BIO 12 U1TC – CHEMISTRY REVIEW & INORGANIC LIFE MOLECULES 1

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You have mastered this topic when you can: 1) describe and give examples matter. 2) outline atomic structure. 3) describe a chemical bond as an attraction between atoms. 4) name, describe and explain the formation of ionic bonds, non-polar covalent bonds and polar covalent bonds. 5) define and/or describe life molecules. 6) identify these inorganic life molecules: acids, bases, buffers and water. 7) describe and give examples of the properties of water that account for its importance to biological systems. 8) distinguish between acids, bases and buffers and indicate the importance of pH to biological systems.

[Section 2.1, pg. 24] CHEMISTRY REVIEWI) Everything you can touch, taste and or smell is an example of matter.

A) MATTER is defined as anything that has mass and occupies space: e.g. Hair, cloth, food, water, steel, chocolate and organisms. 1) Matter is composed of millions of different compounds and molecules: e.g. water, glucose, amino acids,

starch, cellulose, DNA, RNA, albumin, salt. a) Compounds and molecules are composed of fixed combinations of about 92 naturally occurring

elements.

B) ATOMIC STRUCTURE 1) Atoms are composed of varying combinations of 3 subatomic particles: protons, neutrons and electrons.

a) Protons and neutrons reside in the nucleus with electrons circling the nucleus in orbits [Fig. 2.2: pg. 25].

b) Atoms react with each other in order to become more stable. This is accomplished by forming chemical bonds between atoms. i) There are 2 types of chemical bonds that are formed between atoms: ionic and covalent

A} Ionic bonds form between metal atoms and non-metal atoms. The metal atoms give their outermost electrons, called valence electrons, to non-metal atoms creating positive metal ions and negative non-metal ions. The opposite charges of these ions create a strong attraction causing the ions to bond to each other. Compounds such as sodium chloride (NaCl), found in table salt, are formed this way [Fig. 2.5: pg. 27]. 1} Ionic compounds are also called salts. All salts are ionic compounds.

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B} Covalent bonds form when two non-metal atoms share pairs of their outermost electrons [Fig. 2.6: pg. 28]. 1} A non-polar covalent bond forms when an equal

sharing of pairs of electrons occurs between two non-metal atoms.

2} A polar covalent bond forms when an unequal sharing of pairs of electrons occurs between two non-metal atoms.. This results in the shared pair of electrons being closer to one non-metal atom than the other. a} The unequal sharing of electron pairs results in one end of the molecule being negatively

charged while the other is positive – the molecule is now POLAR. e.g. water

II) Pg. 56: Complete Questions 1 & 2. {Answers are on page 523 of the text.} Required Practice 1:

INTRODUCING LIFE MOLECULESI) Life Molecules are the compounds and molecules necessary for an organism to survive.

A) There are 2 broad categories of life molecules: INORGANIC and ORGANIC.

II) INORGANIC Life Molecules A) Inorganic life molecules lack carbon and hydrogen atoms bonded together.

B) WATER: The most important inorganic life molecule is water, H2O. 1) The atoms in water are bonded together by polar covalent bonds. [Fig 2.7a: pg. 28] 2) Water molecules are polar and have a Mickey Mouse shape [Fig 2.7a: pg. 28]. The polarity of water means

it has different charges at its ends: the oxygen end is negative (δ−) while each hydrogen end is positive (δ+).

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a) These opposite charges means water is sticky – it attracts other water molecules and other charged or polar substances [diagram at bottom right of pg. 29].

i) The attraction between the oppositely charged ends of water molecules is called a hydrogen bond. A} Although they are called bonds, hydrogen bonds are not chemical bonds in the same sense as an

ionic or covalent bond. A chemical bond involves electrons and forms between atoms. 1} Ionic and covalent bonds involve electrons being transferred or shared between atoms. 2} Hydrogen bonds involve an attraction between opposite charged ends of specific polar

molecules. Electrons are not part of a hydrogen bond. 3} Ionic and covalent bonds are much stronger than hydrogen bonds.

B} There are several different forms of attraction between molecules – hydrogen bonds are the strongest.

3) Importance of Water a) Many organisms live in water based solutions: e.g. fish, whales, plants, some snakes, bacteria, protists. b) Water makes up the greatest portion of many organisms total mass.

i) About 60% of an adult human’s mass is due to water. ii) About 95% of an jelly fish’s mass is due to water. iii) About 8% of a carrot’s mass is due to water.

c) Chemical reactions of all organisms take place in water. d) The polarity of water gives it life-sustaining properties [Ref: Properties of Water on pgs. 29-30].

Property of Water Function (role) 1. Water absorbs and holds Water controls environmental temperatures:

heat = high heat capacity. Large bodies of water have moderate temperature fluctuations Large amounts of energy helping to minimize land temperature fluctuations. are required to break its H-Bonds. Water controls body temperatures:

High water content allows an organism to distribute heat evenly throughout its body [Fig 2.8: pg. 30]. Sweat absorbs and removes excess body heat as it evaporates.

2. When water freezes its An ice layer insulates the water: molecules align + – + – The layer of ice provides a layer of creating empty spaces, insulation between the warmer water which decreases its density and the colder air. allowing ice to float on water [Fig 2.9: pg. 31]. Organisms won’t be frozen in ice.

3. Water is cohesive (sticky) Due to its polarity, water molecules can creep and pull each other through soil to reach plant roots. Water helps keep body surfaces moist: e.g. trachea, mouth, nasal passages, vagina, anus, surface of eyes.

