Name: Date: Number: Acids

Transcription

1 Acids The sour taste of the lemon juice tells us that it is an acid. Acids are special kinds of chemicals. They are common in everyday life. Some are helpful, others are harmful. There are some that are weak. Others are strong. Many acids are dangerous to touch or taste. You should never touch or taste an unknown acid. Besides the sour taste that acids have, there are other tests for identifying them. Certain chemicals change color when acids are added. Chemicals that change color are called indicators. An example of an indicator is a litmus paper. Litmus paper comes in two colors: red and blue. Acids turn blue litmus paper red. Acids do not change the color of red litmus paper (red litmus paper stays red). When acids mixed with metals a chemical reaction takes place. Hydrogen gas is given off from this reaction. CHECKPOINT: Does the red litmus paper change color with acid? SOME COMMON ACIDS: The chart below lists some common acids and their chemical formulas. It shows what all acids have in common. All acids have the element Hydrogen (H + ). ACID CHEMICAL FORMULA USES 1. Acetic acid HC 2 H 3 O 2 Vinegar 2. Boric acid H 3 BO 3 Eye wash 3. Carbonic acid H 2 CO 3 Club soda 4. Citric acid H 3 C 6 H 5 O 7 Citrus fruits 5. Hydrochloric acid HCl Aids digestion 6. Nitric acid HNO 3 Fertilizers 7. Sulfuric acid H 2 SO 4 Plastics

2 Fill in the blank: Directions: Complete each statement using a term from the list below. Write your answers in the spaces provided. Some words may be used more than once. Never vinegar litmus paper dangerous acid hydrochloric acid Hydrogen blue red citric 1. Lemons contain acid. 2. is a kind of indicator. 3. Acids turn litmus paper red. 4. litmus paper does not change colors in acids. 5. When acids wear away metals is given off. 6. Acetic acid is found in household. 7. Your stomach produces. 8. All acids contain the element. 9. Some acids are to touch or taste. 10. You should touch or taste an. TRUE OR FALSE: Directions: In the space provided, write true if the sentence is true. Write false if the sentence is false. Make the false statement true. 1. Litmus paper is an indicator. 2. Acids turn red litmus paper blue. 3. Acids contain hydrogen. 4. Acids wear away metals. 5. Oxygen is given off when acids wear down metals. Sometimes when rain falls, it mixes with pollution particles in the air. An acid is formed. Why might this be harmful?

3 Bases Bases are a group of chemicals that have certain properties. Their properties are different from the properties of an acid. Often they act opposite to the ways that acids act. However, like acids, bases may be different strengths. Some are very weak. Some are very strong. Some bases are dangerous to touch or taste. You should never touch or taste an unknown base. Bases have a bitter taste. If you touch a harmless base it will feel slippery. Acids do not have any special feel. Bases act the opposite way from acids with indicators. Bases turn red litmus paper blue. They do not change blue litmus paper. There is another indicator that helps us identify bases. It is called phenolphthalein. This solution is clear in acids, but phenolphthalein turns deep pink in bases. Unlike acids, bases do not wear away metals. CHECKPOINT: What happens to red litmus paper in bases? What happens to blue litmus paper in bases? What happens to phenolphthalein in acids? Some Common Bases: The chart lists some common bases and their chemical formulas. It shows you what all bases have in common. All bases contain special groups of oxygen and hydrogen atoms called hydroxides (OH-). BASE CHEMICAL FORMULA USES 1. Potassium hydroxide KOH Soap-lye 2. Magnesium hydroxide Mg(OH) 2 Milk of magnesia (neutralize stomach acids) 3. Calcium hydroxide Ca(OH) 2 Mortar 4. Ammonium hydroxide NH 4 OH Ammonia (used in fertilizers) 5. Sodium hydroxide NaOH Soap

4 FILL IN THE BLANK: bitter chemicals change lye dangerous do not change indicators opposite to pink sour 1. Bases often act the ways that acids act. 2. Both acids and bases can be. 3. Bases have a taste. 4. Acids have a taste. 5. Bases the color of red litmus paper. 6. Bases the color of blue litmus paper. 7. Phenolphthalein turns in bases. 8. Phenolphthalein and litmus paper are. 9. Soap contains a base called. 10. Bases are groups of. MATCHING: 1. Red litmus paper 2. Blue litmus paper 3. Phenolphthalein 4. An acid 5. A base a). ammonia b). turns pink in bases c). turns blue in bases d). stays blue in bases e). vinegar TRUE OR FALSE: Directions: In the space provided, write true if the sentence is true. Write false if the sentence is false. If the sentence is false change the statement to make it true. 1. Bases taste sour. 2. Bases feel slippery. 3. Bases turn blue litmus paper red. 4. Bases turn red litmus paper blue. 5. Phenolphthalein turns deep pink in bases. 6. Bases wear away metals. 7. Bases can be dangerous. 8. Acids contain the OH- groups. 9. Acids contain the H+ groups. 10. All bases are strong. Why are indicators useful?

