A laboratory technician compared two solids that can be used in reusable hot and cold packs. Equal masses of each solid were dissolved separately in 100 cm3...
Question 1 Report
A laboratory technician compared two solids that can be used in reusable hot and cold packs. Equal masses of each solid were dissolved separately in 100 cm3 of water in the insulated cup shown in Fig. 1. The solid was stirred until it had all formed a solution. Both experiments began at the same temperature. The technician recorded the lowest or highest temperature reached after two minutes. The cups, thermometer and volume of water were kept the same so that the temperature changes could be compared fairly.
| solid added | mass / g | initial temperature / degrees C | temperature after 2 minutes / degrees C |
|---|---|---|---|
| ammonium nitrate | 8.0 | 21.0 | 14.6 |
| calcium chloride | 8.0 | 21.0 | 30.8 |
(a) Calculate the temperature change when ammonium nitrate dissolves. [2]
(b) State which solid would be used in a cold pack. [1]
(c) Explain the energy change when ammonium nitrate dissolves in water. [3]
(d) Give two variables that must be controlled if the technician repeats this experiment using sodium hydroxide solid. [2]
(e) Name the apparatus used to measure 100 cm3 of water. [1]
(f) State why the solid should be stirred in the water. [2]
Answer Details
(a) \[14.6-21.0=\mathbf{-6.4\text{ °C}}\] This is a decrease of 6.4 °C. [2]
(b) Use ammonium nitrate in a cold pack because it produces the temperature decrease. [1]
(c) Dissolving ammonium nitrate takes in energy from the water or surroundings. More energy is needed to separate particles than is released when particles interact with water, so the temperature decreases. [3]
(d) Keep the volume or mass of water and the mass of solid constant. Initial temperature, cup, and stirring time are also suitable controls. [2]
(e) Use a measuring cylinder. [1]
(f) Stirring ensures all the solid dissolves and makes temperature uniform throughout the solution. [2]
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