chemistry - separate chemistry: qualitative analysis (5.8 - 5.18)

concentration definition

amount of solute dissolved in a stated volume of solution

5.8 calculate concentrations of solutions in mol dm^-3

5.8 convert concentration in g dm^-3 → mol dm^-3 & vice versa

g dm^-3 → mol dm^-3: ÷ relative formula mass of solute

mol dm^-3 → g dm^-3: x relative formula mass of solute

what’s the purpose of acid-alkali titrations?

find exact volume of acid that neutralises specified volume of alkali or vice versa

5.9 core practical: accurate acid-alkali titration, using burette, pipette & suitable indicator

1. rinse burette with hydrochloric acid

2. fill burette with the acid - ensure jet below tap is also full

3. record initial volume of acid in burette

4. rinse pipette with sodium hydroxide solution

5. fill pipette to 25cm³ mark & empty solution into conical flask

6. add few drops of methyl orange indicator to flask

7. place flask on white tile under burette

8. add acid to sodium hydroxide solution while swirling flask

9. when indicator starts to change colour, rinse tip of burette & sides of flask with small amount of distilled water from wash bottle to ensure all acid in mixture, then add acid drop by drop until end-point reached

10. record final volume acid in burette

11. repeat experiment (don’t repeat initial rinsing of burette & pipette) until concordant results obtained

5.11 percentage yield formula

5.12 is actual yield of reaction usually less/more than theoretical yield?

actual yield usually less than theoretic yield

5.12 why is actual yield of reaction usually than theoretical yield?

incomplete reactions

practical losses during experiment

competing, unwanted reactions (side reactions)

5.13 atom economy definition

shows percentage by mass of useful products (formed by reactants)

5.14 atom economy formula

5.15 why is particular reaction pathway chosen to produce specified product?

chosen based on factors:

• atom economy - high

• yield - high

• rate of reaction - fast

• equilibrium position - lies to right (favours product formation)

• usefulness of by-products - useful

(percentage yield - no indication of amount of waste products)

5.16 molar volume of any gas at room temp. & pressure

volume occupied by one mole of molecules of any gas at room temp. & pressure = 24dm³ (or 24000cm³)

5.17 molar volume equation

volume of gas = amount of gas (mol) x molar volume

volume = moles x 24