Identifying an Unknown Metal from its Density

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Identifying an Unknown Metal from its Density

Density is calculated as the proportion of mass relative to volume. The commonly used units for measuring density are g/, g/mL and Kg/. The density of any pure material remains constant regardless of the quantity of a substance (Cummings, 2005). Consequently, density is a physical property used to identify unknown pure substances or approximate the substances in a mixture. The calculated densities are checked against the records of standard densities for various pure substances. Estimating mass and volume is an essential part of the calculation of density. 

The mass of metal can be easily measured using a scale. However, estimating the volume is a more complicated process that depends on the characteristics of the substance in question. A regularly shaped metal volume is calculated based on the dimensions and the conventional formulas for estimating volume. On the other hand, the volume of irregularly shaped metals is estimated using the displacement method. In the displacement method, a liquid, mainly distilled water, is placed in a volume measuring apparatus such as a graduated cylinder, and the volume is recorded. The substance is then added to the cylinder such that its volume is equal to the volume of distilled water displaced. The final volume is then recorded, and the volume of the substance is estimated as the final volume less the initial volume. 

Procedure

Pour distilled water between 10-20 mL into the graduated cylinder. 

Record the observed volume as the initial volume.

Place the cylinder on the scale, press tare such that the reading on the scale is 0.0000 grams. 

Select the respective metal and pour it into the cylinder with distilled water until the volume displaced is 10 mL and record the final volume. 

Calculate density as the ratio of mass to volume. 

Data analysis and calculations

Table 1 : Metal 1

Trials	Initial volume (mL)	Final volume (mL)	Volume Displacement (mL)	Mass of Metal (g)	Density of Metal (g/mL)
1	10.00	20.00	10.00	105.0000	10.5
2	15.00	25.00	10.00	105.0000	10.5
3	20.00	30.00	10.00	105.0000	10.5

Density = 

Density Trial 1 = 105g/10mL = 10.5 g/mL

Density Trial 2 = 105g/10mL = 10.5 g/mL

Density Trial 3 = 105g/10mL = 10.5 g/mL

Average Density = 

Percent Error = *100% 

Percent Error = *100% = 0%

Table 2 : Metal 2

Trials	Initial volume (mL)	Final volume (mL)	Volume Displacement (mL)	Mass of Metal (g)	Density of Metal (g/mL)
1	10.00	20.00	10.00	124.0000	12.4
2	15.00	25.00	10.00	124.0000	12.4
3	20.00	30.00	10.00	124.0000	12.4

Density = 

Density Trial 1 = 124g/10mL = 12.4 g/mL

Density Trial 2 = 124g/10mL = 12.4 g/mL

Density Trial 3 = 124g/10mL = 12.4 g/mL

Average Density =

Percent Error = *100% 

Percent Error = *100% = 0%

Table 3 : Metal 3

Trials	Initial volume (mL)	Final volume (mL)	Volume Displacement (mL)	Mass of Metal (g)	Density of Metal (g/mL)
1	10.00	20.00	10.00	214.5000	21.45
2	15.00	25.00	10.00	214.5000	21.45
3	20.00	30.00	10.00	214.5000	21.45

Density = 

Density Trial 1 = 214.5g/10mL = 21.45 g/mL

Density Trial 2 = 214.5g/10mL = 21.45 g/mL

Density Trial 3 = 214.5g/10mL = 21.45 g/mL

Average Density =

Percent Error = *100% 

Percent Error = *100% = 0%

Discussion

Even when using different volumes, the density obtained is precise. Precision assesses the variations of the densities obtained in the separate trials for each metal. In the three trials made for each metal, the densities obtained were the same. Each of the three trials for metal 1 had a 10.5g/mL density, metal 2 had 12.4g/mL, and metal 3 had a 21.45 g/mL density. The scale measures mass to the nearest 0.0001 grams while volume is measured to the nearest 0.01 mL. Therefore, the accurate mass maybe 0.0001 grams above or below the recorded while volume can be 0.01 mL above or below the recorded volume. The percentage density error for all three metals was zero, implying that the experiments obtained each of the metals’ real densities. 

The calculated density of metal 1 is 10.5 g/mL, which coincides with the standard density for silver, 10.5 g/mL. The chemical symbol for silver is Ag with an atomic number 47 and an atomic mass of 107.868u. Silver is moderately soft and shiny, and the best light reflector material is known (National Center for Biotechnology Information, 2021). When exposed to air, the surface of silver tarnish because of a gradual reaction with sulfur compounds to form black silver sulfide (National Center for Biotechnology Information, 2021). Silver is mainly used in jewelry making. Other uses include making electrical materials, batteries, tableware, brazing, and dental alloys (National Center for Biotechnology Information, 2021). Silver iodide and bromide were historically used in photography before the invention of digital photography. 

Metal 2 is rhodium with a standard density of 12.4 g/mL. Rhodium Rh has an atomic number of 45, while the atomic mass is 102.9055u. It is a hard, durable metal that is silvery white. Rhodium remains unaffected while in the air up to and is insoluble in acids apart from hot sulfuric acid. The metal is used to create high-temperature-resistant alloys and acts as a catalyst in industrial processes and vehicle converters (National Center for Biotechnology Information, 2021). The shiny nature, ability to reflect light and resistance to tarnishing make rhodium useful in coating jewelry and making searchlight reflectors. 

Metal 3 is platinum with a standard density of 21.45 g/mL. Platinum, Pt has an atomic number and mass of 78 and 195.084u, respectively. Platinum is a shiny and silvery-white metal that’s resistant to corrosion is similar to gold. Platinum is used in making jewelry, vehicle converters, computer hard disks, LCDs, and optical fibers (National Center for Biotechnology Information, 2021). In medicine, platinum is used in making dental fillings, pacemakers, and chemotherapy drugs. 

A traditional method of estimating the density of irregularly shaped solids is the use of a eureka can. The can was filled with water to the brim, after which the solid was immersed to displace water through the sprout. The water was collected, and the volume determined. The mass of the solid was then determined using a spring balance, and the density calculated as the ratio of mass to volume. The spring balance sensitivity is relatively low compared to an electronic scale, hence increasing the risk of the error. There is a risk that the displaced water flowing from the eureka can to the collecting can may splash, thus the possibility of inaccurate volume. In conclusion, the virtual lab method is more precise and accurate relative to the traditional method. 

References

Cummings, B. (2005). Chemical foundations. Chemistry . New York.

National Center for Biotechnology Information (2021). PubChem Compound Summary for CID 23939, Platinum . Retrieved February 24, 2021 from https://pubchem.ncbi.nlm.nih.gov/compound/Platinum .

National Center for Biotechnology Information (2021). PubChem Element Summary for AtomicNumber 45, Rhodium . Retrieved February 24, 2021 from https://pubchem.ncbi.nlm.nih.gov/element/Rhodium .

National Center for Biotechnology Information (2021). PubChem Element Summary for AtomicNumber 47, Silver . Retrieved February 24, 2021 from https://pubchem.ncbi.nlm.nih.gov/element/Silver .