The chalk particles embed themselves into the small pores on the surface.
Although a chalkboard seems smooth to the touch, it is quite rough at the microscopic level, with <em>pores</em> that reach below the surface.
When you drag chalk across the board, friction causes small particles of chalk to rub off onto the surface.
If you leave the markings for a long time, some of the chalk particles will work their way into the pores.
A brush will remove the surface particles, but <em>it will not be able to get at the particles in the pores</em>.
Answer:
The human body contains trillions of microorganisms — outnumbering human cells by 10 to 1. Because of their small size, however, microorganisms make up only about 1 to 3 percent of the body's mass (in a 200-pound adult, that's 2 to 6 pounds of bacteria), but play a vital role in human health.
Complete Question
Magnesium sulfate forms a hydrate with the formula 
. What is the maximum amount of water (in grams) that can be removed from 15 ml of toluene by the addition of 200 mg of anhydrous magnesium sulfate? The molar mass of 
is 120.4 g/mol; H20 = 18 g/mol.
Answer:
The value is 
of 
Explanation:
From the question we are told that
The volume of toluene is 
The mass of anhydrous magnesium sulfate is 
The formula of the hydrate is
The molar mass of is 
From the formula given we see that
1 mole of 
wil remove 7 moles of to for the given formula
Hence
120.4 g (1 mole) will remove 7 moles (7 * 18 g = 126 g ) of to for the given formula
Therefore 1 g of x g of
So
![x = \frac{x]126 * 1}{ 120.4 }](https://tex.z-dn.net/?f=x%20%20%3D%20%20%5Cfrac%7Bx%5D126%20%2A%20%201%7D%7B%20120.4%20%7D)
=> 
From our calculation we obtained that
1 g of will remove of
Then
of will remove z g of of
So
=>
=> of
