C5.1

Question 1

What is theoretical yield?

Answer 1

Maximum mass it is possible to make from a given mass of reactants

Question 2

What is the limiting reactant?

Answer 2

A reactant present in an amount less than that needed to react completely with the other reactant in a chemical reaction

Question 3

How to calculate theoretical yield?

Answer 3

Use Table method
Mass (g)
Mr
Moles
Ration

Question 4

What is actual yield?

Answer 4

The mass of the product you actually make in a chemical reaction - usually less than the theoretical yield

Question 5

What is percentage yield?

Answer 5

(Actual yield/theoretical yield) * 100

Question 6

Reasons why percentage yield may not be 100%

Answer 6

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

Question 7

What is the atom economy?

Answer 7

It is a measure of how many atoms in the reactants form a desired product

Question 8

How to calculate atom economy?

Answer 8

(Sum of Mr of desired product/sum of Mr of all products) * 100
USE BALANCING NUMBERS FROM BALANCED EQUATION

Question 9

Factors considered when choosing a reaction pathway?

Answer 9

Yield of the product
Atom economy
Usefulness of by-products
Rate of reaction
Equilibrium position (compromise)

Question 10

Higher atom economy….

Answer 10

More efficient reaction

Question 11

By-products?

Answer 11

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

Question 12

Conversion between cm^3 and dm^3

Answer 12

1 litre = 1 dm^3 = 1000ml = 1000cm^3
Cm3 -> dm3
DIVIDE BY 1000
dm3 -> cm3
MULTIPLY BY 1000

Question 13

How to calculate concentration?

Answer 13

Mass of solute (g/mol) / Volume of solution (dm3/cm3)

Question 14

Convert from mol/dm3 to g/dm3

Answer 14

Multiply by molar mass of solute

Divide if other way round

Question 15

What is a titration?

Answer 15

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

Question 16

Volumetric flask

Answer 16

Piece of glassware used to make an accurate volume of solution - usually a standard solution

Question 17

Equipment preparations for a titration

Answer 17

Use volumetric pipettes to measure alkali solution (use pipette filler too)
Burette must be clamped VERTICALLY to get accurate readings
Add indicator to alkali

Question 18

What is a titre?

Answer 18

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

Question 19

How to obtain repeatable titre?

Answer 19

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

Question 20

Safety for titration

Answer 20

Eye protection should be worn throughout practical

Question 21

Values gained after titration

Answer 21

Acid and alkali
1 concentration and 1 volume
1 volume and no concentration (needs to be found out)

Question 22

Equation for titrations

Answer 22

Amount in moles = concentration * volume

N = c * v

Question 23

What is the molar volume?

Answer 23

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

Question 24

Fixed equation?

Answer 24

Volume (dm^ 3) = amount in mol * 24dm^3/mol

Question 25

How to measure the volume of Gas?

Answer 25

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