Why did the pennies look dirty before I put them in the vinegar?
Copper atoms can combine with oxygen atoms to make a molecule called copper oxide. The pennies looked dull and dirty because they were covered with copper oxide.
Why did the vinegar and salt clean the pennies?
Copper oxide dissolves in table salt-and vinegar because of its weak acid.
Why did the unrinsed pennies turn blue-green?
When the vinegar and salt dissolve the copper-oxide layer, which makes it easier for the copper atoms to join oxygen and chlorine from the salt to make a blue-green compound called malachite.
How did the nail and the screw get coated with copper?
How did the nail and screw got coated with copper, Atoms are made up of even smaller particles called protons, neutrons, and electrons. Electrons and protons are both electrically charged particles. Electrons are negatively charged and protons are positively charged. Negative charges attract positive charges, so electrons attract protons.
When you put your dirty pennies in the vinegar and salt, the copper oxide and some of the copper dissolve in the water. That means some copper atoms leave the penny and start floating around in the liquid.
When you put the steel nail in the mixture, some of the iron dissolves. Like the copper atoms, each of the iron atoms that dissolves leaves two electrons behind. So you’ve got positively charged iron ions floating in your vinegar with the positively charged copper ions.
The negative charges on the nail attract positive charges in the liquid. Both the iron ions and the copper ions are positively charged. The copper ions are more strongly attracted to the negative charge than the iron ions, so they stick to the negatively charged nail, forming a coating of copper on the steel.
Why did bubbles come off the steel screw?
Each water molecule is made up of two hydrogen atoms and an oxygen atom. In an liquid we have vinegar (a acid) which has lots of hydrogen ions are floating around. In the chemical reactions at the surface of the screw, some of these hydrogen ions join and form hydrogen gas. The bubbles that you see coming off the screw are made of hydrogen gas.