Reaction Alkali Metals and Alkaline Earth Metals

The rates of reaction of Alkali metals and Alkaline Earth meatals are compared in this lab. The pH of each of the resulting metal solutions are tested and the products of the reaction between calcium and water is discovered. The tested elements are sodium, lithium, potassium and calcium and each of them were placed in a beaker filled with water. The resulting solutions pH levels were tested with litmus paper. There were more steps for caclium because it is the only Alkaline Earth metal. For calcium, the gas produced in a test tube by the downward displacement of water was collected. Then, the test tube was lifted out of the water and kept in an inverted position. Finally, the gas collected was tested by bringing a burning splint to the mouth of the test tube. It was concluded that the Alkali metals were more reactice than the Alkaline Earth metals. When the active metals reacted with water, the resulting solutions were basic. Hydrogen gas was produced when calcium reacts with water.

Introduction

Alkali metals are in the first column of the periodic table and they may be readily fused and volatilized with their melting and boiling points becoming lower with increasing atomic mass. They are the strongest electropositive metals. (Kerrod, R. 2009) These elements react vigorously, even violently with water. Alkaline Earth metals are elements in the second column of the periodic table. These elements are in general white, differing by shades of color or casts; they are malleable, extrudable and machinable. (Tutor Vista. 2008) Also, these elements are less reactive than the Alkali metals and have higher melting points and boiling points.

The ionization energy is the amount of energy it takes to detach one electron from a neutral atom. The IE increase from bottom to top and left to right in the periodic table. (The Shodor Education Foundation, Inc. 2000) The IE and atomic radius increase in opposite directions. This makes sense because as the atom gets smaller, the valence electrons become closer to the nucleus. This means the attractive force holding the electron is stronger and it takes more energy to pull the electron off. The ionization energy of an atom is equal to the amount of energy given off when an electron is added to an atom.

Unlike a ball, an atom doesn’t have a fixed radius. The atomic radius of an atom can be obtained by measuring the distances between atoms in chemical compounds. The atoms are pulled closely together and so the measured radius is less than if they are just touching. (Clark, J. 2004) This is what you would get if you had metal atoms in a metallic structure, or atoms covalently bonded to each other. As mentioned previously, the atomic radius decrease in going from left to right across a period. This decrease can be explained in terms of the increasing effective nuclear charge (decease shielding) in going from left to right. This means that the valence electrons are drawn closer to the nucleus, decreasing the size of the atom. Atomic radius increases down a group, due to the increases in the orbital sizes.

When a metal oxide reacts with water, they create a basic solution. Therefore, when the Alkali metals and Alkaline Earth metals react with water, a basic solution is produced. In addition, the term “Alkali” (essentially the opposite of an acid) refers to a substance that forms the negatively charged hydroxide ion (OH−) in contact with water. (Kerrod, R. 2009)Alkali metals and Alkaline Earth metals are known for their vigorous reactions with water, and these reactions become increasingly violent as one moves down the group. The reaction with water is as follows: Alkaline Earth metal + water → Alkaline Earth metal hydroxide + hydrogen gas.

Materials & ApparatusApparatusMaterials600 mL beakertest tubewooden splintswire gauzewatch glasstweezersscoopula lithium metalsodium metalpotassium metalcalcium metalred and blue litmus paperProcedurePart A- Reactions of Alkali Metals with WaterBeaker was half filled with water.

Wire gauze was placed on top on the beaker.

Tweezers were used to drop sodium into a beaker half-filled with water.

Beaker was immediately recovered with wire gauze.

When the reaction was complete, the contents of the beaker were tested with
red and blue litmus paper.

The beaker contents were disposed.

Theses steps were repeated with lithium and potassium.

Part B- Reactions of Alkaline Earth Metals with WaterBeaker was rinsed and half filled wih fresh water.

A test tube was filled with water and inverted into the beaker.

A sampe of calium was obtained using a watch glass.

The calcium was added to the beaker.

The gas produced by the reaction was collected in a test tube by the downward displacement of water.

When the test tube was full, the test tube was lifted out of the water and kept in a n inverted position.

The gas collected was tested by bringing a burning splint to the mouth of the test tube.

The solution was tested with red and blue litmus paper.

ResultsSodiumCreated small bubblesDissolvedBurst into flameHissing noiseLiquid is basicLithiumCreated medium bubblesDissolvedHissing noiseLiquid is basicPotassiumPopping soundHissing noiseLots of smokeBurst into purple flameLiquid is basicCalciumBalls of calcium dissolved into a translucent solution.

Liquid is basicMade a popping sound when the burning splint went into the test tube.

