Chemistry Activity: Concentration of Solutions Name Saturated and Unsaturated Activity! Page 1

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1 Chemistry Activity: Concentration of Solutions Name Saturated and Unsaturated Activity! Page 1 1. Open the file Concentration_en_jar from the Chem L3 labs, Solutions folder of Dropbox. 2. Make sure the meter indicating Concentration (mol/l) is in the solution. Play with the simulation. Click on everything. Move all the sliders. Try different solutes. Notice what happens as Solid solute is added, water is added and when Evaporation occurs. 3. How does the Concentration change as solid solute is added? Increases or Decreases? (circle)!! Is this More Concentrated or More Dilute? 4. How does the Concentration change as additional water is added? Increases or Decreases?!! Is this More Concentrated or More Dilute? 5. How does the Concentration change as Evaporation occurs? Increases or Decreases?!! Is this More Concentrated or More Dilute? 6. What happens when you add additional solute to an Unsaturated solution? Increases or Decreases?!! Is this More Concentrated or More Dilute? 7. Add solute until the meter says Saturated. Add more solid solute to this solution. What happens? How does this change the Concentration of the Saturated solution?! Increases! Decreases! No change 8. How does Evaporation change the concentration of a Saturated solution?! Increases! Decreases! No change 9. Why do you think this is? (7 & 8) 10. Pick a substance (name) and make a Saturated solution. What is the concentration of the saturated solution? 11. Pick a different substance (name) and make a Saturated solution. What is the concentration of this saturated solution? 12. Is the Concentration of a Saturated solution the same for all substances? Yes No! (In grams, this is called Solubility: How much dissolves ) 13. Is Saturated / Unsaturated the same as Concentrated/Dilute? Explain. 14. Watch the teacher demo for a Supersaturated solution. What happens when a crystal is added?

2 Part 2 : Molarity Activity! Page 2 In the first activity, we learned a little about Concentration or how much solute is dissolved. An important chemistry measure of Concentration is Molarity: moles of solute per Liter of solution. M = mol solute which can be rearranged to! mol = L x M! L = mol! L of solution! solve for other variables! M Write these formulas on your handout. 1. Open the file Molarity_en_jar from the Chem L3 labs, Solutions folder of Dropbox. 2. Switch the solute to Cobalt (II) nitrate. Click on Show Values. Play with the sliders. Add water and solute and notice the Molarity. 3. As you add solute to a given amount of solution, does the Molarity Increase or Decrease? 4. As you increase the solution Volume (basically add water) to a given amount of solute, does the Molarity Increase or Decrease? 5. Use the sim to fill in the Data Table below. Slide the sliders and write in the Molarity. Show work in the indicated box. Moles of solute Liters of Solution Work: M = mol! Liter mol 1.00 L Molarity of Solution 6. If you know the moles and Liters, does the Molarity depend on which solute you use? Yes or No? 7. a. How many moles are 40.0 g of NiCl 2? Show work b. What is the Molarity of 40.0 g of NiCl 2 in 0.60 L of solution? You can check your answer using the sim. 8 a. How many moles are 40.0 g of CuSO 4? b. What is the Molarity of 40.0 g of CuSO 4 in L of solution? Show work. 9. If you know the grams per Liter, does the Molarity depend on which solute you use? Yes or No? Explain.

3 Part 2 : Molarity Activity continued! Page 3 The formula for Molarity can be rearranged to solve for other variables: M = mol solute! mol = L x M! L = mol! L of solution!! M 10. Use the rearranged formulas above to fill in the Data Tables below. Show work. Check your answers using the sim. Moles of solute Liters of Solution Work: mol= Liters x M Molarity of Solution Moles of solute Liters of Work: L = mol Solution! M Molarity of Solution Remember Chemists need Moles, but we can only directly measure Grams. 11. If you needed to make 0.60 L of 1.50 M NaOH solution, how many grams of NaOH would you need? (see first problem above. Change your answer in moles to grams NaOH.) 12. How many Liters of 1.25 M NaOH solution contain 24.0 grams of NaOH? (Change g NaOH to moles NaOH, then use the formula that solves for Liters.) Another important formula is the Dilution formula: Start with a Concentrated Stock solution and add water to make it more Dilute. Copy these onto your handout. Dilutions:! V 1 M 1 = V 2 M 2! (calculates V Stock ) V water = V Total V stock! Both volumes must be in the same units, (both ml or both L) 13. How many ml of Stock solution would you need to make these solutions? How many ml of water do you need to add? example: 150 ml of NaCl from 3.00 M NaCl : (150 ml) (0.250 M) = V 2 (3.00 ml)! V 2 = 12.5 ml of the 3.00 M NaCl solution ( stock ) needed! Total Volume needed = 150 ml, so = ml water needed a. 100 ml of M MgSO 4 from 2.00 M MgSO 4 ml stock = ml water =!! (20.0, 80.0 ml) b. 500 ml of M NaCl from 2.00 M NaCl ml stock = ml water =!! (125, 375 ml)