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4. Water is transparent Water allows the passage of light enabling aquatic plants to photosynthesize food.

5. Water is an excellent Many substances dissolve in water meaning water based solutions solvent are able to transport material. Table salt readily dissolves, in water allowing its Na+ and Cl− ions

to dissociate and be transported throughout the body.

C) ACIDS: Important inorganic life molecules that release H+ ions in solution: HCl(aq) ⟶ H+(aq) + Cl−(aq)

D) BASES: Important inorganic life molecules that release OH− ions in solution: NaOH(aq) ⟶ Na+(aq) + OH−

(aq)

E) pH is a measure of the concentration of H+, [H+] (square brackets mean concentration of the substance inside them], dissolved in a solution [Fig 2.10: pg. 31]. 1) The pH of a solution is calculated using this formula: pH = –log [H+]

a) The smaller the pH the greater the [H+]. The larger the pH the smaller the [H+]. i) pH < 7.0 are considered to be acidic and the [H+] > [OH−]. ii) pH = 7.0 are considered to be neutral and the [H+] = [OH−]. iii) pH > 7.0 are considered to be basic and the [H+] < [OH−].

2) Human blood has a pH ≅ 7.4. If the pH increases or decreases by 0.4 the person could die.

F) Buffers are chemical systems that maintain a relatively constant pH within an organism’s internal solutions [Buffers and pH on pages 31 & 32.]. 1) Many life molecules, such as proteins, can only function correctly within a narrow pH range (remember:

pH is a measure of the acidity of a solution). Buffers maintain a relatively constant pH by absorbing excess H+ or OH−.

2) The carbonic acid – bicarbonate ion buffer is extremely important blood based buffer in preventing acidosis (pH ≤ 7.0) or alkalosis (pH ≥ 7.8) by absorbing excess H+ or excess OH−. a) The buffer is essentially this chemical equilibrium system: H2CO3(aq) ⇌ H+

(aq) + HCO3−

(aq)

i) When excess H+ is present it reacts with the HCO3−

(aq) from the above equilibrium to produce H2CO3(aq) as follows:

H+(aq) + HCO3

−(aq) → H2CO3(aq)  

ii) When excess OH− is present it reacts with the H2CO3(aq) from the above equilibrium to produce HCO3

−(aq) as follows:

OH−(aq) + H2CO3(aq) → HCO3

−(aq) + H2O(aq)  

3) Read the section titled Buffers and pH on pages 31 & 32 of your text.

III) Pg. 56: Complete Questions 3, 4, 5 & 6. {Answers are on page 523 of the text.} Required Practice 2:

BIO 12 U1TC – CHEMISTRY REVIEW & INORGANIC LIFE MOLECULES 5

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ASSIGNMENT

Please write your FULL LAST, then FIRST name AND “U1TC – Chemistry Review & Inorganic Life Molecules” AT THE TOP OF YOUR ASSIGNMENT. Answer these questions on your own paper.

MULTIPLE CHOICE: Select the letter of the BEST answer. (1 mark each)

1) Which of these would be the pH of an acidic solution? A. 2 B. 7 C. 10 D. 14

2) Which of these would be the pH of a basic solution? A. 2 B. 5 C. 7 D. 10

3) The purpose of a buffer system is to cause a/an A. basic pH to become acidic. C. acid pH to become basic. B. basic pH to become neutral. D. relatively constant pH to be maintained.

USE THIS DIAGRAM TO ANSWER QUESTIONS 4, 5, 6 & 7

4) The molecules in the above diagram are A. ionic B. non-polar covalent C. polar covalent D. buffers

5) The bonds number 1 is pointing to are called A. ionic bonds. C. polar covalent bonds. B. non-polar covalent bonds. D. hydrogen bonds.

6) The bonds number 1 is pointing to allow many water molecules to A. absorb heat with a huge change in temperature. B. release heat with a huge change in temperature. C. absorb heat without a huge change in temperature. D. require a huge amount of energy input to raise the temperature.

7) The presence of bond 1 accounts for which of these properties of water? I) water has a high heat capacity II) water has a high heat of vaporization III) water is sticky

A. I and II only B. I and III only C. II and III only D. I, II and III

8) Which of these substances releases hydrogen ions into solution? A. HCl B. H2O C. NaCl D. NaOH

9) Which of these substances produces a basic solution? A. H2CO3 B. H2O C. NaCl D. NaOH

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10) Which of these substances will lower the pH of a solution? A. H2CO3 B. H2O C. NaCl D. NaOH

11) Which of these substances will raise the pH of a solution? A. HCl B. H2O C. NaCl D. NaOH

12) Which of these substances maintain the pH of a solution relatively constant when a small amount of base is added? A. a salt B. a base C. an acid D. a buffer

13) Which of these properties of water allow it to dissociate ionic salts? A. its polarity B. its molecular size C. its neutral charge D. its covalent bonding

14) Which of these would occur if the pH of blood dropped below 7.4? A. Buffers would add more hydrogen ions to the blood. B. Buffers in the body would take up the extra hydrogen ions. C. Buffers in the body would take up the extra hydroxide ions. D. Buffers in the body would produce more acids in the body.

SHORT ANSWER: Complete these questions on your own paper. (Marks are indicated in the italicized brackets.)

14) Compare and contrast ionic bonds with covalent bonds. (3)

15) Name the bond that forms between molecules. (1)

16) Explain how the structure of water and its molecular properties contributes to its importance to organisms. (5)

17) What is a buffer? (2)

18) Explain how a buffer functions. Include example equations for the buffer and how it functions in your explanation. (5)

[30 marks in total]