Why might the percent yield of copper produced be less than 100% of the expected amount?

[ ] There are impurities in the substances.
[ ] The reaction might not have gone to completion.
[ ] The amount of one of the reactants might be measured incorrectly.

(you can pick multiple)

If blood contains 150g of hemoglobin per liter of blood, how much hemoglobin would be contained in 10 ml of blood

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.

How does kepler second law of planetary motion overthrow one of the basic beliefs of classical astronomy