4 Another Concentration unit is m = molality = moles solute! Page 4! kg of solvent 1. Calculate the molality (m) of 60.0 g KNO 3 in 200 g water! (2.95 m) 2. How many g of KI must be dissolved in 500 g of water to make a molal solution? (4.98 g) Colligative properties: Properties that change when solutes are added to solvents For water: Boiling point increases: Change in boiling point = T b = (K b ) x (molality)! K b = 0.52 C/m Freezing point decreases: Change in freezing point = T f = (K f ) x (molality) K f = 1.86 C/m 3. Why do we put salt on the roads in winter? 4. How does candy making illustrate the boiling point change? 5. What are the boiling and freezing points of a 1.5 molal solution of sugar in water? ( C, 2.79 C) 6. Antifreeze is Ethylene glycol, C 2 H 6 O 2 (a non-electrolyte). Calculate the freezing and boiling points of a solution of 200 g of C 2 H 6 O 2 in 800 g of water.! ( C, 7.5 C) 9. The freezing point of a glucose solution is 9.00 C. What is the molality of the glucose solution?! (4.84 m) 10. The boiling point of a glucose (C 6 H 12 O 6 ) solution is C. What is the molality of the glucose?! (3.85 m)! b. If you started with 100 g of water, how many g of glucose are in the solution?! (69.2 g)

5 Polarity and Solubility Lab Safety: Wear goggles and aprons In this Lab you will investigate predicting the Solubility of materials. What Dissolves and what Doesn t Dissolve? 1. Using your Types and Strengths of Forces Handout, Classify the materials in the Data Table at right.! Non-Polar (NP)! Polar (or Very Polar) (P)! Ionic (I) 2. In a small test tube, mix 20 drops of Water and 20 drops of mineral oil. Stopper and invert to mix. Then let Settle for a minute. What happens? Do they mix (dissolve) or not? Record in Data Table 2 as Yes or No. Next add 10 drops of Green dye #3. Stopper, mix, let settle. Record results. Last add a small amount of Iodine. Stopper, mix, let settle. Record results. Page 5 1. Name Formula 1. NP, P, I Water H 2 O Mineral Oil C 15 H 32 Green dye #3 C 37 H 37 N 2 O 10 S 3 Iodine I 2 Cyclohexane C 6 H 12 Sucrose, sugar C 12 H 22 O 11 Copper(II) nitrate Cu(NO 3 ) 2 2. Mix Polarities Dissolve? (y/n) H 2 O + oil! + H 2 O + dye! + oil + dye! + H 2 O + I 2! + Oil + I 2! + 3. Sketch what your test tube looks like in the picture at right >! What 2 materials dissolve in the top layer?! What type of materials are they?! What 2 materials dissolve in the bottom layer?! What type of materials are they?! What types of materials don t dissolve? + The mixture like this that doesn t stay mixed, but is suspended when you shake it is called a Suspension. It doesn t all dissolve, and separates on standing. These tend to be cloudy. A Solution is all dissolved, looks clear, and stays mixed. BTW: A Colloid is In between : It stays mixed, but is cloudy. Examples= milk, mayonnaise. Why this happens: Substances Dissolve because there is an Attraction between the solute particles and solvent particles. If there is no attraction, there is no dissolving! When all the solute particles are Solvated (surrounded by solvent) the solute is dissolved, and is free to move about as the liquid. 4. Open the file Dissolving_Sugar_Non-electrolyte in the Chem L3 Labs, Solutions folder in Dropbox. Watch the animation. Solvation is when the solute particles are surrounded by solvent particles. Draw a picture of some Sugar (C 12 H 22 O 11 ) molecules surrounded by water molecules here.