5 What happens when Acids and Bases are Mixed? In chemistry, a liquid is neutral if it is not an acid or a base. Take water for example, water is neutral. It is not an acid. It is not a base. When you mix an acid with a base, a chemical reaction takes place. The atoms from the acid and the base change the way they are linked up. New products are formed. These new products have their own properties. The properties are different from the properties of either acids or bases. What do you get? When you mix the right amounts of an acid and a base, you get a salt and water. The salt is dissolved in the water. It forms a salt solution. A salt solution is not an acid: it is not a base. It is neutral. ACID + BASE MAKES SALT + WATER The link-up of an acid and a base to form a salt and water is called neutralization. There are many kinds of salts. The salt you sprinkle on your food is just one kind of salt called sodium chloride. Its chemical formula is NaCl. Different salts have different formulas. MIXING AN ACID AND A BASE: The beaker in the figure above contains 20mL of sodium hydroxide (NaOH). One drop of phenolphthalein is added. The phenolphthalein turns deep pink. This shows that sodium hydroxide (NaOH) is (an acid/ a base) In the figure above 10mL of hydrochloric acid (HCl) is added to the beaker with NaOHone drop at a time. The solution stays pink. This shows that the solution (is neutral/is an acid/is still a base). More hydrochloric acid (HCl) is added on drop at a time, until the pink disappears. The loss of the pink color shows that the solution is (an acid/no longer a base). The solution is tested with blue litmus paper. The blue litmus paper stays blue. This shows that the solution is not (an acid/a base). The same solution is tested with red litmus paper. The red litmus paper stays red. This shows that the solution is not (an acid/ a base). The mixture (is/is not) neutral.

6 Fill in the boxes below to show that happened: An a a water Hydrochloric acid + sodium hydroxide Sodium chloride + Water HCl + NaCl NaCl + H 2 O NaCl in H 2 O is (an acid/a base/salt water). FILL IN THE BLANK: Directions: Complete each statement using the term from the list below. Write your answers in the spaces provided. Some words may be used more than once. water neutralization litmus paper an acid a base many kinds reaction a salt table neutral phenolphthalein 1. Lemon juice is an example of. Lye is an example of. 2. Any substance that is not an acid or a base is said to be. 3. An example of a neutral liquid is. 4. The mixing of an acid and a base causes a chemical. 5. If we mix the right amounts of an acid and a base, we get and. 6. The chemical reaction between an acid and a base to produce salt and water is called. 7. There are of salts. 8. The most common salt is salt. 9. Salt water does not change the color of or. 10. Salt water is neither nor. Salt water is.

7 MATCHING: Directions: Match each term in Column A with its description in Column B. Write the correct letter in the space provided. Column A 1. HCl 2. NaOH 3. H 2 O 4. NaCl 5. Phenolphthalein Column B a). acid b). water c). base d). indicator e). salt TRUE OR FALSE: Directions: In the space provided, write true if the sentence is true. Write false if the sentence is false. If the sentence is false correct the statement. 1. An acid is neutral. 2. A base is neutral. 3. Water is neutral. 4. There is only one formula for water. 5. There is only one kind of salt. 6. Salt water is neutral. 7. If you mix an acid and a base, you get only water. 8. Blue litmus paper changes red in salt water. 9. Red litmus paper stays red in salt water. 10. Phenolphthalein turns pink in salt water. REACHING OUT: When Hydrochloric acid reacts with potassium hydroxide; potassium chloride is formed. The formula for hydrochloric acid is HCl The formula for potassium hydroxide is KOH What is the formula for water? What is the formula for potassium chloride?

8 ACIDS 1. Contains H+ (proton donor) In water it makes H+ (protons) and will bond with any OH- 2. Blue litmus paper turns red 3. Sour taste 4. Do not feel slippery to touch 5. Indicator color with phenolphthalein is from clear to clear = NO CHANGE!!! 6. Low ph number range 0-6 (how much H+ in water) High concentration of H+ ions Strong acids have ph 0-3 Ex. Car battery Sulfuric acid (H 2 SO 4 ) Stomach acid-hydrochloric acid (HCl) Weak acids have ph 4-6 Ex. Vinegar-acetic acid (HC 2 H 3 O 2 ) -Lemon juice citric acid (citrus fruits)- H 3 C 6 H 5 O 7-7-up soda-carbonic acid H 2 CO 3 BASES 1. Contains OH- (proton acceptor) In water it makes OH- and will bond with (accept) any H+ 2. Red litmus paper turns blue 3. Bitter taste 4. Feel slippery to touch 5. Indicator color with phenolphthalein is from clear to pink 6. High ph number range 8-14 (how much H+ in water) Low concentration of H+ ions Strong bases have ph Ex. Drain Cleaner (Draino) Sodium Hydroxide (NaOH) Laxative (Milk of Magnesia)- Magnesium Hydroxide- Mg(OH) 2 Weak bases have ph 8-11 Ex. Household floor cleaner-ammonia Hydroxide (NH 4 OH) Deodorant or Antacid (Rolaids)- Aluminum Hydroxide Al (OH) 3