Exp 1 Report Food.docx

Experiment 1 : Physical properties of water Objectives 1. 2.

To understand factors affecting boiling rate and boiling point of water. To determine the effect of varying relative humidity on the water activity of foods

Materials : 10g of NaCl , 10g of sucrose, 250mL beaker (x2), magnetic stirring hot plate ( x1), glass rod (x1), thermometer (x2), stopwatch (x2), safety googles x1 , gloves (x2), small container (x2) Methods: A) Boiling rate of the various amounts of water Procedure Part a(i) 1. The hot plate was turned on at heat no. “8” for 10 minutes. Extra attention was given to the surface of the hot plate after it was turned on. 2. 200ml of water was poured into the 250ml beaker. The beaker was then put on the hot plate and a thermometer was left inside the beaker. 3. The temperature of water was recorded at 30 seconds interval until the water is boiled. Then the temperature of every 1 minute was recorded for 6 minutes. Next, the temperature at every 2 minutes interval was recorded until there is 150mL of water left in the beaker. 4. The data was recorded in a template table as shown in Table1. Part a(ii) 1. Steps 1-4 in part a(i) was repeated with 150ml of water and heating was continued until there is 100ml of water left in the beaker. Part 3(iii) 1. Steps 1-4 in part 1a (i) with 100ml of water and heating was continued until there is 50ml of water left in the beaker. 2. A graph of temperature against time was plotted using data collected in part 1a(i) , (ii),(iii) until heating was stopped. B ) Effect of solutes on boiling point of water Procedure : 1. The hot plate was turned on at heat no. “8” for 10 minutes. Extra attention was given to the surface of the hot plate after it was turned on. 2. 10g of Sodium Chloride ( NaCl) was weighed and transferred into a beaker. 200mL of water was poured into a beaker and a thermometer was left inside the beaker. The solution was stirred using a glass rod. 3. The temperature was recorded at 30 seconds interval until the water is boiled. Then the temperature of every 1 minute was recorded for 6 minutes. The temperature at every 2 minutes

intervals was recorded until there was 150ml of water left in the beaker. 4. The data was recorded in a template table as shown in Table 1. Part b(ii) 1. Steps 1-4 in part b(i) was repeated with 10g of sucrose. 2. A graph of temperature against time was plotted until heating was stopped using data collected in part a(i),b(i) and b(ii). Results :

Table 1.1 below shows the Time required to boil 200mL of water

Time (s) 0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600 630 690 750 810 870 930 990 1110 1230 1350 1470 1590 1710 1830

Temperature ◦C 22.0 25.0 32.0 37.0 43.0 47.0 52.0 56.0 60.0 63.0 67.0 70.0 72.0 76.0 79.0 81.0 84.0 86.0 89.0 91.0 93.0 95.0 97.0 99.0 99.0 100.0 100.0 100.0 100.5 100.0 100.5 100.0 100.0 100.0 100.0

Table 1.2 below shows Time required to boil 150mL of water.

Time (s) 0 30 60 90 120 150 180 210 240 270 300 330 360 390 450 510 570 630 690 750 870 990 1110 1230 1350 1470

Temperature ◦C 22.0 27.0 34.0 40.0 48.0 52.0 63.0 69.0 74.0 77.0 86.0 90.0 92.0 95.0 96.0 100.0 100.0 100.0 100.0 100.0 99.0 100.5 100.0 100.0 100.5 101.0

Table 1.3 below shows Time required to boil 100mL of water.

Time (s) 0 30 60 90 120 150 180 210 240 270 300 330 360 420 480 540 600 660 720 840 960 1080 1200 1320 1440

Temperature ◦C 22.0 29.0 34.0 45.0 54.0 61.0 69.0 75.0 81.0 86.0 91.0 94.0 95.0 100.0 101.0 102.0 102.0 101.5 101.0 101.5 101.5 101.0 100.5 101.0 100.0

Table 1.4 below shows Time required to boil 200mL of water with added Sodium Chloride (NaCl)

Time (s) 0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600 630 660 720 780 840 900 960 1020 1140 1260 1380 1500 1620 1740 1860 1980

Temperature ◦C 23.0 24.0 30.0 35.0 39.0 44.0 48.0 52.0 56.0 60.0 65.0 68.0 71.0 74.0 79.0 81.0 83.0 86.0 89.0 91.0 94.0 96.0 98.0 100.5 101.0 101.5 101.5 102.0 102.0 102.0 102.0 102.0 102.5 102.5 102.0 102.0 102.0

Table 1.5 below shows Time required to boil 200mL of water with added Sucrose.

Time (s) 0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 630 690 750 810 870 930 1050 1170 1290 1410 1530 1650 1770

Temperature ◦C 23.0 25.0 30.0 36.0 41.0 46.0 50.0 55.0 60.0 64.0 67.0 73.0 76.0 80.0 83.0 86.0 89.0 92.0 95.0 97.0 100.0 100.5 100.5 101.0 101.0 100.5 101.0 100.0 100.5 100.0 100.0 100.0 100.0

Part A Graph of Temperature against Time with different volumes of water 110 100

Temperature ◦C

90 80 70 60 50 40 30 20 10 0 0

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Time (s) Temperature 200ml of water

Temperature 150ml of water

Temperature 100ml of water

Figure 1 : Graph of temperature against time in different volumes of water.

