Two white powders—granulated sugar (C H O ) and sodium hydrogen carbonate (NaHCO…
CHEMISTRY · Single correct · GCSE · Chemistry · Chemical Analysis · Chemical Analysis
Problem
Two white powders—granulated sugar (C12H22O11) and sodium hydrogen carbonate (NaHCO3)—look identical. A teacher supplies only the following items:
• Bunsen burner and striker
• Watch glasses
• 100 mL of clear limewater (Ca(OH)2(aq))
• Glass tubing and rubber tubing
Which of the following experimental plans would most effectively distinguish whether heating each powder results in a chemical or a physical change?
(a) Heat both powders strongly until they darken, then compare the masses of the remaining solids after cooling.
(b) Gently heat each powder on a watch glass and record whether it melts; melting indicates a physical change, whereas failure to melt indicates a chemical change.
(c) Gently heat a small sample of each powder on a watch glass and direct any gas produced through limewater, observing whether the limewater turns cloudy.
(d) Dissolve equal masses of each powder in water and measure the pH of the resulting solutions before and after gentle heating.