Experimental Design (Cambridge O Level Chemistry)

A student wants to investigate the rate of reaction between marble chips and hydrochloric acid by measuring the volume of carbon dioxide produced with different concentrations of acid.

The equation for the reaction is as follows:

2 HCl + MgCO₃ → MgCl₂ + CO₂ + H₂O

Which of the following lists of equipment can she use to measure the volume of the gas produced?

The steps below are for an acid-base titration. 

1	Record the final volume of hydrochloric acid in the burette
2	Add hydrochloric acid from the burette into the conical flask until the indicator changes colour
3	Record the initial volume of hydrochloric acid in the burette
4	Add a fixed volume of sodium hydroxide to a conical flask using a pipette
5	Add indicator

What is the correct order of these steps?

A student is following the written procedure for an experiment. The instruction states:

'Quickly add 25 cm³ of sodium hydroxide'

Which piece of apparatus would be most suitable to use?

W, X, Y and Z are pieces of laboratory apparatus.

Which row describes the most appropriate use of the apparatus for the measurement taken?

	Apparatus	Measurement taken
A	W	0.5 cm3 of acid to add to marble chips in a rate of reaction investigation
B	X	20 cm3 of sodium hydroxide for use in a titration
C	Y	26.70 cm3 of hydrochloric acid added to sodium hydroxide in a titration
D	Z	85 cm3 of gas given off in a rate of reaction investigation

A student decided to investigate the rate of reaction between marble chips and dilute hydrochloric acid at 35 ^oC. 

She had access to the following apparatus:

W a balance

X a thermometer

Y a measuring cylinder

Z a stopwatch

Which pieces of apparatus did she use?

A student has to measure 28.2 cm³ of aqueous sodium bromide.

Which piece of apparatus should the student select?

A

B

C

D

A student prepared crystals of potassium(II) chloride by the following method.

1	25.0 cm3 of dilute hydrochloric acid was accurately measured into a conical flask using a measuring cylinder
2	Aqueous potassium hydroxide was added from a burette until the solution was neutral
3	The solution was evaporated and the crystals washed with approximately 20 cm3 of water measured using a pipette

Which steps do not use the most appropriate piece of apparatus for the measurement taken?

A student prepared a solution of copper(II) sulfate by mixing dilute sulfuric acid with an excess of copper(II) oxide.

They filtered the mixture using the apparatus below.

Which terms best describes each substance?

	Solvent	Solute	Filtrate	Residue
A	water	copper(II) sulfate	copper(II) sulfate solution	copper(II) oxide
B	dilute hydrochloric acid	copper(II) oxide	water	copper(II) oxide
C	water	copper(II) sulfate solution	copper(II) oxide	copper(II) sulfate
D	copper(II) sulfate solution	water	dilute hydrochloric acid	water

A student performed a titration to find the volume of hydrochloric acid required to neutralise 25.0 cm³ of sodium hydroxide using the following method.

• Add a fixed volume of sodium hydroxide to a conical flask using a measuring cylinder
• Add methyl orange indicator
• Record the initial volume of hydrochloric acid in the burette 
• Add hydrochloric acid from the burette into the conical flask until the indicator changes colour
• Record the final volume of hydrochloric acid in the burette

Another student suggested the following changes.

1	Use a pipette to measure the sodium hydroxide
2	Use universal indicator as the indicator
3	Repeat the experiment until the results are concordant
4	Ensure that the initial volume of hydrochloric acid reads 0.00 cm3 on the burette

Which suggestions would improve the experiment?

A student titrated sodium carbonate solution against 25 cm³ of hydrochloric acid. 

They used methyl orange as an indicator.

What is the colour changed observed at the end point?

Why is it important to fill the space below the tap in a burette with acid or alkali before beginning a titration?