Chemistry

I am conducting this experiment to find out the Molarities of various concentrations of Hydrochloric Acid (HCl). I am using four various concentrations of Hydrochloric Acid. The controlled variables are the amount of Hydrochloric Acid used, the amount of Phenolphthalein used, and the washed materials used; the independent variable is the amount of Sodium Hydroxide (NaOH) used; and the dependent variable is the Molarities of the various Hydrochloric Acids. I will keep the amount of Hydrochloric Acid controlled by using 25mL, I will keep the amount of Phenolphthalein controlled by using 3 drops, and I will keep the materials controlled by washing them all the same, thoroughly. Materials used: -Burette -Two Graduated Cylinders -Four 250mL Beakers -Four Unknown Concentrations of Hydrochloric Acid (HCl) -Sodium Hydroxide (NaOH) (Undetermined Amount) -Phenolphthalein -Eye dropper This is how I conducted this experiment: 1) Gather and wash materials 2) Fill burette with 50mL of Sodium Hydroxide 3) Fill beaker with 25mL of Hydrochloric Acid 4) Put three drops of Phenolphthalein into the beaker 5) Let the Sodium Hydroxide drip into the beaker and swish around until it turns a light shade of pink 6) Use the equation for Molarity (M1V1/M2V2) to find the Molarities of the Hydrochloric Acid 7) Repeat steps 1 – 5 for the remaining three Hydrochloric Acids My hypothesis is that the Hydrochloric Acid that is more highly concentrated will have a lower Molarity. Acid | Amount of Hydrochloric Acid | Molarity of Hydrochloric Acid | Amount of Sodium Hydroxide | Molarity of Sodium Hydroxide | A | 25mL | x | 78.7mL | 1 M | B | 25mL | x | 23mL | 1 M | C | 25mL | x | 25.7mL | 1 M | D | 25mL | x | 16.6mL | 1 M | mL converted to L 25mL / 1000 = .0250 L 78.7mL / 1000 = .0787 L 23mL / 1000 = .0230 L 25.7mL / 1000 = .0257 16.6mL / 1000 = .0166 Molarity Equations Acid A - (1)(.0250) / (x)(.0787) .0250x = .0787 x = 3.148 M Acid B - (1)(.0250) / (x)(.0230) .0250x = .0230 x = 0.920 M Acid C - (1)(.0250) / (x)(.0257) .0250x = .0257 x = 1.028 M Acid D - (1)(.0250) / (x)(.0166) .0250x = .0166 x = 0.664 M Hydrochloric Acid | Amount of Hydrochloric Acid | Molarity of Hydrochloric Acid | Amount of Sodium Hydroxide | Molarity of Sodium Hydroxide | A | 25mL | 3.148 M | 78.7mL | 1 M | B | 25mL | 0.920 M | 23mL | 1 M | C | 25mL | 1.028 M | 25.7mL | 1 M | D | 25mL | 0.664 M | 16.6mL | 1 M | The Molarities I got were 3.148 M for Hydrochloric Acid A, 0.920 M for Hydrochloric Acid B, 1.028 M for Hydrochloric Acid C, and for Hydrochloric Acid D 0.664 M. This proves that my hypothesis, Hydrochloric Acid that is more highly concentrated will have a lower Molarity, was wrong. The Hydrochloric Acid that was more highly concentrated also had a higher Molarity. Some errors I could have made were that I did not clean all of the materials well enough; some excess solutions, acids, bases, etc. could have still been on them when I used them. This would have contaminated the Hydrochloric Acid or Sodium Hydroxide, affecting my results. I also could have let the Sodium Hydroxide drip into the Hydrochloric Acid/Phenolphthalein solution too long, causing my results to be affected. The next time I perform this experiment, I will make sure that these errors will be fixed. I will cleanse the materials well, with soap and water and maybe a neutralizing agent, to ensure all excess solutions, acids, bases, etc. are gone. I will also make sure to stop the Sodium Hydroxide from dripping when the Hydrochloric Acid/Phenolphthalein solution turns a light shade of pink instead of a darker shade of pink, as it did in my experiment.