Unknown Metals Chemical and Physical Properties

Identification of metals

Abstract

This experiment will investigate chemical and physical properties of three unknown metals in order to identify them from nine different metals Mg, Al, Fe, Zn, Ni, Pt, Ag, Sn, Pb. Chemical and physical properties were tested through density, Sodium Hydroxide, displacement and Hydrochloric acid tests. The density and sodium hydroxide tests were acceptable while displacement and hydrochloric acid tests were inconsistent; hence, the four results contracted to each other. However, the analysis proved that metal A was aluminum, metal B was zinc, and metal C was Iron. Since the results were inconsistent, they became unreliable, for the final identification of the metals may be incorrect.

Aim: To test the chemical and physical properties of three unknown metals by using four methods, density, sodium hydroxide, displacement and hydrochloric acid, in order to identify the specific metals out of nine different choices – Mg, Al, Fe, Zn, Ni, Pt, Ag, Sn, Pb.

Introduction – 1

This EEI investigates students’ understanding of the unique properties of metals which they are required to design and perform four different tests. The experiments examine both physical and chemical properties of the three unknown metals in order to identify them.

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All substances have chemical and physical properties that we use to distinguish or compare from a substance from another. In addition, chemical and physical properties can help us model the substance; thus, understanding how a substance will behave under various conditions. “The chemical property of an element describes its potential to undergo some chemical change or reaction by virtue of its composition to produce a new compound. On the other hand, physical properties are those which a substance can show without losing its identity and can be used to describe their behaviour (Ophardt, C., 2003)”

Furthermore, the structure of a metal explains the chemical and physical properties. For instance, metal is a lattice of positive ions in a sea of delocalised electrons (Spence, R. Gemellaro, T. Bramley, L. Wilson, D.

In the experiment, four tests were chosen to identify the metals which were density, displacement, hydrochloric acid and sodium hydroxide.

1.1. Density

First, density, which is defined as the measure of the relative mass of objects with a constant volume, is a physical property, as each element and compound has a unique density associated with it. Density test is relatively accurate and can be used to identify the metals since they all have their own unique density.

Formula to find density: (Ophardt, C., 2003)

Density = mass/volume = g/cm3

The densities of silvery metals: (Density of metals, n.d.)

Substance

Density (g cm-^3)

Substance

Density (g/cm-^3)

Aluminium

2.70

• Lead

11.34

Nickel

8.912

• Magnesium

1.74

Zinc

7.14

• Tin

7.31

Iron

7.86

• Silver

10.49

• Table 1

Platinum

21.45

1.2. Sodium Hydroxide

Second, the sodium hydroxide test mixes two solutions and an insoluble substance is formed (France, C. n.d.).

For example:

Copper sulfate + Sodium hydroxide à Copper hydroxide solid(precipitate) + Sodium sulfate

CuSO4(aq) + 2NaOH(aq) à Cu(OH)2(s) + Na2SO4(aq)

Precipitation of silvery metals: (Laboratory tests, n.d.)

1.3. Displacement reaction 

Third, the displacement reaction test measures chemical properties of metals where a metal displaces a less reactive metal in a metal salt solution (AUS-e-TUTE, n.d.)

For example:

Fe(s) + CuSO4(aq) à FeSO4(aq) + Cu(s)

Note that copper (II) sulphate is blue, and iron sulphate is colourless. During the reaction, the blue solution loses its colour, and the iron turned into pink-brown as the displaced copper becomes deposited on it. If a less reactive metal is added to a metal salt solution there will be no reaction; therefore, nothing will happen. For instance, Iron is less reactive than magnesium.

The orders of the metals in the reactivity series can be worked out by using displacement (see figure ). Moreover, the reactivity of a metal is affected by the number of valence electrons and the energy levels (TutorVista, n.d.).For instance, the greater the number of shells and lesser the number of valence electrons, the greater the reactivity of the metal is.

The order of reactivity series or silvery metals: (TutorVista, n.d.)

Most reactive to less reactive

Number of energy levels and valencies.

Mg

2,8,2

Al

2,8,3

Zn

2,8,18,2

Fe

2,8,14,2

Ni

2,8,16,2

Sn

Pb

Ag

Pt

Table 3

1.4. Hydrochloric acid 

Fourth, the hydrochloric acid test is similar to the displacement test which determines the reactivity of metals. The higher the reactivity of the metal is the louder the “pop” sound will occur.

Example:

Zn + 2HCl à ZnCl2 + H2

Displacement and Hydrochloric acid tests were chosen for the experiment because these two experiments identifies the metals by testing the reactivity of each metal, and, from the order of reactivity series (see figure x) the metal can be identified.

