name: jadarrian crump 5th block
properties of water and ph
1. write the chemical equation for water, and draw a stick model of a water molecule. show polarity by label positive and negatively charged regions of the molecule.

3. what kind of bond holds the hydrogen to the oxygen in one water molecule?

4. what kind of bonds can hold two separate water molecules together?

5. what is a polar molecule?

6. the polarity of water allows it to ____________ most substances. because of this it is referred to as the ____________________ ____________________.

7. water molecules stick to other water molecules. this property is called ______________.

8. water molecules stick to other water molecules. this property is called ______________.

9. why does ice float on water?

10. why is it important that water resists temperature changes?

critical reading: ph
when some substances dissolve in water they break up into ions. a compound that releases a hydrogen ion (a proton) when it dissolves in water is an acid. bases are compounds that remove, or accept, hydrogen ions. a solution’s acidity, or its hydrogen ion concentration, is measured on the ph scale. an acid has a low ph (ph below 7) and a high hydrogen ion concentration. a base has a high ph (ph above 7) and a low hydrogen ion concentration. organisms must maintain a stable ph. even a small change in ph can disrupt many biological processes.

11. describe what the ph of a substance is measuring.

12. draw the ph scale and label acid, neutral, and base.

13. what has more hydrogen ions, acids or bases?

Question

name: jadarrian crump 5th block
properties of water and ph
1. write the chemical equation for water, and draw a stick model of a water molecule. show polarity by label positive and negatively charged regions of the molecule.

3. what kind of bond holds the hydrogen to the oxygen in one water molecule?

4. what kind of bonds can hold two separate water molecules together?

5. what is a polar molecule?

6. the polarity of water allows it to ____________ most substances. because of this it is referred to as the ____________________ ____________________.

7. water molecules stick to other water molecules. this property is called ______________.

8. water molecules stick to other water molecules. this property is called ______________.

9. why does ice float on water?

10. why is it important that water resists temperature changes?

critical reading: ph
when some substances dissolve in water they break up into ions. a compound that releases a hydrogen ion (a proton) when it dissolves in water is an acid. bases are compounds that remove, or accept, hydrogen ions. a solution’s acidity, or its hydrogen ion concentration, is measured on the ph scale. an acid has a low ph (ph below 7) and a high hydrogen ion concentration. a base has a high ph (ph above 7) and a low hydrogen ion concentration. organisms must maintain a stable ph. even a small change in ph can disrupt many biological processes.

11. describe what the ph of a substance is measuring.

12. draw the ph scale and label acid, neutral, and base.

13. what has more hydrogen ions, acids or bases?

