Chapter 4: Acids, bases, titrations

acids are…

proton donors

What is a strong acid?

completely dissociates in aqueous solution.

what is a weak acid?

partially dissociates in aqueous solution

(the equilibrium sign shows that the reaction is incomplete)

is ethanoic acid strong?

no!!

what is an alkali?

a bas that is dissolved in water, released OH^- ions.

what are all these?

common bases

in neutralisation, what happens to the H+ ions from the acid?

they are replaced by metal / ammonium ions

acid + metal oxide/hydroxide → (aren’t my old hats somewhere west???) 🤠

salt + water

acid + alkali →

salt + water

ionic equation of HCl + NaOH → H2O + NaCl

H⁺(aq) + OH^-(aq) → H₂O (l)

acid + metal carbonate →

salt + water + carbon dioxide (gas)

what is a standard solution?

a solution of known concentration

what is the tolerance of a 100cm³ volumetric flask?

± 0.20cm³

what is the tolerance of a 250cm³ volumetric flask?

± 0.30cm³

how to prepare a standard solution:

1. the solid is weighed accurately on a mass balance

2. dissolve solid in beaker, using distilled water

3. solution is transferred to volumetric flask → last traces of solution are rinsed into flask with distilled water

4. flask carefully filled to graduation line with distilled water → until bottom of meniscus lines up exactly with graduation line

   1. view at eye level for accuracy!

5. volumetric flask is inverted several times to mix solution thoroughly (with bung in!)

a burette recording is measured to the nearest…

half division → 2dp with the last number being a 0 or 5.

how to carry out an acid-base titration?

1. add measured volume of one solution → conical flask using a pipette.

2. other solution to burette, and take initial reading to the nearest 0.05cm3

3. add a few drops of indicator to conical and swirl

4. run solution from the burette into the conical flask, swirling conical flask → indicator changing colour indicates exact point at which reaction occurs.

5. record final burette volume

6. repeat accurately, adding solution dropwise until endpoint

7. keep doing titrations until 2 accurate titres are concordant.

what are concordant results?

within 0.10cm³

the oxidation number of an element is always…

zero

what is the oxidation number of H in metal hydrides?

-1

what is the oxidation number of Oxygen in peroxides?

-1 → H₂O₂

what is the oxidation number of Oxygen when bonded to Fluorine?

+2 → F₂O

do oxidation numbers have the sign before or after the number?

before → +2, -1

sum of oxidation numbers =

total charge

what do Roman numerals represent?

the oxidation state of an element → iron (III) is Fe³⁺ with an oxidation number of +3

nitrite vs. nitrate?