Laboratory Equipment and Safety: Quiz

Laboratory Equipment and Safety: Quiz

7 questions

1. Question 1EasyA bottle of ethanol carries the flame pictogram. What does it mean?

   AToxicBFlammableCCorrosiveDExplosive
   Show answer

   Answer: Flammable

   The flame pictogram means the substance or its vapour catches fire easily. Keep it away from flames; heat it with a water bath or hot plate.

2. Question 2EasyWhat is the safe way to dilute concentrated sulfuric acid?

   APour water quickly into the acidBAdd the acid slowly to the water, stirringCAdd both at once into an empty beakerDHeat the acid first, then add water
   Show answer

   Answer: Add the acid slowly to the water, stirring

   Mixing releases a lot of heat. Adding acid to a larger volume of water spreads the heat; adding water to acid can boil the water and spray acid.

3. Question 3EasyWhich equipment would you use to add a measured volume of acid drop by drop in a titration?

   ABeakerBMeasuring cylinderCBuretteDVolumetric flask
   Show answer

   Answer: Burette

   A burette delivers a variable volume that is read accurately (to two decimal places) and can be added a drop at a time.

4. Question 4MediumWhat is the percent uncertainty when 25.0 mL is measured with a measuring cylinder of uncertainty ±0.5 mL?

   A0.5 %B2 %C0.02 %D50 %
   Show answer

   Answer: 2 %

   (0.5 mL ÷ 25.0 mL) × 100 % = 2 %. A 25 mL pipette (±0.03 mL) gives only 0.12 %.

5. Question 5MediumA burette reads 1.20 mL before and 24.70 mL after a titration. What is the titre?

   A25.90 mLB23.50 mLC24.70 mLD23.5 mL
   Show answer

   Answer: 23.50 mL

   Titre = final − initial = 24.70 mL − 1.20 mL = 23.50 mL, recorded to two decimal places like the readings.

6. Question 6MediumWhy must your eye be level with the meniscus when reading a scale?

   ATo avoid parallax errorBTo see the colour betterCTo stop the liquid evaporatingDBecause the meniscus moves
   Show answer

   Answer: To avoid parallax error

   Viewed from above or below, the meniscus lines up with the wrong mark on the scale. This is parallax error.

7. Question 7HardWhich choice gives the most precise way to make exactly 250.0 mL of a solution?

   AA 250 mL beakerBA 250 mL conical flaskCA 250 mL volumetric flaskDFive 50 mL measuring cylinder fills
   Show answer

   Answer: A 250 mL volumetric flask

   A class A 250 mL volumetric flask is accurate to about ±0.15 mL (0.06 %). Beakers and conical flasks have only approximate marks, and five cylinder fills add five uncertainties.