1. CHAPTER 4 4.3 Chemical Reactions in the Lab Physical and Chemical Change

2. 2 4.3 Chemical Reactions in the Lab Why would the presence of water on Mars be a sign that life might exist there?

3. 3 4.3 Chemical Reactions in the Lab Many reactions, including those that sustain life, involve chemicals dissolved in water. Why would the presence of water on Mars be a sign that life might exist there?

4. 4 4.3 Chemical Reactions in the Lab DRY Light blue powder No reaction

5. 5 4.3 Chemical Reactions in the Lab DRY No reaction IN SOLUTION Light blue powder NaS( aq ) CuSO 4 ( aq ) Chemical reaction A precipitate is an insoluble compound.

6. 6 4.3 Chemical Reactions in the Lab A solution with water as the solvent is called an aqueous solution. “Aqua” means “water.” SYMBOLS (s) indicates a s olid (l) indicates a l iquid (g) indicates a g as (aq) indicates a substance dissolved in water (an aq ueous solution)

7. 7 4.3 Chemical Reactions in the Lab SO O O OCu SO O O O 2–2– 2+ O HH O HH O HH O HH A salt is an ionic compound that forms ions when dissolved in water.

8. 8 4.3 Chemical Reactions in the Lab Can you translate what you see into a chemical equation?

9. 9 4.3 Chemical Reactions in the Lab Can you translate what you see into a chemical equation? Zn(s) + CuSO 4 (aq) Cu(s) and Zn(s) is disappearing

10. 10 4.3 Chemical Reactions in the Lab Zn(s) + CuSO 4 (aq) Cu(s) and Zn(s) is disappearing Can you translate what you see into a chemical equation? a salt in water!

11. 11 4.3 Chemical Reactions in the Lab Cu 2+ (aq) SO 4 2– (aq) Can you translate what you see into a chemical equation? Zn(s) + Cu(s) and Zn(s) is disappearing

12. 12 4.3 Chemical Reactions in the Lab Cu 2+ (aq) SO 4 2- (aq) Zn(s) + Cu(s) and Zn(s) is disappearing The copper ion gains 2 electrons to form solid copper. reduction: a chemical reaction that decreases the charge of an atom or ion by accepting electrons. Cu 2+ (aq) + 2e – Cu(s)

13. 13 4.3 Chemical Reactions in the Lab Cu 2+ (aq) SO 4 2- (aq) Zn(s) + Cu(s) and Zn(s) is disappearing The copper ion gains 2 electrons to form solid copper. Where could those electrons come from? Cu 2+ (aq) + 2e – Cu(s)

14. 14 4.3 Chemical Reactions in the Lab Cu 2+ (aq) SO 4 2- (aq) Zn(s) + Cu(s) and Zn(s) is disappearing Zn(s)Zn 2+ (aq) + 2e – Zinc gives up 2 electrons to become a zinc ion, dissolved in water. Cu 2+ (aq) + 2e – Cu(s)

15. 15 4.3 Chemical Reactions in the Lab Zn(s)Zn 2+ (aq) + 2e – Zinc gives up 2 electrons to become a zinc ion, dissolved in water. oxidation: a chemical reaction that increases the charge of an atom or ion by giving up electrons.

16. 16 4.3 Chemical Reactions in the Lab Cu 2+ (aq) + 2e – Cu(s) Reactants Products reduction REACTION NAME

17. 17 4.3 Chemical Reactions in the Lab Cu 2+ (aq) + 2e – Cu(s) Zn(s)Zn 2+ (aq) + 2e – Reactants Products reduction REACTION NAME oxidation

18. 18 4.3 Chemical Reactions in the Lab Cu 2+ (aq) + 2e – Cu(s) Zn(s)Zn 2+ (aq) + 2e – Reactants Products reduction REACTION NAME oxidation These 2 reactions are happening at the same time. To obtain the overall reaction add the reactants, then the products.

19. 19 4.3 Chemical Reactions in the Lab Cu 2+ (aq) + 2e – Cu(s) Zn(s)Zn 2+ (aq) + 2e – Reactants Products Cu 2+ (aq) + Zn(s)Cu(s) + Zn 2+ (aq) reduction REACTION NAME oxidation redox

20. 20 4.3 Chemical Reactions in the Lab O HH O H H - + dissociation H 2 OOH – + H + The double arrow indicates that the reaction goes in both ways. The heavier arrow means that the reverse reaction is favored.

21. 21 4.3 Chemical Reactions in the Lab Classify these items as acids or bases.

22. 22 4.3 Chemical Reactions in the Lab HCl(l)H + (aq) + Cl – (aq) H 2 O(l) acid: a chemical that dissolves in water to create more H + ions than there are in neutral water. Acids give foods like lemons their sour taste. Acids react with metal to create hydrogen gas (H 2 ). Acids can corrode metal and burn skin. Example: Hydrochloric acid

23. 23 4.3 Chemical Reactions in the Lab NaOH(l)Na + (aq) + OH – (aq) H 2 O(l) Bases create a bitter taste. Bases have a slippery feel, like soap. Bases can neutralize acids. Example: Sodium hydroxide

24. 24 4.3 Chemical Reactions in the Lab NaOH(l)Na + (aq) + OH – (aq) H 2 O(l) Bases create a bitter taste. Bases have a slippery feel, like soap. Bases can neutralize acids. Example: Sodium hydroxide OH – (aq) + H + (aq)H 2 O(l) Result: fewer H + ions

25. 25 4.3 Chemical Reactions in the Lab NaOH(l)Na + (aq) + OH – (aq) H 2 O(l) Example: Sodium hydroxide OH – (aq) + H + (aq)H 2 O(l) Result: fewer H + ions base: a chemical that dissolves in water to create fewer H + ions (or more OH – ions)than there are in neutral water.

26. 26 4.3 Chemical Reactions in the Lab

27. 27 4.3 Chemical Reactions in the Lab Higher H + concentration Lower H + concentration The pH scale helps to determine whether a solution is acidic or basic.

28. 28 4.3 Chemical Reactions in the Lab A solution with water as the solvent is called an aqueous solution. Redox reactions (transfer of electrons) Acid-base reactions (transfer of protons, H + ions) two types of chemical reactions that take place in an aqueous environment. Higher H + concentration Lower H + concentration