Chemistry, quantative (copy)

where do lots of reactions in chemistry take place?

between substances that are dissolved in a solution

what is concentration?

the amount of a substance in a certain volume of a solution

what makes concentration bigger?

more solute being added in a given volume

how do you measure concentration? ( in g/dm³)

concentration (g/dm³) = mass of solute (g) / volume of solvent (dm³)

how do you measure concentration? ( in mol/dm³)

concentration (mol/dm³) = number of moles of solute (mol) / volume of solvent (dm³)

how to calculate no. of moles

concentration x volume

how do you convert cm³ to dm³?

divide by 1000

what are titrations?

experiments that let you find the volumes of 2 solutions that are needed to react together completely

how do you work out the concentration of one of the solutions in a titration?

use the concentration of the solution we know, volumes of the titration experiment and the reaction equation (conc = no. of moles / vol)

where is the example for this

pg 80 of chemistry book ex. 1

why will titration experiments be repeated?

to find the average, or until you get concordant results

what are concordant results?

results within 0.1cm³

how do you change mol/dm³ to g/dm³?

mass = moles x rfm

what do a lot of reactions make?

more than one product. some will be useful, others will be a waste

what does atom economy of a reaction tell you?

how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as the desired product

whats the equation for atom economy?

atom economy = (rfm of desired product / rfm of all reactants) × 100

what does 100% atom economy mean?

all of the atoms in the reactants have been turned into the desired product

the higher the atom economy…?

… the ‘greener’ the process of the reaction

whats a problem in terms of atom economy?

if you are making a lot of waste

what do reactions with low atom economy do? (2)

• use up resources very quickly

• make lots of waste materials that have to be disposed of somehow, which makes the reactions unsustainable

why can low atom economy be a problem?

because they may not be profitable - raw materials are expensive to buy and waste products can be expensive to remove responsibly

whats the best way to solve low atom economy?

finding a use for the waste products rather than just throwing them away

what are reactions with the highest atom economy?

the ones which have only one product, which has an atom economy of 100%

what are other factors to decide choosing which reaction to use to make a specific product besides atom economy? (4)

• yield

• the rate of reaction

• the position of equilibrium for reversible reactions

• useful by-products

what is the yield?

the amount of product you get

how you get a higher yield?

the more reactants you start with

what is the formula for percentage yield?

percentage yield (%) =( mass of product actually made (g) / maximum theoretical mass of product (g)) x 100

what is percentage yield always in between?

0 and 100

what does 100% yield mean?

you got all the product you expected

what does 0% yield mean?

no product was made

what should industrial processes have?

a high percentage yield to reduce waste and costs

what are all yields?

less than 100%, as some product or reactant always gets lost along the way

what can the yield depend on?

what sort of reaction it is and what apparatus is being used

whats one issue with yield being lost?

not all reactants react to make a product → in reversible reactions the products can turn back into reactants so the yield will never be 100%

whats another issue to yield being lost?

side reactions → some of the reactants might react with gases in the air, or impurities in the reaction mixture so they end up forming other useless products

whats a final issue to yield being lost?

some product is lost when you separate it from the reaction mixture → e.g. filtering (some product is always left behind), transferring materials from one container to another (droplets left or spillages)

what do titrations allow you to do?

find out exactly what vol of acid is needed to neutralise a measured volume of alkali. you can use this data to work out the concentration of the acid/alkali

how do you do the titration? (example of an alkali)

1. use a pipette and pipette filler to add a set vol of the alkali to a conical flask. also add a few drops of indicator

2. use a funnel to fill a burette with some acid of known concentration. do below eye level and record initial vol of acid in burette

3. use burette to add acid to the alkali slowly, while swirling the conical flask. go slower when you reach near the end point

4. the indicator will change colour when all the alkali has been neutralised

5. record the final vol of acid in the burette

what does a pipette do?

measures only one vol of solution

what does a burette do?

measures different vols and lets you add a solution drop by drop

what do scale marks down a burette do?

shows the vol of acid used

how do you increase the accuracy and spot anomalous results of a titration?

get several readings and repeat experiment

what should your first titration be?

a rough titration to get an approximate idea of where the solution changes colour

what do you do after the first titration?

repeat the whole experiment a few times making sure you get concordant results (results within 0.1cm³), then calculate a mean

what is universal indicator used for?

estimating the pH of the solution because it can turn a variety of colours. each colour indicates a narrow range of pH values. it changes from red (very acidic), to purple (very alkaline)

what colour is phenolphthalein in acids?

colourless

what colour is phenolphthalein in alkalis?

pink

what colour is litmus in acids?

red

what colour is litmus in alkalis?

blue

what colour is methyl orange in acids?

red

what colour is methyl orange in alkalis?

yellow