Accepted Answer

### Question 3 # Brief Explanations: In a water molecule ($\ce{H_2O}$), the bond between hydrogen (H) and oxygen (O) within one molecule is a covalent bond. A covalent bond is formed when atoms share electrons. In water, oxygen and hydrogen atoms share electrons to achieve a stable electron configuration. Specifically, it is a polar covalent bond because oxygen is more electronegative than hydrogen, causing an unequal sharing of electrons and a partial charge separation. # Answer: Covalent bond (specifically polar covalent bond) ### Question 4 # Brief Explanations: Two separate water molecules are held together by hydrogen bonds. A hydrogen bond is an intermolecular force that occurs when a hydrogen atom, which is covalently bonded to a highly electronegative atom (like oxygen in water), is attracted to another electronegative atom (usually oxygen or nitrogen) in a neighboring molecule. In water, the partially positive hydrogen of one water molecule is attracted to the partially negative oxygen of another water molecule, forming a hydrogen bond. # Answer: Hydrogen bonds ### Question 5 # Brief Explanations: A polar molecule is a molecule in which there is an unequal distribution of electron density, resulting in a molecule with a partial positive charge on one side and a partial negative charge on the other side. This occurs when there is a significant difference in electronegativity between the atoms in the molecule, leading to a dipole moment (a separation of positive and negative electrical charges within the molecule). For example, in water ($\ce{H_2O}$), the oxygen atom is more electronegative than the hydrogen atoms, so the electrons in the covalent bonds are pulled closer to the oxygen, giving the oxygen a partial negative charge and the hydrogens a partial positive charge. # Answer: A molecule with unequal electron distribution, having partial positive and negative charge regions (due to electronegativity differences between atoms), resulting in a dipole moment. ### Question 6 # Brief Explanations: The polarity of water allows it to dissolve most substances. Because of this ability to dissolve a wide variety of substances (especially polar and ionic substances), water is referred to as the universal solvent. The polar nature of water molecules (with partial positive and negative charges) allows them to interact with and surround charged or polar particles, pulling them apart and dispersing them in the water. # Answer: dissolve; universal solvent ### Question 7 (and Question 8, which seems to be a repeat of Question 7) # Brief Explanations: The property where water molecules stick to other water molecules is called cohesion. Cohesion is due to the hydrogen bonds between water molecules. These hydrogen bonds cause the water molecules to be attracted to one another, leading to phenomena like surface tension (where the surface of water acts like a stretched membrane) and the ability of water to form droplets. # Answer: Cohesion ### Question 9 # Brief Explanations: Ice floats on water because the density of ice is less than the density of liquid water. When water freezes into ice, the water molecules form a crystalline structure (a hexagonal lattice) due to hydrogen bonding. In this structure, the molecules are spaced further apart from each other compared to the more random arrangement of molecules in liquid water. Since density is mass per unit volume, and the same mass of water occupies a larger volume in the solid (ice) state, the density of ice ($\approx 0.92\ ext{g/cm}^3$) is less than the density of liquid water ($\approx 1.0\ ext{g/cm}^3$). An object with a lower density than the fluid it is in will float. # Answer: Ice has lower density than liquid water (due to its hexagonal lattice structure from hydrogen bonding, which spaces molecules further apart), so it floats. ### Question 10 # Brief Explanations: It is important that water resists temperature changes (has a high specific heat capacity) because this property helps to stabilize temperatures in the environment and within organisms. For the environment, large bodies of water (like oceans, lakes) can absorb or release a large amount of heat with only a small change in temperature, moderating the climate of nearby areas (e.g., coastal regions have more moderate temperatures). Within organisms, water's ability to resist temperature changes helps maintain a stable internal temperature (homeostasis), which is crucial for the proper functioning of enzymes and other biological processes that are sensitive to temperature. # Answer: Stabilizes environmental/organismal temperatures (moderates climate, maintains homeostasis for biological processes). ### Question 11 # Brief Explanations: The pH of a substance measures the acidity or basicity (alkalinity) of a solution, which is related to the concentration of hydrogen ions ($\ce{H^+}$) in the solution. More specifically, pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration: $ ext{pH} = -\log_{10}[\ce{H^+}]$, where $[\ce{H^+}]$ is the molar concentration of hydrogen ions. A low pH (below 7) indicates a high hydrogen ion concentration (an acidic solution), while a high pH (above 7) indicates a low hydrogen ion concentration (a basic solution), and a pH of 7 is neutral (equal concentrations of $\ce{H^+}$ and $\ce{OH^-}$ ions). # Answer: pH measures the hydrogen ion ($\ce{H^+}$) concentration (acidity/basicity) of a solution (via $ ext{pH} = -\log_{10}[\ce{H^+}]$). ### Question 12 # Brief Explanations: The pH scale ranges from 0 to 14. A pH of 7 is considered neutral (e.g., pure water at 25°C has a pH of 7, with equal concentrations of $\ce{H^+}$ and $\ce{OH^-}$ ions). Values below 7 (from 0 to just below 7) are acidic, meaning the solution has a higher concentration of hydrogen ions ($\ce{H^+}$) than hydroxide ions ($\ce{OH^-}$). Values above 7 (from just above 7 to 14) are basic (alkaline), meaning the solution has a higher concentration of hydroxide ions ($\ce{OH^-}$) than hydrogen ions ($\ce{H^+}$). To draw the scale: draw a horizontal line, label the left end as 0 (most acidic), the middle as 7 (neutral), and the right end as 14 (most basic). Then label the regions: "Acid" below 7, "Neutral" at 7, and "Base" above 7. # Answer: pH scale: 0 (acid) ———— 7 (neutral) ———— 14 (base) (draw a horizontal line with 0 on left, 7 middle, 14 right; label acid <7, neutral =7, base >7). ### Question 13 # Brief Explanations: Acids have more hydrogen ions ($\ce{H^+}$) than bases. By definition, an acid is a substance that releases (or donates) hydrogen ions when dissolved in water, increasing the hydrogen ion concentration of the solution. A base, on the other hand, removes (or accepts) hydrogen ions, resulting in a lower hydrogen ion concentration compared to an acidic solution of the same concentration range. From the pH scale, acids have a pH below 7 (where $[\ce{H^+}] > [\ce{OH^-}]$) and bases have a pH above 7 (where $[\ce{H^+}] < [\ce{OH^-}]$). # Answer: Acids

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