Part B: Reactivity of Metals in Hydrochloric Acid
The materials were selected and brought to the station. Safety protocol was followed and safety glasses were worn throughout the experiment. The appropriate data tables were drawn in which to record the data observations. A graduated cylinder was filled with approximately 20.0 mL of dilute hydrochloric acid. 5.0 mL were poured into four clean test tubes, which were then placed on the test tube rack. On a folded piece of paper towel, the professor placed small quantities of magnesium, iron, zinc, and aluminum. The physical properties of each of the metals were recorded. One at a time, each of the metals was carefully dropped into a different test tube of hydrochloric acid. Reactions were observed for a 20 minute period (amendment: because of the lack of time, reactions were only observed for five minutes) and observations were recorded. Masking tape was used to lightly cover the test tube in order to collect gas from the elements that bubbled in the acid. After the reactions were complete, a wooden splint was lit using a Bunsen burner and the masking tape was removed. The glowing splint was held just inside the mouth of the test tube. Observations were recorded and the waste was disposed of.
Observations
Part A: Reactivity of Metals in Water
Part B: Reactivity of Metals in Hydrochloric Acid
Analysis
The objective of the experiment was to observe what happens when seven metals are placed in water and/or hydrochloric acid. Calcium, magnesium, and copper were all placed in water and of the three, only the calcium reacted. Zinc, iron, aluminum, and magnesium were placed in the hydrochloric acid. There was a reaction in every test tube, but the magnesium showed the greatest reaction with iron being the least reactive to the acid. Even though the metals may be in the same period, how it reacts to the water or hydrochloric acid depends on the type of metal.
Error(s)
When the lit splint was held just above the mouth of the test tube with the magnesium, there was no reaction, unlike the high-pitched popping sounds emitted by other groups’ experiments. Perhaps this is because the masking tape was removed from the mouth of the test tube minutes before the wooden splint was lit, giving the collected gas enough time to diffuse.
A reason for the zinc and aluminum not reacting with the hydrochloric acid could have involved dirty glassware or the lack of time allowed for observation.
Conclusion
The purpose of this lab was to explore the patterns in reactivity in the periodic table. Through careful observation and planning during this experiment, the hypothesiswas deemed successful. Not all metals react with water and hydrochloric acid.
Questions
- Rank the elements tested in Part A from least reactive to most reactive.
- From the elements tested in Part A, calcium reacted the most with water (it produced hydrogen), while both copper and magnesium did not have a reaction.
- Sort the elements that you tested into groups. State the apparent order of reactivity as one proceeds down a group. Does reactivity increase or decrease?
- Group 2 (alkaline earth metal): magnesium, calcium
Group 8: iron
Group 11 (coinage metal?): copper
Group 12: zinc
Group 13: aluminum
For the metals, the reactivity increases as one proceeds down the group. This is because it is easier for electrons to be given farther down the periodic table.
- Sort the elements that you tested into periods. State the apparent order of reactivity as one proceeds across a period. Does reactivity increase or decrease?
- Period 3: magnesium, aluminum
Period 4: calcium, iron, copper, zinc
For the metals, the reactivity decreased as one moves from left to right across periods, because it is easier for electrons to be taken away farther to the left of the periodic table.
- Is the solution that is produced when a metal reacts with water acidic or basic?
- The solution that is produced when a metal reacts with water is basic, because the pH increased.
- Based on your gas test observation in Step 16, what gas is produced?
- Based on the gas test observation in Step 16, hydrogen gas is produced. This can be determined by the ‘squeaky pop’ sound that is heard when the lit wooden splint is placed at the mouth of the test tube.
- Rank the elements tested in Part B from least reactive to most reactive.
- In part B, copper would be the least reactive, because there was little-to-no reaction with it and the hydrochloric acid. Iron is the second least reactive, as its reaction was slow but there were a few observed bubbles. Zinc would be the second most reactive and magnesium the most reactive, with a quick reaction and the plenty of heat that was released.
- Does the reactivity increase or decrease as one moves across a period of elements?
- As one moves across the periodic table from left to right, for the metals, the reactivity decreases, this is because the farther to the left, the easier it is for electrons to be given or taken away. But for the non-metals, the reactivity increases(excluding the nobles gases), because the farther right, the higher the electronegativity, resulting in a greater exchange of electron.
- Based on your gas test results, what is the gas produced in these reactions (Steps 16 and 25)?
- Based on the gas test results and the similar ‘squeaky pop’ sound the elements emitted, the gas produced from the magnesium and hydrochloric acid reaction and also the calcium and water reaction is hydrogen gas.
- Does the reactivity increase or decrease as one moves down a group of elements?
- As one moves down a group of elements on the periodic table, for the metals, the reactivity increases, this is because the farther down, the easier it is for electrons to be given or taken away. But for the non-metals the reactivity decreases as one goes down because the farther up, the higher the electronegativity, resulting in a greater exchange of electron.
- Evaluate this investigation. Did the design enable you to collect enough evidence to answer the questions? How could it have been improved? Would your suggested improvements raise any safety concerns?
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The design was decent, but it did provide all the evidence needed to answer all the questions; a few of the questions required further research. I think the investigation could have been improved by writing clearer instructions and being more descriptive to avoid confusion. Also, students should be able to experiment with different metals to help them expand their understanding of the reactivity of metals in water and hydrochloric acid (this may raise a few safety concerns).
- Predict what might happen if you were to drop a piece of potassium (or lithium) into a beaker of water.
- Because potassium is an alkaline metal (lithium as well), it is extremely reactive. I predict that dropping it in water would cause it to react quickly and intensely, and produce hydrogen gas.
- Connect the trends observed in Parts A and B to atomic radius, ionization energy, and electron affinity. Write a paragraph to explain the trends.
- The elements moving from left to right across a period, the atomic radius decreases, as does the ionization energy(the nucleus of the atom gains protons).The atomic radius increases moving down a group, but the ionization energy decreases moving down a group (gains protons and new energy shells of electrons).And opposite to the ionization energy, electron affinities increase from left to right across a period. Electron affinities change little moving down a group, becoming slightly more positive.
by
salmayoussef (student)
