7.3 The pH Scale PDF

# The pH Scale ## Chapter 7.3 ### The pH Scale - Chemists measure the acidity of a solution using a scale called pH. - pH is a measure of how acidic or basic a solution is ($pH$ = power of Hydrogen). - The pH scale is a numerical scale ranging from 0 to 14. | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7...

# The pH Scale ## Chapter 7.3 ### The pH Scale - Chemists measure the acidity of a solution using a scale called pH. - pH is a measure of how acidic or basic a solution is ($pH$ = power of Hydrogen). - The pH scale is a numerical scale ranging from 0 to 14. | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | |-----|---- |---- |---- |---- |---- |---- |---- |---- |---- |---- |---- |---- |---- |---- | | | | | | | | | | | | | | | | | - Solution with a pH less than 7 is considered acidic (0 - 6.9). - Solution with a pH greater than 7 is considered basic (7.1 - 14). - Solution with a pH equal to 7 is considered neutral. ### Review: Acids and Bases #### Acids - conduct electricity - taste sour - turn blue litmus red - neutralize bases - HCl - NaOH - NaCl #### Bases - conduct electricity - taste bitter - feel slippery - turn red litmus blue - neutralize acids ### pH Scale - The pH scale is a **logarithmic** scale meaning that one unit on the scale is equivalent to a **ten fold change** in concentration. - **Therefore**: - A pH of 3 is 10 times more acidic than a pH of 4 - A pH of 10 is 1000 times less basic than a pH of 13 | pH | Acidity | pH | |-----|-------------------|-----| | 6 | 10 times > 7 | | | 5 | 100 times > 7 | | | 4 | 1000 times > 7 | | > means greater than ### Acidic Solutions - Acids form **hydrogen ins** ($H^+$) in solution. - **Concentration** of these hydrogen ins determines the solution's pH. - **Concentration** is a measure of the quantity of a substance dissolved in a given volume of solution. - Greater the concentration of $H^+$ in solution, the **stronger the acidic properties**. - Solutions with the **highest** $H^+$ **concentration** are near the "zero" end of the pH scale. - **Highly acidic solutions** have a low pH. - **Highly acidic solutions** are very corrosive and reactive. - **Strong acids** must be treated with extreme care. ### Basic Solutions - pH scale also indicates the concentration of **hydroxide ins** ($OH^-$). - Solutions with a pH **greater than 7** have a higher concentration of $OH^-$ than $H^+$. - Solutions with distinctly **basic properties** are near the "14" end of the pH scale. - **Highly basic solutions** have a high pH. - **Highly Basic solutions** are also very corrosive and reactive. - **Strong bases** must also be treated with extreme care. - Another term for basic is **alkaline** ### Neutral Solutions - Solutions with a pH of 7 is **neutral**. - $H^+$ and $OH^-$ concentrations are **equal** and balance each other out. ### Examples of pH Conditions | pH 2 | pH 4 | pH 5 | pH 7 | pH 7.4 | pH 10 | pH 12 | |--------------|--------------|----------------|------------------|---------------|--------------|---------------| | Gastric juices | Tomato juice | Human Urine | Pure water | Human blood | Hand soap | Household bleach | ### pH in Our Lives - Living organisms are **sensitive** to small pH changes. - Certain plants grow best in specific conditions of **soil acidity**. - Increasing $CO_2$ levels & pollution is causing oceans to become more **acidic** - this corrodes **coral reefs** and **shells** of living things. - Healthy skin has a pH of about 5.5 (slightly **acidic**). - This helps to kill **bacteria** and **fungi** growing on your skin. Some soaps have a pH of 7 or 8, which can upset the pH balance of your skin. Remember to moisturize - skin creams are often slightly acidic. - Since your skin is slightly acidic, it may also **react** with some **metals**. You may get a rash from jewelry or cell phones. ### The Lemon Challenge - Lemon is _____ times more _____ than milk - Ammonia is _____ times les _____ than pure water - Soap is _____ times more _____ than bleach This document is missing the answer to the "lemon challenge". The reader needs to determine those answers based on their knowledge of the pH scale.