Amount of substance Flashcards
What is meant by relative atomic mass? Ar
- average mass of one atom of an element
- divided by 1/12th mass of a C-12 atom
What is meant by relative molecular mass?
- average mass of one molecule
- divided by 1/12th mass of a C-12 atom
Moles/mass/Mr equation
Mass (g) = moles x Mr
Moles/concentration/volume equation
moles = conc x volume (dm3)
State the ideal gas equation
PV = nRT
P = Pascals
V = m3
T = Kelvin
R = 8.31 jk-1 mol-1
Kpa into pascals?
multiply by 1000
m3 to dm3?
multiply by 1000
cm3 to m3?
divide by 1 x 10^6
dm3 to m3?
divide by 1000
dm3 to cm3?
multiply by 1000
m3 to cm3?
multiply by 1 x 10^6
m3 to dm3?
multiply by 1000
What is meant by empirical formula?
- Simplest whole number ratio of atoms
- of each element in a compound
What is meant by molecular formula?
- Actual number of atoms
- of each element in a compound
% yield formula?
amount of specific product formed (actual) / theoretical maximum amount of product that could be formed (theoretical) x 100
Describe how to make up a standard solution
Stage 1:
- weigh a sample bottle containing solid
- transfer to beaker and reweigh sample bottle
- record difference in mass
Stage 2:
- add distilled water
- stir with glass rod
- until all solid has dissolved
Stage 3:
- Transfer to volumetric flask
- with washings
- make up to 250cm with water
- shake/invert
How to calculate percentage error?
% error = error of equipment/amount measured x 100
Suggest a reason for removing the funnel after it has been used for filling the burette
- droplet from funnel could enter burette
- affects volume of
During the titration, the inside of the conical flask is rinsed with distilled water.
Suggest why rinsing improves the accuracy of the titre
ensures all reactants are able to react
During a titration, a chemist rinsed the inside of the conical flask with deionised water. The water used for rinsing remained in the conical flask.
Explain why the water used for rinsing has no effect on the accuracy of the titre.
does not change the number of moles of reactants in the conical flask
A teacher noticed that a student had not cleared a large air bubble from below the burette tap in preparing the burette for use before starting the titration. This air bubble was ejected during the first titration of the volumetric flask mixture.
State the effect that this mistake would have on the value of the first titre.
Increase in volume of titre
Space will fill during titration and titre will be too high. What is the cause of this?
not filling burette tap before starting titration
Ensures all reagents are able to react. What is done in a titration to ensure this?
rinsing the walls of the conical flask with deionised water
Less chance of losing liquid on swirling. What is done in a titration to ensure this?
using conical flask instead of a beaker
A droplet could enter the burette and increase the titre. What is the cause of this?
leaving the funnel in the burette
