Defining the Difference Between Physical and Chemical Changes

Introduction

Identifying a Physical Change

A physical change is a change in which the composition of the substance remains unaltered and no new substances are produced. A change of state is still a physical change, as water freezing into ice is still water in a different form. A physical change can be identified using a substance’s physical properties. There are two types of physical properties, qualitative and quantitative. A qualitative property is a property that is not measured and has no numerical value, such as colour, odour, texture, luster, viscosity, scent, crystal shape, and taste. Quantitative property is a property that is measured and has a numeric value, such as height, temperature, and mass. This lab looked at many qualitative physical properties including crystal shape, solubility, state of matter, and optical clarity. Crystal shape is the configuration of crystalline substances. For example, salt has a cubic shape. Solubility is a substance’s ability to dissolve in water. For example, salt is soluble. “State of matter is one of the four principle conditions in which matter exists”. For instance, water is a liquid, calcium is a solid, and oxygen is a gas. Optical clarity is a substance’s ability to allow light through, and example of this could be glass compared to wood. Glass allows all light to pass through, making it translucent, and wood allows no light through, making it opaque.

Identifying a Chemical Change

A chemical change is a change in which the starting substance or substances and the production of one or more substances. Some clues that can help you identify a chemical change include, the appearance of a new colour, heat or light are given off, bubbles of gas are formed, a solid material called a precipitate is formed, and/or the change is difficult to reverse. A chemical change can also be identified using a substance’s chemical properties. The two chemical properties of a substance are combustibility and reaction with an acid. Combustibility measures a substance’s ability to burst into flames. For example, propane and ethanol require little to no heating or increase in pressure to combust, whereas portland cement plaster is classified as a non-combustible substance. Reaction with an acid is how a substance acts when it comes in contact with an acid. For example, metals located on the left side of the periodic table (alkali metals, alkaline earth metals) are more reactive in hydrochloric acid than those located on the right side.

Safety Warnings and Symbols

Copper sulphate is an electric blue power that is better known as bluestone. It is a poisonous element that is toxic to humans if it comes in contact with eyes or skin, as well as through ingestion and inhaling dust or powder. When handling copper sulphate, protective eyewear, gloves, and boots should be worn to avoid any contact with the chemical. Hydrochloric acid is a transparent, colourless liquid that has many uses such as the making of dyes, fertilizer, and chlorides. It is a corrosive compound that can damage eyes, skin, and mucous membranes. If inhaled, it can cause nose, eye, and respiratory tract irritation. Gloves and safety goggles should be worn when working with hydrochloric acid.

Purpose

The purpose of this investigation was to identify the difference between physical and chemical changes.

Procedure

Part 1

Safety goggles were put on. Copper sulphate was put in a test tube using a sucpula. 7 mL of distilled water was obtained in a clean graduated cylinder. The physical properties of copper sulphate and distilled water were described in the observation chart. The distilled water was poured into the test tube with the copper sulphate. A stopper was out on the test tube and the contents were mixed by turning it upside downObservations about the type of change you may have observed were recorded.

Part 2

About half of the copper sulphate solution from part 1 was poured into another clean test tube. A small piece of steel wool was obtained and its physical properties were described in the observation chart. The piece of steel wool was pushed into the copper sulphate mixture using a glass stirring rod. Observations about the type of change you may have observed were recorded.

Part 3

2 mL of sodium carbonate was measured using a clean graduated cylinder. The sodium carbonate was poured into a clean test tube. The physical properties of the sodium carbonate solution and remaining copper sulphate solution were described in the observation chart. One solution was poured into the other. Observations about the type of change you may have observed were recorded.

Part 4

2 mL of hydrochloric acid was measured out using a clean graduated cylinder. The hydrochloric acid was poured into a clean test tube. A small piece of magnesium ribbon was obtained. The physical properties of hydrochloric acid and the magnesium ribbon were described in the observation chart. The piece of magnesium ribbon was carefully dropped into the test tube of hydrochloric acid. Observations about the type of change you may have observed were recorded. The bottom of the test tube was felt. Observations were recorded in the chart. All the mixtures were disposed of down the drain and the sink was flushed with plenty of water. All glassware was cleaned with soap and water and materials were returned to where they belong.

