28: You have a glass of pure water. Are chemical reactions occurring in the water? If so, what are they? If not, explain why not.
29: While investigating the effects of acid rain in your area, you discover a lake that is surprisingly resistant to changes in pH caused by acid rain. Using what you have learned in this unit, explain why the lake resists changes in pH.
41, Information: Hydrochloric acid (HCI) is a relatively strong acid. Imagine that HCI is added to a buffer solution containing the weak acid phosphoric acid (H3PO4) and a salt (Na2HPO4). Answer the following questions.
41, A: Will HCI react to the weak acid (H3PO4), or will it react with the salt (Na2HPO4).?
41, B: One product of this reaction will be a new salt (NaCl). What will the other product be?
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28: Yes, because the reaction for water is reversible, so some atoms are evaporating and others are recombining to form water molecules maintaining a balance in the solution.
29: The lake may act as a buffer and either be composed of a weak acid and its conjugate base or vice versa and therefore resists changes in the pH.
41, A: It will react with the salt (Na2HPO4).
41, B: I'm not positive of what they mean?
The answer to 28 is pure garbage. Evaporation of water is a physical process and not a chemical one. And if you leavae the glass of water uncovered, the water will completely evaporate and you will not maintain the balance. Water goes undergo autoioniation as follows:
H2O + H2O ==> H3O^+ + OH^- and that is an ongoing chemical process at work continuously.
29. This answer looks ok.
41A. This answer looks ok.
41B. They mean that if HCl will react with the salt, what are the products? They tell you one of the products is NaCl. They want you to tall what the other product is.
HCl + Na2HPO4 ==> NaCl + ??
To find the answer to question 41, B, we can use our understanding of the reaction between hydrochloric acid (HCI) and the salt Na2HPO4. When an acid reacts with a salt, it typically forms a new salt and releases a proton (H+ ion). However, the question mentions that one product is a new salt (NaCl), indicating that the HCI is reacting with the salt rather than the weak acid (H3PO4).
Now, let's focus on the other product. Since HCI is a strong acid, it completely ionizes in water, forming H+ ions and Cl- ions. The salt Na2HPO4 contains sodium ions (Na+) and the HPO4 2- ion. When HCI reacts with Na2HPO4, the Cl- ion from HCI will combine with one of the sodium ions from Na2HPO4 to form NaCl, the new salt mentioned in the question.
Therefore, the other product of the reaction between HCI and Na2HPO4 will be a proton (H+ ion) from the acid reacting with the HPO4 2- ion to form H2PO4- (dihydrogen phosphate ion).
In summary, the products of the reaction between HCI and the buffer solution containing H3PO4 and Na2HPO4 are NaCl (salt) and H2PO4- (dihydrogen phosphate ion).