When a chemical reaction takes place one or more changes occur. These may include changes in appearance and temperature. In this activity you will find out what happens to the mass of the reactants and products.
Equipment
Obtaining evidence
1Copy the table and use it to record your results.
Solutions / Mass before / Mass after / Other observations or measurementssodium sulphate and barium nitrate
citric acid and potassium hydroxide
hydrochloric acid and sodium hydroxide
2Pour sodium sulphate solution into a test tube until
about one-quarter full. Stand this test tube in a 250 cm3 beaker so that it does not fall over.
3Pour barium nitrate solution into a second test tube until this also is about one-quarter full. Stand this test tube in the same beaker.
4Use a top pan balance to measure the mass of the beaker, including the test tubes and solutions. Note down this mass before the reaction.
5Pour the liquid in one test tube into the liquid in the other test tube. Mix the two solutions by holding the top of the test tube firmly with one hand and tapping the bottom of the test tube sharply with a finger of the other hand. Be careful not to spill any of the mixture. Note down any changes that you have seen. Also note down if the tube begins to feel hot.
6Place both test tubes back into the beaker and measure the mass of beaker, tubes and mixture. Note down this mass after the reaction.
7Using two clean test tubes, repeat steps 2 to 6, but this time use a solution of citric acid to which you have added a few drops of the indicator phenolphthalein in one test tube, and a solution of potassium hydroxide in the other test tube. Phenolphthalein is colourless in acid and pink in alkali.
8Using two clean test tubes, repeat steps 2 to 6, but this time use a solution of hydrochloric acid in the one test tube and a solution of sodium hydroxide in the other test tube. Before you measure the mass each time, use a thermometer to measure the temperature of the solutions and of the mixture.
Considering the evidence
In each of these three chemical reactions the reactants changed to form the products. In which reactions did this involve a change in appearance? In which reaction was a change in temperature involved?
Did any of the three reactions involve a significant change in mass?
How do you know that a chemical reaction took place each time?
Write a sentence about the mass of reactants and the mass of products in a chemical reaction.
© Harcourt Education Ltd 2004 Catalyst 3
This worksheet may have been altered from the original on the CD-ROM.