Paper activity for serial dilutions

See also youtube demo at
http://www.youtube.com/watch?v=_araJt0GOvU

Make colored copies of graphing papers: red, blue, and white.

Basic idea: 1 cm2 of paper = 1 part of Things or water.
Red papers represent Things
Blue papers represent water.
White papers are containers.

For 10X red stock:
Draw a 20 parts rectangle in a white graphing paper. This is volume of the 10X stock solution.
Cut 10 part red and 10 part blue paper to fill the space.
The concentration of this solution is 50% red.

To make 1X 20 parts solution, we need 2 parts of 10X. The 2 parts of 10X contain 1 part of red and 1 part of blue (water).
Draw a 20 parts rectangle, cut 1 part of red and 1 part of blue from the 10X stock area, and move to the 1X area. The remaining area of the 1X stock is 18 parts and should be filled with water (blue papers).
The concentration of this 1X solution is 5% red.

To make 0.1X 20 parts solution, we need 2 parts of 1X which contains 2x5%=0.1 part of red and 1.9 parts of blue (water). The concentration of this solution is 0.5% red.

-----------------------The older version,  v1---------------
Make colored copies of graph papers: red, blue, and white.

Basic idea: 1 cm2 of paper = 1 part of things or water

10X red stock: 10 cm2 red paper + 10 cm2 white paper.
The concentration of this solution is 50% red, and its total volume is 20 parts.

5X blue stock: 5 cm2 blue paper + 15 cm2 white paper.
The concentration of this solution is 25% blue, and its total volume is 20 parts.

Exercise 1: To make a volume of 20 parts solution of 1X red and 1X blue, we need 1 part of red and 1 part of blue: 
 1. Use scissor to cut 1 part (1cm2) of red and 1 part (1cm2) of water  from 10X red stock, add to an empty beaker labelled with "1X red, 1X blue".
  2. Use scissor to cut 1 part (1cm2) of blue and 3 part of (3 cm2) of water from 5X blue stock, add to the '1X red 1Xblue' beaker.
  3. How much water should we add?
  20 - 1(red) - 1(water) - 1 (blue) - 3 (water) = 14 parts of water.
This 1X solution should contain 1cm2 red, 1cm2 blue, and 18 cm2 water. 


Exercise 2: To make a 1/10 X solution in a volume of 50 parts: 
1. Take 10 part of 1X: Cut 0.5 part red, 0.5 part blue, 9 part of water from 1X stocks
2. Add 50 - 0.5 - 0.5 - 9 = 40 part of water.

Materials needed: Three beakers; 1 piece of red graph paper, 1 piece of blue graph paper, 3 pieces of white graph papers; 1 Scissor.