Periodicity Lab

In lecture, we are about to study trends on the Periodic Table. In this lab we will be conducting experiments to determine if metal reactivity shows group (column) and period (row) trends. There are likely many trends on the periodic table, but we are investigating only a few today.

Safety Concerns

Alkali metals are very dangerous. They react explosively with water, including the water in the air. During the demonstration, be sure to stand far back and wear your goggles.

Hydrochloric acid (HCl) is highly corrosive, especially when heated. It is important to use caution when handling containers with HCl, and always wear your goggles! Hot HCl is even more corrosive. Acids must be heated in a hot water bath to prevent overheating. A hot water bath is a beaker of water heated on a hotplate. A ring stand and clamp are used to secure the test tube of acid in place.

Many of the reactions in this experiment produce bubbles, fumes, and energy (heat). Hake sure you place your test tube in the specified container while the reaction occurs, and so not pick it up. Stay at least one foot back from the test tube while the reaction proceeds.

When a reaction reaches completion, notify a teacher and they will come around to collect the waste. We can't dump it down the sink because the products of the reaction are toxic.

Pre-Lab Questions

  1. What is the safe way to heat acids?
  2. How do we make a hot water bath?
  3. What is a safe way to view a reaction?
  4. Why can't we dump our reaction down the sink when it has completed?

Goals

Today we will explore the reactivity of a few metals: Na, Mg, Al, Fe, and Cu. We need to look for TRENDS in REACTIVITY based on the column and row of each metal. A couple quick definitions and reminders before we begin:

Trend

The general direction in which something tends to move.

Signs of a reaction

Other Notes:

Part I: A Demonstration of Very Reactive Metals

Group I elements on the periodic table are often called the alkali metals. We will look at the first three metals, lithium (Li), sodium (Na) and potassium (K).

Record your observations (a) when a small piece of Na is added to water.
Record your observations (b) when a small piece of Mg is added to HCl. / (a)
(b)

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Part II: Lab Activity, the Alkaline Earth Metals and Aluminum.

Group II elements on the periodic table are often called the alkaline earth metals. You will investigate the two metals, magnesium (Mg) and calcium (Ca) and the Group III metal aluminum (Al). Wear your safety goggles and aprons.

Your materials manager will bring you everything except the acid. A teacher will bring the acid group by group. You should finish each section by the time the teacher brings you the materials for the next one (~3-4 min). If you are waiting for materials at any point, look over the post-lab questions.

Obtain a sample of Al and record the color and appearance (a) the surface. Record your observations (b) when a small piece of Al is added to 1 molar hydrochloric acid (1 M HCl). / (a)
(b)
Obtain a small sample of Fe metal and record the color and appearance (c) of the surface. Record your observations (d) when a small piece of Fe is added to 1 molar hydrochloric acid (1 M HCl). / (c)
(d)
Obtain a sample of Cu metal and record the color and appearance (e) of the surface. Record your observations (f) when a small piece of Cu is added to 1 M HCl in a test tube. / (e)
(f)

Post Lab Questions:

  1. Look at the periodic table. What electron configurations do each metal have? What trends do you notice?
  1. Arrange the metals Al, Na, Fe, Mg, and Cu in order of decreasing activity as observed in this lab (most reactive first).
  1. Describe the activity of metals as you move across a period. Explain the feature(s) of electron configuration that are important in interpreting these behaviors.

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