Acids, Bases and ph. Biology Honors. Acidic, Basic or Neutral (indicate if strong or weak acid or base) Substance ph More H + More OH - Vitamin C

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1 Biology Honors Name Acids, Bases and ph Substance ph More H + More OH - Acidic, Basic or Neutral (indicate if strong or weak acid or base) Vitamin C Tap water Hydrochloric acid (HCl) Sodium hydroxide (NaOH) Lemon juice Ammonia Coffee Regular aspirin Buffered aspirin Milk Detergent Vinegar Maalox (antacid) Bleach 1

2 1. If you put a strong acid in 100 ml of water and then you put the same amount of a weak acid in 100 ml of water, why would the ph be lower in the beaker with the strong acid? 2. When the compound NaOH (sodium hydroxide) is placed in water, sodium ions (Na + ) and hydroxide ions (OH - ) are present. (a) Would NaOH be considered an acid or a base, or neither? (b) Explain your answer (c) Would sodium hydroxide change the ph of the water?. Would the ph go up or down? 3. When HNO 3 (nitric acid) is in solution, hydrogen ions (H + ) and nitrate (NO 3 - ) are present. (a) Would this compound be considered an acid or a base, or neither? (b) Explain your answer (c) Would nitric acid change the ph of the water?. Would the ph go up or down? 4. When NaCl (sodium chloride) is placed in water, sodium ions (Na + ) and chloride ions (Cl - ) are present. (a) What is the common name for sodium chloride? (b) Would this compound be considered an acid or a base, or neither? (c) Explain your answer (d) What was the ph of tap water? (refer to the chart) Put a teaspoon of salt into a quarter-cup of tap water. (e) Does the ph of the solution change? (yes or no). Does the ph go up or down? 5. What term is used to describe the separation of ionic compounds into individual ions when dissolved in water? 2

3 Compounds that yield ions in solution can be acids, bases, or salts. Only acids and bases will change the ph of the solution. 6. The following compounds yield ions in solution as indicated. Are they acids, bases, or salts? a. Na 2 CO 3 2Na + + CO 3-2 b. Ca(OH) 2 Ca OH - c. MgCl 2 Mg Cl - d. H 2 SO 4 2H + + SO 4-2 e. KOH K + + OH - f. NH 4 OH NH OH - ph Values of Various Human Body Fluids Most body fluids are approximately neutral in ph, while some can be either acidic or basic. Some common body fluids are described below. 1. The ph of saliva lies between 5.5 and 6.9, indicating a solution. 2. Bile, a substance produced in the liver, stored in the gall bladder, and secreted into the small intestine to help aid in fat digestion, has a ph of 7.8 to 8.6, so it is a/an solution. 3. Urine has a ph range of 5.5 to 6.9, so it is a/an solution. 4. Blood has a ph range of 7.3 to 7.5, so it is a/an solution. 5. Gastric juices in the stomach contains hydrochloric acid, having a ph range of 1.6 to 1.8. This would be a solution. 6. The pancreas is a gland that secretes pancreatic juice into the small intestine. It has a ph range of 7.5 to 8.0. This juice is a solution. 3

4 You must type the rest of the answers to this lab and staple them to the first 3 pages. You should type the heading of lab section and then type the questions. Use the format shown below as a guide. Some of the question numbers have been changed, and a few of the questions have been changed slightly. Use the questions as they are written on this document, not as they are written in the lab. Using a ph Indicator to Compare Acids and Bases 1. Using ph paper, test the ph of the solution. ph = 2. Add 2 drops of NaOH to the cup and stir. Record the color change: 3. Using ph paper, test the ph of the solution: ph = Describe the color change and explain the molecular changes that occurred: 4. Add 5 drops of HCl and stir. Record the color change: 5. Using ph paper, test the ph of the solution. ph = Describe the color change and explain the molecular changes that occurred: ph and concentration 1. Explain the change in ph between the 2 solutions. You must use the term concentration in your answer. Stomach Acid and Antacids 1. Look at the formulas for these compounds, and explain how they might neutralize stomach acid. Results Initial ph of stomach acid Type of Antacid ph after 3 minutes 4

5 !!!!!!! Buffers and ph 1. What is a buffer, and why are buffers important? 2. Would a change in blood ph from 7.4 to 8.4 be significant? Explain. 3. What condition would result if the blood ph was changed to 8.4? 4. If you were a physician, how might you treat this condition? 5. How does this buffer system respond to a rise in ph? 6. How does this buffer system respond to a drop in ph? Shampoo and ph 1. Ingredient that is supposed to balance the ph of shampoo: 2. How would this ingredient help to balance the ph? 3. Why do some people put lemon juice in their hair to help control split ends? ph and the Environment 1. How is acid rain formed? 2. What is the ph of acid rain? 3. How do sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ) decrease the ph? (look at the chemical formula) 4. Why is acid rain an ecological problem? Give an example. 5. Explain how human beings are responsible for acid rain. How do Acids and Bases Taste? lemon juice vinegar Vitamin C yogurt aspirin 5

6 Buffered Aspirin vs. Regular Aspirin 1. You have a headache and you are deciding whether to take regular aspirin or buffered aspirin. Considering that you also have a tendency to suffer from heartburn you decide to take the buffered aspirin instead. Why is this a good idea? (Refer to to the ph chart for the ph of these 2 types of aspirin) 6