2. Materials and methods

2.1. Density 

Materials:

• Electronic scale
• Micrometre screw-gauge
• Vernier caliper

Method:

• All materials and apparatus was attained
• The three unknown metals were weighed on the electronic scale to figure out their weight
• The density of the three unknown metals was worked out through the measurement of their length, width and height and then multiplied to find the volume; the mass was then divided by the volume to figure out its density

2.2. Sodium Hydroxide 

Materials

Spotter tile

2M Sodium Hydroxide

Method:

The three unknown metal nitrates were placed into 3 different spots on the spotter tile

The sodium hydroxide was then added to each one and observations were recorded

The metals were then worked out by comparison with the table below and recorded

2.3. Displacement 

Materials:

Tin-snips

Magnesium Nitrate

Aluminium Nitrate

Iron Nitrate

Zinc Nitrate

Nickel Nitrate

Silver Nitrate

Tin Nitrate

Lead Nitrate

Piece of A4 paper

9 test tubes

Test tube rack (must have more than 9 test tube holes)

Method:

The Chemical terms for all 9 nitrates were written on a piece of paper and then slipped under the test tube rack to make sure the solution in each test tube was correct

9 test tubes were placed into the test tube rack with each being filled with the specified solution

Each unknown metal were cut up into 9 small strips

The first unknown metal strips were placed into each test tube

The degree of reactivity was recorded into the table below

Steps 2 – 4 were repeated with cleaned test tubes, new solutions and the other unknown metals until all 3 were tested

2.4. Hydrochloric Acid 

Materials:

• Matches
• 6M Hydrochloric acid
• 3 test tubes
• Test tube rack (3 test tube holes minimum)
• Tin snips
• Stop watch

Method:

• 6M Hydrochloric acid (HCl) was obtained and 3 test tubes were placed into a test tube rack
• Metal A, B and C were cut up and each one was placed separately into each of the test tubes
• Hydrochloric acid was added and the test tube was then covered with a thumb and timed for 1 minute using a stop watch
• After 55 seconds a match was lit up and ready to be placed into the mouth of the test tube as soon as the thumb was taken off
• The thumb was taken off, the match was placed in and the intensity of the reaction was recorded

3. Analysis

By testing and analysing the chemical and physical properties of each give metal, we eliminate the possibilities and identify the specific metal.

3. 1. Density

First, the experimental results for density were compared to the theoretical values (see table 1) to identify the metals. For instance, metal A had a density of 1.15g/cm3 which was close to magnesium’s theoretical value of 1.74 g/cm3 or aluminium’s density of 2.70 g/cm3. Metal B had density of 7.28 g/cm3 which was extremely close to tin’s theoretical value of 7.31 g/cm3 and zinc’s density of 7.13 g/cm3 and iron’s density of 7.86 g/cm3. Finally, metal C’s density was 7.16 g/cm3 which was close to density of zinc, 7.13 g/cm3 and tin, 7.31 g/cm3 and iron, 7.86 g/cm3. The density test indicated that metal A is magnesium or aluminium and metal B and C are iron or zinc or even tin.

3.2. Sodium hydroxide

Second, the sodium hydroxide test examined the precipitation of each given metal and compared them with theoretical results (See table 2 and 5). Metal A and B showed faint white precipitation while metal C produced hard white precipitation. These results were used to further analyse the possibility for metal A, B and C. For instance, metal A, which could be magnesium or aluminium, precipitated white. According to the table (?), metal A was still unknown since aluminium and magnesium both had white precipitation. Metal B, which could be zinc or iron or tin, precipitated white. However, the theoretical results showed that iron and tin do not precipitate white; therefore, metal B can be identified as zinc. Similarly, metal C showed almost same result as metal B; therefore, it could be identified as zinc. However, as metal B and C cannot be both zinc, further analysis will clarify the contradictory and anomalous results

