Question

Part 2 – Comparing the reactivity of some metals with acids Many metals react with acids, via an electron-transfer (oxidation-reduction) reaction that transforms the metal into dissolved metal ions. A co-product of this reaction is hydrogen gas, formed when hydrogen ions in the acid solution take up electrons from the metal and couple. Your task here is to test a few different metals to see how their reaction intensities compare. 1. Obtain 12 clean small test tubes (they can be slightly wet). Divide them into three sets of four tubes, and label the sets as: “HCl”, “acetic acid” and “water”. 2. To the four “water” test tubes, add about 1 mL of water. To the four “HCl” test tubes, add about 1 mL of 3 M hydrochloric acid using the 1 mL graduated pipette that goes with the reagent bottle. To the four “acetic acid” tubes, add 1 ml of 3 M acetic acid. (Do not mix up the droppers!) Carefully note the smells of the two acids. Do this by wafting air over the sample towards your nose with your hand - never smell a chemical directly. Exp.2: OBSERVATIONS 2 - 4 3. Now divide the tubes into four sets, one of each kind. Label them (or place them on a labeled sheet of paper) as: “steel wool”, “Mg”, “Al sheet” and “Al foil”. 4. To each “steel wool” tube: add a small loosely packed ball of steel wool about 3 mm in diameter. Make initial observations and note the time, then push the steel wool down into the liquids with a clean glass stir rod. Record your observations immediately after mixing and again as time passes: colour changes, gas formation, solid formation (cloudiness), odours, and heat evolution all provide evidence of chemical reaction. [Make notes on Observations/Data page.] Note: compare the acid-treated samples to the “control” water-treated sample – only then can you determine whether any chemical reactions observed are caused by the acid or simply by the water also present. 5. Repeat step 4 with the other metals: ~5 mm strip of magnesium ribbon, 5 mm square of aluminum sheet, and 5 mm diameter loose ball of aluminum kitchen foil.

Regarding Part 2: Consider the physical nature of the metals you tested, their positions on the periodic table, and the different strengths of the acids you used. What conclusions can you draw from your observations of the action of the acids on the different metals you tested? Be careful to explicitly distinguish between speculations you cannot back up and speculations based on any chemistry you may already have learned.

Answer 1

Heat is released when metals reacts with strong acids.

The reaction between the metal and HCl acid will be much faster because the HCl acid is much stronger due to the fact that it is more highly ionized. Acetic acid is weak because its H+ is tightly held and it is reluctant to leave the C2H3O2 ion in order to react with the metal.

1. Magnesium reacts with hydrochloric acid according to the equation:

Mg (s) + 2 HCl (aq) --> MgCl₂ (aq) + H₂ (g)

the generation of hydrogen gas. The reaction will be strong and will be exothermic, high heat will be generated. Effervescence due to emission of hydrogen gas.

1. Magnesium ribbon, the reaction is less vigorous with acetic acid than HCl
2. Very clean magnesium ribbon has a very slight reaction with cold water. After several minutes, some bubbles of hydrogen form on its surface, and the coil of magnesium ribbon usually floats to the surface. However, the reaction soon stops because the magnesium hydroxide formed is almost insoluble in water and forms a barrier on the magnesium preventing further reaction.

Aluminiun reacts with HCl

The reaction that occurs is

2 Al + 6 HCl ---> 2 AlCl₃ + 3 H₂

the generation of hydrogen gas. The reaction will be strong and will be exothermic, high heat will be generated. Effervescence due to emission of hydrogen gas

Aluminium and water nothing happens in the air aluminum is covered with thin layer of aluminium oxide and it's stopping it to react with water.

Aluminium acetate or aluminium ethanoate will be formed when Al reacts with acetic acid. The rescion will be slow.

Steel wool with HCl

3HCl + Fe₃C --> H₃C + 3FeCl₃

Iron Chloride would be a ppt (black residue?), H₃C may break down into H₂ gas (bubbles?) and HC-2 which might ionize or something, but would likely stay in the solution as a liquid.

This reaction will be mild, heating is required to speed up the reaction

Steel wool with water

steel wool undergoes oxidation, the iron molecules in the steel wool combine with oxygen in the air to form a new compound, iron oxide, or rust. the steel wool begins to rust inside the test tube, the water level in the tube rises to displace the oxygen used in the oxidation process

Steel wool with Acetic Acid

The heat wold be generated , you might even notice the test tube getting foggy. Steel wool in acetic acid the protective coating of the steel wool is removed and the iron in the steel to rust. Rusting (or oxidation) is a chemical reaction between iron and oxygen, this chemical reaction creates heat energy,

Metalsare arranged in an order to show how easily they form compounds.

Magnesium Aluminium Iron

More reactive metals ↑ ↓ Less reactive metals

Metals nearer the top of the list will Burn more rapidly in air. React faster with water. React faster with acids. Be able to displace a lower metal from one of its compounds More likely to be found in a compound.