6 Polarity and Solubility Lab Continued Page 6! If Both Solute and Solvent are Polar, the + end of the solute is attracted to the end of the solvent, and vice versa. This lets Solvation occur. Polar/VP dissolves Polar. 5. Look at the back of your handout. Which picture of particles represents solvated (dissolved) Polar sugar molecules in Polar water, like in the animation? On your Handout, Label the Polar + Polar picture and write an example. Is it a Solution or Suspension? 6. If both Solute and Solvent are Non-Polar: Remember that Non-polar Dispersion force is very weak. In this case, the weak attraction means the solute and solvent particles don t care if they are next to a solvent or solute. NP solute particles and NP solvent particles all mix together fairly easily. NP dissolves NP. 7. Which picture is NP + NP? Label it, give an example, and is it Solution or Suspension. 8. But if the Non-Polar force is so weak, why didn t the Non-Polar oil dissolve in the Polar water? Open the file Polar_vs_NonPolar. Watch the animation. Draw a picture of the NP hexane (C 6 H 14 ) particles and water in the flask.! Since the NP particles don t have + or ends, there is no attraction from the NP solute to break apart the strong Hydrogen Bonding holding the water molecules to each other. The water molecules would rather stay stuck to other water molecules, and won t let the NP solute in between. So P and NP don t dissolve. P + NP make Suspensions, not Solutions. 9. Which two pictures are NP + Polar? Label them, give examples, Solution or Suspension? 10. Do you think Ionic compounds would dissolve in VP/P solvents like water or NP solvents like oil? Think about this as you watch the file Dissolving_NaCl-Electrolyte. Draw a picture of the water molecules surrounding some Na + and Cl ions. 11. Which picture shows Ionic solute dissolved in water? Label, give example, Sol or Susp? 12. Picture F is an Ionic solute and NP solvent, like NaCl in oil. Notice it is NOT dissolved. Label it.! Picture G is an Insoluble ionic compound with water. Notice: NOT dissolved! Label it. An example is CaCO 3. You can find Insoluble ionic compounds using your Solubility chart. **All the pictures on your handout should now be labelled, have examples, and identified as Solutions or Suspensions. These will be very helpful for the next part of the Lab. 13 Summarize the General Rules for Solubility on your Handout. These rules can also be summarized as Like dissolves Like.

7 Polarity and Solubility Lab Continued Page 7 Applying what you ve learned 14. Look back at #1 on Page 5. Label the materials in this Data Table as NP, P, I. 15. Using the General Solubility Rules you just discovered, predict what will happen if you mix the various combinations together. 16. Try it. In separate small test tubes, add 10 drops liquid + tip of the stick of solid. Stopper and mix. Let settle. For the H 2 O + C 6 H 12, add a few drops of green dye to help you see the result. Names H 2 O + C 6 H NP, P, I? 15. Predict Dissolve? Y/N P + NP H 2 O + C 12 H 22 O 11 + H 2 O + Cu(NO 3 ) 2 + C 6 H 12 + oil + C 6 H 12 + C 12 H 22 O 11 + C 6 H 12 + Cu(NO 3 ) Solution or Suspension 17. Are these mixtures Solution or Suspensions? Indicate in the Data Table. Were your predictions correct? If not, fix your answers, and make sure you understand what s happening! For this next step, you must use a DRY Test tube. 18. Here is the structural formula for Ethyl alcohol, C 2 H 5 OH. Circle in Red the C 2 H 5, which is NonPolar. Circle in Blue the OH which is Polar/Very Polar. 19. Do you think the Ethyl alcohol will dissolve in P/VP water or NP C 6 H 12 (hexane), or both or neither? Use your General Solubility Rules to explain why you think so. 20. Mix 10 drops of Ethyl alcohol with! 10 drops H 2 O in one test tube.! Mix 10 drops Ethyl alcohol with! 10 drops C 6 H 12 in another DRY!!! test tube. Fill in the Data Table. 20. Names NP, P, I? Predict Dissolve? C 2 H 5 OH + H 2 O + C 2 H 5 OH + C 6 H 12 + Solution or Suspension 21. So what does Ethyl Alcohol dissolve in?! P! NP! both! neither! If your prediction in # 19 was incorrect, try explaining again. Hint: Look at the NP and P ends of Ethyl alcohol. Wash your tubes with SOAP and water!!!!! Use a test tube brush. See why on next page!

