Amount of Substance Flashcards
What is an empirical formula?
- simplest whole number ratio of atoms of each element in a compound
What is a molecular formula?
- actual number of atoms of each element in a compound
How to work out the empirical formula
Identify the mass of each element
Divide by RAM to get N of M
Simplify
What is atom economy?
- a measure of the amount of products which is desired and the amount which is waste
Atom Economy equation?
(Mr of desired product/Mr of all products) x100
What is percentage yield?
- ratio of actual yield to the theoretical yield
Percentage yield equation?
(mass of product actually made / maximum theoretical mass of product) x 100
Percentage purity formula?
mass of pure substance / mass of impure sample x 100
What is Avogadro’s constant?
- the amount of molecules in one mole of a substance (6.022 x 10^23)
Equation for number of particles?
number of particles = number of moles x Avogadro’s constant
Equation for Number of Moles in a solid ?
- Nm=Mass/Mr
Equation for moles in a solution?
Nm = concentration (moldm-3) x volume (dm3)
How to find conc in gdm-3?
Conc in moldm-3 x Mr
Equation for density?
- Density = mass/volume
Percentage Uncertainty/Apparatus error equation
= (margin of error/ quantity measured) x 100
how to decrease percentage uncertainty/apparatus errors?
Increase quantity measured
What is the Ideal Gas Equation?
Pressure x Volume = Number of Moles x Gas Constant x Temperature
What are the units of measurement of each variable in the ideal gas equation?
pressure in pascals
volume in metres³
temperature in kelvin (°C + 273)
Describe how to make up a volumetric solution? (6)
- Place the weighing boat on a (2 dp) balance and tare, then transfer solid to weighing boat and record mass.
- Transfer solid to beaker and rinse washings into beaker with deionised water
- Add approx 100cm³ of deionised water and stir with a glass rod until all the solid has dissolved.
- Transfer to a volumetric flask with a funnel and rinse the beaker,stirring rod and funnel with deionised water into volumetric flask.
- Make up to the 250cm³ graduation mark with deionised water.
- Invert flask to make sure the solution is thoroughly mixed
What is a Titration used for?
- used to determine the concentration of an unknown solution
Describe how to carry out a simple Acid-Base Titration?(6)
- Rinse the burette with deionised water and then the standard solution then fill burette with standard solution below tap/jet and take initial reading
- Rinse pipette with deionised water and then the unknown conc. solution and then transfer 25cm³ to a conical flask
- Add 3-4 drops of indicator to conical flask
- Add solution from the burette with constant swirling of the conical flask until the indicator barely changes colour
- Continue to add dropwise towards end until definite colour change, record final burette reading and calculate titre volume
- Repeat until you have two concordant results
Why would a rough titration be useful before doing subsequent titrations?
- its use to determine the approximate amount of standard solution needed to neutralise an unknown solution
Why use a conical flask during acid-base titration?
- used so no solution spills when swirling
Why remove the filter funnel before starting the titration?
- removing the filter funnel ensures no additional drops enter from the burette and lower your titre
How to improve the accuracy of your acid base titration?
- rinse the sides of the conical flask during titration to ensure all of the solution is reacting
