Properties of Substances Lab Graded Assignment Question:

| September 12, 2019

Properties of Substances Lab Graded Assignment Question: What changes occur when chemicals are mixed, and which changes signal that a physical or chemical reaction has occurred? Hypothesize: Look at the substances in the materials list. Make an educated guess about what physical or chemical changes might occur when some of them are mixed. Write your hypothesis as an if-then statement such as, “If I mix water and chalk powder, then the chalk will dissolve but no chemical change will take place” (You must make 3 educated guesses of what you believe will happen or what you will observe…3 points) !. If you mix citrus acid and baking soda then it will react and you will get a chemical change 2. If you mix distilled water with sugar then it will dissolve and a physical change will occur 3. If you mix calk with vegetable oil then it will cause a physical change Procedure: 1. Using the scoopula, fill well 1A of the microplate approximately one-fourth of the way with chalk. Using a pipette, slowly add 25 drops of distilled water to the chalk. Stir with a toothpick. Record your results in the “Observations Immediately After Mixing” chart. 2. If there is no Reaction, write NR. 3. Use the scoopula to put the chalk and other solids into the microplate wells. 4. Add 25 drops of citric acid solution. Use a clean pipette to add the citric acid solution. Stir with a clean toothpick. Record results. 5. Repeat with 25 drops of vegetable oil and then .1M NaOH. Record all results 6. Allow enough time for the liquids to evaporate. After the liquids evaporate, study each well with your hand lens. 7. In the data table “Observations of Mixtures After Evaporation”, record your observations of the dry samples that are left behind. Consider such factors as change in crystal appearance. Data Table 1 Observations of Mixtures Immediately After Mixing (7 points) 1 Chalk 2 NaCl 3 KCl 4 Baking Soda 5 Sugar 6 Vinegar Bubbles of a colorless gas are produced Gas released color changes from white to bluish NR Clear solution forms liquid Sugar dissolves NR NR NR NR NR CLEAR solution formed A Distilled water Solution is misty and has a precipitate. Clear solution gas B 3M Citric Acid Mixture dissolves gives off gas Gas immediately forms clear solution Gas immediatley forms clear solution C Vegetable Oil NR NR NR D .1M NaOH NR NR NR..CLEAR SOLUTION FORMED Data Table 2 Observations of Mixtures Immediately After Evaporation (7 Points) 1 Chalk 2 NaCl 3 KCl 4 Baking Soda 5 Sugar 6 Vinegar Since the reaction is physical, the water evaporates leaving powder Since the reaction is physical, the water evaporates Evaporations leaves out sugar crystals Clear solution formed Evaporations leaves out sugar crystals Clear solution formed A Distilled water White powder of chalk remains after evaporation White crystals of sodium chloride are formed Pellets of potassium hydroxide are formed B 3M Citric Acid powder is left after evaporation NR White crystals C Vegetable Oil Chalk powder remains Evaporation leaves sodium chloride crystals NR leaving powder NR D .1M NaOH NR NR NR NR Sugar pellets remain as sediment NR NR Crystal form Analyze Answer each of the following thoroughly. 1. Go back to your observations tables and underline all observed changes that you noted that you think were physical changes.(3 points) 2. Clear solution between sugar and distilled water indicated physical change 3. Vegetable oil mixed with sodium chloride is physical; the oil can be extracted with adding water then evaporating to leave only NaCl 4. Soluble mixture of vinegar and distilled water is physical, doesn’t have any further reaction 5. Go back to your observations tables and either circle or highlight all observed changes that you think were chemical changes.(3 points)Formation of White crystals of sodium citrate 6. Formation of Crystals 7. Pellets of potassium hydroxide are formed from distilled water with potassium chloride 8. Calcium citrate powder is left after evaporation when chalk is mixed with citric acid 9. In considering your observations of the mixtures, look for similar patterns of behavior. Which pairs of substances produced almost the same results in each mixture that they were found in? (3 points) 10. Both NaCl and KCl behaved similarly when in mixture with citric acid 11. Sugar and vinegar behave similarly when mixed with distilled water. 12. Both potassium chloride and baking soda behave similarly in citric acid 13. 4. Make a general statement about whether your hypotheses were validated or rejected. Must your hypotheses be correct for this to be a successful laboratory? (4 points)t. 5. The hypothesis was validated the mixtures did react and cause a chemical change, and the other mixtures produced a physical change. A hypothesis dose not have to be correct in order to have a successful laboratory, because a hypothesis is just an educated guess. 6. …
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