Discovering Acids and Bases

8.1 – Discovering Acids and Bases Unit 8 – Solutions, Acids and Bases Background Information: Acids and bases are two kinds of special chemicals. Almost all liquids are either acids or bases, which is determined by the type of ions in them. An acid has many hydrogen ions, and splits apart in water to release these hydrogen ions. On the contrary, bases have hydroxide ions that combine with hydrogen ions. Scientists us a pH scale to determine whether a liquid is an acid or a base. Key Questions: ●​ What substances are acids/bases? ●​ How are all acids/bases similar? ●​ What happens to the pH level of substances when it is diluted? Instructions: Using the “pH Basics” simulation on the PhET website, we will explore and answer the important questions of this investigation. We will gain experience using a virtual pH scale, and test the pH levels of different substances in order to determine them as an acid or base. Based on our results, we will analyze how the discovered acids are similar, and discovered bases are similar. We will use our discoveries to explore and understand how pH levels of substances are affected when diluted. Explore 1.​ Type this link into your browser: https://phet.colorado.edu/en/simulation/ph-scale-basics OR type into your search bar “pH Scale Basics PhET” and select the first link that opens. 2.​ Click on the start symbol to open the simulation. 3.​ Press the drop down at the top of the screen to view the substances you will be testing. 4.​ Choose a liquid and use the dropper to fill the beaker to 1/2L. 5.​ Fill the beaker to 1L by clicking the water faucet until the liquid level reaches the 1L mark. 6.​ Empty your beaker by clicking the bottom faucet until the measurement arrow reads 0.00 L. Prediction Predict which substances in the chart will be determined as acids and bases on the pH scale. Explain how/why you categorized the substances the way you did. What characteristics of the substances helped you predict whether the substance was an acid or base? Acids have a pH less than 7. The lower the pH, the stronger the acid. Bases have a pH greater than 7. The higher the pH, the stronger the base. Investigation Substance Drain Cleaner Hand Soap Blood Milk Chicken Soup Coffee Orange Juice Vomit Water 1.​ Set the substance to drain cleaner. 2.​ Press the dropper and fill the beaker to ½ L. 3.​ Place the pH scale sensor in the beaker so that the center of the sensor is touching the liquid in the beaker. 4.​ Observe the pH reading on the scale. 5.​ Record the substance’s pH level and whether it is an acid or a base in the table on the next page. 6.​ Repeat these steps with each substance listed in the table. Substance Drain Cleaner Hand Soap Blood Milk Chicken Soup Coffee Orange Juice Vomit Water pH Level 13.0 10.0 7.40 6.50 5.80 5.00 3.50 2.00 7.00 Acid or Base Base Base Acid Acid Acid Acid Acid Acid Base Acid or Base Base Base Base Acid Acid Acid Acid Acid Neutral Analyzing Data Analyze your data, and place each substance in the proper place on the pH scale. Which substance is most acidic? Vomit Which substance is most basic? Drain Cleaner Which substance is considered neutral? Water What do you notice about most of the substances that are considered acids? What do they have in common? They are consumable____________________________________________________________________ __________________________________________________________________________________________________ What do you notice about most of the substances that are considered bases? What do they have in common? Their cleaning supplies_______________________________________________________________________ __________________________________________________________________________________________________ Which substances were closest to neutrality? What do they have in common? They have extreme water bases_____________________________________________________________________ __________________________________________________________________________________________________ Other substances in the simulation that were not tested are spit, battery acid and soda pop. Based on your data and observations of acids and bases, which category would you place these substances in and why? Check your answer using the simulation. Spit, Neutral Battery Acid Acidic, Soda Pop, Acidic________________________________________________________ __________________________________________________________________________________________________ Why do you think water is a neutral substance? it's a universal dissolver, and its polar__________________________________________________________________ __________________________________________________________________________________________________ Application -What happens to the pH level of a substance when it is diluted? 1.​ Using what you know about acids and bases, predict what will happen to the pH level when water is mixed with each substance? I think the pH level will increase/decrease/stay the same/vary (circle) when diluted because…decrease because of it being diluted with water_____________________________________________________________________ __________________________________________________________________________________________________ Explanation Phase Use the simulation to fill in the following table, using the drain cleaner example that is already completed for you as a guide. You will be testing the pH of five solutions before and after adding various amounts of pure water to test how dilution affects pH levels. This will be done by placing the green detector into the beaker’s solution after adding the appropriate amount of each liquid. In this experiment you will be testing five substances, along with three dilution levels of each substance when combined with water. Each solution should be 1.0 Liter (see image below) when testing. After each experiment it is important to drain the entire solution before beginning your next experiment. Aim: Create a rule that describes what happens when pure water is added to various acidic and basic substances. Substance Name pH of Pure Substance (100%) Is it an acidic or basic substance? 0.75 L of substance 0.25 L of water 1.0 L total 0.50 L of substance 0.50 L of water 1.0 L total 0.10 L of substance 0.90 L of water 1.0 L total Is the final solution an acid or base? Drain Cleaner 13.0 Basic 12.88 12.69 12.00 Base Spit 7.40 Neutral/Base 7.33 7.24 7.07 Neutral Water 7.00 Neutral 7.00 7.00 7.00 Neutral Blood 7.40 Base 7.16 7.24 7.06 Base Milk 6.50 Acidic 6.91 6.68 6.92 Acidic Soda Pop 2.50 Acidic 2.63 2.81 2.57 Acidic Making Observations and Analyzing Data: 1.​ What happens to the pH of acidic solutions as you add water? They diluted by megatons________________________________________________________________________ __________________________________________________________________________________________________ 2.​ What happens to the pH of basic solutions as you add water? They diluted by megatons_____________________________________________________________________________ __________________________________________________________________________________________________ 3.​ In general, when we dilute and acid or a base, the pH always moves toward what pH value? 7.00__________________________________________________________________________ __________________________________________________________________________________________________ 4.​ Did an acid ever become a base or did a base ever become an acid? Why do you think so? Acid because the water diluted the aspects that made the liquids acidic _________________________________________________________________________ __________________________________________________________________________________________________