8 Polarity and Solubility Lab Continued Page 8 Here s How Soap works. 22. If you had just rinsed out the oily test tubes with water, would the NonPolar oil, etc. in the test tubes be gone? Why do you think so? 23. If you had just rinsed out the test tubes with C 6 H 12, would the Ionic Cu(NO 3 ) 2, Polar Sugar, etc. in the test tubes be gone? Why do you think so? 24. Then how does soap work?? Here is a picture of a soap particle: Circle in Red the Non-polar end. Circle in Blue the Polar end. A Soap molecule has a NP end and a P/Ionic end. 25. Color the center oil droplet yellow. Color the NP tails red, the Polar heads blue. Label 1 water molecule. The non-polar tail (C s and H s), called Hydrophobic {water hating}. It surrounds oily dirt. The Ionic head ( COO Na + ), called Hydrophilic (water loving). It s attracted to the water molecules. This lets the soap dissolve NP dirt, and wash it away in water. This is similar to the Ethyl alcohol experiment you did in step 20. More Polar NonPolar and Solubility Practice at home: 26. Classify each material as : Non-Polar molecular, Polar (or Very Polar) Molecular, Ionic! Would each more likely dissolve in Water (H 2 O) OR in C 8 H 18! Which picture of particles ( A to G) on the Handout would correspond to each solution? a. LiCl! d. Methanol, CH 3 OH b. I 2! e. kerosene,c 9 H 20 c. K 2 SO 4! f. Lactose, C 12 H 22 O Which of the following mixtures make Solutions (dissolve) or Suspensions (separate, don t dissolve)? Which picture (A to G) on the Handout would each correspond to? a. Mothballs, C 10 H 10, in water! c. NaNO 3 in Oil! b. C 4 H 8 O 2 in pentane, C 5 H 12! d. C 4 H 10 in C 5 H 12

9 Electrolytes Lab: Page 9 Safety: Wear goggles and aprons Be careful with the Acids. They are corrosive.! 1.! In this lab you will investigate how some materials conduct electricity. We have classified some of them for you in the bold box below. Using your Types and Strengths of Forces Handout, classify the materials in the dashed line box below to fill in the rest of the Types of Materials box). Rubber stopper (Neoprene, (C 4 H 5 Cl) n )! C 2 H 5 OH, ethyl alcohol! Mineral oil, C 15 H 32 Copper! Glucose, C 6 H 12 O 6! Sulfur! Zinc! NaCl H 2 O!! Cu(NO 3 ) 2! KI! I 2! NH 4 NO 3 Types of Materials Metals Polar (or Very Polar) Molecular compounds Non-metals (elements, Non-polar) Non-polar molecular compounds Soluble Ionic compounds Insoluble Ionic compounds CaCO 3 Covalent network compounds Glass stirring rod ( Silicon dioxide, (SiO 2 ) n ) Strong Acids HCl (Hydrochloric acid) Weak acids HC 2 H 3 O 2 (acetic acid, vinegar) Investigation 1: Conductors vs. Non-conductors: 2. Test these Dry substances with the conductivity probe. Glass stirring rod, Rubber stopper, Copper, C 6 H 12 O 6, Sulfur, Zinc, NaCl. Add to the appropriate box below. Bright light, or Blinking Light Conductors: Conduct electricity No light Non-Conductors: Don t Conduct electricity What types of materials are they? What types of materials are they? 3. To be a Conductor, electrons must be free to move. Refer to your Types and Strengths of Forces Handout and your results. Why are the material(s) you found good Conductors?

10 Lab Part 2: Wet Materials or Mixed with Water : Electrolytes! Page The filled spot plate contains materials to be tested in water. The labeled template identifies the materials. Dispense some tap water into a 50 ml beaker and use this water to rinse between samples. Test the conductivity of each mixture and add each material to the appropriate box below. Be sure to rinse between wells. If time allows, test a few other materials (Tap water, soda, gatorade, koolaid, etc.) Bright light, Blinking light Strong Electrolytes: Conduct electricity in water Dim light Weak Electrolytes: Weakly Conduct electricity in water Hint: There s only one!! No light (or very dim) Non-Electrolytes: Don t Conduct electricity in water What types of materials are they? What type of material is it? What types of materials are they? *** To be a Strong Electrolyte: Need Ions (+ and - charges must be able to separate)! and these Ions must be free to move about (not stuck in place) {**Enter this info on Handout} To see how this works, Open the Java App sugar-and-salt-solutions_en.jar from the Chem L3 Labs, Solutions folder in Dropbox. Click on the Micro tab to see the particles. 5. a. Start by shaking NaCl into water. What happens to the Na + and Cl ions in the water? Are there Ions? Are they free to move? If yes to both, this is a Strong Electrolyte. If either is no, it is a Non-electrolyte! Does this match what you found in the lab? Yes or No b. Try dry NaCl, (which also represents an Insoluble Ionic compound). Select Lots of evaporation until the water is all gone. Are there still Ions? Can they move? Strong or Non-electrolyte? c. Click Reset all. Switch to Sucrose and shake some in the water. What happens to sucrose in water? Are the particles free to move? But are there ions? Strong or Non-Electrolyte? d. Click on the Orange arrow next to Solute and try some other solutes. 6. Conclusion: What type of material is a Strong Electrolyte? Why? Notice! This is not the same as what dissolves in water. Dissolve in water = Polar or Ionic! Don t dissolve in water = Non-Polar Strong Electrolyte = Non-Electrolyte = (Weak electrolytes are weak acids, but that s next chapter.) 7. Fill in the bottom of the Handout (Electrolytes section) with what you ve learned. Only one picture of particles at the top is a Strong Electrolyte (Ions, free to move). Which one? Be sure to Label it!!