Analysis

Chemical Changes

Tests 2, 3, and 4 were all examples of a chemical change. They all showed characteristics of a chemical change as explained in the introduction. In test 2, it was evident that the steel wool rusted in the copper sulphate solution, and the copper sulphate changed colour. This was a chemical change because a new substance was formed on the steel wool and its colour changed. In test 3, the copper sulphate solution and sodium carbonate made a white, buoyant precipitate. It gave the mixture a higher viscosity. Test 4 proved to be a chemical change because when submerged in hydrochloric acid, the magnesium ribbon began bubbling and changing colour. These two characteristics are both clues when looking at how to identify a chemical change.

Physical Changes

Test one was a physical change. When the two substances were combined, the resulting solution was predictable, and no new substances were made. Copper sulphate is an electric blue colour, and the copper sulphate solution was also an electric blue colour.

Change in Physical Properties

Many of the physical properties of the starting substances stayed the same, but some of them were altered by a chemical change. In part 1, the colour of the copper sulphate stayed the same after the experiment, although it’s state of matter changed from solid to liquid. The physical properties of the starting substances in part 2 of the lab changed. The steel wool was a gun metal grey, after the experiment, it rusted and turned red. In part 3, the physical properties of both substances were altered. For example, the copper sulphate took on a murky turquoise colour and the sodium carbonate created a white precipitate. In part 4, the hydrochloric acid remained the same throughout, but the magnesium ribbon changed colour and had a higher lustre after being submerged in the acid.

Discussion

The hypothesis that was made for part 1 of this experiment was correct. When the copper sulphate and water were combined, the copper sulphate solution had a sky blue colour, similar to that of the copper sulphate. For part 4 of this experiment, the hypothesis was incorrect. The magnesium ribbon created gas bubbles and changed the colour of the magnesium ribbon from slate grey to silver, giving it a higher luster.

Errors

There were many errors that could have occured during this lab that could have affected the outcome of the different experiments. These experiments were all done in a non sterile environment. The equipment was only rinsed with water, which could have left behind chemicals or bacteria that was used in a previous experiment. Also, the chemicals and substances that were used could have been contaminated by bacteria from a person conducting the experiment, as protective gloves were not used in this lab. If there were impurities in the substances or on the equipment, it could have altered the outcome of the experiment.

Another factor that could have skewed the results was the amount of chemicals that were used. For example, in part 1, if the ratio of water to copper sulphate of was too high, the solution would have been more diluted, which could have changed the outcome of parts 2 and 3.

Improvements

The experiments that were conducted in this lab were all successful, although, some things could have been done better. The equipment that was used could have been cleaned with soap and water to avoid contamination. The environment that the lab took place in could have been more sterile to avoid impurities in the event that a substance should come in contact with the lab bench. Anyone who conducted an experiment should have been wearing protective gloves to ensure that no chemicals could come in contact with their skin.

Conclusion

The experiments were designed to discern the differences between physical and chemical changes. Test 1 was a physical change because when copper sulphate and water were combined, it resulted in a blue solution. This is a result of the copper sulphate (solid form) dissolving in the water but the chemical composition of both substances remain the same. The remaining tests were examples of chemical changes because the chemical composition of each compound was altered. These experiments showed the differences between physical and chemical changes. All the findings in this experiment were important in accomplishing the goal of the lab. Tests 1 through 4 determined the differences between physical and chemical changes. Test 1 showed the characteristics of a physical change, which was important when comparing it to the other parts of the experiment. In test 3, precipitate that was formed when the copper sulphate solution and sodium carbonate were mixed. This demonstrated properties of a chemical change, allowing them to be differentiated from those of a physical change.

Application

A petroleum engineer is one of many careers that use physical and chemical changes in their everyday work. They need to know the difference between physical and chemical changes in order to perform their tasks. “Petroleum engineers develop and implement effective techniques for recovering, processing, and producing oil and natural gas”. They work to minimize the negative effects of drilling on the environment. An entry level worker can get paid anywhere $39,500 to $43,00 a year. With years of experience, their salary can be as high as $85,000. Petroleum engineers extract crude oil from the ground and boil it to separate the different components and impurities so they can make different materials for profit. This is an example of a physical change because the elements within the oil are still present and no new substances were formed. They also need to use these elements and turn them into other materials. For example, a byproduct of crude oil is gasoline. In order to make gasoline, petroleum, as well as other chemical compounds are mixed together to create a power source used in many motorized vehicles. When the gasoline is used, it combusts inside the engine of the vehicle, which is a chemical change. Petroleum engineers must know about these 2 changes in order to perform to the best of their ability.