3.3. Displacement

Third, the displacement test examined the reactivity. The displacement test places the metals in a more accurate spot on the reactivity series (See table 9). It showed the reactivity level of each metal by observing the metal salt solutions they displaced. However, the displacement test should have provided more precise indication to identify each metal, but they became unreliable as the results were inaccurate. According to the result, metal A displaced nickel, tin and silver, but didn’t displaced lead and any higher reactivity metals above nickel, which indicated that metal A was more reactive than nickel, yet less than zinc, for metal A was an iron. However, the results and the analysis of density and sodium hydroxide are contradicting the displacement results; hence, further analysis through of hydrochloric acid test will identify metal A. On the other hand, metal B displaced all the metals below zinc, except iron. This proved that metal B cannot be zinc; in fact, it was magnesium or aluminium. Once again, the results were contradicting the density and sodium hydroxide results. Furthermore, metal C displaced all of the metals except magnesium, zinc and lead. According to the density and sodium hydroxide analysis, metal C is zinc or iron; therefore, it cannot be more reactive than aluminium. However, the result suggested that metal C was magnesium as it did react with aluminium. To sum up, metal A had could be identified as iron, aluminium and magnesium. However, since the density of iron is 7.86 g/cm3, and the metal A’s density is only 1.15g/cm3, which is close to aluminium or magnesium, iron cannot be metal A. Also, metal B’s density is close to zinc and iron, but is more reactive than iron; hence, metal B may be identified as zinc. Since the same element cannot react each other, this can be seen as an anomalous result. The analysis of metal C suggested that it cannot be zinc nor can it be iron. Metal C cannot be magnesium or aluminium since there is huge difference in density. However, further analysis of hydrochloric acid test will reveal the specific metals.

3.4. Hydrochloric acid

Finally, the hydrochloric acid test was similar to the displacement test as both determined the reactivity of given metals. However, the hydrochloric acid test reacts with hydrogen. In this experiment, metal A and B displaced hydrogen gas from the hydrochloric acid, while metal C did not react (See table 7). Metal A had a small reaction when the flame went out instantly without making a pop sound. However, metal B was extremely reactive, making the loud pop sound. However, the solution reacted with the metal only for one minute; however, some metals take more than one minute to react. For instance, metal A only had a small reaction under one minute, but reacted aggressively after two minutes, which indicates that metal A is aluminium. On the other hand, the results revealed that metal B is zinc as it was very reactive with hydrochloric acid, suggesting that it is the most reactive metal from the possibility of zinc and iron. Furthermore, metal C did not react with hydrochloric acid at all which was evident from the flame as it didn’t go out. Analysis of the previous tests showed that metal C had possibility zinc or iron. Since the reaction of metal C is smaller than metal B; metal C can be identified as iron.

In short, the analysis of the four tests for chemical and physical properties revealed that metal A is aluminium, metal B is zinc and metal C is iron.

5. Discussion

The three given metals were identified by using four tests: density, sodium hydroxide, displacement and hydrochloric acid. By carrying out these experiments, the chemical and physical properties were tested to identify the metals. The experiment identified metal A as aluminium, metal B as zinc and metal C as iron. However, even though the tests identified the metals, many anomalous results were found.

Firstly, the density test was measured by the micrometre screw gauge, the vernier calliper and electronic scale. The anomalous results of this experiment were that the density of metal A, B and C did not match the theoretical values. For instance, metal A, which was identified as aluminium, has a density of 1.15; therefore, does not match with theoretical value of 2.70. In fact, the density of metal A is more close to magnesium. Same anomalous were observed the metal B and C. To modify and improve the density experiment, one has to measure the width, breath and length correctly. In addition, putting the metals into water and see how much they dispersed is another way to improve the test.

Secondly, the sodium hydroxide test had consistent results. All of the metals had a white precipitation which was expected.

Thirdly, the displacement tests had major inconsistent results; hence, unreliable. For instance, metal B cannot be zinc when it reacted with zinc. This can be seen as an anomalous. This peculiar reaction is thought to be a repercussion of using unclean equipment, or the accidental mixing of solutions, for the test tubes were not cleaned before use. The same anomalous results occurred when testing metal B and C. For example, metal C reacted with aluminium but did not react with zinc, lead and tin. This is a false result since aluminium is more reactive than zinc or lead or tin. This experiment can be improved by having cleaned test tubes and the test tubes to avoid mix ups.

Finally, the hydrochloric acid tested the reactivity of metal A, B and C. In this experiment, a stop watch was used to measure how fast the metal reacted with hydrochloric acid in one minute, and matches were used to test the reactivity of the metals and hydrogen. However, this test also had numerous anomalous results because metals did not react in just one minute. For instance, if metal C which had no reaction and thought to be iron was left three to five minutes longer, there might have been a reaction. In fact, after recording and disregarding the test tube for three minutes, it started to react despite no reaction in one minute. The same anomalous results were recorded for metal A and B. To modify and improve the experiment, the time for the reaction need to be extended to three minutes or five minutes. This will give time for metals to react; therefore, trap more hydrogen, making the results more accurate. Moreover, the time taken to insert the flame into the test tube was approximately 3 seconds. If the time was decreased to one second, there might have been a reaction for metal C.