Question

determining the decomposition of nahco₃
experiment introduction
alexandra designed an experiment to determine the reaction occurring when sodium bicarbonate, nahco₃, is decomposed through strong heating.

she massed a sample of sodium bicarbonate in a tared (zeroed) test tube. the initially recorded mass was 7.53 grams of sodium bicarbonate. she then heated the tube over a cool flame for two minutes, a much hotter blue flame for five minutes, and then a cooler flame for two more minutes.

after being allowed to cool, the mass was measured again.

which state of matter would remain in the test tube after the heating and cooling processes?

• gas
• solid
• liquid

Explanation:

When sodium bicarbonate ($\ce{NaHCO_{3}}$) is heated, it decomposes according to the reaction: $\ce{2NaHCO_{3}(s) \xlongequal{\Delta} Na_{2}CO_{3}(s) + H_{2}O(g) + CO_{2}(g)}$. The water vapor and carbon dioxide gas will escape (or condense and then evaporate/escape during heating and cooling), leaving behind the solid sodium carbonate ($\ce{Na_{2}CO_{3}}$) in the test tube. So the state of matter remaining is solid.

Answer:

B. solid