Practical Skills

Question 1

what is a standard solution?

Answer 1

a solution of known concentration

Question 2

how do you make a standard solution?

Answer 2

1. weigh sample bottle containing solid on 2 d.p. balance
2. transfer to beaker and reweigh empty sample bottle
3. record difference mas; this is = mass of solid
4. add distilled/deionised water
5. stir with glass rod or swirl
6. until all solid has dissolved
7. Transfer to volumetric/graduated flask using funnel with washings
8. make up to 250cm^3/mark with water
9. shake/invert/mix

Question 3

what equipment is used to carry out a titration?

Answer 3

• a pipette and pipette filler are used to accurately measure out the volume of a reactant before transferring it to a conical flash
• a burette is used to add small volumes of one reactant to the other reactant

Question 4

how do you carry out a titration?

Answer 4

1. once the pipette has been used to place one reactant into the conical flask, fill the burette with the other reactant. record initial volume
2. add a few drops of indicator into the conical flask
3. open the burette tap and allow the reactant to flow into the conical flash, swirling it to mix the contents
4. close the burette tap once the expected colour change occurs. use a white tile so the colour change is easy to identify
5. record final burette volume
6. repeat until you get concordant results, then calculate a mean titre

Question 5

why are acid-base indicators used?

Answer 5

to detect when a reaction reaches completion, usually by the presence of a colour change

Question 6

what are concordant results

Answer 6

results within 0.1cm3 of each other

Question 7

what are some common potential hazards in the lab, and how can you control them?

Answer 7

• bunsen burner - risk of burns - keep away from flammable chemicals and away from the edge of the desk
• chemicals - may be an irritant or corrosive causing irritation to the skin, eyes, lungs; may be toxic; may be flammable - handle with care and while wearing gloves; wear eye protection; keep away from the edge of the desk and an open flame; don’t ingest
• glassware - may break and cut you - handle with care; keep away from the edge of the desk

Question 8

what is Hess’ Law?

Answer 8

the enthalpy change for a chemical reaction is always the same, regardless of the route from reactants to products

Question 9

how can you reduce the uncertainty in mass measurement

Answer 9

• use a balance with a greater resolution
• use a larger mass

Question 10

give an example of an irritant

Answer 10

mild acid or alkali