C5.1 Flashcards
What is theoretical yield?
Maximum mass it is possible to make from a given mass of reactants
What is the limiting reactant?
A reactant present in an amount less than that needed to react completely with the other reactant in a chemical reaction
How to calculate theoretical yield?
Use Table method Mass (g) Mr Moles Ration
What is actual yield?
The mass of the product you actually make in a chemical reaction - usually less than the theoretical yield
What is percentage yield?
(Actual yield/theoretical yield) * 100
Reasons why percentage yield may not be 100%
1) Reactants may react in a different way than expected
2) Reaction may not go to collection - some of the reactants present do not react (often happens in reversible reactions)
3) May lose some of the product during separation or as a gas
What is the atom economy?
It is a measure of how many atoms in the reactants form a desired product
How to calculate atom economy?
(Sum of Mr of desired product/sum of Mr of all products) * 100
USE BALANCING NUMBERS FROM BALANCED EQUATION
Factors considered when choosing a reaction pathway?
Yield of the product Atom economy Usefulness of by-products Rate of reaction Equilibrium position (compromise)
Higher atom economy….
More efficient reaction
By-products?
Substances formed in addition to the desired product
IF by product is useful and can be sold THEN it too becomes desirable and improves the efficiency by improving atom economy
Conversion between cm^3 and dm^3
1 litre = 1 dm^3 = 1000ml = 1000cm^3 Cm3 -> dm3 DIVIDE BY 1000 dm3 -> cm3 MULTIPLY BY 1000
How to calculate concentration?
Mass of solute (g/mol) / Volume of solution (dm3/cm3)
Convert from mol/dm3 to g/dm3
Multiply by molar mass of solute
Divide if other way round
What is a titration?
Add a known volume of alkali to a conical flask and a few drops of indicator - phenolphthalein
Then add acid to the flask from a burette (neutralisation reaction) which is a long graduated glass tube with a tap at the bottom - at the end point (when alkali is neutralised) you stop adding acid
Determine concentration of acid/alkali
Volumetric flask
Piece of glassware used to make an accurate volume of solution - usually a standard solution
Equipment preparations for a titration
Use volumetric pipettes to measure alkali solution (use pipette filler too)
Burette must be clamped VERTICALLY to get accurate readings
Add indicator to alkali
What is a titre?
A titre is the difference between the initial and final burette reading of acid - the volume of acids added to the alkali in the flask in order to neutralise it ; record your readings to two decimal places ending in 0 if the bottom of the meniscus is on a burette line or 5 if between
How to obtain repeatable titre?
Swirl the flask during a titration to mix it’s contents
First titration is usually a rough run - then in later runs you can be more accurate and add the acid to within a few cm3 of the rough titre (until adding it drop by drop)
Repeat titration until 2 concordant tires obtained (within 0.1cm3 of each other) - allows you to calculate a mean titre with high precision
Safety for titration
Eye protection should be worn throughout practical
Values gained after titration
Acid and alkali
1 concentration and 1 volume
1 volume and no concentration (needs to be found out)
Equation for titrations
Amount in moles = concentration * volume
N = c * v
What is the molar volume?
It is the constant volume that one mole of any substance in the gas state of furies at the same pressure and temperature (RTP)
24dm^3/mol
Fixed equation?
Volume (dm^ 3) = amount in mol * 24dm^3/mol
How to measure the volume of Gas?
1) Fill measuring cylinder with water and while keeping its head underwater turn it upside down
2) Clamp measuring cylinder securely
3) Mix reactants in conical flask and attach delivery tube
4) Measure volume of gas produced in the reaction by recording end reading on measuring cylinder
MAKE SURE MOUTH OF CYLINDER UNDERWATER - PREVENTS AIR GETTING IN OR OUT OF WATER (would affect reading on measuring cylinder) ; eye protection should be worn