Based on the results in Figure 1, all the temperatures of the 3 experiments increases and then plateau. All 3 experiments boiling points are the same at 95◦C.The time taken for 200mL of water to reduce its volume by 50ml is the longest with 1830 seconds. Next, the time taken for 150mL of water to reduce its volume by 50ml is 1440 seconds while the time taken for 100ml of water to reduce its volume by 50ml of water was 1470 seconds which does not follow the trend of as volume of water increases , time taken for 50ml of water to evaporate is longer. This could results in a few source of errors. For example, heat may be lost to the surrounding due to lack of insulation, this results in the sudden increase in temperature then decrease in temperature for example in experiment aii table 1.2 from 1210 seconds to 1360 seconds. Next, there could be impurities in the pure water as well. Impurities will increase our boiling point to above 100◦C as shown in Table 1.1,Table 1.2 and Table1.3 which should not happen as pure water boiling point is 100. In addition, taking the temperature slower may also caused an effect on the result. We may improve this by using the staggered timing method.

Part B

Temperature ◦C

Graph of Temperature against Time with pure water and water with solute 110 100 90 80 70 60 50 40 30 20 10 0 0

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Temperature (s) Temperature 200 ml of water with 10g of NaCl Temperature 200 ml of water with 10g of Sucrose Temperature 200ml of water

Figure 2 : Graph of temperature against time with pure water and water with solutes. Based on Figure 2, all temperature increases and then plateau. Water with NaCl has a higher temperature compared to water and water with sucrose. Water with Sucrose reduce 50ml of water the fastest followed by Pure distilled water and lastly water with NaCl added. Based on theory, Pure distilled water should have been the fastest in reducing 50ml of water as the boiling point of pure distilled water is lowest. This could be due to some errors like heat lost to surrounding. To overcome this we may insulate the beaker with aluminium foil to reduce heat lost.

Discussion questions Part A 1.Do the curves in part a(i),(ii) and (iii) have a flat section? Is so, explain the flat section ( 3 marks) Yes they do. As water reaches the boiling point, the temperature will remain constant when the water molecules will transform from liquid to gas causing the flat section on the graph. (Courses.lumenlearning.com, 2019) 2.Does the boiling point of water depend on the amount of the water? Please explain your answer. ( 3 marks) No, the boiling point does not depend on the amount of water because they are at the same altitude which have the same vapor pressure. Boiling rate of water only depends on the amount of heat that is required to vaporise the water. Therefore if volume of water increases, time taken for water to reach the boiling point increases but boiling point remains the same. Boiling point depends on the vapor pressure of the solution at and liquid will only boil when the vapor pressure of a liquid reaches the equivalent value of the atmospheric air pressure (Compound Interest, 2019) and not based on volume. 3.Which of the samples boils faster? Why? ( 2marks) 100ml of water because less amount of water require lesser energy to achieve the boiling point.

Part B 1.Compare the graph that consists of experimental work of part a(i),b (i) , and b(ii), which of the sample has the highest boiling point? What can you conclude on the boiling point of water and the solution. Water which contains NaCl has the highest boiling point. This is because addition of solute lowers the surrounding vapour pressure of the solution (Barghouthi & Tullis, 2000). Solution only starts to boil when vapour pressure is equals to atmospheric pressure.Thus, a higher temperature compared to ordinary boiling point (100◦C) is needed for vapour pressure to equal to atmospheric pressure.The ion dipole interaction between Na+ and Cl- is much stronger than hydrogen bonds between water,more energy is needed to break the interaction and into vapor phase.

2.Comparing NaCl and sucrose , which solute increases more on the boiling point of the water. Give reasons. NaCl will increase more on the boiling point. This is because NaCl molecule will break into two ions which is Na+ and Cl- when dissolved in water. Sucrose does not split further when dissolved in water.Thus, NaCl will have a higher number of particles compared to sucrose .In addition, when 10 g of NaCl and sucrose is added in 200mL of water respectively, NaCl will give a higher number of moles compared to sucrose because sucrose has a higher molar mass of 58.4g/mol while sucrose has 342 g/mol, hence increasing the boiling point. (Silver, 2005)

Conclusion The volume of water increases, the boiling rate decreases. Solute addition affects the rate of distilled water boiling. Addition of solutes decreases the vapor pressure thus affects the boiling point.

Reference Breslyn,, W. and Wyler, C. (2016). Boiling. Chemistry LibreTexts. Available at: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook _Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Propert ies_of_Matter/States_of_Matter/Phase_Transitions/Boiling [Accessed 20 Mar. 2019]. 2. Courses.lumenlearning.com. (2019). Heating and Cooling Curves (also called Temperature Curves) | Chemistry for Non-Majors. [online] Available at: https://courses.lumenlearning.com/cheminter/chapter/heating-and-cooling-curves-alsocalled-temperature-curves/ [Accessed 21 Mar. 2019]. 1.

Bright Hub. (2019). Which Boils or Freezes Faster, Salt or Sugar Water? The Technical Explanation. [online] Available at: https://www.brighthub.com/education/homeworktips/articles/91923.aspx [Accessed 22 Mar. 2019]. 4. Helmenstine, A. (2018). Why Adding Salt Increases the Boiling Point of Water. [online] ThoughtCo. Available at: https://www.thoughtco.com/adding-salt-increases-waterboiling-point-607447 [Accessed 22 Mar. 2019]. 5. Barghouthi, S., & Tullis, K. (2000). Determination of the Vapor Pressure Curve of a Liquid in the Presence of a Nonvolatile Solute. Chem. Educator, 5(4), 183-186. 6. Silver, T. (2005). Cracking the SAT chemistry subject test. New York: Random House. 3.