Indicators and titrations curves

Equivalence point

the point at which an acid/base is completely neutralised in a chemical reaction, according to stoic ratio

end point

the point at which an indicator changes color in a titration ideally matches EQ point

Indicators

are weak acids or bases which are sensitive to H+ conc

Types of indicators

methyl red/orange, phenolphthalein, bromothymol blue, litmus

What do you use for a strong acid-weak base titration (ph5)

methyl orange

What do you use for a weak acid-strong base titration (ph9)

phenolphthalein

What do you use for a weak acid-weak base (ph7)

phenolphthalein

Requirements for a primary standard

• Available as an analytical grade solid (high purity)

• Low reactivity (so it doesn’t react with oxygen in the air or CO2/other gases)

• Relatively high molar mass (reduces weighing errors)

• Non-hydroscopic (should not absorb moisture from the air, so the mass won’t change)

Produces by weighing a solid and dissolving it to make a known volume of soltuion

Making a primary standard

1. determine mass of solid

2. rinse volumetric flask with distilled water

3. weigh solid in a small

4. transfer solid to volumetric flask

5. rinse funnel used to ensure all primary standard is in flask

6. add a small amount of distilled water and swirl until dissolved

7. add distilled water until bottom of meniscus is touching line on flask

Standard solutions

rinsing

• volumetric flask: distilled water

• beaker- rinsed with solution to be stored in beaker

• pipette: solution

• burette- solution

• conical flask- distilled water

Performing a titration