Hydrogen gas is produced.

DiscussionAll of the theories discussed in the introduction on first ionization energy, atomic radius and metal oxides have all been proven in this lab. Alkali metals are much more reactive than Alkali earth metals and this is due to ionization energy and atomic radius. The Alkali metals rates of reaction increase as you go down the periodic table and this is also explained by ionization energy and atomic radius. Metal oxides react with water to produce basic solutions and this is due to their chemical equation. Alkali metals produce hydrogen gas when they react with water due to the chemical equation and Alkali metals with oxides create basic solutions due to the oxides and water rule.

Sodium, lithium and potassium were much more reactive than calcium was and this is due to ionization energy and atomic radius. Due to a very large size of the atoms, Alkali metals have very low ionization energies. Down the group the ionization energy decreases as atomic size increases. This is due to new shells being added and the increase in the magnitude of the screening effect of inner shell electrons. (Chem 1 . 2005, November 14) Members of Alkaline Earth metals have higher ionization energies values compared to Alkali metals because of their smaller size, with the electrons being more attracted towards the nucleus of the atoms. The less attracted the electrons of an element are to their nucleus, the more reactive an element is because it is more willing to participate in reactions.

As you go down the Periodic table, the reactivity of the Alkali metals increases and this is due to ionization energy and atomic radius. The lower the ionization energy, the more willing an Alkali metal is to lose an electron. The larger the atomic radius, the less significant each electron becomes and therefore, the less of a problem it is for an Alkali metal to lose one. Each element in the Alkali metal group, and in every group for that matter, becomes more reactive because they are more willing to lose electrons and therefore more willing to take part in chemistry.

The definition of Alkaline is a non acidic solution, therefore it is not surprising that all of the solutions were basic. When Alkali metals react with water, one hydrogen atom splits off from the water molecule to form hydrogen gas, while the other hydrogen atom joins the oxygen to form hydroxide. (Kerrod, R. 2009) This also explains why all of the solutions were basic because the hydroxide ion was present in all of the solutions. The presence of a hydroxide ion is the number one way to check for a base and this gets formed when one of the hydrogen atoms splits off from the water molecule to form hydroxide.

Five factors that could have cause experimental error are concentration, temperature, medium, catalysts, and surface area. A higher concentration of reactants leads to more effective collisions per unit time, which leads to an increasing reaction rate (except for zero order reactions). Similarly, a higher concentration of products tends to be associated with a lower reaction rate. (Helmenstine, A.2009) Usually, an increase in temperature is accompanied by an increase in the reaction rate. Temperature is a measure of the kinetic energy of a system, so higher temperature implies higher average kinetic energy of molecules and more collisions per unit time. The rate of a chemical reaction depends on the medium in which the reaction occurs.

It may make a difference whether a medium is aqueous or organic; polar or nonpolar; or liquid, solid, or gaseous. (Purchon, N. 2006, Novemeber 10) Catalysts work by increasing the frequency of collisions between reactants, altering the orientation of reactants so that more collisions are effective, reducing intramolecular bonding within reactant molecules, or donating electron density to the reactants. Surface are can also influence the rate of reaction because the types of molecules can only bump into each other at the liquid solid interface, i.e. on the surface of the solid. Therefore, the larger the surface area of the solid, the faster the reaction will be.

Conclusion

The Alkali metals were more reactice than the Alkaline Earth metals. When the active metals reacted with water, the resulting solutions were basic. Hydrogen gas was produced when calcium reacts with water.

References

Chem 1 . (2005, November 14). Periodic properties of the elements. Retrieved from
http://www.chem1.com/acad/webtext/atoms/atpt-6.html#SIZEClark, J. (2004). Atomic and ionic radius. Retrieved from http://www.chemguide.co.uk/atoms/properties/atradius.htmlHelmenstine, A. (2009). Factors that affect chemical reaction rate. Retrieved from http://chemistry.about.com/od/stoichiometry/a/reactionrate.htmKerrod, R. (2009). Alkali metal. Retrieved fromhttp://www.answers.com/topic/Alkali-metalPurchon, N. (2006, Novemeber 10). Rates of reaction. Retrieved from http://www.purchon.com/chemistry/rates.htm#surfaceThe Shodor Education Foundation, Inc. (2000). Ionization energy. Retrieved from http://www.shodor.org/chemviz/ionization/students/background.htmlTutor Vista. (2008). Alkaline Earth metals characteristics. Retrieved from http://www.tutorvista.com/content/chemistry/chemistry-iii/s-block-elements/Alkaline-earth-metals.php