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Lesson 7 Properties of Ionic and Molecular Compounds


  Properties of Acids and Bases

Did you know that citrus fruits taste sour because of their acidic content?


B7.20 Girl eating a lemon
You already learned how to recognize that a substance is an acid or a base by analyzing its chemical formula. In acid formulas, “H” is written first (e.g., HCl and H2SO4) or ends with “COOH” (e.g., CH3COOH). In bases, the formula is a metal bonded to hydroxide (e.g., NaOH and LiOH). In addition to recognizing formulas as acidic or basic, you also need to be able to distinguish between acids, bases, and neutral compounds by observing their properties.

Here is a table that compares the properties of acids to bases.

Properties of Acids
 Properties of Bases
  • taste sour
  • is corrosive
  • turn blue litmus red
  • pH below 7
  • conduct electricity
  • react with active metals to produce hydrogen gas
  • taste bitter
  • feel slippery
  • turn red litmus blue
  • pH above 7
  • conduct electricity

Note: Even though taste is a characteristic property of acids and bases, this should not be used as an analysis technique in laboratory settings! The same goes for touching a solution to determine if it is slippery.

  Did You Know?


© Wikimedia Commons
B7.21 Detergent pod

Manufactures put certain chemicals with bitter tastes (bases) into items that they do not want people to ingest? One such additive is denatonium benzoate. This substance is a base and is classified as one of the bitterest substances in the world. It is added to rat poison, antifreeze, and even detergent pods in the hopes that if a human accidently ingests one of these toxic substances, they will immediately spit it out. https://letstalkscience.ca/Explore/ArticleId/6171/dont-eat-laundry-pods.aspx

Learn More

  Virtual Lab

Mystery Powder Analysis @ Explore Learning
Please work through this lab to identify unknown substances as acidic, basic, or neutral based on their properties.

Please click on the procedure tab to continue. 

Please note: if you scroll down while in the Gizmo you will see a list of questions. You DO NOT need to complete these questions. You are able to complete them for extra practice if you would like.

  1. Click on the play icon to open the virtual lab. The virtual lab can also be accessed by going to the Online Resources for Print Students section in your online course.
  2. In your notebook, create a data table similar to the one found below. 
  3. Set “Select a sample” to “Unknown”:  .
  4. Drag sample 1 to “Place tube here.”
  5. Click “Test” at the bottom of “Litmus test.”
  6. Record the results.
  7. Click “Reset.”
  8. Repeat steps 4 to 7 for unknown samples 2 and 5.
  9. Click on the analysis tab to complete the analysis questions.

Sample
 Litmus Test Results
Red Litmus
 Blue Litmus
1
2
5

    Sample
    		 Litmus Test Results
    Red Litmus
    		 Blue Litmus
    1 red blue
    2 blue blue
    5 red red

  1. Classify each unknown as acidic, basic, or neutral.

    Sample 1—neutral
    Sample 2—basic
    Sample 5—acidic
Remember that acids turn blue litmus red, bases turn red litmus blue, and neutral substances do not affect litmus paper.

  1. Identify which sample would most likely contain the following substances: HOOCCOOH, LiOH, KNO3.

    Sample 1—KNO3
    Sample 2—LiOH
    Sample 5—HOOCCOOH

  Read This

Please read pages 62 to 68 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on identifying substances as acidic, basic, or neutral based on their properties. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.

  1. Based on the following observations, classify each substance as acidic, basic, or neutral.

    Observed Properties
    		 Classification
    conducts electricity and tastes sour
    conducts electricity and has a pH of 10
    produces bubbles when mixed with magnesium metal and turns blue litmus red
    causes red litmus to stay red and has a pH of 7
    feels slippery and tastes bitter

    Observed Properties
    		 Classification
    conducts electricity and tastes sour acidic
    conducts electricity and has a pH of 10 basic
    produces bubbles when mixed with magnesium metal and turns blue litmus red acidic
    causes red litmus to stay red and has a pH of 7 neutral
    feels slippery and tastes bitter basic