ⁰C to K?
+ 273
How do you convert from cm3 to m3?
÷ 1,000,000
How do you convert from cm3 to dm3?
÷ 1,000
How do you convert from dm3 to m3?
÷ 1,000
What’s the equation for the number of particles in a substance?
No of particles = amount of substance (in mol) X Avogadro’s constant
What is Avogadro’s number?
6.02 x 10 (to the power of) 23
State the equation for density
Mass/volume
Define empirical formula
Simplest ratio of atoms of each element in the compound
Define molecular formula
The actual number of atoms of each element in the compound
State the equation percentage yield
Actual yield/theoretical yield x 100
State the equation for percentage atom economy
Mass of useful products/mass of all reactants x 100
What is the method for finding out the water of crystallisation of calcium sulphate crystals using a crucible?
- Weigh an empty clean dry crucible and lid.
- Add 2g of hydrated calcium sulphate to the crucible and weigh again.
- Heat strongly with a Bunsen for a couple of minutes
- Allow to cool
- Weigh the crucible and contents again
- Then heat up the crucible again and reweigh until you reach a constant mass.
State the units for density
g cm-3
Why should small amounts of solid such as 0.100 g not be used in a crucible water of crystallisation experiment?
Errors in weighing are too high
Why should large amounts of solid such as 50 g not be used in a crucible water of crystallisation experiment?
The decomposition is like to be incomplete
Why does the crucible need to be dry?
Wet crucible would cause inaccurate results as mass loss to be too large as water would be lost when heating
What are 3 potential errors of a gas syringe?
- Gas escapes before bung inserted
- Syringe sticks
- Some gases like carbon dioxide or sulphur dioxide are soluble in water so the true amount of gas is not measured
What are the steps for how you would make a standard solution in a volumetric flask?
- Weigh the sample bottle containing the required mass of solid on a 2 decimal places balance
- Transfer to beaker and reweigh sample bottle
- Record the difference in mass
- Add 100cm3 of distilled water to the beaker
- Use a glass rod to stir to help dissolve the solid.
- If necessary heat gently until all the solid had dissolved
- Pour solution into a 250cm3 volumetric flask via a funnel.
- Rinse beaker and funnel and add washings from the beaker and glass rod to the volumetric flask
- Make up to the mark with distilled water using a dropping pipette for last few drops.
- Invert flask several times to ensure uniform solution.
What are the steps for carrying out a titration?
- Rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water)
- Pipette 25 cm3 of alkali into conical flask
- Touch surface of alkali with pipette ( to ensure correct amount is added)
- Adds acid solution from burette
- Make sure the jet space in the burette is filled with acid
For the method for finding out the water of crystallisation of calcium sulphate crystals, what is the purpose of the lid?
xxxxxx