11 Practice: Electrolytes Page Examine the particle pictures A, B, C below. (Water molecules are omitted for clarity).! a. Which picture represents a Strong electrolyte? How does the picture show how an electrolyte conducts electricity?! b. Which picture represents a non-electrolyte? How does the picture show why non-electrolytes don t conduct electricity?! c. Which picture represents a weak electrolyte? Is is mostly ions or mostly molecules? 2. Do the following refer to a non-electrolyte, strong electrolyte or weak electrolyte. When they are put into water solution, they:!! a. Conduct electricity very well!! e. Exist as ions! b. Don't conduct electricity!! f. Exist as ions and molecules! c. Conduct electricity a little!! g. Exist as molecules! d. most ionic compounds!! h. most molecular compounds 3. Are the following materials Non, Strong or Weak electrolytes? a. sugar, C 12 H 22 O 11! d. KCl! g. Citric acid, a weak acid b. Na 2 SO 4! e. Br 2! h. HNO 3, a strong acid c. pentane, C 5 H 12! f. NH 4 Cl! i. methanol, CH 3 OH 4. Write the ionic equation for each of the following strong electrolytes breaking up into ions (dissociating) as they dissolve in water. Example : MgCl 2(s) ----> Mg +2 (aq) + 2 Cl (aq) a. K 2 SO 4 (s) ---->! d. Ca(NO 3 ) 2 (s) ----> b. CaCl 2 (s) ---->! e. KNO 3 (s) ----> c. NH 4 Cl(s) ---->! f. Na 2 CO 3 (s) ---->! A B C

12 Chemistry : Review sheet: Solutions Page Use your "Forces chart to classify these materials : NP molecular, P (or VP) molecular, Ionic a. Br 2! d. CuCl 2! g. HCl _strong acid! b. C 3 H 6 OH! e. C 6 H 14! h. H 3 PO 4 weak acid! c. KNO 3! f. H 2 O! i. CCl 4 Non-polar 2. a. Which of the above are Strong Electrolytes! b. Which of the above would likely Dissolve in water 3. Which "Picture of particles" on the Handout represents KNO 3 mixed with CCl 4?! Would it make a Solution, Suspension or Colloid? (circle) Would it conduct electricity? Yes or No! If shaken, would it stay mixed? Yes or No Could you see through it (is it clear?) Yes or No 6. Which "picture" represents C 3 H 6 OH mixed with H 2 O?! Would it make a Solution, Suspension or Colloid? (circle) Would it conduct electricity? Yes or No! If shaken, would it stay mixed? Yes or No Could you see through it (is it clear?) Yes or No 7. The Solubility of KClO 3 is 10 g/100 g water at 20 C. If you mixed 20 g of KClO 3 in 100 g water at 20 C, what would happen? Would it make an Unsaturated, Saturated or Supersaturated Solution? Why do you think so?!what would happen if you added a crystal to it? 8. How many ml of 0.10 M NaNO 3 solution contain 4.25 g NaNO 3?! (500 ml) 9. You need to make 600 ml of 1.5 M NaOH. How many grams NaOH do you need?! (36.0 g) 10. You need to make 750 ml of 0.20 M NaCl by diluting 2.0 M NaCl. How many ml of stock solution and water would you need?! (75, 675 ml) 11a. What is th molality of a solution made by dissolving 50.0 grams of urea, CON 2 H 4, (a nonelectrolyte) in 250 grams of water? b. What is the Boiling point of the solution?! (3.33 m, C) 12. The freezing point of a solution of ethylene glycol, C 2 H 6 O 2, in 300 g water is 10.0 C. a. What is the molality of the C 2 H 6 O 2? b. How many g of C 2 H 6 O 2 are in the solution?! (5.38 m, 100 g)