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Acids Bases

Content objective:

What are we learning? Why are we learning this?

content, procedures, skills

Vocabulary objective

Tier II: High frequency words used across content areas. Key to understanding directions, understanding relationships, and for making inferences.

Tier III: Low frequency, domain specific terms

Building on what we already know

What vocabulary & concepts were learned in earlier grades?
Make connections to prior lessons from this year.
This is where we start building from.

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Intro: What are acids and bases?

Acids are bases are complimentary types of chemicals. Acids perform one kind of chemical reaction; bases perform the opposite action.

Acids and bases are natural; they are ubiquitous {they are found everywhere}

They are found in all cells, in all life

They are found in all lakes, rivers, streams, oceans

They are found in the soil, here on Earth and on all other planets.

Acids and bases in biology

They are not healthy or unhealthy: rather, when it comes to living, what matters is whether or not acids and bases are working in a healthy balance.

If a living organism has too much acid, then too many acidic chemical changes occur, which lead to the organism becoming sick or dying.

If a living organism has too much base, then too many basic chemical changes occur, which lead to the organism becoming sick or dying.

A healthy organism – and a healthy ecosystem – is in a balance between extremes.

Many biological molecules are acids.

Nucleic acids include DNA and RNA.

Cell membranes contain fatty acid esters

General Characteristics

Acids
Sour taste (though you should never use this characteristic to identify an acid in the lab)
Reacts with a metal to form hydrogen gas
Increases the H+ concentration in water
Donates H+ ions
Turns blue litmus indicator red

General Characteristics of Bases:
Bitter taste
Slippery feel
Increases the OH- concentration in water
Accepts OH- ions
Turns red litmus indicator blue

Which are more dangerous?

“Acids get the reputation for being scary and corrosive, but a strong base can often do the same damage — or worse. In this GIF, Coke cans are subjected to a strong base (sodium hydroxide) and a strong acid (hydrochloric acid).”

“At the molecular level, bases are donating oxygen atoms, and acids are donating hydrogens. Corrosion results from this disruption of molecular structure.”

Large amounts of base are as dangerous as large amounts of acid.

Visualizing acids and bases

H atoms have a positive charge.

O has a negative charge.

H2O Water molecule has a + end and a – end.

water molecule

These + and – charges give water special abilities. Molecules of water stick to each other, to form chains. These chains create surface tension.

Another quality of water is dissociation:

when these molecules bump into each other, sometimes a H atom breaks away from the remaining OH atoms.

H2O                      ↔     H+          +             OH

Water                                                  hydrogen ion                                       hydroxide ion

(neutral)                                               (positive)                                             (negative)

water decomposition hydrogen hydroxide

Consider the H+ ions, when they get near regular water molecules.

H+ ions are not stable: They bond with H2O molecules, to form H3O+   (hydronium ion).

H+ bond with H2O to form Hydronium

In the end, water breaks apart into hydroxide ions and hydronium ions.

2H2O          ↔      OH             +       H3O+

water               ↔      hydroxide   +       hydronium

neutral ph            basic pH              acidic pH

______________________________________________________

In neutral water there are an equal number of basic and acidic ions.

Ratio of acidic to basic ions determines whether it is neutral, an acid, or a base.

pH scale developed in 1920.

It stands for “pondus hydrogenii” – the potential for hydrogen ions (H+).

pH ranges from 0 to 14

0 = very strong acid

7 = neutral solution (equal number of H+ ions and OH- ions)

14 = very strong base

Lemon juice has pH  =  2.  Seven-up soda has pH = 4

But lemon juice is not twice as acidic as Coca-Cola…it is 100 times more acidic than the Seven-up!

How is that? The pH scale is based on powers of ten.

Water              ->         pH = 7

Root Beer        ->         pH = 6

The one unit difference means there’s a ten times difference in strength.

So there are 10 times the number of H+ ions.

pH Powers of ten copy

External links

“When Should I Use Logarithmic Scales in my Charts and Graphs?”
Originally published by Naomi Robbins on blogs.forbes.com.
http://datadrivenjournalism.net/resources/when_should_i_use_logarithmic_scales_in_my_charts_and_graphs

MathBench Biology Modules – “Data for scaling studies are almost always displayed and analyzed using log-transformed data. We are going to show you why and how – and make sure you are comfortable looking at these kinds of data and graphs. To do this, we are going to use our full data set of 600 mammals, and you will see why it is easier to see and analyze patterns in the data. In fact, you can see it just by looking at this picture!”
http://mathbench.umd.edu/modules/misc_scaling/page07.htm

 

Ph and equlibrium

https://kaiserscience.wordpress.com/2018/05/22/ph-and-equilibrium/

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-PS1-9 (MA). Relate the strength of an aqueous acidic or basic solution to the extent of an acid or base reacting with water, as measured by the hydronium ion concentration (pH) of the solution. Make arguments about the relative strengths of two acids or bases with similar structure and composition.

Science and Engineering Practices

Mathematical and computational thinking in 9–12 builds on pre-K–8 and experiences and progresses to using algebraic thinking and analysis, a range of linear and nonlinear functions including trigonometric functions, exponentials and logarithms, and computational tools for statistical analysis to analyze, represent, and model data.

Benchmarks for Science Literacy, AAAS

Most cells function best within a narrow range of temperature and acidity. At very low temperatures, reaction rates are too slow. High temperatures and/or extremes of acidity can irreversibly change the structure of most protein molecules. Even small changes in acidity can alter the molecules and how they interact. 5C/H7

The temperature and acidity of a solution influence reaction rates. Many substances dissolve in water, which may greatly facilitate reactions between them. 4D/M4

ACS Middle School Chemistry Lessons

From middleschoolchemistry.com, contact staff at ACS. Copyright 2015 American Chemical Society

Online textbook: Chapter 5: Acids Bases and their reactions

http://www.chem4kids.com/files/react_acidbase.html

http://www.chemistryland.com/CHM151S/04-Solutions/acids/AcidsBases151.html

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