2 Amount of substance Flashcards
What is the equation that links moles, mass and Mr
Moles=mass/mr
What is the equation that links moles volume and concentration
Concentration=moles/volume
Describe what is meant by Avogadro’s constant
- The number of particles / atoms / ions in 1 mole of a substance
- 6.022x10^23
- number of particles= moles X 6.022x10^23
What is the ideal gas equation
PV=nRT
How do you convert °C into K
+273
Describe what is meant by the molecular formula of a compound
The actual number of each atom of an element in a compound
Describe what is meant by the empirical formula
- The simplest whole number ratio of each atom of an element, in a compound
Describe what is meant by atom economy and write the formula
- The percentage of reactants that become useful products
- Atom economy(%) = mass of desired product/total mass of product X100
What is the atom economy when there is only one product in the equation
100%
Describe how to calculate percentage yield
mass of product actually made/maximum theoretical mass X 100
Why is the percentage yield never 100%
- Not all the reactants are being used up
- Products escaping from the reaction vessel
- Physical loss of products during transfer
Describe how to prepare a standard solution
(RP1) A
- Transfer an accurate mass of solid into a weighing boat and measure the mass using a top pan balance
- Transfer the solid into a clean, dry beaker and weigh the empty weighing boat
- Calculate the difference in mass
- Add 100cm3 of distilled water to the same beaker, to dissolve the solid, stirring with a glass rod
- Transfer the contents in the beaker to a 250 cm3 volumetric flask using a funnel
- Rinse the beaker, funnel and glass rod with distilled water, using a wash bottle
- Transfer the washing to the same 250cm3 volumetric flask
- Fill the volumetric flask with distilled water up to the 250cm3 meniscus, at eye level.
- Place a stopper on the flask and invert several times to mix thoroughly, so the concentration is the same throughout the flask,
Describe how to carry out titration
(RP1) B
- Rinse the burette with the standard solution
- Discard the rinsings and fill the burette with the standard solution to the 0cm3 meniscus
- Rinse a pipette with the sodium hydroxide solution
- Using a pipette and pipette filler, transfer 25cm3 of this solution into a conical flask
Add 2-3 drops of phenolphthalein indicator to the conical flask - Add the standard solution from the burette, with constant swirling, until the indicator just changes colour. This is a rough titration.
- Repeat the steps above several times to achieve 2-3 concordant results, adding the solution dropwise near the endpoint
- Calculate the mean titre from concordant results
Describe how to calculate uncertainty
(Uncertainty / quantity measured ) x 100
Describe how to calculate uncertainty if 2 measurements are taken
(Uncertainty x 2 / quantity measured ) x 100
Explain what the effect of the titre would be if the pipette used to transfer the acid solution was filled to slightly above the mark.
Increased titre because more moles of acid are transferred to the conical flask
Explain what the effect of the titre would be if the pipette used to transfer the acid solution was filled to slightly below the mark.
Decreased titre because less moles of acid are transferred to the conical flask
Explain what the effect of the titre would be if the volumetric flask was filled to slightly above the mark
Decreased titre because the concentration of the acid is lower
Explain what the effect of the titre would be if the volumetric flask was filled to slightly below the mark
Increased titre because the concentration of the acid is higher
A student suggests washing out the pipette with water before filling it with acid solution.
Explain why this is not a good idea.
Water left in the pipette would dilute the acid, therefore, the titre will decrease
