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Edexcel IAL Chemistry 3.P6 Evaluating experimental methods

Name the purpose of each step, connect it to the chemistry or measurement and propose a specific change whose effect on the result is clear.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
AS

Exam points

  • Explain apparatus choices such as a loose lid that retains solid while releasing gas.
  • Use heating to constant mass as evidence that reaction or water removal is complete.
  • Suggest a method improvement and state how it changes loss, completion or measurement bias.

3.P6—Evaluating an experimental method question 1

[Maximum number: 2]

A class of students carried out experiments to determine the enthalpy change for the reaction of magnesium metal with hydrochloric acid. The following method was used. Step1 A 1.00 m length of magnesium ribbon was cleaned using sandpaper, weighed and cut into 10 cm lengths. Step 250 cm3250 \mathrm{~cm}^{3} of dilute hydrochloric acid (an excess) was placed into a polystyrene cup and the temperature measured. Step 3 A 10 cm length of magnesium ribbon was added to the hydrochloric acid. The solution was stirred gently and the maximum temperature recorded.

Mg+2HCl→MgCl2+H2\mathrm{Mg}+2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_{2}+\mathrm{H}_{2}

Results

Table for Question 3.P6—Evaluating an experimental method question 1 — Edexcel A-Level Chemistry AS

Explain why the magnesium ribbon was cleaned with sandpaper before being weighed.

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