1. Module 4 Intro

1.10. Page 8

Lesson 1

Module 4—Properties of Solutions

Reflect and Connect

 

Self-Check

 

SC 7. For each of the following, determine whether the statement is true or false. For those that are false, write a brief sentence indicating the required correction.

  1. Mixtures may be homogeneous or heterogeneous.

  2. Distilled water is obtained by letting the water sit until impurities settle out.

  3. Homogenized milk is a heterogeneous mixture.

  4. A perfectly clear solution is a pure substance.

  5. In a solution, the solute is the substance present in a lesser amount.

  6. Liquid water in air forms a solution of humid air.

  7. A solution of ethanol does not conduct electricity since C2H5OH is a molecular compound.

  8. Pure water does not conduct electricity.

  9. Pure water may be classified as a solution.

SC 8. There are four beakers with visually identical liquids—Sr(OH)2(aq), C12H22O11(aq), H3PO4(aq), and H2O(l). A student must correctly identify which liquid is in each beaker.

  1. For each beaker, identify the results of a conductivity test and a litmus test.

    Beaker Contents

    Result of Conductivity Test

    Result of Litmus Test

    Sr(OH)2(aq)

    		    

    C12H22O11(aq)

    		    

    H3PO4(aq)

    		    

    H2O(l)

    		    
    2.  
  2. Is it possible to correctly identify all four solutions by only performing conductivity and litmus tests? Explain.

SC 9. Read the following information and then answer the questions.

 

Gold jewellery is very common in society, and an understanding of alloy solutions will help you next time you make a purchase at a jewellery store. First, the purity of gold rings is measured in karats (k). A 24-k gold ring is 100% gold, an 18-k gold ring is 75% gold, and so on. To determine the percentage of gold in a ring, simply divide the karat number by 24 and multiply by 100%.

 

Gold rings need not be confined to the traditional yellow colour; white gold is an enormously popular alternative. The difference between yellow gold and white gold comes from other metals present in the alloy solution. Yellow gold contains elemental gold mixed with metals such as copper and zinc, while white gold contains elemental gold mixed with metals such as silver and palladium. Since white gold is still not completely white even after the addition of these metals—it’s more of an off-white or light grey—a layer of rhodium is added to the ring to give the final shiny appearance. This layer can be rubbed off over time, so white gold jewellery typically requires a rhodium replating after approximately two or three years of use.

 

White gold has led to some health concerns in the past, as nickel metal was used as one of the metals in the alloy. About 12% to 15% of the population suffers from skin allergies from nickel. Often, white gold rings will be described as “hypoallergenic,” meaning that no nickel was used in the production of the ring. Palladium is typically used as an alternative.


  1. What percentage of a 10-k gold ring is actually gold?

  2. 22-k gold rings and higher are typically not produced. Why would these rings make poor jewellery?

  3. Is it possible to make a 24-k white gold ring?
     
  4. Give three examples of how the use of alloys in ring production is advantageous.

  5. Suggest two reasons why it is important to replace the rhodium coating on a white gold ring.
Check your work.
Self-Check Answers

 

SC 7.

  1. True

  2. False

  3. True

  4. False

  5. True

  6. False

  7. True

  8. True (to any measurable extent)

  9. False

SC 8.


  1. Beaker Contents

    Result of Conductivity Test

    Result of Litmus Test

    Sr(OH)2(aq)

    Conductive

    Red litmus turns blue

    C12H22O11(aq)

    Not conductive

    No change

    H3PO4(aq)

    Conductive

    Blue litmus turns red

    H2O(l)

    Not conductive

    No change

  2. No, C12H22O11(aq) and H2O(l) both have the same test results.

SC 9.

  1. % = (10K/24K) 100 = 42%

  2. Gold is a soft (malleable) metal and quickly loses its shape.

  3. No, 24K means no other metals are added.

  4. Reason 1: Adding other metals makes the ring less malleable and therefore it will last longer.

    Reason 2: Addition of less expensive metals makes ring less costly.

    Reason 3: Adding other metals changes the colour of the ring, providing more choice to the consumer.

  5. Reason 1: The rhodium coat is required to give the ring its shiny appearance, since white gold actually has a dull grey colour.

    Reason 2: Some people have allergies to metals such as nickel. The rhodium coating prevents contact between these metals and the skin.

 

Reflect on the Big Picture

 

Proactive Citizen Projects

 

In this module you will complete two of the Proactive Citizen Projects listed in the Module 4 Summary and Assessment document. Choose which two topics to complete and when you wish to complete them. More information, including a list of topics and a scoring guide, is available in the Module 4 Summary and Assessment document.

 

Assessment

 

Submit the following item to your teacher:

  • Module 4: Lesson 1 Assignment

You may have selected your topics for the Proactive Citizen Projects listed in the Module 4 Summary and Assessment document. As you work on these projects, save your work to your course folder. You will receive information later in this module about submitting your completed work to your teacher.