Water & pH Do Now: What are the special properties of water we discussed last week, and what’s so special about them anyway? Make a prediction: place the.

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Presentation transcript:

Water & pH Do Now: What are the special properties of water we discussed last week, and what’s so special about them anyway? Make a prediction: place the following in order from the MOST acidic to the LEAST acidic: Water, Soda, Coffee, Soapy water

Dissociation of Water – What pH is All About

Arrhenius Acids & Bases Acid: A substance which produces H + when dissolved in water. Base: A substance which produces – OH when dissolved in water.

pH measures H+ ACIDSBASES Low pHHigh pH Lots of H + / H 3 O + Little H + / H 3 O + Little - OHLots of - OH Taste sour (e.g. lemon juice, vinegar) Feel soapy (e.g. bleach)

Quick Math Refresher What is a logarithim? Log 10 = ? What is an exponential equation?

pH of Solutions What was the average pH of each of the liquids? What are we measuring?

A Word About Hydrogen Ions and Hydronium H+ is a proton. In solution, H+ is always stuck to a water molecule (which part?) Therefore, the following terms are all refer to what there is more of in an acid : protons H+ Hydronium

Hydroxide and hydronium Hydronium = H 3 O+. Higher concentration  more acidic solution  lower pH Hydroxide = -OH. Higher concentration  more basic solution  higher pH

The pH Scale and Some Examples

The pH scale is logarithmic pH = -log [H+] [H+] = concentration of H+ in mol / L Examples: Neutral water: [H+] = mol/L -log = 7 Vinegar: [H+] = mol/L -log = 3 Notice: Even though there is10,000 times as much [H+] in the vinegar the pH is different by 4. A change of 1 unit on the pH scale indicates a 10x change in ion concentration!

K w : The Ionization Constant of water It’s a constant… it doesn’t change, no matter what the pH is. K w = [H+][ - OH] = In other words, as [H+] goes up, [-OH] goes down. This is an example of an inversely proportional relationship.

Example Problems Type 1: What is the concentration of H+ in one sample compared to another. –A sample of water is pH 7. A sample of HCl has a pH of 1. How many times as much H+ ions are in the HCl? 7-1 = 6. Therefore, there is 10 6 times as much H+ in the acid. Type 2: What is the concentration of H+ or –OH, if the other is known, using K w. –A sample has a –OH concentration of What is the pH of the sample? Since K w = = [H+][10 -8 ] [H+] = pH = -log [10 -6 ] = 6

Tomorrow’s Lab Question: What is the effect of (recently) living matter on pH change? Plan: We will add small amounts of acid to a sample of liver homogenate (think liver shake) and compare the pH changes to a control group.

Hypothesis / Prediction Liver will (increase/decrease/have no effect on) the pH change when acid is added to a sample. If liver (affects pH change the way we hypothesize), then the pH of the liver will change (more/less/the same as) the pH of the water

Homework