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Effect of temperature on pH of water samples

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Introduction

´╗┐Lab on effect of temperature on pH of water Lab type: DCP & CE/DCE. Theory: Water contains both hydrogen ions, H+, and hydroxide ions, OH?. The relative concentrations of these two ions determine the pH value.1 Water with a pH of 7 has equal concentrations of these two ions and is considered to be a neutral solution. If a solution is acidic, the concentration of H+ ions exceeds that of the OH? ions. In a basic solution, the concentration of OH? ions exceeds that of the H+ ions. On a pH scale of 0 to 14, a value of 0 is the most acidic, and 14 the most basic. A change from pH 7 to pH 8 in a lake or stream represents a ten-fold increase in the OH? ion concentration. Rainfall generally has a pH value Between 5 and 6.5. It is acidic because of dissolved carbon dioxide and air pollutants, such as sulfur dioxide or nitrogen oxides. If the rainwater flows over soil containing hard-water minerals, its pH usually increases. Bicarbonate ions, HCO3?, resulting from limestone deposits react with the water to produce OH? ions, according to the equation: HCO3? + H2O ? H2CO3 + OH? As a result, streams and lakes are often basic, with pH values between 7 and 8, sometimes as high as 8.5. The measure of the pH of a body of water is very important as an indication of water quality, because of the sensitivity of aquatic organisms to the pH of their environment. ...read more.

Middle

Testing Procedure 1. Plug the pH Sensor into Channel 1 of the Venire interface. 2. Turn the Vernier computer interface ON 3. You are now ready to collect pH data. 4. Remove the pH Sensor from the storage bottle. Rinse the tip of the sensor thoroughly with Distilled water. 5. Place the tip of the probe into the test tube. 6. Submerge the sensor tip to a depth of 3–4 cm. 7. Important: Leave the probe tip submerged for the 30 seconds that data is being collected. 8. Run the sample for 30 seconds, stop data collection and record the average pH on the Data & Calculations sheet. 9. Repeat step 4 to 8 for every sample at different temperatures starting from 29°c (room temp), 32°c, 35°c, 38°c,41°c,44°c respectively. Table 1: showing the pH of Tap water at different temperatures (uncertainty ± 0.01). TEMPERATURE Seconds/ Sample No. 29â° C 32â°C 35â°C 38â° C 41â°C 0 7.85 10.49 7.78 7.99 7.75 2 7.7 7.42 8.7 7.46 7.44 4 7.78 7.83 8.68 7.39 7.93 6 7.88 7.8 8.28 7.29 7.66 8 7.82 7.77 7.63 7.75 7.46 10 7.73 7.47 7.48 7.91 7.91 12 7.83 7.44 7.65 7.5 7.44 14 7.85 7.32 7.73 7.76 7.54 16 7.7 7.35 9.05 7.53 7.8 18 7.75 7.47 8.08 7.89 7.43 20 7.88 7.53 7.98 8.16 7.94 Mean 7.8 7.81 8.09 7.69 7.66 Std dev 0.07 0.91 0.49 0.28 0.21 Table 2: Showing pH of distilled water at different temperature (uncertainty ± 0.01). ...read more.

Conclusion

Temperature has very less and not much effect on pH of water. As temperature increases, the pH of water decreases. The most acidic was rain water at 32â°C with an average of 7.55 pH due to effect of acid rain. Evaluation-: While doing the experiment my all the data was perfect. There was no error, while doing the experiment. My result supported my hypothesis showed at the temperature. The temperature of each sample at each stage was not equally controlled due to contact with room temperature. There may be some external substances may have entered the sample and cause a variation in the pH level of the sample. The samples should have been covered to avoid any external substances in entering the sample. The pH value of each sample at different temperature was not the exact value as the pH value of the sample was counted only till 20 seconds. But getting more accurate value of pH the time (seconds) should have been more than 20 seconds like till 30 seconds or more. Conclusion-: My hypothesis was as the level of temperature increases the pH of water samples will decrease. My prediction seems to be supported my result that I collected. As the level of the temperature increase, the level of pH also increased is what I got. Graph 5. Showing mean value of pH at each different temperature mostly each sample at 35ºC was high as compared to others. As we can even see that 32C has the least mean in all. ...read more.

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